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CHRISTMAS ISLAND, INDIAN OCEAN

GROUNDWATERINVESTIGATIONS ANDMONITORING REPORT

Prepared for GHD Pty Ltdand Christmas Island Administration

byTony Falkland

ACTEW Corporation LtdOctober 1999

CHRISTMAS ISLAND, INDIAN OCEAN

GROUNDWATERINVESTIGATIONS ANDMONITORING REPORT

Prepared for GHD Pty Ltd

and Christmas Island Administration

by

Tony Falkland

ACTEW Corporation Ltd

November 1999

Christmas Island – Groundwater Investigations and Monitoring Report, November 1999 page i

Table of ContentsTable of Contents i

List of Annexes iv

List of Tables iv

List of Figures v

Abbreviations vi

EXECUTIVE SUMMARY 1Introduction 1Summary and Conclusions 1Summary of Recommendations 6

1. INTRODUCTION 81.1 Overview 81.2 Background 81.3 Structure of the Report 8

2. DRILLING AND TESTING PROGRAM 92.1 Water Resources Monitoring Boreholes 9

2.1.1 Background 92.1.2 Details 92.1.3 Monitoring data 192.1.4 Analyses of data - overview 192.1.5 Analysis of Smithson Bight borehole data 202.1.6 Analysis of north-eastern area borehole data 242.1.7 Summary and conclusions from the 1996 drilling program 252.1.8 Selected results from previous drilling programs 26

2.2 Pollution Monitoring Boreholes 272.2.1 Details 272.2.2 Monitoring results 282.2.3 Conclusions 28

2.3 Stormwater Discharge Boreholes 28

3. GROUNDWATER RECHARGE ASSESSMENT 303.1 Overview 303.2 Outline of Recharge Assessment Procedure 303.3 Rainfall Data 323.4 Evaporation Data 333.5 Recharge Estimation Model 353.6 Analyses and Results 373.7 Discussion of Results 403.8 Estimated Sustainable Yield 403.9 Conclusions 41

4. SATELLITE IMAGERY STUDY FOR COASTAL OUTFLOWS 424.1 Background 424.2 Summary of the Study 424.3 Conclusions 42

5. RAINFALL-FLOW MODEL FOR JEDDA CAVE 435.1 Background 435.2 Jedda Cave 43

5.2.1 Rainfall and flow data 43

Christmas Island – Groundwater Investigations and Monitoring Report, November 1999 page ii

5.2.2 Linear regression model 445.2.3 Non-linear models 45

5.3 Springs 475.3.1 Waterfall Springs 475.3.2 Ross Hill Gardens Springs 47

5.4 Conclusions 48

6. AQUIFER CLASSIFICATION AND VULNERABILITY 496.1 Summary of the Island’s Geology and Hydrogeology 496.2 Aquifer Classification 50

6.2.1 Overview 506.2.2 Perched groundwater 506.2.3 Basal groundwater 516.2.4 Summary of aquifer classification 52

6.3 Groundwater Vulnerability 576.3.1 Sources of contamination 576.3.2 Groundwater vulnerability assessment 576.3.3 Aquifer vulnerability map 58

6.4 Conclusions 58

7. WATER MONITORING PROGRAM 597.1 Overview 597.2 Weir Flows 59

7.2.1 Background 597.2.2 Locations and purposes 597.2.3 Monitoring equipment 607.2.4 Data obtained from Jedda recorder 607.2.5 Analysis of Jedda data 617.2.6 Data obtained from Ross Hill Gardens recorder and flow meters 647.2.7 Analysis of Ross Hill Gardens recorder data 647.2.8 Data obtained from Ross Hill Gardens meters 677.2.9 Summary of key results 687.2.10 Future monitoring requirements 68

7.3 Flow and Salinity Recording in Daniel Roux Cave 687.3.1 Background 687.3.2 Locations and purpose 697.3.3 Monitoring equipment 697.3.4 Data obtained from the recorders 707.3.5 Analysis of DR gusher data 717.3.6 Analysis of DR channel data 717.3.7 Summary of flow and water quality data for the Daniel Roux gusher 727.3.8 Conclusions and future monitoring requirements 73

7.4 Water Supply System Flows, Storage and Usage 747.4.1 Background 747.4.2 Improvements to metering 747.4.3 Additional flow monitoring and analyses 757.4.4 Available flow meter data 767.4.5 Analysis of daily flows from sources and main storage tanks 767.4.6 Analysis of continuous flow data from selected tanks 797.4.7 Analysis of consumer meter data 827.4.8 Assessment of system losses 84

7.5 Water Chemistry 877.5.1 Background 877.5.2 Results of water chemistry tests 87

Salinity 87Hardness 88Other parameters 89Summary 89

Christmas Island – Groundwater Investigations and Monitoring Report, November 1999 page iii

7.5.3 Results of testing for chemical pollution 897.5.4 Future monitoring 89

7.6 Microbiological Test Results 907.7 Water Monitoring Program 90

7.7.1 Outline of monitoring program during the Project 907.7.2 Current data archives 907.7.3 Monitoring problems experienced during the Project 917.7.4 Ongoing monitoring program 91

General 91Current water sources 92Daniel Roux Cave 92Monitoring boreholes 93Water meter readings 93Water Quality 94Chlorination 94Data processing and archiving 94Analysis and reporting 94

7.7.5 List of water resources monitoring equipment 957.7.6 Costs for ongoing monitoring 95

8. CONCLUSIONS AND RECOMMENDATIONS 98

9. ACKNOWLEDGEMENTS 98

10. REFERENCES 99

11. ANNEXES 101

Photographs on Front Cover:

Top Left: Ron De Cruz interrogating data logger at terminal box, Daniel Roux Cave

Top Right: Lee Swee Chow inspecting leak in pipeline (from Grant’s Well to Jedda storage tank)

Bottom Left: Drilling of groundwater monitoring borehole BH2

Bottom Right: Jason Tan measuring salinity of groundwater sample with portable conductivitymeter

Christmas Island – Groundwater Investigations and Monitoring Report, November 1999 page iv

List of AnnexesA. Project Brief 95

B. Summary Details of Boreholes drilled in 1996 97

C. Water Resources Monitoring Boreholes (BH1 to BH8), Details and Data 98

D. Water Resources Monitoring Boreholes (BH1 to BH8), Graphs 122

E. Pollution Monitoring Boreholes (BH9 to BH11), Details and Data 131

F. Monthly and Annual Rainfall Data, Airport, Jan 1973 - May 1999 138

G. Monthly and Annual Rainfall Data, Jedda, Jan 1994 - May 1999 143

H. Monthly and Annual Pan Evaporation Data, Airport, Sep 1972 - Apr 1981and Rocky Point, Settlement, Feb 1968 - Oct 1972 145

I. Monthly Recharge Estimates for period 1986 - 1998 150

J. Jedda Cave flow monitoring, 1996 - 1999 157

K. Ross Hill Gardens weir flow monitoring, 1996 - 1998 164

L. Ross Hill Gardens meter flows and gauge height monitoring, Nov 1997 - June 1999 168

M. Daniel Roux Cave water monitoring, Site 1: Gusher, 1996 - 1999 170

N. Daniel Roux Cave water monitoring, Site 2: Channel to Sea, 1996 - 1998 174

O. Meter Flows - Sources and Distribution Tanks, 1995 - 1999 180

P. Detailed Meter Flows at Distribution Tanks, 1998 186

Q. Water Quality Monitoring Tests, 1968 - 1986 195

R. Water Quality Monitoring Tests, 1998 200

S. Christmas Island Water Monitoring Program, October 1998 205

List of Tables1. Summary of monitoring tubes at water resources monitoring boreholes 15

2. Summary of freshwater conditions at water resources monitoring boreholes 22

3. Summary of water level and salinity data from boreholes WB72 and WB73 23

4. Summary of average pan evaporation data for Christmas Island 29

5. Summary of average annual recharge estimates for various cases 32

6. Annual recharge estimates using selected case (case 1) 33

7. Average Monthly Flows at Jedda, Nov 1996 – June 1999 56

8. Average Monthly Flows at Ross Hill Gardens, Nov 1996 – May 1999 58

9. Summary of Instantaneous Flows from Ross Hill Gardens springs 60

10. Summary of the Daniel Roux Cave gusher flows, 1967-1998 66

11. Summary of flows from sources 1997-1999 70

12. Summary of flows from main distribution tanks, 1996-1999 71

13. Flows at Drumsite, George Fam & Hospital tanks, 28 Apr-10 May 1997 72

14. Flows from Drumsite, George Fam & Hospital tanks for periods in 1998 74

Christmas Island – Groundwater Investigations and Monitoring Report, November 1999 page v

15. Water Consumer Statistics by Category, to September 1998 77

16. Salinity (EC) results (µS/cm) for selected sites 81

17. Chloride ion results (mg/L) for selected sites 81

18. Hardness results (mg/L) for selected sites 82

19. Estimated costs and replacement timetables for monitoring equipment 89

List of Figures1. Christmas Island showing location of water sources and monitoring boreholes 10

2. Detailed location map of boreholes BH1-BH5 in Smithson Bight area 11

3. Detailed location map of boreholes BH6-BH13 in north-eastern area 12

4. Cross section through monitoring boreholes, BH1-BH3 13

5. Cross section through monitoring boreholes, BH1-BH3 and Jane Up,Jedda Cave and Grant’s Well 14

6. Jedda monthly rainfall and drought indices, Jan 1995 – May 1999 17

7. Water balance model for typical surface zone on a small island(from Falkland & Woodroffe, 1997) 27

8. Monthly Pan Evaporation at Rocky Point (Settlement) & Airport 30

9. Annual rainfall at Airport & estimated annual recharge, 1986-1998 33

10. Monthly Jedda flows and rainfall, 1996-1999 37

11. Monthly Jedda flows and Grant’s Well rainfall, 1965-1974 38

12. Relationship between actual and predicted flow for Jedda, 1965-1973,using non-linear flow model 41

13. Christmas Island groundwater aquifer classification map 48

14. Christmas Island groundwater vulnerability map 49

15. Monthly Ross Hill Gardens weir flows and Jedda rainfall, 1996-1999 59

16. Monthly Ross Hill Gardens weir flows and Grant’s Well rainfall, 1967-1974 59

17. Meter Flows - Sources and Distribution Tanks, January – June 1999 69

18. Drumsite tank outflow meter, 19-22 June 1998 73

19. Water Consumption Curves for Residential, Commercial and Public Categories 76

20. Christmas Island Water Supply Balance, 1998 78

Christmas Island – Groundwater Investigations and Monitoring Report, November 1999 page vi

AbbreviationsAC asbestos cement

ACTEW ACTEW Corporation (formerly ACT Electricity and Water)Administration Christmas Island AdministrationARMCANZ Agriculture and Resource Management Council of Australia and New Zealandbgl below ground levelBoM Bureau of MeteorologyBPC British Phosphate CommissionersBTEX benzene, toluene, ethylbenzene and xyleneCEO Chief Executive OfficerCIP Christmas Island Phosphates (Mining Company)CIR Christmas Island ResortCOAG Council of Australian GovernmentsCSO community service obligationDOEH Department of the Environment and HeritageDTRS Department of Transport and Regional ServicesEC electrical conductivity (a measure of salinity)ESD ecologically sustainable developmentGHD Gutteridge Haskins and Davey Pty LtdGIM Groundwater Investigations and MonitoringGL gigalitre (= one thousand ML = one million kL)IOT Indian Ocean TerritorieskL kilolitre (= one thousand litres)L litresL/p/d litres per person per dayL/s litres per secondm metresm3 cubic metres (for water, m3 = kL)ML megalitres (= one million litres)MOU Memorandum of UnderstandingMSL mean sea levelOC organochlorine (pesticides)OP organophosphate (pesticides)OSS Office of the Supervising Scientist (DOEH)PCBs polychlorinated biphenylsPMCI Phosphate Mining Corporation of Christmas Island (before CIP)RL reduced level relative to MSL (by survey)Shire Shire of Christmas IslandSMB salinity monitoring boreholeTPHs total petroleum hydrocarbonsWA Western AustraliaWMP Water Management PlanWSI Water Source ImprovementsµS/cm microsiemens per centimetre (unit of electrical conductivity, and used as an

indicator of salinity)

Christmas Island – Groundwater Investigations and Monitoring Report, November 1999 page 1

Executive Summary

IntroductionThe objective of this report is to present the results of the groundwater investigations and monitoringundertaken on Christmas Island during the period from October 1996 to June 1999.

The water resources monitoring systems, as established during this project, should be continued.While the data obtained during the course of this study has yielded very valuable information, thereremains a need for long-term monitoring to assess the impacts of natural and possible human-induced influences on the island’s water resources.

The Groundwater Investigations and Monitoring (GIM) Program included the following majorcomponents:

• the drilling and testing program;

• assessment of groundwater recharge;

• a pilot study using satellite imagery to locate freshwater outflows from the island;

• development of a rainfall-flow model for Jedda Cave,

• development of an aquifer classification and vulnerability map; and

• development of a water monitoring program, and associated processing, archiving,analysis and reporting procedures for water resources and water supply data.

Relevant information gained from the GIM Program has been integrated into the accompanyingChristmas Island Water Management Plan (WMP).

Summary and Conclusions Drilling and Testing Program

A significant volume of fresh ‘basal’ groundwater was found from monitoring boreholes in theSmithson Bight area. The basal groundwater in the Smithson Bight area is in the form of a coastalaquifer above and in contact with seawater. This groundwater could be developed in the future bydrilling production boreholes to target depths just below sea level.

The area of the island north of Smithson Bight offers good potential for the development of freshgroundwater. Based on monitoring results, there is unlikely to be freshwater within about 500 m ofthe coastline. If production holes are drilled, they should be located at distances of 1,000 m or morefrom the coastline and pumped at rates 3-5 L/s per borehole. It may be possible to alter these ratesafter a period of monitoring of the salinity response within the groundwater, as measured at salinitymonitoring boreholes. A salinity monitoring borehole should be drilled close to each productionborehole.

A limited amount of perched groundwater (above volcanic rock) was found in the north-eastern partof the island. The area around one monitoring borehole in this area (BH8) has potential and could befurther proven by additional drilling and test pumping.

For the definition of fresh groundwater on Christmas Island, it is recommended that a salinity value(in electrical conductivity units) of 1,500 µS/cm be used as an upper limit. A desirable objectiveshould be 1,000 µS/cm. This is based largely on a comparison with the salinity of the water supplyfrom current sources which is approximately 500-600 µS/cm.

From the limited data available, it appears that the groundwater level and salinity response in theSmithson Bight boreholes lags at least 4 months behind significant rainfall variations.

To better understand the groundwater dynamics within selected boreholes, it is recommended that asmall diameter water level sensor and data logger be purchased and used as part of the futuregroundwater monitoring program on the island. The sensor and logger should be installed on a


rotating basis at several boreholes to establish the variations in water level due to tides and otherinfluences. The estimated cost is $5,000.

It is possible that the basal groundwater extends under the island from the Smithson Bight area upto, and further north than this area, but no deep drilling to near or below mean sea level has beenundertaken north of BN1 to investigate this matter. The nature and extent of any basal groundwaterin this zone would be dependent on the permeability of the volcanic rock near mean sea level. It isrecommended that two investigation holes be drilled between BN1 and WB30, south-west ofJane Up, to assess the basal groundwater potential further. This drilling should be done at the sametime as possible future production and monitoring borehole drilling. If hard volcanic rock isintersected in either or both of these boreholes then the drilling can cease. The water levelconditions should be checked after drilling to assess the potential for future pumping from either aperched or basal aquifer.

From the analyses of groundwater levels there were some anomalies with boreholes BH4 and BH5.The water levels at BH4 are lower than expected when compared with the salinity data from thisborehole and the comparison of the results for BH1 and BH2. The water levels at BH5 are higherthan expected when compared with the high salinity in this borehole. The survey levels on the topsof boreholes BH4 and BH5 should be checked.

Assessment of groundwater recharge

The estimated average annual recharge for Christmas Island, based on a detailed analysis usinglocal data, is 50% of average annual rainfall or about 1,000 mm. This is greater than the 30% valuein Falkland (1986), which was based on comparisons with other islands rather than local data.

Over the area of the island where fresh groundwater is present, the average annual recharge isequivalent to about 100 gigalitres, which is equivalent to a flow of about 3,200 L/s. The estimatedsustainable yield of the groundwater system is half the available recharge (i.e. 1,600 L/s). Averageand estimated minimum flows at present sources are much less than this potential yield (5% and2% of the estimated sustainable yield, respectively).

Pilot study using satellite imagery

A pilot study using Landsat satellite imagery was not successful at locating freshwater outflowsalong the coastline. Imagery obtained with sensors (on satellite or aeroplane) having a thermalresolution of better than 0.1°C may be more useful than the resolution available for this study(0.5°C). However, the method of using remote imagery appears to be of limited use, as the mixingof freshwater and seawater within the caves and fissures along the coastline results in outflowswhich are already quite diffuse even where freshwater outflows are known to occur.

Rainfall-flow model for Jedda Cave

For Jedda Cave, a simple formula was derived to predict flows for a given month based on theprevious 5 months rainfall recorded at the Jedda raingauge. This could be applied only in low flowperiods when the flow is between about 50 and 20 L/s, and the 5 month rainfall is less than about250 mm.

Based on analysis of lows in 1997 and 1998, the flow response in Jedda Cave is lagged between 2and 3 months behind Jedda rainfall.

A more complex (non-linear) model was developed for Jedda for higher flow periods. This modelcan estimate the current month’s flow from the average of monthly rainfall for the previous 2 monthsand the average monthly flow at Jedda for the preceding month. It should be used with caution as itcan under-estimate or over-estimate actual flows and should be refined as more data becomesavailable in the future.

Predicted flows from these models should be checked against future monitored flows at Jedda andthe results reported in the proposed quarterly monitoring reports. Suggested modifications can thenbe recommended.

In the future, similar models could be developed for the springs at and near Waterfall and for those atRoss Hill Gardens. The Waterfall springs will firstly require the installation of flow monitoringequipment and then collection of data over at least 12 months.


Aquifer classification and vulnerability map

A simple classification of the island’s fresh groundwater into perched aquifers (above sea level) andbasal aquifers (in contact with seawater) is presented and summarised in a map (refer Figure 13 insection 6.2). This map should be considered preliminary as much of the data has been inferred.Based on limited data, particularly in the Smithson Bight area, it is assumed that the basalgroundwater within 500 m of the coastline is likely to have a salinity level higher than freshwater dueto mixing with seawater, particularly during extended dry periods. The actual distance may vary from500 m depending on local differences in permeability, especially if volcanic rock is present below sealevel near the coastline (e.g. parts of the eastern and western coastlines). For a given location, theposition of the freshwater/seawater boundary will vary according to preceding rainfall and hencerecharge conditions. The area of most uncertainty in the map is the exact delineation betweenperched and basal groundwater. It is further noted that there may be a multi- layer aquifer systemunder the areas marked as perched aquifer. For instance it is quite possible, although unproven thatthe basal aquifer extends underneath the area marked as being perched aquifer.

As an approximate guide, no basal groundwater should be developed by pumping within 500 m of thecoastline because there is a strong possibility that this groundwater would be brackish in extendeddry periods, and even if it was not, the action of pumping is likely to induce seawater intrusion.

The groundwater resources of Christmas Island are rated as having a high to very high vulnerabilityto contamination. A groundwater vulnerability map has been prepared (refer Figure 14 insection 6.3). Strict controls over potential pollution sources, particularly waste disposal sites andsewerage systems, are absolutely essential. In particular, planning procedures should take accountof the vulnerability of groundwater when siting waste disposal sites, urban developments withassociated sewerage and stormwater systems, and other potential sources of pollution. It isrecommended that a ‘zero discharge’ policy is the most appropriate for all potential pollutants togroundwater over the whole island.

Water monitoring program

Overview

A water monitoring program was developed during the course of the WMP project to enable vitalwater resources information to be collected at key sites, including some of the presently developedsources and some potential sources. These sites were Jedda Cave, Ross Hill Gardens Springs,Daniel Roux Cave and the water resources monitoring boreholes installed during the project.Unfortunately, it was not possible to establish monitoring systems at the very important sites ofWaterfall, Freshwater and Jones Springs. In addition to the water resources monitoring sites, flowmeters were installed at key sites on major pipelines, particularly at all sources (Jedda, Jane Up,Ross Hill Gardens and Waterfall). Water quality information was obtained at water resources sitesand pollution monitoring boreholes, and a program for ongoing monitoring has been prepared.Training was provided to two staff from the Shire during the course of the project. Data processingand analysis was undertaken by Ecowise Environmental and key results reported to the Shire duringthe course of the Project.

Jedda and Ross Hill Gardens flows

Flows obtained from the two automatic recorders have provided a valuable insight into the flowvariations due to prior rainfall and other factors, particularly pumping at the Jedda Cave site. Theflow data obtained at Jedda indicates that the minimum flow in the period of observations (October1996 - May 1999) was approximately 20 L/s in February 1998. Of this flow, approximately two thirdswas pumped and one third by-passed the pumps and went through the weir. This minimum flow of20 L/s in the recent monitoring period was substantially greater than the minimum flow of 13.6 L/srecorded in January 1966 (all pumped and no overflow).

The flow data obtained at the Ross Hill Gardens pump station weir (from Harrison’s Springs andHewan’s Spring) indicates that the minimum flow in the period of observations (October 1996 - May1999) was approximately 3 L/s in September 1997. This was greater than the flow of 1 L/s recordedin the early months of 1966.


The Jedda Cave flow has a much greater range than for the Ross Hill Gardens pump well flow. Theratio between maximum and minimum flows is about 10:1 compared with about 3:1 for the Ross HillGardens flow.

Daniel Roux Cave

Water level and salinity data were obtained from automatic data loggers at two sites in Daniel RouxCave, one at the ‘gusher’ and the other in the channel system between the gusher and the coastline.

The water salinity data confirms that it would not be possible to pump from the Daniel Roux channelsystem, even from close to the gusher, without causing extensive saline intrusion. However, directcollection of water from the low salinity Daniel Roux gusher provides an option for future freshwaterdevelopment on the island. From the monitoring over several years, it appears that the minimumflow is approximately 15 L/s. This is a substantial flow when it is compared with the minimum flowrecorded at Jedda of 13.6 L/s.

A number of technical, environmental, safety and potential source pollution issues, however, need tobe considered before a decision could be made to develop this source of freshwater flow. Theseissues are beyond the scope of this report but are considered further in the WMP (ACTEW, 1999).

It is recommended that the data logger at the Daniel Roux gusher site continues to be maintained.The channel site logger can be removed at the next available opportunity.

At this stage, it is not recommended that a flow measuring weir be built around the DR gusher. If thesite is seriously considered in the future as a possible source of freshwater then it would beadvisable to build such a weir structure, or another suitable flow measuring device, so thatmeasurements of flow can be estimated from a rating table (similar to Jedda and Ross HillGardens). Based on experiences with water level recorders and weir boxes at this site, it isconsidered that a more permanent structure under the gusher with an outflow pipe would be moreuseful for measuring the flow. A pipe flow meter with a data recorder could be installed on theoutflow pipe at a point away from the gusher where it would be easy to read. The meter would needto be capable of working under water (at high tide).

Monitoring boreholes

A full description of the data obtained from the boreholes monitoring and discussion of the results ispresented in section 5 and summarised at the start of this Executive Summary.

Water meters on main water supply system

During the course of the project, additional meters were installed at key sites on the main supplysystem. These enabled a water balance of the water supply system to be developed. Key resultsare presented below:

• The total flow from sources was approximately 22 L/s during 1998 and the first half of1999. For an estimated population of about 1,500 on the island, the flow of 22 L/s isequivalent to about 1,270 litres per person per day (L/p/d). This is very high and issimilar to previously identified per capita flows (e.g. 1,130 L/p/d in 1985/86: Falkland,1986). There has been an overall reduction in flows since 1996. This is partly due todetection and repair of some leaks and most probably also due to a reduction in theoverall demand for water with the reduction in population in this period.

• Data loggers at outlet meters on the main tanks (Drumsite, George Fam and Hospital)have provided a very useful means of analysing flows, particularly minimum night flows,during 1997 and 1998. Analysis of flows led to the detection and later repair of majorleaks in 1997 and 1998. Subsequent more detailed leakage detection work by GHD inearly 1999 found further leaks including a major leak in a Drumsite 100 mm pipeline.This was subsequently repaired.

• Analysis of flows in 1998, showed the amount of water being used for ‘productive use’was between 32% and 41% of total water supplied from sources. While these figuresseem low they are not surprising for a water supply system such as that on ChristmasIsland, when compared with similar pipe systems in urban centres on some Pacificislands. It is possible to reduce leakage to much lower levels (say 20%, with an upperlimit of 30%), with the introduction of leakage control measures.


• The studies during the course of the project have shown that system losses have been asubstantial proportion of total water supply, and leak control efforts can lead tosubstantial reductions in leakage. Leak detection and rectification efforts are required ona regular basis, as short term ‘gains’ can be lost in the medium to longer term asadditional leaks occur. This can best be achieved by developing and sustaining acapability within the local water supply authority to undertake an ongoing programme of‘leakage control’ (comprising both leak detection and rectification). This means thatsome staff must be trained in the necessary techniques for leakage detection and thatrecurrent budget must be supplied to rectify leaks that are found, or to replace sectionsof pipeline that are beyond further repair.

Consumer meters

As part of the project, a detailed analysis of consumer meter data was conducted for the period frominstallation of meters until September/October 1998. Most meters were installed in early 1997, sothis period represents approximately 18 months. From the data obtained, some key results were:

• approximately 90% of residential consumers (house or unit with a meter) used less than1,100 kL/year, or approximately 3,000 L/day. For a house of 3 people this is equivalent to1,000 Litres per person per day. The median residential water use (50% of consumerswith lower consumption, and 50% with higher consumption) was 390 kL/year (or1,060 L/day). For the residential sector, the top 20% of consumers used as much wateras the remaining 80%.

• the median water use in the commercial sector was 193 kL/year. The top 7% ofconsumers used as much water as the other 93%. The highest water user was the GolfCourse followed by the CIP Workshop.

• the median water use in the public sector was 364 kL/year. The top 8% of consumersused as much water as the other 92%. The four highest consumers in this sector werethe power station, the nursery, the hospital and the school. These four consumersrepresented 73% of the consumption in this sector.

• the residential sector uses the largest proportion of water (74%), followed by thecommercial sector (16%). However, the public sector shows the highest average waterusage (total water usage/number of consumers), followed by the commercial sector.

Water quality - chemistry

The salinity of the present (Jedda, Jane Up, Waterfall and Ross Hill Gardens) and former (Grant’sWell) water sources are well within the guidelines for salinity. These sources are all from perchedgroundwater. Other perched groundwater, for example, from a number of the monitoring boreholes(refer section 2) and the Daniel Roux cave gusher shows similar results. Basal groundwater, abovethe transition zone with seawater, also shows similar results.

Hardness values of water samples from current sources show moderate to high levels. It is wellknown that Christmas Island water is hard and scale forms on heater elements (e.g. electric kettlesand hot water systems).

Other physical and chemical quality parameters (e.g. pH, turbidity and common specific ions) allmeet guideline values.

In summary, the basic water chemistry of groundwater on Christmas Island meets the requirementsof the Australian Drinking Water Guidelines (NHMRC/ARMCANZ, 1996) except for hardness.

Water quality - bacteriology

The microbiological quality of the water is generally good. However, there were some samplesshowing positive counts for all parameters. In particular, occasional samples showed positive E.Coli counts, which is not acceptable. As the microbiological quality of water supply can directlyimpact on public health, it is essential that the water delivered to consumers continues to bedisinfected. The chlorination systems at Jedda and Waterfall need to be properly operated andmaintained and regular chlorine residual tests need to be continued.


Ongoing monitoring programIt is essential to continue the water monitoring program established during the project as a long termactivity for the rational assessment, development and management of the island’s water resources.A key issue addressed in the WMP (ACTEW (1999)) concerns the role and responsibilities of theAdministration (Commonwealth) for water resource management; in particular, the allocation ofwater for supply to the island community and also to the environment for conservation of flora andfauna. The national water reform agenda (refer COAG, 1994) places emphasis on the importance ofthis function and the need to use water resources on a sustainable basis. These objectives will bedifficult to achieve without commitment to the continuation of the water monitoring program nowdeveloped for Christmas Island.

In the foreseeable future, the current procedure for data processing, analysis and storage should becontinued. This requires data to be forwarded on a regular basis to an external agency (currentlyEcowise Environmental) for these tasks to be undertaken.It is recommended that the data is analysed and regular reports are prepared by the external agencyand submitted to the agency responsible for water resources management on the island. Theseshould comprise quarterly reports at the end of March, June, September and a longer annual reportat the end of December. This would be similar to procedures already implemented in the Cocos(Keeling) Islands. The reports should provide an analysis and summary of the previous period’sdata, provide an assessment of the general status of the water resources and highlight anynecessary corrective action. The annual report should provide a summary of all data for the yearand make recommendations about any necessary modifications to the monitoring program in thelight of possible changed circumstances.At some stage in the future, it may be possible to transfer some of the water resources analysisfunction to the appropriate agency on the island.

The costs of ongoing monitoring has been estimated according to three categories (data collectionand initial processing in Christmas Island, data analysis and reporting by an external agency andequipment repairs and periodic replacement). The average annual costs for two of the threecategories are:

• Category 2: (data analysis and reporting): $18,500• Category 3: (equipment repairs and periodic replacement): $3,500• Total $22,000

The costs for category 2 include an inspection visit (maximum of one week) to the island at two yearintervals. Costs for Category 1 (data collection and initial processing) can be obtained from theShire.In the immediate future, some specific monitoring items should be purchased and other workimplemented, as outlined in the recommendations.

Summary of RecommendationsSpecific recommendations are listed below. These recommendations are for consideration by theCommonwealth, the Administration and the Shire.

• Continue the water monitoring program, as outlined in section 7.7, as a long term activityfor the rational assessment, development and management of the island’s waterresources on an ecologically sustainable basis.

• The current procedure for data processing, analysis and back-up storage of the watermonitoring data should be continued. In the foreseeable future, this requires data to beforwarded on a regular basis to an external agency (currently Ecowise Environmental)for these tasks to be undertaken.

• Establish a formal reporting system whereby quarterly reports are prepared by theexternal agency and submitted to the agency responsible for water resourcesmanagement on the island. The reports should provide a summary of results andrecommendations arising from the monitoring and subsequent review and analysis ofdata. This would be similar to procedures already implemented in the Cocos (Keeling)


Islands. The estimated average annual costs are $18,500 for analysis, reporting and amonitoring visit at two year intervals.

• Provide funding for monitoring equipment replacements at an average annual cost of$3,500 (details are provided in Table 19, section 7).

• Predicted flows for Jedda from the rainfall-flow models developed during this Projectshould be checked against future monitored flows at Jedda and the results reported inthe proposed quarterly monitoring reports. Suggested modifications should berecommended.

• Purchase a small diameter water level sensor and data logger for monitoring selectedsalinity monitoring boreholes (approximate cost of $5,000).

• Purchase a replacement portable computer for water monitoring (approximate cost of$3,000).

• The survey levels on the tops of boreholes BH4 and BH5 should be checked.• Periodic flow data should be collected at the data loggers on the three key distribution

tanks (Drumsite, George Fam and Hospital) to check the status of the pipe systems fedby these tanks.

• Collect and analyse water samples every 12 months from the pollution monitoringboreholes at the current rubbish disposal area, nearby water sources (Jedda, Waterfall,Ross Hill Gardens) and selected Smithson Bight monitoring boreholes. Analyse thesefor water chemistry and potential contaminants. Ensure similar monitoring practice isadopted for approved new waste disposal sites. Note the importance of monitoring forpollutants and the procedures required in the event of pollution of an existing watersupply source.

• Adopt a salinity value (in electrical conductivity units) of 1,500 µS/cm as an upper limit forfreshwater groundwater, with a desirable objective of 1,000 µS/cm.

• If additional water resources development is undertaken in the future, install adequatemonitoring systems and allocate human resources to ensure that the impacts ofextraction on, and possible pollution of, the water resources are assessed.

• Employ land use controls, waste disposal restrictions and best waste managementpractice, together with the licensing provisions of the environmental protection legislation,to protect vulnerable groundwater resources. A ‘zero discharge’ policy is the mostappropriate for all potential pollutants over the whole island.

• As an approximate guide, no basal groundwater should be developed by pumping within500 m of the coastline.

• If production holes are drilled in the Smithson Bight area, they should be located atdistances of 1,000 m or more from the coastline and initially pumped at rates 3-5 L/s perborehole.

• Two investigation holes should be drilled between BN1 and WB30, south-west ofJane Up, to further assess the basal groundwater potential. This drilling should be doneat the same time as possible future production and monitoring borehole drilling.

• A capability to undertake an ongoing programme of ‘leakage control’ (comprising bothleak detection and rectification) should be developed and sustained within the watersupply authority. Equipment should be purchased and staff should be trained in thenecessary techniques for leakage detection. The budget needs to allow for such workas well as the ongoing repairs of pipelines as leaks are detected (refer to the WMP forfurther information on this aspect).


1. INTRODUCTION

1.1 OverviewThe objective of this report is to present the results of the Groundwater Investigations and Monitoring(GIM) Program undertaken on Christmas Island during the period from October 1996 to June 1999.This program was an integral part of the overall Christmas Island Water Management Plandevelopment process. Relevant information gained from the GIM program has been integrated intothe Water Management Plan (WMP).

1.2 BackgroundIn June 1995, ACTEW Corporation (ACTEW) was engaged by GHD Pty Ltd (formerly WORKSAustralia), acting as agents for the Department of Transport and Regional Services (formerly theDepartment of Environment, Sport and Territories) and the Christmas Island Administration, toundertake this project.

A significant part of the project, and the WMP Project for Christmas Island, was a major groundwaterdrilling program, followed by a period on monitoring. This component was required to better assessthe groundwater potential of the island and its vulnerability to contamination. The information gainedhas been integrated into the Water Management Plan (ACTEW, 1999). For the groundwater drillingactivity, ACTEW associated with Douglas Partners to undertake planning and supervision of thisprogram.

As outlined in the project brief (refer Annex A), the GIM program was required to address thefollowing components.

• Conduct a drilling and testing program (GIM1) to investigate:- the location and yields of fresh groundwater in both the perched groundwater in the

high level volcanic rock, and the basal groundwater body underlying the island, and- potential pollution in the vicinity of existing landfill and proposed landfill sites.

• Conduct the following specific studies in conjunction with, and following, the drilling:- recharge analysis (GIM2);- use of satellite imagery to locate freshwater flows (GIM3);- development of a rainfall-flow model for springs and Jedda Cave (GIM4);- development of an aquifer classification and vulnerability map (GIM5);

• Prepare a monitoring program for water resources and water supply (GIM6); and• Prepare a processing, archiving, analysis and reporting program and procedure for water

resources and water supply data (also GIM6).

The GIM components identified above were sub-components of ‘WMP3’ of the WMP project(ACTEW, 1999).

1.3 Structure of the ReportThis report follows the project brief in the same order as set out above. Where necessary, additionalsections with supporting information are included. The main sections of this report are:

• the drilling and testing program (section 2);• groundwater recharge assessment (section 3);• pilot satellite imagery study to locate coastal outflows (section 4);• rainfall-flow model for springs and Jedda Cave (section 5);• aquifer classification and vulnerability map (section 6); and• water monitoring program and data management procedures (section 7).


2. DRILLING AND TESTING PROGRAM

A network of 8 boreholes for water resources monitoring and 3 boreholes for pollution monitoring atthe current rubbish disposal landfill site were drilled in late 1996. While the drilling rig was on theisland, an additional 2 boreholes, beyond the scope of this project, were drilled for potentialstormwater disposal.

Full details of the boreholes for water resources monitoring, pollution monitoring and stormwaterdisposal are contained in a compendium of progress reports prepared by Douglas Partners, thedrilling supervisor (refer Douglas Partners, 1996). The locations of the boreholes are described inDouglas Partners, 1996 and shown in Figure 1.

Summary details of the 13 boreholes are provided in Annex B.

2.1 Water Resources Monitoring Boreholes

2.1.1 Background

Five of the water resources monitoring boreholes, denoted BH1 to BH5, are located in the SmithsonBight area, in two lines of holes at right angles to the coastline (refer Figure 2). This area wasconsidered to have the greatest potential for the occurrence of fresh groundwater, based on previousinvestigations (Barrett, 1985) and as outlined in the proposal for this project (ACTEW, 1995a). Thegroundwater in this area is often referred to as basal groundwater and it is found at and below sealevel.

The other three water monitoring boreholes, denoted BH6 to BH8, are located in the north-easternarea of the island. These are shown in Figure 3 with other boreholes drilled for pollution monitoring(BH9-BH11: refer section 2.2) and stormwater disposal (BH12, BH13: refer section 2.3). The north-eastern area was seen as having a lower but nevertheless a moderate potential for freshgroundwater compared with the Smithson Bight area (ACTEW, 1995a). The north-eastern area ofthe island is also considerably closer to settlements and, hence, if groundwater could be found there,it would be cheaper to develop than that located near the Smithson Bight area.

2.1.2 Details

All of the water resources monitoring boreholes, except one (BH3), consist of a set of between 3 and5 monitoring tubes, made from 25 mm PVC pipes. These tubes are terminated at different depthsand hydraulically isolated from each other by means of bentonite seals between the tube ends. Thepurpose of having multiple tubes in each borehole is to enable the groundwater to be tested at anumber of levels, which enables the relationship between depth below water table and salinity to beestablished at each monitoring visit. Borehole BH3 has a single tube, because of persistentcollapses within the borehole preventing further tubes from being installed.

Details of the depths of each of the monitoring tubes are contained in Annex C and summarised inTable 1. Annex C contains additional data on levels including the level of volcanic rock, if intersected.In Table 1, all levels which show negative values are below mean sea level (MSL).

Problems were experienced with cave-ins or collapses within the boreholes during installation ofsome monitoring tubes. This prevented all tubes from being terminated at the design depths. Anexample is BH1 where 5 tubes were intended for installation but only 4 were installed owing tocollapses. The top 2 tubes were designed for installation at depths of 164 m and 158 m belowground level (bgl). After the borehole partially collapsed, only one of these tubes was able to beinserted. This tube was subsequently found to be above the water table (151.2 m bgl or 4.2 m aboveMSL) and hence is ‘dry’ and not useful for groundwater monitoring purposes. Despite this problem,the 3 tubes below water table have provided good data. Another example is BH4 where tube 5 wasdesigned to be installed to a depth of 165 m (i.e. just below MSL) but this was not possible due to apartial collapse within the borehole to 161.6 m bgl. As a result, tube 5 of BH4 was installed to thisdepth which is approximately 3.3 m above MSL and found to be above the water table.


Figure 1 Christmas Island showing location of water sources and monitoring boreholes


Figure 2 Detailed location map of boreholes BH1-BH5 in Smithson Bight area


Figure 3 Detailed location map of boreholes BH6-BH13 in north-eastern area


Figure 4 Cross section through monitoring boreholes, BH1-BH3


Figure 5 Cross section through monitoring boreholes, BH1-BH3 and Jane Up, Jedda Cave and Grant’s Well


Table 1 Summary of monitoring tubes at water resources monitoring boreholes

Borehole Number of Levels relative to mean sea level (m)

Number Monitoringtubes

Tube 1 Tube 2 Tube 3 Tube 4 Tube 5 Top of volcanicrock

BH1 4 -30.19 -20.59 -14.59 4.21 -22.6

BH2 3 -18.16 -0.21 4.69 not intersected

BH3 1 -1.18 not intersected

BH4 5 -24.14 -18.14 -12.14 -6.14 3.28 -32.6

BH5 5 -33.72 -27.73 -21.73 -15.73 -9.73 -35.3

BH6 3 8.04 14.05 20.05 13.2

BH7 3 36.38 47.98 50.88 40.4*

BH8 3 72.66 80.66 96.64 97.2

Notes: 1. permanently ‘dry’ tubes (i.e. terminated above the water table (except in initial stages) are shaded grey2. BH7 (*): volcanics with limestone from 31 – 67 m bgl (RL 109.4 –74.4) and 90 - 100 m bgl (RL 50.4 -

40.4); volcanics (basalt?) below 100 m bgl (RL 40.4).

From Table 1, it can be seen that all boreholes in the Smithson Bight area (BH1 to BH5) had tubesinserted at depths below MSL. All boreholes in the north-eastern area were completely above MSL.

The ‘dry’ tubes indicated in Table 1 comprise two types, with one type corresponding to boreholes inthe Smithson Bight area and the other type to boreholes in the north-eastern area. In all cases, thedry tubes are the shallowest in the affected boreholes. The dry tubes in boreholes BH1, BH2 andBH4 are due to their bases being above the water table of the basal groundwater. These tubes hadwater in them only for a short period after the drilling process. The dry tubes in BH6 and BH7 aresignificantly above the volcanic basement. In BH6, the dry tube terminates approximately 7 m abovethe volcanic basement in limestone. In BH7, one dry tube terminates in limestone about 0.5 m abovea volcanic layer in a sequence of limestone and volcanic layers (about 10 m above the apparentvolcanic basement). The middle (no. 2) tube at BH7, also located in this sequence about 7 m abovethe apparent volcanic basement, has also been dry since early 1998.

2.1.3 Monitoring data

Since installation of the boreholes in late 1996, monitoring of water level and salinity has beenundertaken by Shire staff on a periodic basis. Depths to water table are measured with a water level‘dipper’. This procedure enables the water level to be measured in each tube from a known level atthe top of each borehole. The water salinity (measured in terms of electrical conductivity or EC) ismeasured in each tube by obtaining samples with a bailer and measuring the salinity with a portableEC meter.

Depth, water level and salinity (EC) data is presented in Annex C for each borehole. The period ofmonitoring is from shortly after drilling (October/November 1996) to May 1999. Graphs showing thevariations in salinity and water level over time are shown in Annex D for each tube in boreholes BH1to BH8.

2.1.4 Analyses of data - overview

The data obtained at each borehole for the period October/November 1996 to May 1999 has beenused in the analyses. These analyses were firstly made of the data from individual boreholes. Inaddition, the data from all five boreholes in the Smithson Bight was reviewed to assess the general


groundwater situation in that location. A similar general assessment was done for the threeboreholes in the north-eastern area of the island.

2.1.5 Analysis of Smithson Bight borehole data

The five boreholes in the Smithson Bight area (refer Figures 1 and 2) show that a freshwater aquiferoccurs in contact with underlying seawater. This is a typical coastal aquifer situation whereoutflowing freshwater from the island gradually mixes with the underlying seawater. This coastalaquifer occurs as a thin wedge of freshwater that is thicker inland and gradually diminishes towardsthe coastline. This can be seen in the cross section diagrams though boreholes BH1 to BH3 andother relevant locations in Figures 4 and 5.

If the freshwater extends under the island, and consequently through the volcanic core of the island,then the known coastal aquifer at this location would be part of an island-wide three dimensional‘freshwater lens’. The actual situation is not known as no deep investigatory drilling has occurred inthe centre of the island. For the purposes of the WMP it cannot be assumed that the freshwaterextends under the island. Further deep drilling would be required to assess this situation.

In order to estimate the extent of the freshwater resource in a coastal aquifer/freshwater lenssituation, it is necessary to define a maximum salinity (EC) value for freshwater. From previouswork in the Cocos (Keeling) Islands (e.g. Falkland, 1992; Pink & Falkland, 1999) an EC value of2,500 µS/cm was used as a maximum limit for freshwater based on its approximate equivalencewith a chloride ion concentration of 600 mg/L. A desirable upper limit of 1,500 µS/cm was alsodefined for the Cocos (Keeling) Islands which is approximately equivalent to the drinking waterguideline value of 250 mg/L for chloride ion (NHMRC/ARMCANZ, 1996). For Christmas Island, it isrecommended that 1,500 µS/cm be used as an upper limit and a desirable objective be defined as1,000 µS/cm. This is based largely on a comparison with the salinity of the water supply fromcurrent sources which is approximately 500-600 µS/cm. It could reasonably be argued that as thepopulation has become used to a salinity value at this level and as the water resources of ChristmasIsland are more extensive than in the Cocos (Keeling) Islands, a 1,000 µS/cm upper limit should beadopted.

A description of the results from each borehole, as shown in Annexes C and D, follows.

Borehole BH1

This borehole is approximately 1,400 m from the coastline. Data obtained from BH1 showsfreshwater extending to a depth between the bottom of tubes 2 and 3, (i.e. to a depth between14.6 and 20.6 m below MSL: probably to about 18-19 m below MSL or about 19-20 m belowwater table). From Graph D1 in Annex D, the salinity varies with time. The initial salinity valuesin late 1996 should be disregarded as these were obtained soon after drilling when the watercolumn was disturbed and not representative of the surrounding aquifer conditions. All threetubes show a decrease in salinity to the middle of 1997, followed by an increase until early1998, followed by another decrease. These variations are consistent with the preceding (orantecedent) rainfall patterns, as described later in this section.

The least variation in salinity occurs in the shallowest (No 3) tube and the most variation in thetwo deeper tubes. Since 1997, the salinity in tube 3 has not been greater than 650 µS/cm,which is a very good result. Since the end of 1998, the salinity has been below 500 µS/cm.The salinity in tube 2 has varied from less than 1,500 to greater than 2,100 µS/cm (or slightlyabove the defined upper limit for freshwater).

In addition to salinity data, the water level data for the three tubes was reviewed (refer toAnnex C and Graph D2 in Annex D). Water level in this general area can be influenced bytides, by seasonal variations in recharge and, if it is occurring, by the influence of pumping.Borehole BH1 is sufficiently far inland for the tidal influence to be small, although no specificmeasurements of this were undertaken to prove this. In general, the water level responds inan inverse manner to salinity (i.e. increases in salinity are mirrored by decreases in water leveland vice versa). The water level movements in the three tubes tend to be similar.


One exception is the reading from tube 2 on 6 August 1997, which may be a reading error.This seems to be the most likely explanation, as on other occasions all 3 tubes give similarreadings. It is noted that readings at tube 3 only were obtained in late October and earlyNovember 1998, as by then it was apparent that similar responses were observed in all3 tubes. No readings were obtained in February 1999 due to a broken ‘dipper’. The readingobtained on 29 October 1998 may be in error (3.31 m) as only a few days later a reading of2.61 m was obtained.

As would be expected, the variations in salinity and water level appear to be influenced byantecedent rainfall conditions, and hence the pattern of recharge to groundwater. The linkageof groundwater salinity and water level patterns with rainfall is apparent from inspection of themonthly rainfall pattern and ‘drought index’ (refer Figure 6). The drought index is a measure ofhow dry the conditions are at a particular time based on preceding rainfall over the previous12 months.

Figure 6 Jedda monthly rainfall and drought indices, Jan 1995 – May 1999

As is the case with the response of flow at Jedda Cave and spring sources (refer section 5),the response of the groundwater at BH1 is delayed some months behind rainfall changes.This can be explained by a couple of examples. The lowest rainfall during the period ofobservation fell in the 5 month period September 1997 to January 1998. The correspondinghighest salinity and lowest water levels occurred in February 1998. Although the frequency ofdata collection was 6 months at this time, which is too coarse for accurate assessments oflags, it appears that the groundwater response is several months behind the rainfall decrease.Likewise, significant salinity decreases and water level increases occurred in November 1998due to heavy rainfall in the period from March to July 1998. From the limited data available, itappears that the groundwater level and salinity response lags at least 4 months behindsignificant rainfall variations. This is consistent with the observations at Jedda cave that flowlags between 2 and 3 months behind rainfall (refer section 5).

0

100

200

300

400

500

600

700

800

Jan-95 Jul-95 Jan-96 Jul-96 Jan-97 Jul-97 Jan-98 Jul-98 Jan-99

Month & Year

Mon

thly

Rai

nfal

l (m

m)

0

500

1,000

1,500

2,000

2,500

3,000

Dro

ught

Inde

x

Jedda monthly rain Drought Index (using 0.9 factor)


In borehole BH1, volcanic rock was intersected at a depth of 22.6 m below MSL, or about 2 mbelow the base of tube 2 and 7.6 m above the base of tube 1. The similar salinity and waterlevel responses observed in both tubes indicates that the volcanic rock in this location is quitepermeable and similar in a hydrogeological sense to that of the overlying limestone. Thisindicates that at least in this area, the volcanic rock represents no effective barrier to themixing of fresh and salt water.

From the data obtained to date, the water level at this location has generally been between 1 mand 1.5 m above MSL. This is an indication in itself of a reasonably thick freshwater zone, andsupports the salinity observations. Based on the water level and salinity data, the approximatethickness of the freshwater zone at this borehole (from water table to the depth at whichsalinity equals 1,500 µS/cm) is estimated to be about 20 m.

Borehole BH2

This borehole is approximately 850 m from the coastline. Data obtained from BH2 showsfreshwater extending at least to the base of tube 1 (i.e. to a depth 18.2 m below MSL). Thevariation in salinity follows a similar pattern to that shown for BH1. The reading of salinity on5 August 1998 (200 µS/cm) is suspected of being in error, as it is much lower than previousand subsequent readings. It is also not consistent with the majority of other readings forfreshwater in this area (generally in range from 450 to 600 µS/cm). The data in Graphs D3 andD1 shows that salinity at BH2 tube 1 is consistently lower than at for BH1 tube 2, although thelatter tube is only 2.4 m lower than the former. This may indicate that the limit of thefreshwater zone (to 1,500 µS/cm) is at or about 20 m below MSL in the general area of bothboreholes BH1 and BH2. This represents a substantial thickness of freshwater. It isinteresting to note that the freshwater zone did not contract much during the significantly lowerthan average rainfall in 1997 and early 1998.

Water level variations at the two tubes (refer Graph D4) show consistent results. Thevariations show similarity with those of BH1, although there are some differences. In particularthere are significant water level fluctuations in the second half of 1998. The reasons for thismay be variations in rainfall, tidal effects (not determined) or possibly some data inaccuracies.

To better understand the dynamics within the borehole, it would be necessary to install a waterlevel recording device. Small diameter water level sensors, suitable for use in the PVC tubes,are available. Such a sensor could be linked to a data logger at the surface and set to recordat intervals of approximately 10 minutes. The sensor and logger could be installed on arotating basis at several boreholes to establish the variations in water level due to tides andother influences. It is recommended that one such unit be purchased and used as part of thefuture monitoring program on the island.

Volcanic rock was not intersected at this borehole.

From the data obtained to date, the water level at this location has generally been betweenabout 1 m and 1.5 m above MSL. As with borehole BH1, this is an indication of a reasonablythick freshwater zone, and supports the salinity observations. Based on the water level andsalinity data, the thickness of the freshwater zone at this borehole (from water table to thedepth at which salinity equals 1,500 µS/cm) is at least 19 m.

Borehole BH3

This borehole is approximately 450 m from the coastline on the same line as BH1 and BH2.There is only one tube at BH3 which shows that the salinity is well above the freshwater limit(refer Graph D5). The values have generally been in the range 5,000 - 10,000 µS/cm duringthe period of record. The measured water levels at BH3 (refer Graph D6) are much lower, asexpected, than at BH1 and BH2. This observation is also consistent with the higher salinity atBH3. The water levels have generally been in the range from 0 to 0.5 m above MSL. Theaverage groundwater level at this site is probably only a few centimetres above MSL. Also, thegroundwater level fluctuations at this site, close to the coastline, are most probably atapproximately the same amplitude as that in the open sea. This conclusion is based on


observed water level measurements made within Daniel Roux Cave on the north side of theisland at approximately the same distance from the coastline.

Volcanic rock was not intersected at this borehole.

From the available data at borehole BH3, there is no freshwater at this site. This indicates themixing of freshwater and seawater occurs at a distance of at least 450 m in from the coastlinein this zone. This is not surprising given the highly karstic limestone in this area (and most ofthe island’s coastline) which enables easy passage of water and hence mixing within the manyfractures and cave systems.

Borehole BH4

This borehole is approximately 1,250 m from the coastline on a line with BH5 and is equippedwith 4 tubes. Data obtained from BH4 (refer Graph D7) shows freshwater extending to thebase of (the deepest) tube 1 (i.e. to a depth of 24.1 m below MSL). There has been aremarkable consistency in salinity values, which have remained low (below about 650 µS/cm)for the top 3 tubes during the period of record. The salinity in tube 1 has remained below1,200 µS/cm during the same period.

Water level variations at the four tubes (refer Graph D8) show reasonably consistent results.The very high value (2.75 m) obtained on 28 October 1998 is suspected of being a data error.Only further data collection will indicate if this is a realistic result or not. The water levelsshown at BH4 are generally between 0.5 and 1.0 m above MSL. The water levels are lowerthan expected when compared with the salinity data from this borehole and the comparison ofthe results for BH1 and BH2. It would be expected that the water levels should be somewherebetween 1 m and 2 m above MSL, based on the low salinity data obtained and the distancefrom coastline. This may indicate a survey level error at this borehole. It is recommended thatthe survey level at the top of this borehole be checked.

According to the drill logs (Douglas Partners, 1996), volcanic rock was possibly intersected ata depth of 197.5 m (approx 32.6 m below MSL).

From the data obtained to date, the freshwater zone is at least 24 m thick at BH4, which liesentirely within the limestone sequence.

Borehole BH5

This borehole is approximately 650 m from the coastline and is equipped with 5 tubes, with thedeepest (tube 1) extending to 33.7 m below MSL and the shallowest (tube 5) extending to9.7 m below MSL. Apart from one monitoring date (29 October 1998) when salinity values ofabout 2,000 µS/cm were measured in 3 of the 5 tubes (data is suspected of error), all othersalinity values have been in the range from about 4,700 µS/cm to about 40,000 µS/cm (referGraph D9). These latter values represent relative salinities of about 10% and 80% ofseawater. They are well beyond the freshwater limit, showing that there is no freshwater atthis location.

The measured water levels at BH5 (refer Graph D10) are higher than expected for a holewhere the salinity is high. The levels have generally been in the range from 0.5 to 1.5 m aboveMSL. A lower level, somewhere between 0 and 1.0 m above MSL would be more plausible,given the salinity data. This may indicate a survey level error at this borehole. Thegroundwater level at BH5 is likely to be largely affected by tides as for BH3. This would havesome impact on observed levels depending on the time of observations. However, all readingsare relatively high. Accordingly, it is recommended that the survey level at the top of thisborehole be checked.

It is noted in Graph D10 that the water levels at the deepest tube (tube 1) are consistently lessthan at the other 4 tubes (except for readings for tube 2 on 12 August 1997 and for tube 5 on18 May 1999). The reason for these differences is not known at this stage. Future datacollected at tubes 1 and 5 will need to analysed to determine if the differences continue or havelargely gone, as indicated in the May 1999 readings.

Volcanic rock was intersected at a depth of 131.9 m below the ground (or 35.3 m below MSL).


2.1.6 Analysis of north-eastern area borehole data

The three water monitoring boreholes in the north-eastern area (refer boreholes BH6, BH7 and BH8in Figures 1 and 3) show evidence of perched freshwater within the volcanic rock. A brief descriptionof the results for each borehole, as shown in Annexes C and D, follows.

Borehole BH6

This borehole is approximately 750 m from the coastline. All three monitoring tubes wereterminated above MSL (8.0, 14.0 and 20.0 m, respectively, above MSL). Volcanic rock waspenetrated at a depth of 122.8 m, or 13.2 m above MSL. This means that the deepest tube(tube 1) is terminated in the basalt while the other two are wholly within limestone. As all tubesterminate well above sea level, there is no direct hydraulic connection with seawater andhence no chance of mixing with it.

During the monitoring period, only the middle tube (tube 2) has shown consistent evidence ofwater. The other two tubes have normally been found dry or have inconsistent results. Thesalinity of the water in tube 2 has varied between about 440 and 930 µS/cm, with the highestvalue occurring near the end of the dry period in 1997 and early 1998 (refer Graph D11).

The depth of water in tube 2 has varied from about 1.3 m to 2.5 m above the base of the tube(14.0 m above MSL) as shown in Graph D12. The first reading, which shows a level below14.0 m can be discounted (most probably a data error). The depth of water is quite shallowwithin the hole, although it remained consistent through the dry period.

The fact that tube 2, which terminates in limestone just above the volcanic rock, holds waterwhile tube 1, terminating within volcanic rock, does not hold water indicates the complex natureof the geology. It would appear that in this hole, the volcanic rock is quite permeable at thelevel of tube 1, and that the zone near the limestone-volcanic interface is quite impermeable.

Based on the salinity and water level data, the potential for reasonable groundwater yields islow. The fact that only one of the three tubes showed consistent freshwater indicates thepotential difficulty of selecting suitable target depths for production boreholes. The only tubethat showed freshwater has a limited depth of water that could easily be drawn down atpumping rates of more than about 1 L/s. Even this water showed an increase in salinity in thedry period which adds to the uncertainty of the suitability of this site for drilling. Overall, thepotential for fresh groundwater development in the immediate area of BH6 is low.

Borehole BH7

This borehole is approximately 1,000 m from the coastline. All three monitoring tubes wereterminated above MSL (36.4, 48.0 and 50.9 m, respectively, above MSL). Interbedded volcanicrock with limestone was intersected at a depth of 90 m and fully volcanic rock was penetratedat a depth of 100 m, or 40.4 m above MSL (refer Annex C). Thus the deepest tube (tube 1) isterminated in volcanic rock, the middle tube is terminated in mixed limestone and volcanicsand the highest tube is wholly within limestone. As all tubes are well above sea level, there isno direct hydraulic connection with seawater and hence no chance of mixing with it.

Only tube 1, the deepest tube, has shown consistent evidence of water. Tubes 2 and 3 initiallyshowed some evidence of a water table but no samples could be collected. This probablymeant that wet sediment only was present. Later monitoring has shown both of these tubes tobe dry. The salinity of the water in tube 1 has varied between about 880 and 1,250 µS/cm, withthe highest values occurring in mid-1998 (refer Graph D13). This salinity is higher than inborehole BH6 and in the shallower tubes of the freshwater boreholes (i.e. BH1, BH2 and BH4)in the Smithson Bight area.

The depth of water in tube 2 has varied from about 1.9 m to 2.7 m above the base of the tube(36.4 m above MSL) as shown in Graph D14. The first water level shown was obtained justafter drilling (28 November 1996) when the water column was disturbed by the drilling process,and should not be considered in this analysis. The depth of water within the hole is quiteshallow and the water is entirely within the volcanic rock (i.e. not above RL 40.4 m). During thedry period of 1997, the water level dropped about 0.5 m. By May 1999, the water level reachedthe highest level during the monitoring period.


Based on the salinity and water level data, the potential for reasonable groundwater yields islow. This opinion is based mainly on the fact that the water salinity is reasonably high and thatthe depth of water in tube 2 is reasonably low. This limited water could easily be drawn downat pumping rates of more than about 1 L/s. As with borehole BH6, only one of the three tubesshowed freshwater, indicating the potential difficulty of selecting suitable target depths forproduction boreholes. Overall, the potential for fresh groundwater development in theimmediate area of BH7 is assessed as low.

Borehole BH8

This borehole is approximately 850 m from the coastline. As for BH6 and BH7, all threemonitoring tubes were terminated above MSL (72.7, 80.7 and 96.6 m, respectively, aboveMSL). Volcanic rock was penetrated at a depth of 47.5 m below surface, or 97.2 m above MSL(refer Annex C). All tubes are terminated in volcanic rock. They are well above sea level andhence there is no chance of mixing with seawater.

The lower two tubes (Nos 1 and 2) have shown consistent evidence of water. Tube 3, theshallowest, has never shown sufficient water to obtain a sample. The salinity of the water intube 1 has varied between about 470 and 800 µS/cm (refer Graph D15), while the salinity ofthe water from tube 2 has been lower (250-600 µS/cm). As with most other boreholes, thehighest salinities were observed in late 1997 and the first part of 1998. The lowest salinitieshave been observed in early 1999. Overall, the water salinity at this location is the best of allthree boreholes in the north eastern part of the island.

The thickness of water in the two tubes is substantial. The water depth in tube 1 has variedfrom about 21 m to 22 m above the base of the tube (at 72.7 m above MSL) as shown inGraph D16. Similarly, the water depth in tube 2 has varied from about 13.5 m to 14 m abovethe base of the tube (at 80.7 m above MSL). The variation in water level at tube 2 has beensmall even during the drought period of 1997. These water depths are much greater thanobserved in the BH6 and BH7 monitoring tubes. Also the water level in the two tubes is atapproximately the same elevation above mean sea level indicating that the tubes areterminated in the same groundwater system (aquifer).

Based on the salinity and water level data, the potential for reasonable groundwater yields ismoderate. It appears that a substantial body of water may be located in the volcanic rock inthis area. The extent of the aquifer is unknown and further exploratory drilling and pump testingwould be required to ascertain its extent and potential for groundwater extraction.

2.1.7 Summary and conclusions from the 1996 drilling program

The monitoring boreholes in the Smithson Bight area found a significant volume of fresh ‘basal’groundwater, while those in the north-eastern area of the island found perched groundwater inrelatively small quantities. The basal groundwater in the Smithson Bight area is in the form of acoastal aquifer above and in contact with seawater.

A summary of freshwater conditions identified at each of the eight boreholes is shown in Table 2.

The area of the island to the north of Smithson Bight offers good potential for the development offresh groundwater. Based on data from boreholes BH3 and BH5, there is unlikely to be freshwaterwithin about 500 m of the Smithson Bight coastline. It is recommended that production boreholes beinitially at distances of 1,000 m or more from the coastline and pumped at rates 3-5 L/s per borehole.It may be possible to alter these rates after a period of monitoring of the salinity response within thegroundwater, as measured by a network of salinity monitoring boreholes. A salinity monitoringborehole should be drilled close (at a distance of approximately 10 m) to each production borehole.

Limited perched groundwater was found in the drilling investigations as part of this project in thenorth-east part of the island at boreholes BH6, BH7 and BH8. Based on monitoring of water levels inthe monitoring tubes at each borehole, only BH8 is considered to have potential for moderate yields(possibly 1-2 L/s). Further exploratory drilling and pump testing in the area of BH8 would be requiredto confirm this. No pump testing was planned nor conducted as part of the current investigations.


Table 2 Summary of conditions at water resources monitoring boreholes

BoreholeNumber

Distance fromcoastline (m)

Freshwater conditions & potential for groundwater extraction

Smithson Bight area

BH1 1,400 Freshwater zone approx. 20 m thick. High potential. Good access.

BH2 850 Freshwater zone at least 19 m thick. High potential. Difficult access.

BH3 450 No freshwater zone. Potential nil.

BH4 1,250 Freshwater zone at least 24 m thick. High potential. Good access.

BH5 650 No freshwater zone. Nil potential.

North eastern area

BH6 750 Small quantity of freshwater. Low potential.

BH7 1,000 Small quantity of freshwater; higher salinity than BH6. Low potential.

BH8 850 Substantial quantity of freshwater. Moderate potential. Would requirefurther exploratory drilling & pump testing to confirm potential.

Comparing the north-eastern area with the Smithson Bight area, the former has the advantages ofless depth to groundwater (approx. 50-100 m compared with approx. 150 m) and proximity topresent and likely demand centres. The Smithson Bight area has the advantage of larger yield perborehole, greater ability to cope with extended droughts and it is further from present pollutionsources. On balance, it is concluded that the Smithson Bight area is a better location for futuregroundwater development than the north-eastern area. The north-eastern area, in the vicinity of BH8should be further investigated, however, if a drilling rig is brought to the island to undertake drillingwork for proposed production and monitoring boreholes in the Smithson Bight area

2.1.8 Selected results from previous drilling programs

(a) WB72 and WB73 in Smithson Bight areaPrevious drilling for water resources purposes has been undertaken on Christmas Island, betweenthe mid 1960s and the early 1980s. Results are summarised in Barrett (1985) and in section 6 ofthis report. The results of the previous drilling indicated the best potential was in the Smithson Bightarea, which is the reason for this project targeting that location as a primary option.

Two boreholes (WB72, WB73) that were drilled in a preliminary investigation of the Smithson Bightarea in 1994 were monitored during the current project. The locations of these boreholes are atdistances of 560 m and 400 m, respectively, from the coastline (refer Figure 2).

The results of water level and salinity monitoring at both boreholes for two periods, one in late 1986and the other in late 1996 are summarised in Table 3. The water levels were measured with thedipper and converted to heights above MSL using survey data shown in Annex B. Salinities ofsamples bailed from the boreholes were measured with a portable EC meter.

The 1986 results show that the groundwater in both boreholes was fresh while the 1996 resultsshow salinities above the freshwater limit. This is most probably due to the lower rainfall conditionspreceding the 1996 tests than those occurring prior to the 1986 tests. It would be expected that thewater level range from the 1986 tests were higher than those in 1996, but the data indicates theopposite. The reason(s) for this are not known, but could be partly due to the times of observationwith respect to tidal movements.

From a water resources viewpoint, the most important data is the water salinity. It appears that indrier periods, such as experienced at the time of the 1996 tests (after a very dry six months), thewater in these boreholes becomes unacceptable. Any pumping of water from these locations would


quickly lead to higher salinities being induced due to intrusion (upconing) of underlying brackishwater/seawater.

Table 3 Summary of water level and salinity data from boreholes WB72 and WB73

BoreholeNumber

Period Water levelrange(m) bgl

Water Levelrange

(m) above MSL

Salinity(measured as EC)

(µS/cm)

WB72 30 Sep – 4 Oct 1986 40.4 - 40.5 0.6 - 0.7 1,230 – 1,330

“ 27 Oct – 16 Nov 1996 39.6 – 40.4 0.7 - 1.2 2,480 - 2,920

WB73 30 Sep – 4 Oct 1986 14.7 – 15.1 0.3 – 0.7 660 - 670

“ 27 Oct – 16 Nov 1996 14.2 - 14.6 0.8 - 1.2 1,700 - 2,080

Overall, the data from these two boreholes confirms the results from the 1996 drilling program. Thelimit of the freshwater aquifer under dry conditions is likely to be inland from WB72 but not as farinland as BH2.

(b) Area near WB30An area which has potential for basal freshwater and has the advantage over boreholes in theSmithson Bight area in being closer to existing water supply infrastructure (e.g. the large storagetank at Jedda), is the area near Water Bore 30 (WB30) to the south-west of Jane-Up (refer Figures 1and 2). This location is north-east of the line of boreholes BN1-BN2-BN3, and has an elevation ofapproximately 170-180 m above MSL. This elevation is not much higher than the elevation of theground at the two deepest boreholes drilled in 1996 (BH1 and BH4 at 155 m and 165 m above MSL,respectively). A number of water bores in the area of WB30, drilled in the 1960s, intersectedperched water above the volcanic rocks. Borehole WB30 has a surface elevation of approximately172 m above MSL. The elevation of the perched groundwater at this site was approximately 147 m(depth approximately 25 m bgl) in April 1969 ((BPC Drawing 69-X9E/X63). In September-October1986, the depth to water level was measured at 33-34 m bgl (138-139 m above MSL).Hence, it is known that perched groundwater is evident in this area. This appears to be perchedabove volcanic rock; BPC Drawing 69-X9E/X63 indicates ‘hard basalt’ at 123 m above MSL, near thebase of the hole. Limited pump testing in the 1960s from this hole indicated a yield of 4,500 gallonsper hour (i.e. 5.6 L/s).

It is possible that the basal groundwater extends under the island from the Smithson Bight area upto, and further north than this area, but no deep drilling to near or below MSL has been undertakennorth of BN1 to investigate this matter. The nature and extent of any basal groundwater in this zonewould be dependent on the permeability of the volcanic rock near the mean sea level. It isrecommended that two investigation holes be drilled between BN1 and WB30 at suitable locations toassess the basal groundwater potential further. This drilling should be done at the same time asother drilling described above. If hard volcanic rock is intersected in either or both of these boreholesthen the drilling can cease. The water level conditions should be checked after drilling to assess thepotential for future pumping from either a perched or basal aquifer.

2.2 Pollution Monitoring Boreholes

2.2.1 Details

Three monitoring boreholes (BH9, BH10 and BH11) were drilled around the edge of the presentrubbish disposal area. Each borehole is cased with 50 mm PVC pipe, which is screened over thebottom 6 m. Details of each of the three boreholes is given in Annex E.

Due to early problems with the drilling program, each borehole was initially not drilled to below watertable, but rather was terminated at a depth of about 50 m below ground surface. Later, boreholes


BH9 and BH10 were deepened to, respectively, 91.7 m and 108.8 m. Volcanic rock was intersectedat depths of 87 m (RL 210.1) and 107.5 m (RL 186.6), respectively, in these two holes. BoreholeBH11 is entirely within limestone.

From the results for BH9 and BH10, it is apparent that there is a significant variation in the level of thelimestone-volcanic contact even over relatively short distances. The distance between BH9 andBH10 is only 130 m.

2.2.2 Monitoring results

Boreholes BH9 and BH10 have consistently had water in them, indicative of a perched groundwatersystem. At BH9, the water level has varied between RL 206.6 and RL 210.3 (water depth in the holebetween 1.2 m and 4.9 m). At BH10, the water level has varied between RL 199.7 and RL 200.5(water depth in the hole between 11.8 m and 12.6 m). From these results, there is a moreconsistent water level in BH10 where the level of the volcanic contact was lower than at BH9.

Measurements of salinity at both boreholes indicate generally similar values obtained from otherperched groundwater sites on the island (e.g. Waterfall, Jedda).

Two sets of water quality tests for a range of potential pollutants were obtained from boreholes in1998. These are described in section 7.5.3 and the results are shown in Annex R. Water samplesfrom Jedda Cave were also tested. The tests covered a range of hydrocarbons, pesticides, PCBs,nutrients and heavy metals.

The test results showed there was no sign of pollution at these three sites except for a higher thanguideline value for lead at BH10. The test result showed 19 µg/L compared with the AustralianDrinking Water Guidelines (NHMRC/ARMCANZ, 1996) value, based on health considerations, of10 µg/L.

2.2.3 Conclusions

The two operational pollution monitoring boreholes have so far indicated no chemical pollution exceptfor a higher than acceptable level of lead in one borehole.

An ongoing monitoring program is required for these boreholes. Details are provided in section 7.7.

2.3 Stormwater Discharge BoreholesDetailed consideration of two boreholes (BH12 and BH13), which were drilled in the 1996 programfor potential stormwater discharge, is beyond the scope of this report. However, a summary of theresults from a water resources viewpoint is provided.

Details of the drilling logs and initial water level and salinity data are contained in Douglas Partners(1996). The subsequent monitoring data is not shown in the Annexes of this report but is availableon a spreadsheet of borehole monitoring data established for the Shire of Christmas Island(Boreholes.xls).

BH12 is located in Poon Saan near Christmas Island Hardware, while BH13 is located in the lowerpart of Silver City near the ‘incline’. The approximate distances of these boreholes from the coastlineat the Settlement are 800 m and 350 m, respectively. Borehole BH12 was drilled to a depth ofapproximately 10 m below MSL (160 m bgl). Monitoring of water level from the time of drilling inNovember 1996 to May 1999 shows that the water level has fluctuated slightly above and below MSL(from RL -0.91 m to RL +0.14 m). Salinity values have varied between about 15,000 µS/cm(approximately 30% seawater) and 25,000 µS/cm (approximately 50% seawater) during this period.These results show a high level of connectivity with underlying seawater and the absence of afreshwater zone. From a water resources viewpoint, this is an interesting result given the location ofthe borehole. It effectively means that there is no freshwater within the basal groundwater at adistance of 800 m from the coastline in this area.


It is further noted that BH12 could be converted into a stormwater discharge bore for two reasons:• the data suggests a highly permeable formation, and• there is saline water at the base and hence there is very little chance of polluting

available freshwater resources.

It is further noted that the area around BH12 is urbanised and hence pumping of fresh groundwater inthis area, even if it did exist, would be highly unlikely due to the potential for contamination.

Borehole BH13 was drilled to a depth of approximately 15 m below MSL (103 m bgl). BH13 wasconverted into a stormwater discharge borehole in late 1997. Prior to this, the available data(November 1996 to August 1997) indicated variable salinity results from quite saline (37,000 µS/cm)to quite fresh (682 µS/cm). The reason for this large variation is not known, but it could indicate adata error. Water levels varied between RL +0.13 m and RL +0.95 m.


3. GROUNDWATER RECHARGE ASSESSMENT

3.1 OverviewAn assessment of recharge to groundwater from rainfall is an integral part of normal groundwaterinvestigations, and is necessary in order to estimate sustainable yields of groundwater systems.Such an assessment provides knowledge of the input of water to the island groundwater systemand, through this, can provide an upper limit to the amount that can be developed in a sustainablemanner. For small islands, such as Christmas Island, where significant quantities of the freshgroundwater are in contact with seawater, only a fraction of recharge can be safely extracted. Someis required to maintain the integrity of the freshwater zone by flushing salts from the base of thiszone.

A previous estimate of recharge for the island was 30% of rainfall (Falkland, 1986). This was basedon a comparison with some other islands, and not on local data.

For this project, a more accurate assessment was carried out by means of a water balanceprocedure, which made use of local rainfall and evaporation data and took account of the island’svegetation and soil conditions.

3.2 Outline of Recharge Assessment ProcedureAs mentioned above, a water balance procedure was adopted to determine recharge togroundwater. The main elements of the hydrological cycle are often analysed by means of a waterbalance equation, which equates inputs to outputs, storage terms and a possible error term toaccount for both errors in measurement and unknown or unquantified terms.

For a small island, the water balance is normally considered on an island wide scale, although forspecific problems sub-areas may also be considered. Once the domain is defined, the waterbalance can be conveniently considered within two reference zones (Chapman, 1985). These arethe island's surface, consisting of vegetation, soils and the unsaturated zone (above the water table),and the groundwater system (below the water table).

At the surface of the island, rainfall is the input and evapotranspiration and recharge to groundwaterare outputs. Soil moisture and interception on leaves and other surfaces are storage terms. For thegroundwater system, recharge is the input with the outputs being losses to seawater (due tooutflows at the perimeter and dispersion at the base of the groundwater system) and abstraction.For the present analysis, it is the water balance at the surface that is of interest, as this is the waterbalance used to estimate recharge.

On small islands with highly permeable soils there is no or very little surface water runoff from theisland. The soils on Christmas Island are permeable and allow fast percolation of water after rainfall.Runoff does not generally occur except on paved areas and compacted surfaces, which arenormally associated with the urbanised areas in the north-eastern part of the island. In the urbanareas, stormwater collection systems direct the runoff via pipes and channels to the sea or in onecase to a stormwater discharge borehole. On unaltered terrain, runoff does not normally occurexcept after very heavy rain and on steep slopes. If runoff occurs, most of this re-enters the groundbefore it reaches the edge of the island. In isolated cases around the island, runoff occurring on thefirst terrace can discharge directly to the sea. On an island-wide scale and in the long term, theamount of runoff that is lost from the island is considered to be negligible. Hence, for the island’swater balance, surface runoff can be ignored. Thus, the water balance equation at the surface canbe expressed as:

R = P - ETa + dVwhere

R = recharge to groundwater,P = rainfall,Eta = actual evapotranspiration, and


dV = change in soil moisture store.

If surface runoff was important then it would be another component of the right hand side of theabove equation.

Figure 7 shows the relationship between these parameters and others described below.

Interception by vegetation and other surfaces can be treated as a separate term in the waterbalance, but here it is included with ETa since the intercepted water is evaporated. ETa can beconsidered to comprise three components, namely, interception losses (EI), evaporation andtranspiration from the soil zone (ES), and transpiration of deep rooted vegetation directly fromgroundwater (TL).

Figure 7 Water balance model for typical surface zone on a small island (fromFalkland Woodroffe, 1997)

Normally, it is assumed that the ‘interception storage’ is filled first before any excess rainfall entersthe soil moisture zone. Evaporation is assumed to occur from interception storage at the potentialrate.

Roots of shallow rooted vegetation (grasses, bushes) and shallow roots of trees can obtain waterfrom the soil moisture zone (SMZ). Water requirements of vegetation from the SMZ are assumed tobe met before any excess water drains to the water table. At soil moisture contents above fieldcapacity (FC), water is assumed to drain to the water table. Below the wilting point (WP), no furtherevaporation is assumed to occur and shallow rooted vegetation wilts and possibly dies. Evaporationfrom the SMZ is normally assumed to be linearly related to the available soil moisture content. AtWP, evaporation is assumed to be nil from the SMZ. Evapotranspiration is assumed to reach fullpotential (potential evapotranspiration, ETp) when the SMZ is at FC. Vegetation types are assigned"crop factors" (Doorenbos & Pruitt, 1977) so as to compare their potential evaporation rate with thatof a “reference crop”. The 'reference crop' evaporation (or evapotranspiration) is defined as the 'rateof evapotranspiration from an extensive surface of 8 to 15 cm tall, green grass cover of uniformheight, actively growing, completely shading the ground and not short of water'. The reference cropevaporation is equal to the potential evaporation, ETp, of the reference crop as derived from arecognised approach. The crop factor is a coefficient that is used to derive an adjusted potentialevaporation of other crops from the reference crop evaporation.


Excess water from the SMZ drains to the water table ("gross recharge" to the freshwater lens). Afurther evaporative loss (TL) can occur due to transpiration of trees whose roots penetrate to thewater table. "Net recharge" is the excess water remaining in the lens after TL is deducted fromgross recharge. On Christmas Island, the water table is generally much lower than the depth towhich tree roots can penetrate and hence TL is nil or very small, except near areas where springsoccur (groundwater is close to the surface). On low lying islands such as atolls (e.g. Cocos(Keeling) Islands), TL can be a large proportion of evaporation losses.

Further details of the water balance procedure are beyond the scope of this report but are availablein a number of publications including UNESCO (1991) and Falkland (1993).

The time step for the surface water balance should not exceed one day because the turnover time inthe soil zone is measurable on this time scale (Chapman, 1985). The use of either mean or actualmonthly rainfall data rather than actual daily rainfall data will underestimate recharge.

In practice, the water balance is undertaken by using actual daily rainfall data and estimates of dailyevaporation based on mean monthly values. For Christmas Island, daily rainfall records areavailable for long periods, and pan evaporation data was collected for a period of about 10 years inthe 1970s and early 1980s. Details of the rainfall and evaporation data used in the analyses isprovided in sections 3.3 and 3.4. A description of the water balance analyses undertaken with acomputer program and explanation of the results obtained are provided in sections 3.5 and 3.6.

3.3 Rainfall DataDaily rainfall has been collected at a number of sites on the islands at various times during thiscentury. A full description of these sites and the periods of record (to 1986) is provided in Falkland(1986). The primary station is at the Airport (Station No 200790) which has been operating since1973. This station is operated by the Bureau of Meteorology. A listing of monthly rainfall for theAirport station is provided in Annex F. There are some gaps in the rainfall records. Discountingsome small gaps in the record in 1994, the longest period of full annual data is the 13 years fromJanuary 1986 to December 1998. The average annual rainfall during this period is 1,981 mm. Bycomparison, the average annual rainfall over the 19 years of full annual data during the period 1973-1998 was 2,146 mm.

Prior to 1973, the primary meteorological station (station No 200304) was sited at Rocky Point in theSettlement. That station commenced operation in 1901. The average annual rainfall at that site forthe 50 years of full record during the period 1902-1973 was 1,931 mm. This amount isapproximately less 10% than the average annual rainfall at the Airport for the 19 years of full annualdata during the period 1973-1998. As indicated in an analysis of available rainfall data in Falkland(1986), it is apparent that average rainfall is higher in the elevated parts of the island than around theedges.

Daily rainfall records have been collected at a raingauge near Jedda Cave in recent years by theShire of Christmas Island. A listing of monthly and annual rainfall for the Jedda station for the periodJanuary 1994 - May 1999 is provided in Annex G. There are no gaps in the rainfall record during thisperiod, which is an excellent achievement by Shire staff. Some earlier data was also recorded butnot all of it could be located.

The average annual rainfall at Jedda for the 5 year period 1994-1998 is 2,375 mm. During thisperiod, the average annual rainfall was 10% higher than at the Airport (2,166mm). The annual rainfallduring this period was consistently higher at Jedda than at the Airport.

The average annual rainfall at Jedda for 1994-1998 is similar to that obtained at nearby Grant’s Well(2,422 mm) for the 18 year period from 1956-1973. This shows an expected level of consistencybetween these two sites

The average annual rainfall at South Point for the 21 year period 1950-1970 was 1,907 mm(Falkland, 1986) which is similar to that at the Settlement. It appears that the rainfall at the southernend of the island is less than in the centre, even though the elevation of the raingauge wasreasonably high (approx. 220 m).


In recent years, automatic raingauges (tipping bucket raingauges connected to data loggers) havebeen operated by the Bureau of Meteorology at the Airport, at the Settlement, near North East Point(now closed), at Grant’s Well and at South Point. Data from these sites was not used for this report.

For the purposes of this recharge analysis, daily rainfall records are appropriate. The Airportraingauge offers the longest record for an area of the island where reasonably representative rainfalloccurs. As shown above, the Airport rainfall is about 10% less than in the area of Jedda and GrantsWell and is about 10% more than at the Settlement and South Point.

The daily rainfall data for the 13 year period 1986 to 1998 was selected for the water balanceanalysis. This was a full set of data except for some days in the very low rainfall months of June andAugust 1994. It was assumed that the missing days of record in these two months (4 days in Juneand 26 days in August) had zero rainfall. This is a reasonable assumption given the very dryconditions at the time. If the rainfall differed from zero on these days, the error would be veryminimal over the full period of analysis.

3.4 Evaporation DataA US Class A evaporation pan was used to obtain pan evaporation data from the Airport site (station200790) from 1 September 1972 to 27 April 1982. Monthly and annual totals of the data are shown inTable H1 of Annex H. Monthly data is also shown in Figure H1 of Annex H. During this period, therewere 79 days when readings was missed and a further 5 days when accumulated readings over 2days were obtained (details in Table H2 of Annex H). In Tables H1 and H2, the months with missingdata are shaded. Average monthly pan evaporation data is shown at the base of Table H1 for allmonths and for only those months with no missing data. Equivalent average daily values, used forinput to the daily water balance analysis are also shown for the latter case in Table H1 and aresummarised in Table 4.

Table 4 Summary of average pan evaporation data for Christmas Island

Site Month Annual

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total

Airport 4.0 3.9 3.9 4.1 3.5 3.3 3.9 3.7 4.4 4.4 4.2 4.3 1,443

Settlement 5.4 5.4 4.9 5.6 5.2 5.0 5.7 6.1 6.5 6.4 6.5 5.0 2,063

Ratio (S/A) 1.4 1.4 1.3 1.4 1.5 1.5 1.5 1.6 1.5 1.5 1.5 1.2 1.43

Notes: 1. Records collected at Airport site from September 1972 to April 19822. Records collected at Settlement site from February 1968 to October 19723. The ratio (S/A) = pan evaporation at Settlement divided by pan evaporation at the Airport

In the water balance analysis for recharge, pan evaporation data can be used to estimate potentialevapotranspiration, ETp by using a pan factor, Kpan, as follows:

ETp = Epan * Kpan

The pan factor is dependent on many variables, but is generally in the range from 0.7 to 0.9. Anappropriate pan factor can be established for each month by comparing pan evaporation to theresults from an independent method of evaporation estimation (e.g. Penman formula using climaticvariables). For Christmas Island, this process was not done although it could be done in the future,as climatic data from the Airport is available. Rather, a sensitivity analysis was conducted on thepan factor using the water balance procedure to assess the effect on the estimates of recharge.

Pan evaporation data is also available for the period February 1968 to October 1972 from the RockyPoint, Settlement site (station 200304). Monthly and annual totals of the data are shown in Table H3of Annex H. Monthly data is also shown in Figure 8 below. During this period, there were 31 dayswhen readings were missed and 2 days when accumulated readings were recorded (refer Table H4,Annex H). In Tables H3 and H4, the months with missing data are shaded. Equivalent average daily


values, used for input to the daily water balance analysis are also shown for the latter case inTable H3 and are summarised in Table H4.


Figure 8 Monthly Pan Evaporation at Rocky Point (Settlement) & Airport

The data collected at the Settlement shows higher pan evaporation rates, on average, for everymonth of the year than at the Airport (refer values and ratios in Table 4). The ratios indicate that theaverage monthly pan evaporation is between 20% and 60% higher at the Settlement than at theAirport. The annual average value was 43% higher at the Settlement than the Airport. Some of thisdifference may be explained by the different periods of record for the two sites and the exposureconditions at each site. The results are consistent with observations of cloud cover which suggestthat the cloud cover at the elevated parts of the island is higher than near the coastline. Increasedcloud cover would decrease the solar radiation, which is the main influence on evaporation rates. Adetailed analysis of cloud cover and other influences such as temperature, relative humidity betweenthe two stations was not conducted for this study, principally because pan evaporation data wasavailable. In the future, a more detailed analysis of the climatic differences between the two siteswould be a worthwhile study. It is not essential, however, for the present purpose of rechargeestimation.

Figure 8 and Table 4 above show that the variations in pan evaporation throughout the year aregenerally similar at the two stations. The months with the highest evaporation for the Settlement areSeptember to November. At the airport, the months with the highest evaporation are September andOctober.

3.5 Recharge Estimation ModelA computer programme (called WATBAL) was used to simulate the water balance for the surface ofthe island, as described in section 3.2, and derive recharge estimates for Christmas Island. Thissection outlines the model process and estimation of the input parameters.

The model allows for interception by vegetation. A maximum value for the interception store (ISMAX)is defined and it is assumed that this store must be filled before water is made available to the soilmoisture storage. Typical values of ISMAX are 1 mm for predominantly grassed areas and 3 mm forareas consisting predominantly of trees. For Christmas Island, as most of the inner part of the

0

50

100

150

200

250

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Mo

nth

ly P

an E

vap

ora

tion

(m

m)

Rocky Point, Settlement (average of 1968-1972 data)Airport (average of 1972-1981 data)


island is well forested, a value of 3 mm was used. Evaporation is assumed to occur from this storeat the potential rate.


The model incorporates a soil moisture zone from which the roots of shallow rooted vegetation(grasses, bushes) and the shallow roots of trees can obtain water. Water requirements of plantstapping water from this zone are assumed to be met before any excess water drains to the watertable. Maximum (field capacity) and minimum (wilting point) limits are set for the soil moisture in thiszone. Above the field capacity, water is assumed to drain to the water table. Below the wilting point,no further evaporation is assumed to occur.

The thickness of the soil moisture zone (SMZ) is estimated as 2,000 mm based on localobservations of the soil profile. Field capacity (FC) is assumed to be 0.25 based on observations oflocal soil type and typical values for this type of soil. Wilting point (WP) is assumed to be 0.15. Thevalues of FC and WP are equivalent to typical values of clay loam (Table 3.1 of UNESCO, 1991).The operating range of soil moisture is thus assumed to be from a maximum of 500 mm(2,000*0.25) to 300 mm (2,000*0.15). The sensitivity of recharge estimates to changes in theseparameters was evaluated in the analyses.

The amount of evaporation from the SMZ is assumed to be related to the available soil moisturecontent. At WP, zero losses due to evaporation are assumed to occur from this zone. Maximum orpotential evaporation is assumed to occur when the soil moisture zone is at FC. A linear evaporativeloss relationship is assumed to apply between the two soil moisture limits. Thus, at a soil moisturecontent midway between FC and WP, for instance, the evaporation rate is assumed to be half that ofthe potential rate.

Water entering the water table is assumed in the model to be 'gross recharge' to the freshwaterlens. A further loss, however, may be experienced due to transpiration of trees whose rootspenetrate to the water table (denoted by TL in section 3.2). 'Net recharge' is that water remainingafter this additional loss is subtracted from 'gross recharge'. As outlined in section 3.2, TL isassumed to be negligible for Christmas Island.

Vegetation is assigned a 'crop factor' according to its type. It is generally assumed that the cropfactor for most grasses and other shallow rooted vegetation is equal to 1.0. This value was adoptedfor shallow rooted vegetation on Christmas Island. Crop factors of 0.8 to 1.0 are normally used fortrees (e.g. 0.8 for coconut trees on small coral islands: Falkland, 1994a). Thus, ETp for trees istaken as 80%-100% of that for shallow rooted vegetation which is in turn assumed to be equal to ETpof the "reference crop" (Doorenbos & Pruitt, 1977). For Christmas Island, a conservative approach(leading to lower estimate of recharge) was adopted and a crop factor of 1.0 was adopted for trees.

The model allows for the proportional area covered by trees and by shallow rooted vegetation to bespecified. This is only necessary when different crop factors for trees and shallow rooted vegetationare used. As the same crop factors have been adopted, the parameter describing the arealproportion of trees (DRVR) does not require a specific value. It was set to 1.0 for convenience.

3.6 Analyses and ResultsComputations using the WATBAL program were conducted using a daily time interval. Asmentioned in section 3.3, daily rainfall data from the Airport for the 13 year period 1986 to 1998 wasselected for the water balance analyses.

For the water balance analyses, average monthly evaporation estimates or equivalent average dailyevaporation estimates for each month are suitable. The two sets of daily values in Table 4 wereused to assess the effects of higher and lower pan evaporation estimates. In addition two estimatesof pan factor, 0.75 and 0.9 were used, giving a total of four possible sets of potential evaporationestimates.

The results of a sample water balance analysis is listed in Annex I. The input data is summarised inthe first part of the results. Monthly and annual values of the main parameters are shown, includingthe recharge (in mm) and the recharge ratio (recharge divided by rainfall) for the month or year. Atthe end of the listing is a summary for the full 13 year period. An explanation for the acronyms usedin the column headings of the results is also provided at the end of the listing.

Table 5 summarises the results of a number of water balance simulations showing the values of theinput parameters and the resulting estimated average annual recharge (in mm and %) for the13 year period.


Table 5 Summary of average annual recharge estimates for various cases

Case PanEvaporation

Input Parameter Average AnnualRecharge

Data Kpan ISMAX(mm)

SMZ(mm)

FC WP (mm) (% of averagerainfall)

1 Airport 0.9 3 2,000 0.25 0.15 975 51

2 “ 0.7 3 2,000 0.25 0.15 1,117 58

3 Settlement 0.9 3 2,000 0.25 0.15 789 41

4 “ 0.7 3 2,000 0.25 0.15 932 49

5 Airport 0.9 3 4,000 0.25 0.15 872 45

6 Airport 0.9 3 4,000 0.25 0.05 767 40

Notes: 1. All water balance simulations used the 13 year rainfall record (1986-1998) for the Airport

2. Crop factors assumed as 1.0 for all vegetation

3. ISMAX = interception store capacity, SMZ = soil moisture zone thickness

FC = field capacity, WP = wilting point

4 Average recharge is the estimated average recharge over the full 13 year period

5. Average rainfall over the 13 year period was 1,919 mm

In all, 6 cases were analysed using the water balance program. The average recharge estimatesvaried between 40% and 58% of average rainfall. Cases 1 and 2 used pan evaporation from theAirport and pan factors of 0.7 and 0.9, respectively. These cases showed approximately 10% higherrecharge than the corresponding analyses (cases 3 and 4) using pan evaporation for the Settlement.It is considered that the Airport evaporation is more representative of the whole island and hence thehigher estimated recharge values are likely to be more accurate. Without further analysis, beyondthe scope of this report, it is not possible to determine which pan factor is more accurate or whetheranother factor (e.g. 0.8) would be more appropriate.

Cases 4 and 5 varied other input parameters. In case 4, the soil moisture zone (SMZ) thicknesswas increased by 100% from 2 m to 4 m. This had the effect of decreasing recharge from 51%(case 1) to 45% of rainfall, representing a 12% decrease in recharge. In case 5, the wilting point(WP) was decreased from 0.15 to 0.05. Compared with case 4, the average recharge decreasedfrom 45% to 40% of rainfall, representing a 14% decrease in recharge. Overall, the estimates ofrecharge are not very sensitive to changes in the parameters affecting the soil moisture content(SMZ, FC and WP).

From the above analyses, it is concluded that a reasonable estimate of average annual recharge is50% of average annual rainfall (based on case 1 results).

Using the analysis for case 1 (refer Annex I), the comparison of annual rainfall and estimatedrecharge values are shown in Table 6 and Figure 9.


Table 6 Annual recharge estimates using selected case (case 1)

Year Annual Annual Annual

Rainfall (mm) Recharge (mm) Recharge (%)

1986 2,199 1,134 52

1987 1,067 359 34

1988 1,475 549 37

1989 2,954 1,866 63

1990 1,595 693 43

1991 1,629 720 44

1992 2,094 991 47

1993 2,098 1,039 50

1994 1,167 698 59

1995 2,781 1,574 57

1996 1,319 436 33

1997 1,279 571 45

1998 3,283 2,040 62

Average 1,919 975 51

Figure 9 Annual rainfall at Airport & estimated annual recharge, 1986-1998

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3.7 Discussion of ResultsThe results in Table 6 show that recharge varies from year to year, according to the amount ofrainfall. The ratio of recharge to rainfall (recharge ratio) is not constant as shown by the right handcolumn in Table 6 and in Figure 9. This is due to recharge being influenced not only by the amountbut also the distribution of rainfall. For instance, the rainfall was higher in 1996 than in 1997, yet therecharge was lower in 1996 than 1997. Inspection of the sequence of monthly data in Annex I showsthat larger recharge in 1997 was primarily associated with heavy rainfall at the start of that year. Thisis indicative of the process of recharge, whereby most recharge tends to occur in months of heavyrainfall. In months with lower rainfall, often there is no recharge, as all the rainfall is subsequentlyevaporated from the interception store and soil moisture zone. Depending on the sequence ofrainfall, recharge can even be zero in months with 170 mm of rainfall (refer to results for December1990 in Annex I). This apparently large amount of rainfall is stored within the soil moisture zone andsubsequently evaporated resulting in no recharge to groundwater below the soil zone.

The sequence of months and years of recharge is important from a water resources viewpoint. Ifthe groundwater is small in volume, then a sequence of below average recharge months or yearscan lead to significant reduction in groundwater volume and outflow. This is particularly importantfrom the viewpoint of ‘perched’ groundwater feeding springs (e.g. Ross Hill Gardens springs) andsubterranean flows (e.g. Jedda cave and Jane Up) which are fed from the recharge. For instancefrom Figure 9 and Table 6, critical periods of lower than average recharge were 1987-1988 and1996-1997.

For larger groundwater systems with residence times of more than a few years (e.g. groundwatersystem in Smithson Bight area), there is sufficient groundwater storage for such low rechargesequences to be of little concern. In these cases, the long term average recharge condition is ofmost interest and years with lower than average recharge do not have a significant impact on longterm storage levels. For the Smithson Bight freshwater aquifer, the maximum depth was found to beabout 20 m (refer section 2.1). If the effective porosity of the rock is assumed to be about 0.3, theactual thickness of freshwater within the aquifer would be about 6 m. As the annual averagerecharge is about 1 m (975 mm), then the average residence time of the groundwater is estimated tobe about 6 years (thickness divided by average annual recharge). Allowing for some loss of waterthrough dispersion with underlying seawater, a slightly more accurate estimate of residence time is5 years.

The average annual recharge of 1 m is equivalent to a volume of approximately 135 x 106 m3 (or135 gigalitres) over the total island area of approximately 135 km2. Recharge which adds to theavailable freshwater reserves (effective recharge) would not occur over the whole island. Forinstance, there is unlikely to be freshwater that is capable of being effectively developed within 500 mof the coastline over much of the island. The approximate area of the island where effectiverecharge occurs is estimated as 75%. Hence, the effective annual recharge to the island’sgroundwater systems is estimated as approximately 100 x 106 m3 (or 100 gigalitres). This isequivalent to a flow of about 3,200 L/s.

The average recharge value estimated for Christmas Island is higher than for other islands (e.g.Cocos (Keeling) Islands. This is largely because the evaporation estimates on Christmas Island arelower. It is noted that the estimated average annual recharge is 50% of average annual rainfall whichis greater than the 30% value in Falkland (1986). The earlier value was based on comparisons withother islands rather than local data.

3.8 Estimated Sustainable YieldThe proportion of recharge that can be safely extracted (or the ‘sustainable yield’) is based on manyfactors including the distribution of the groundwater on the island and the method(s) of groundwaterextraction. For small islands, not all recharge can be extracted as some is required to flush salts atthe base of basal aquifers, as mentioned previously. If all the recharge was extracted, such aquiferswould eventually diminish until no freshwater was available.

Other small island studies (e.g. UNESCO, 1991) have indicated that approximately 25% to 50% ofrecharge to basal aquifers (or freshwater lenses) can be safely extracted. For the perched aquifers,


where there is no contact with sea, the maximum amount that could be extracted would be 100% ofrecharge. In practice, much less than this percentage would be capable of being extracted becauseof the complexity of the geology and the efficiency of borehole pumping systems. It would be unlikelythat more than 50% could be easily extracted. So for both basal and perched aquifers, but fordifferent reasons, the estimated upper limit of sustainable yield would be 50% of recharge.

Using 50% of recharge as being a reasonable estimate of sustainable yield for Christmas Island, themaximum amount of water available for extraction would be 50 gigalitres per year, or 1,600 L/s. Bycomparison, the average combined flow of the presently developed water sources is about 80 L/s or5% of this value. The estimated minimum combined flows of the presently developed sources isabout 31 L/s (Falkland, 1986) or only 2% of this value.

3.9 ConclusionsThe estimated average annual recharge for Christmas Island is 50% of average annual rainfall. Inround terms the average annual recharge is thus about 1,000 mm. Over the area of the island, thisis equivalent to an annual recharge of about 100 gigalitres, which is equivalent to a flow of about3,200 L/s. The estimated sustainable yield of the groundwater system is half the available rechargeor 1,600 L/s. Average and estimated minimum flows at present sources are much less than thispotential yield (5% and 2% of the estimated sustainable yield, respectively).


4. SATELLITE IMAGERY STUDY FOR COASTAL OUTFLOWS

4.1 BackgroundThe use of satellite imagery for a pilot study to detect possible freshwater outflows along theChristmas Island coastline was recommended in Falkland (1994b) and ACTEW (1995a). Ifsuccessful, such imagery would be a valuable tool for identifying possible water supply sources nearthe coastline that would not be easily identified by more conventional methods.

4.2 Summary of the StudyA Landsat Thematic Mapper satellite image obtained on 30 November 1996 was acquired andexamined for evidence of freshwater emerging from the Christmas Island coastline into thesurrounding ocean. This image was one of 5 possible images available in the period June 1994 tolate 1996, and it was selected for analysis as it appeared from previews to be the least affected bycloud cover. Details of the analysis and selected images are contained in a separate report by thesub-consultants engaged for this component of the project (refer Webb and Shepherd, 1997).

Characteristics of the imagery used for the study are:• Three spectral bands spanning the visible range and one in the thermal range;• The pixel resolution being 30 m square in the visible range and 120 m square in the

thermal range; and• A standard quarter scene of 45 km square, which comfortably encompasses Christmas

Island.

The selected image produced no evidence of emerging freshwater, which was attributed to:• The rapid descent of the waters around Christmas Island to open ocean depths,

combined with minimal surface runoff, resulting in very clear surrounding waters, whichprovide little colour contrast to emerging freshwater; and

• Mixing of ocean waters with emergent freshwater to a degree where surfacetemperatures varied by no more than 0.5°C, the threshold of detection for the thermalband of the Landsat satellite.

As part of this study, surface sea temperature and salinity data were obtained at selected locationsnear known cave entrances (Daniel Roux Cave and nearby Grimes Cave, Freshwater Cave andLost Lake Cave) along the northern coastline of the island during the October/November 1996 visit.The data was obtained with a portable salinity/temperature meter lowered from a boat. The boatwas brought into the limestone cliffs as close as safety permitted (approximately 5 m). The readingsof salinity and temperature near the cave entrances showed no discernible variations in salinity ortemperature from open water values (200 m from the coastline). This lack of any freshwater‘signature’ is no doubt due largely to mixing of freshwater with seawater within the cave before itemerges. Measurements of salinity profiles within the main channel system of Daniel Roux Caveusing a portable meter and an automatic recorder (refer section 7.3) indicated that the freshwaterlayer at a distance of about 120 m from the cave entrance was less than a metre thick. The water inthe cave shows a tidal response and hence a mechanism for easy mixing of freshwater with salinewater at a distance of 200 m from the coastline at the site of the ‘gusher’ (refer section 7.3).

4.3 ConclusionsThe pilot study using Landsat satellite imagery was not successful at locating freshwater outflowsalong the coastline. Imagery obtained with sensors (on satellite or aeroplane) having a thermalresolution of better than 0.1°C may be more useful. However, this method appears to be of limiteduse, as the mixing of freshwater and seawater within the caves and fissures along the coastlineresults in outflows which are already quite diffuse even where freshwater outflows are known tooccur.


5. RAINFALL-FLOW MODEL FOR JEDDA CAVE

5.1 BackgroundA rainfall-flow model for Jedda Cave and selected springs was recommended in Falkland (1994b) asit could enable predictions of flows based on current and expected rainfall patterns. This would allowthe water supply authority to better plan the operation of the system and advise consumer’s of anynecessary adjustments caused by a potential shortfall in supply.

The focus for this component of the GIM program was the Jedda Cave flow since this provides aprimary water supply source for the island.

Comments are also provided about similar rainfall-flow models that could be developed for springsources on the island.

5.2 Jedda Cave

5.2.1 Rainfall and flow data

Available rainfall and flow data for Jedda Cave for two periods of monitoring are discussed in detaillater in this report (section 7.2). A graphical summary of data is presented in Figures 10 and 11.Figure 10 shows data for the recent period from 1996 to mid-1999, during which time flowmeasurements at Jedda have been undertaken. The figure shows pumped flow (as measured by aflow meter), weir flow (as measured at the overflow weir) and total flow which is the combination ofthese two flows. Full details of flow measurements are presented in section 7.2 and summarised inTable 7 in that section. Rainfall data shown in Figure 10 is for the Jedda daily read raingauge.

Figure 10 Monthly Jedda flows and rainfall, 1996-1999

Figure 11 shows the flows at Jedda and rainfalls, as measured at the former Grant’s Well raingauge,for an earlier period of active measurements from 1965 to 1974 (from BPC Drawing 67-X9E/X133).

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Figure 11 Monthly Jedda flows and Grant’s Well rainfall, 1965-1974

A brief review of the two figures, especially the longer period shown in Figure 11, shows that there isa relationship between rainfall and flow, but that this relationship is not a simple one.

Observations of rainfall and flow data at Jedda and past reports (e.g. Barrett, 1985) suggest thatthere is a lag between monthly rainfall and monthly flow at Jedda.

The following sub-sections outline analyses that were undertaken in an attempt to establish amathematical relationship (or ‘model’) between the rainfall and flow (runoff).

5.2.2 Linear regression model

A number of linear regression analyses were made. Firstly, only flow and rainfall data for the lowrainfall period from March 1997 to February 1998 was used. The correlation of Jedda flow data forthese 12 months of data was checked against a number of options for describing the rainfall data.The various options tested are listed below together with the coefficient of determination (r2) for eachregression:

Option 1 average of rainfall for past 3 months (r2 = 0.81),Option 2 average of rainfall for past 4 months (r2 = 0.94),Option 3 average of rainfall for past 5 months (r2 = 0.96),Option 4 average of rainfall for past 6 months (r2 = 0.91),Option 5 rainfall lagged 2 months behind current month (r2 = 0.63),Option 6 rainfall lagged 3 months behind current month (r2 = 0.77),Option 7 rainfall lagged 4 months behind current month (r2 = 0.44),Option 8 average rainfall from months t-1 and t-2 (r2 = 0.61),Option 9 average rainfall from months t-2 and t-3 (r2 = 0.85), andOption 10 average rainfall from months t-3 and t-4 (r2 = 0.77).

[Note: t-1 refers to the month before the current month, t-2 is the month preceding t-1, etc.]

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From the above list, the best regression (based on the highest the coefficient of determination) wasfound for the average of the previous 5 months of rainfall (Option 3). The second best was Option 2for the previous 4 months of rainfall. Both options indicate that the flow is lagged behind rainfall byseveral months. The lag appears to be between 2 and 3 months, based on the coefficients ofdetermination obtained for Options 5 to 7 and Options 8 to 10. In particular, Option 9 which averagesthe rainfall in months t-2 and t -3, shows the highest correlation for these 6 options.

The linear regression formula which best described the rainfall-flow relationship for the low-flowperiod November 1996 to February 1998 is:

q = 0.118*Pav5 + 19.34where

q = average monthly flow at Jedda (for current month) (L/s), andPav5 = average of monthly rainfall for previous 5 months (mm).

For the relatively short period of recent continuous flow data, the correlation between rainfall and flowfor the selected period could be expected to be good, as there were no significant variations in eitherparameter. Using the above formula, the estimated flows for the period of record showed that thelargest deviations from actual flows were an under-estimation of 5.7 L/s (10.3%) in April 1997 andover estimation of 3.2 L/s (7.6%) in June 1997. The above formula could only be applied withconfidence within the range of flows and rainfall data used in the derivation of the formula. Theseranges, corresponding to the relatively dry and low flow period, are as follows: total Jedda flow lessthan about 50 L/sec and greater than 20 L/s, and average Jedda rainfall for 5 months less than about250 mm. Further data from dry periods is required to verify the validity of this formula.

The performance of Option 9 and the formula above were checked against the earlier flow andrainfall records, as presented in Figure 11. The data from May 1965 to July 1974 was used (109months were available as 3 months of flow data was missing). For this case, the correlationbetween flow and the average of the previous 5 months of rainfall (Option 3) was poor (r2 = 0.48). Asimilar result was found if the previous 6 months of rainfall were averaged (Option 4 above). Thepoor correlation for the longer data period is because there was far more variability in the data, withmany occurrences of high rainfall and high flow.

The poor correlation shows that there is no simple relationship between rainfall and flow. Thisfeature is common in hydrological systems, where a ‘non-linear’ response between rainfall andrunoff is normally found. In particular, groundwater systems such as those found in karsticlimestone are typically non-linear in their response, as there are often multiple flow paths andunderground storages. Many of these storages only start to contribute to flow once they reach acritical or threshold level which is determined by the preceding rainfall and recharge conditions.

In summary:• Linear regression is not an adequate technique for describing the long-term response of

the Jedda flow from a nearby raingauge, and• Linear regression could be used in low flow periods (the critical periods) once the flow

has fallen below a threshold flow value (say 50 L/s) and it is above about 20 L/s. Apossible formula is shown above but further data from dry periods is required to verify thevalidity of this formula.

5.2.3 Non-linear models

A number of non-linear equations were analysed to assess whether an improvement in the ability topredict flows was possible. For this purpose, the monthly flow record from Jedda for the period 1965to 1973 was used, as well as the monthly rainfall record for Grant’s Well for this period.

The types of relationships analysed were:a) Flow at Jedda (current month) = fixed minimum flow + function of rainfall for preceding

monthsb) Flow at Jedda (current month) = fixed minimum flow + function of recharge for preceding

months


c) Flow at Jedda (current month) = flow for preceding month + function of rainfall for precedingmonths

d) Flow at Jedda (current month) = flow for preceding month + function of recharge forpreceding months

Within each one of these relationships various options were tested. For relationships (a) and (b), thefixed minimum flows used were 10 and 20 L/s, as these are close to the minimum flows recorded.

The functions of monthly rainfall and recharge that were tested for relationships (a) to (d) were:• Monthly rainfall (or recharge) lagged by one month• Monthly rainfall (or recharge)• Average monthly rainfall (or recharge) for preceding two months• Average monthly rainfall (or recharge) for preceding three months• Average monthly rainfall (or recharge) for preceding five months

Monthly recharge estimates were calculated using a monthly water balance model, similar to the onedescribed in section 3, but modified to use monthly rather than daily rainfall data. This wasnecessary, as monthly but not daily rainfall was available for the Grant’s Well raingauge for theperiod 1965-1973. The soils and vegetation parameters were adjusted to provide an average annualrecharge value consistent with that obtained for the daily data from the Airport raingauge, asdescribed in section 3.3. The evaporation data obtained from the evaporation pan at the Airport(refer section 3.4) was also used in the water balance analysis.

From the analyses, the best fit between actual and predicted flows were obtained from relationships(c) and (d), with those from (c) being slightly better than from (d).

Overall, the best fit was for the following equation:

qt = 0.8*q t-1 + (0.58*Pav2)0.51

whereqt = average monthly flow at Jedda for current month (L/s)qt-1 = average monthly flow at Jedda for preceding month (L/s), andPav2 = average of monthly rainfall for previous 2 months (mm).

Using this equation and others, predicted flows were matched to actual flows to minimise the sum ofthe residuals and to maximise the regression coefficient of determination (r2). The r2 value for theequation above was 0.67, which can be considered fair.

Figure 12 shows the relationship between actual and predicted flows using the above equation.

Other options within relationships (c) and (d) gave similar results. Relationships (a) and (b) gavepoor results (r2 values less 0.3).

Overall, there is a reasonable fit between actual and predicted flows, but in some months thepredictions are significantly different from actual flows. The worst predictions were an under-prediction of 90 L/s (by 68%) in June 1973 and an over-prediction of 36 L/s (by 58%) in August 1973.These are significant variations from actual flows, assuming the actual flows are correct. Suchvariations indicate that the equation would need to be used with considerable caution.

This type of flow prediction model (equation) also suffers from the disadvantage of requiring the flowdata from the month before to predict the flow for the current month (at the start of the month). Thismeans that flow data must be available in order to make the prediction.

In conclusion, the analysis of possible non-linear flow equations did not produce an adequateequation to be used for accurate flow predictions. However, the above equation could be adopted asa guide for possible future use.

It is noted that flow predictions are most required when the flows are low and during these times itwould probably be preferable to use the linear equation in 5.2.2.


Figure 12 Relationship between actual and predicted flow for Jedda, 1965-1973,using non-linear flow model

5.3 SpringsThe presently developed springs are the three springs at and near Waterfall (Waterfall, Freshwaterand Jones) and those at Ross Hill Gardens (Harrison’s Nos 1 and 2 and Hewan’s).

5.3.1 Waterfall Springs

A rainfall-flow model was not developed for these springs as there has been no recent datacollected. The earlier period of data collection in the 1960s and 1970s (refer BPC Drawing 67-X9E/X133) could be used to establish such a model, but it would require verification with recent data.This should be done at some stage in the future after water resources measuring equipment hasbeen installed at the site, and operated for at least 12 months.

The Waterfall springs have shown a relatively minor variation in flow with rainfall unlike Jedda Cave.Further detailed information about flows in these springs from the period 1964-1975 is presented inBarrett (1985) and Falkland (1986).

5.3.2 Ross Hill Gardens Springs

Details of flows recorded at the Ross Hill Gardens springs are presented in section 7.2. The RossHill Gardens flows are much lower and less variable than those at Jedda. The ratio betweenmaximum and minimum flows at Jedda is about 10:1 compared with about 3:1 for the Ross HillGardens flow.

A rainfall-flow model was not developed at this stage for Ross Hill Gardens owing to this source’srelatively low significance in the overall water resources of Christmas Island. However, a similarapproach to that used for Jedda could be used. The fact that the flows are less variable than atJedda should enable a model to be developed with more ease than at Jedda.

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5.4 Conclusions For Jedda, a simple formula was derived to predict flows for a given month based on the previous5 months rainfall recorded at the Jedda raingauge. This could be applied only in low flow periodswhen the flow is between about 50 and 20 L/s, and the 5 month rainfall is less than about 250 mm.

Based on analysis of flows in 1997 and 1998, the flow response in Jedda Cave is lagged between 2and 3 months behind Jedda rainfall.

A more complex (non-linear) model was developed for Jedda for higher flow periods. This modelcan estimate a given month’s flow from the average of monthly rainfall for the previous 2 months andthe average monthly flow at Jedda for preceding month. This model should be used with caution asit can under-estimate or over-estimate actual flows and should be refined as more data becomesavailable in the future.

Predicted flows from these models should be checked against future monitored flows at Jedda andthe results reported in the proposed quarterly monitoring reports (refer section 7.2). Suggestedmodifications could then be recommended.

In the future, similar models could be developed for the springs at and near Waterfall and for those atRoss Hill Gardens. The Waterfall springs will firstly require the installation of flow monitoringequipment and collection of data over at least 12 months.


6. AQUIFER CLASSIFICATION AND VULNERABILITY

6.1 Summary of the Island’s Geology and HydrogeologyKnowledge of the island’s geology is documented in a number of reports including Trueman (1965),Rivereau (1965), Barrie (1967), Polak (1976) and Pettifer & Polak (1979). In addition, numerousother unpublished reports by the various mining companies (BPC, PMCI and CIP) have been writtenby resident geologists. Summaries of important geological features related to the water resources ofthe island are contained in Barrett (1985) and Falkland (1986). It is beyond the scope of this report toconsider the details of the geology but a brief summary is provided because of the strong influenceon the island’s hydrogeology, aquifer types and water resources.

Christmas Island was formed by an undersea volcano approximately 60 million years ago.Subsequent coral growth formed a limestone capping. A combination of uplifting and weatheringover the period of limestone formation resulted in the island’s present stepped formation beneath thecentral plateau. Weathering and erosion of the limestone rock has developed the present ‘karst’features including extensive cave systems, sinkholes and fissures. The process of limestonedissolution (or ‘karstification’) is an ongoing process through the interaction of water with thelimestone (calcium carbonate) and hence new sinkholes and caves are likely to be exposed in thefuture. Major karstic features are most evident in areas of major water flow. Extensive phosphatedeposits, originating from the guano of large numbers of sea birds, were formed over much of theisland’s surface.

The shape of the island and various studies including gravity and magnetic mapping suggest that thecore of the island consist of a cone and three rift zones (Polak, 1976). The cone is under the centralpart of the island and the rift zones radiate along the main axes of the island. Polak (1976) suggeststhat deep erosion channels cut through the rift zones and divided the volcanic plateaus into foursections, and that the resulting valleys subsequently were filled with coral limestone.

The volcanic rock underlies the limestone. In some places, volcanic rock is exposed at the surface,believed to be caused by localised landslides removing the limestone capping (Polak, 1976).Examples of volcanic rock outcrops are found in the Dales at the western end of the island and atRoss Hill Gardens.

The limestone is generally flat but there are occurrences of dipping limestone due to faults. It isnormally very porous and ‘vuggy’ (Polak, 1976). The scarcity of surface runoff channels is a cleardemonstration of the highly permeable nature of the soils and underlying limestone.

The island’s hydrogeological features are described in some of the above reports, notably Polak(1976), Pettifer & Polak (1979). These two reports present the results of extensive geophysicalresearch conducted in the mid-1970s in the central plateau area. Their aim was to locate watersupply sources additional to the Grant’s Well, Jedda Cave and Jane-Up underground flow system.

Knowledge of the water resources of the island including springs and groundwater aquifers (knownand presumed) are summarised in Barrett (1985) and Falkland (1986; 1994b). Extensive recordsand internal reports were also written by various cave explorers notably Powell and Bishop in the1960s. Some of their reports and observations are documented in Barrett (1985) and Falkland(1986).

While there is quite a large body of information about the island’s groundwater, there are someaspects that are not well described, including exact distribution, flow paths and thickness. This ispartly because of the incomplete knowledge of the distribution and nature of the volcanic andlimestone rocks under the island’s surface. In particular, variations in the permeability of the volcanicrock underlying the island, which has a major influence on the distribution of groundwater systems,is not well known.


6.2 Aquifer Classification

6.2.1 Overview

Groundwater aquifers on islands can be broadly classified as either:

• Perched aquifers, or

• Basal aquifers.

Perched aquifers are located above sea level. Perched aquifers commonly occur over horizontalconfining layers (aquicludes) including impermeable or low permeability volcanic rock, which is foundin parts of Christmas Island. Dyke-confined perched aquifers are a less common form of perchedaquifer and are formed when vertical volcanic dykes trap water in the intervening compartments (e.g.some of the islands of Hawaii and French Polynesia). On Christmas Island, perched aquifers arenormally formed above the interface between limestone and underlying volcanic rock. This is due tothe relatively low permeability of the volcanic rock, which prevents or retards the downward flow ofgroundwater into lower parts of the island. There may be some occurrences of dyke-confinedperched aquifers on Christmas Island, but they are not common.

Basal aquifers consist of unconfined, partially confined or confined freshwater bodies which form atand below sea level. They are effectively freshwater bodies on top of seawater. Except wherepermeabilities are very low, as on some volcanic and bedrock islands, most islands would havesome form of basal aquifer in which the freshwater body comes into contact with seawater. Onmany small coral islands, such as the Cocos (Keeling) islands, the basal aquifer takes the form of afreshwater lens that underlies the whole island.

Basal aquifers tend to be more important than perched aquifers because they normally have greaterstorage volume and are less susceptible to depletion than perched aquifers during extended dryperiods. Basal aquifers are, however, vulnerable to saline intrusion owing to the freshwater-seawater interaction and must be carefully managed to avoid over-exploitation with resultantseawater intrusion.

For Christmas Island, a classification of aquifers can be made on the basis of whether they areperched or basal. These two types of aquifers are described in more detail below.

6.2.2 Perched groundwater

There is much evidence of perched aquifers in Christmas Island, but these appear to have relativelylow yields.

The springs on the island, the Jedda Cave flow system and the flows at the Dales are all outflowsfrom perched aquifers. The Jedda Cave flow system is a major outflow from a perched aquifersystem in the centre of the island.

From various tracing studies using salt and dye over a number of years, and from exploration withinthe cave system, the Jedda flow is known to be a connected flow path between Grant’s Well, JeddaCave, Jane-Up and Water Bore 30 (WB30). After WB30, this discrete flow is presumed to movealong the limestone-volcanic rock interface and eventually discharge into the basal aquifer in theSmithson Bight area. It might also move down fractures in the volcanic rock to the south of WB30and become part of a more extended basal aquifer to the north of the Smithson Bight area. In eithercase this flow would combine with other and most probably more diffuse freshwater outflows andeventually discharge at the edge of the island or mix with underlying seawater.

From an analysis of simultaneous flow data in the 1960s and 1970s (from BPC Drawing 67-X9E/X133) the total flow at Jedda (pumped plus overflow) was approximately 3 times the total flow atGrant’s Well. This would suggest that the volume of the aquifer contributing to the Grant’s Well flowis probably significantly smaller than that contributing to the Jedda flow.

Most of the central plateau of the island has potential for perched aquifers but in most areas theyappear to be shallow in depth and not a sustainable water resource during extensive dry periods.The central plateau area was extensively investigated with geophysical methods by Pettifer and


Polak (1979). Follow-up drilling work resulted in very little sustainable water supply being located inthis perched groundwater area.

Barrett (1985) describes the various drilling programs that were undertaken in the plateau area,including 27 bores in late 1966, which were drilled in locations around Grant’s Well/Jedda Cave,East-West baseline, South Point and Phosphate Hill. Only three of these bores produced minorgroundwater quantities. In early 1969, a further 18 bores were drilled in the Drumsite and Grant’sWell/Camp 4 areas. The five holes at Drumsite were found to be dry. Three of the holes in theGrant’s Well/Camp 4 area found water with the most productive being Water Bore 30 (WB30) to thewest of Jane-Up. Test pumping from WB30 (BPC Drawing 69-X9E/X63) indicated a yield of 4,500gallons per hour (i.e. 5.6 L/s). However, pump tests showed that this borehole was on the sameflow system as Jane-Up and was therefore redundant. Further drilling for water continued, including7 unsuccessful boreholes in Field 5A, north of the airport and above the Golf Course. A further13 bores were drilled near WB30 in 1971. Water was located in most holes but after tests over twodry seasons, it was concluded that only a relatively minor additional yield (approx 6 L/s) wasavailable from these combined bores. In 1973 and 1974 another six boreholes were drilled to assistwith the geophysical work in the Jane-Up/WB 30 area (Polak, 1976). These yielded small quantitiesof water.

While the history of drilling in the central plateau area has had a low success rate, the potential stillremains for additional water supply to be developed in this area from perched aquifers, although onlyin modest quantities (in the order of 1- 2 L/s per borehole). These aquifers suffer from the with thethreat of diminished supply in dry periods when the water is most needed. The benefits of thecentral plateau area are its proximity to existing infrastructure and relatively shallow target depths fordrilling.

Perched groundwater was found in the drilling investigations as part of this project in the north-eastpart of the island at boreholes BH6, BH7 and BH8 (refer section 2.1 and Annexes B, C and D).These three holes were drilled to see if basal groundwater with moderate to high yield potentialexisted in this part of the island. The drilling showed that volcanic rock was intersected above sealevel (13 m, 40 m and 97 m, respectively, for BH6, BH7 and BH8). Based on monitoring of waterlevels in the monitoring tubes at each borehole, only BH8 is considered to have potential formoderate yields and then only after further exploratory drilling and pump testing in the area of BH8.No pump testing was planned nor conducted as part of the current investigations.

Perched groundwater was found in two of the three pollution monitoring boreholes that were drilledas part of the project at the rubbish disposal and landfill site (refer section 2.2 and Annexes B and E).Borehole BH9 intersected volcanic rock at a depth of 87m (approx. 210 m above sea level). Thegroundwater level in BH9 has varied between about 207 m and 210 m above MSL, indicating only asmall amount of water. Borehole BH10 intersected volcanic rock at a depth of 108 m (approx. 187 mabove MSL). The groundwater level in BH10 has varied only slightly between about 199.7 m and200.5 m above MSL, indicating a moderate amount of groundwater (between 11.8 m and 12.6 m ofwater in the hole). It is interesting to note that while these two holes are not far apart (approximately130 m), there is a reasonably large difference between the levels of the volcanic rock and the depthof water. This is indicative of the variations shown in perched water characteristics in the centralplateau area.

Where perched groundwater is found, its quality is generally good. In fact, the present water supplysystem for the island is based entirely on water from such perched aquifers (Jedda, Jane-Up, thethree springs at and near Waterfall and, occasionally, the Ross Hill Gardens springs). This water is,however, vulnerable to pollution because of the relatively fast flow paths through the soil and karsticlimestone. Aquifer vulnerability is considered further in section 6.3

6.2.3 Basal groundwater

Basal aquifers are found in some places around the edge of the island, for example, along thenorthern coastline and in the Smithson Bight area. Evidence is provided by freshwater outflows incaves, such as Daniel Roux, Freshwater Cave and Lost Lake Cave on the northern coastline. InFreshwater Cave, there is evidence of basalt at a distance of about 300 m from the coastline (BPCDrawing 67-DX9E/X5, “Freshwater Cave”). This may indicate the approximate limit of the basalgroundwater, and beyond this the groundwater may be perched.


In the Smithson Bight area, the basal aquifer is known from Freshwater Cave (a second one by thisname on the island) and from a number of investigation boreholes drilled in the area, at distances ofbetween 450 m and 1,400 m from the coastline (refer Table 2, section 2.1.7). There are likely to beother basal aquifers, but these have not been located owing to the lack of data (e.g. from drilling).

Barrett (1985) describes the results of drilling of seven water exploration boreholes in the SmithsonBight area in 1984. All boreholes intersected freshwater and yielded flows of between 2 and 3 L/swithout causing saltwater intrusion. The success with these holes prompted the drilling program forthis project, and in 1996 five monitoring boreholes (BH1-BH5) were drilled to further investigate thefreshwater potential in this area. The results of the 1996 drilling program are described in DouglasPartners (1996) and are summarised in section 2.1 of this report, while a summary of the drilling andmonitoring data is contained in Annexes B, C and D.

The conclusion from the drilling in the Smithson Bight area is that there is an extensive basal aquifer,possibly part of a more extensive freshwater lens under much of the island, which offers goodpotential for development of fresh groundwater. The primary sites are in the area between boreholesBH1 and BH4 where the freshwater zone was found to be at least 20 m thick. The disadvantage isthat relatively deep production boreholes are required to develop the groundwater. The depths towater table at boreholes BH1 and BH4 are approximately 153 m and 165 m, respectively. Access tothese sites is, however, reasonably easy.

At three of the five monitoring holes (BH1, BH4 and BH5) volcanic rock was intersected below sealevel (approximately at 22 m, 33 m and 36 m, respectively, below MSL). This indicates that thevolcanic core of the island is not far below sea level in this area. The intersection between thesloping volcanic rock and mean sea level under the island occurs between BH1 and Jane-Up, wherethe volcanic rock is found at an elevation of 130 m. The intersection is likely to be closer to BH1 thanJane-Up, as indicated in the cross section shown in Figure 5 and by the division between perchedand basal aquifers in Figure 13. This observation is consistent with the findings of the report byPettifer and Polak (1979). In Plate 18 (Interpretation Map) of that report the area just to the south ofthe ‘East-West Baseline’ is indicated as being where the top of the volcanics is at sea level.

It is noted that the basal aquifer is not entirely within limestone rock sequence. It was postulated byPettifer and Polak (1979) that the volcanics are of sufficient permeability to sustain a basal aquiferover most of the central part of the island. This is proven to a degree by the monitoring at boreholeBH1 in the Smithson Bight area (refer section 2.1), where freshwater was found in tube 1 locatedwithin the volcanics. The water level response to tidal and other influences was similar in that tubeas to the response in tube 2 which was terminated higher up in the limestone sequence. The similarsalinity and water level responses observed in both tubes indicates that the volcanic rock in thislocation is quite permeable and similar in a hydrogeological sense to that of the overlying limestone.This indicates that at least in this area, the volcanic rock represents no effective barrier to the mixingof freshwater and seawater.

As mentioned in section 2.1.8, it is possible that the basal groundwater extends under the islandfrom the Smithson Bight area to areas further north. The nature and extent of any basal groundwaterin this zone would be dependent on the permeability of the volcanic rock near mean sea level. It isrecommended that two investigation holes be drilled between BN1 and WB30 at suitable locations toassess the basal groundwater potential further. This drilling should be done at the same time asother possible future drilling. If hard volcanic rock is intersected in either or both of these boreholesthen the drilling can cease. The water level conditions should be checked after drilling to assess thepotential for future pumping from either a perched or basal aquifer.

6.2.4 Summary of aquifer classification

A map showing a simple classification of the island’s groundwater into perched and basal aquifer isshown in Figure 13. It is noted that this map should be considered preliminary as much of the datahas been inferred from the limited data available.

Some features of the island’s’ hydrogeology which have led to the delineation of perched and basalaquifers are as follows:

• There is a known basal aquifer in the Smithson Bight area and this aquifer extends inlandat least to the contact between limestone and volcanic rock. The east-west limits of this


aquifer are not known but are presumed to extend in an easterly direction to the south ofDolly Beach and the Ravine (where volcanic crops are known), and in a westerlydirection to the western coastline to the south of the Dales. In support of the adoptedmapping, there is no evidence of any springs or volcanic rock outcrops on the peninsularleading to South Point and Egeria Point (south west tip of the island).

• There is known to be freshwater outflows along the northern coastline at sea level andthere are no known springs occurring on basalt along this coastline.

• Boreholes BH12 in Poon Saan and BH13 in Silver City were drilled below mean sea levelwithout intersecting volcanic rock and the water levels indicate basal aquifer conditions.

• The area near the Grotto and Runaway Cave in the north eastern part of the island, is indirect connection with the sea.

• Areas along the eastern coastline which show volcanic rock and water tables or outflowsabove MSL, indicating perched aquifer conditions, are:- Waterfall, Freshwater and Jones Springs in the north eastern part of the island,- Boreholes BH6, BH7 and BH8 also in the north eastern part of the island,- Hosnies Spring,- the Ross Hill Gardens Springs (Harrison’s Nos 1 and 2, Hewan’s and Hudson’s),- Dolly Beach streams, and- the Ravine (stream)

• Evidence of perched groundwater in the central part of the island including:- boreholes BH9 and BH10 near the current rubbish disposal and landfill area,- the Grant’s Well, Jedda, Jane-Up and WB30 flow system, and- numerous past water investigation boreholes in the Grant’s Well, Jedda and Jane-

Up area.• Evidence of surface outflows from perched groundwater on top of outcropping volcanic

rock in the western part of the island in the area of the Dales.

On the basis of boreholes in Smithson Bight, and some knowledge of the groundwater conditionswithin Daniel Roux Cave, it is assumed that the basal groundwater within 500 m of the coastline hashigher salinity than acceptable for freshwater. The water in this zone is likely to have salinitiesvarying from slightly brackish to almost seawater, due to mixing with seawater, depending on thedistance from the coastline and the preceding rainfall conditions. This zone is marked as a shadedstrip around the island’s perimeter. It is narrower in areas where the volcanic rock is known to comeclose to the perimeter.

The actual distance from the coastline at which basal groundwater becomes fresh may varyaccording to local differences in permeability, especially if volcanic rock is present below sea levelnear the coastline (e.g. parts of the eastern and western coastlines). The distance will also varyaccording to wet and dry seasons with the line advancing closer to the coastline during or after wetperiods, and away from the coastline during dry periods. However, it is considered that as anapproximate guide, no basal groundwater should be developed by pumping within 500 m of thecoastline because there is a strong possibility that this groundwater would be brackish in extendeddry periods, and even if it was not, the action of pumping is likely to induce seawater intrusion.

The area of most uncertainty in the aquifer classification map (Figure 13) is the exact delineationbetween perched and basal groundwater. It is further noted that there may be a multi- layer aquifersystem under the areas marked as perched aquifers in Figure 13. For instance it is quite possible,although unproven that the basal aquifer extends underneath the area marked as being perchedaquifer. This would imply a differential permeability in the volcanic rock with depth under the island,whereby the perched aquifer would be positioned above a low permeability layer of volcanic rock.Underlying this would be a higher permeability volcanic sequence allowing freshwater to accumulateabove seawater. Recharge to the basal aquifer could occur through discrete fractures in certainsections of the largely perched aquifer area.

The aquifer classification map may be useful at identifying possible future locations for developmentof groundwater in basal aquifers. The map should be used with caution due to the uncertaintiesassociated with it.


Figure 13 Christmas Island aquifer classification map


Figure 14 Christmas Island aquifer vulnerability map


6.3 Groundwater VulnerabilityGroundwater systems are often vulnerable to contamination, particularly where soils are either thinor highly permeable. The latter condition applies on Christmas Island.

If contamination occurs, it is extremely difficult and often very costly to remedy. The most effectiveway of dealing with the issue is to prevent contamination from occurring.

This section examines the sources of contamination, both actual and potential and assesses thevulnerability of the groundwater to contamination.

6.3.1 Sources of contamination

The groundwater on Christmas Island is, in many locations, potentially vulnerable to contaminationfrom a number of present and possible future sources.

Contamination of groundwater can be caused by a number of localised sources (‘point sources’) andfrom activities over a wide area (‘non-point sources’ or ‘diffuse sources’). Examples of point sourcesof pollution are hydrocarbon spills, leachate from rubbish disposal areas and sewerage discharges.Examples of non-point sources of pollution are agricultural chemicals for weed control, etc.

On Christmas Island, the most likely sources of contamination are point sources such as rubbishdisposal areas and hydrocarbon discharges from leaking pipes or ruptured tanks. Other possiblesources are leaks in sewerage systems and accidental oil or fuel leaks from vehicles.

Most of the present potential sources of pollution are currently located in the north-eastern part of theisland, where the population is centred. Other potential sources of pollution are temporary mineworkings (mainly from associated vehicles) and future developments (e.g. development of a satellitelaunch facility and associated infrastructure at South Point).

6.3.2 Groundwater vulnerability assessment

Various methods have been used for assessing the vulnerability of groundwater systems tocontamination. One commonly used approach is the so-called DRASTIC system, developed in theUSA (Aller et al, 1987) which uses a series of contributing factors and a weighting system to providerelative vulnerability rankings for different hydrogeological environments. The factors used in thissystem are: depth to watertable, recharge, aquifer media, soil media, topography, impact of vadose(unsaturated) zone and hydraulic conductivity (permeability) of the aquifer. Using a numericalscoring system, five classes of vulnerability to contamination can be assessed, these being veryhigh, high, moderate, low and very low.

An example of the use of this system is a groundwater vulnerability assessment of the Perth basin(Appleyard, 1993). The highest rankings for these factors, indicating the highest vulnerability tocontamination are for shallow water tables, high recharge, limestone aquifers, thin soils, flattopography, karst limestone vadose zone and high hydraulic conductivity. For Perth, it was foundthat the karst limestone along the coast and areas on the coastal plains with a shallow watertablehad the highest vulnerability.

Most of these higher rankings apply to Christmas Island especially in the central plateau area. Inparticular, Christmas Island is characterised by limestone aquifers, a vadose zone with karstlimestone and other materials, and high hydraulic conductivity. Also, the recharge is moderatelyhigh, the soil is variable in thickness but is permeable, and the topography in the central plateau areahas relatively mild slopes.

Most of Christmas Island was rated with a score of 160-180 using the DRASTIC system, whichplaces it in the high and very high vulnerability classes. This process was done by using the tablesas presented in Appleyard (1993). The higher scores applied in the central plateau area,corresponding approximately to the perched aquifer area indicated in Figure 13. There may be someareas where a lower ranking (moderate) is applicable due to large depths to watertable and steeptopography (e.g. near the cliff areas of the island) but in some cases the depths to water table arenot well known. A conservative approach was adopted, and it was decided to rank the whole island


as either very high or high vulnerability, with these classes applying to perched and basalgroundwater, respectively.

The DRASTIC system does not take account of the quality of the groundwater at risk fromcontamination. As indicated in section 6.2, the basal groundwater around the edge of the island islikely to be brackish (salinity above the freshwater limit) within about 500 m of the coastline. It couldbe argued that the vulnerability of this groundwater is lower than elsewhere owing to its lower quality.However, the issue of vulnerability is usually linked to potential for contamination and not to theproperties of the groundwater at risk. For present purposes, it was decided to show the coastalmargin of 500 m as having a vulnerability similar to the rest of the basal aquifer area.

It is noted that the DRASTIC system does not take account of the type of pollutants and their mobilitywithin the unsaturated zone (above the groundwater). The mobility of various compounds isinfluenced by a number of factors including the degree of adsorption onto soil particles and organicmatter. For present purposes, the mobility of various compounds was not taken into account in theassessment of vulnerability.

6.3.3 Aquifer vulnerability map

Figure 14 shows the aquifer vulnerability map for the island, showing only two classes ofvulnerability, namely, very high (red) and high (pink).

Because of the high groundwater vulnerability to contamination, it is very important that land planningincludes strict controls over potential contamination sources. As can be seen there is effectively nosafe distance for groundwater from sources of pollution (e.g. rubbish disposal areas, seweragesystems and fuel storages). All of these potential contaminants and others could lead to detrimentalimpacts on the island’s groundwater, at either current sources or potential future sources. It isimportant that the ‘precautionary principal’ be adopted in this regard and that pollution be preventedrather than left to occur and to be dealt with in the future.

Given the high to very high vulnerability of the groundwater, it is recommended that a ‘zero discharge’policy would be the most appropriate for all potential pollutants in all areas of the island.

In particular, this will require very strict guidelines for waste disposal areas (impermeable liners tocontain all wastes, leachate treatment and effective disposal, special measures for hazardouswaste, and monitoring systems) and sewerage systems. Preferably all waste disposal sites shouldbe located away from the very high vulnerability areas. Given the shortage of land on the island, therestrictions on sea dumping, and the costs of back-loading materials to the mainland, it is importantthat waste for landfill be minimised and that every cubic metre of waste landfill space is usedefficiently. This requires appropriate planning, design and funding. Issues of waste separation,incineration of hospital waste, and alternative arrangements for handling of toxic and hazardouswaste need to be carefully addressed.

6.4 ConclusionsThe groundwater resources of Christmas Island are rated as having a high to very high vulnerabilityto contamination. Strict controls over potential pollution sources, particularly waste disposal sites,and sewerage systems are absolutely essential. In particular, planning procedures should takeaccount of the vulnerability of groundwater when siting waste disposal sites, urban developmentswith associated sewerage and stormwater systems and other potential sources of pollution. It isrecommended that a ‘zero discharge’ policy is the most appropriate for all potential pollutants overthe whole island.


7. WATER MONITORING PROGRAM

7.1 OverviewThe project brief (refer Annex A) required a monitoring program to be developed for the followingcomponents:

• Weir flows• Flow and salinity recording in Daniel Roux cave• Pumping and pipeline flows• Storage, flows and usage• Water chemistry• Chlorine and microbiological tests• Water level and salinity in boreholes• Daily evaporation

This section is organised according to the above list of components, with some modifications asexplained below:

• The third and fourth components are linked, as they both deal with the operation of thebulk water supply system. These two sections have been renamed under the heading‘Water supply system flows, storage and usage’ (refer section 7.4).

• The component dealing with ‘Water level and salinity in boreholes’ is not covered in thissection, but rather in section 2 with other aspects of the drilling and monitoring program.

• The daily evaporation section has been deleted. It was originally intended to re-commence pan evaporation measurements at the airport (refer Falkland, 1984b). Thisfunction is the responsibility of the Bureau of Meteorology. However, due to changes intheir operations and staffing, they did not see it appropriate to re-commence this activity.Instead, evaporation could be determined from other climatic measurements includingsolar radiation, wind speed, temperature and humidity using a method such as thePenman equation. As this assessment would have been well beyond the scope of thestudy, it was not undertaken. Rather, the existing pan evaporation data was used in theassessment of recharge (refer section 3), the main reason for wanting the panevaporation data to continue.

The section also includes a review of the monitoring program during the project andrecommendations regarding ongoing monitoring needs including equipment and approximate costs.

7.2 Weir Flows

7.2.1 Background

Deficiencies in the monitoring of the island’s water resources has been raised in reports prior to thisproject (e.g. Barrett, 1985; Falkland, 1986 and 1994b). In earlier years, monitoring of weir flows atsprings and at Jedda Cave were done on a regular monthly basis. Monitoring was done by manuallyreading the weir heights and converting heights to flows using a ‘rating table’. As outlined in Falkland(1986), the most intensive period of monitoring was from April 1965 to July 1974 during which periodmonthly flows were recorded at many developed and undeveloped water resources sites. This earlydata is summarised in BPC Drawing 67-X9E/X133.

7.2.2 Locations and purposes

During this project, automatic recorders was installed at two locations to monitor presently usedwater resources. These locations were:

• Jedda Cave: water level recorder to measure flow in the cave system downstream of thepump intakes; and


• Ross Hill Gardens pump well: water level to measure overflow from the pump sump.

At Ross Hill Gardens, flow meters were also installed on the pipelines from the Harrison’s Springsand Hewan’s Spring. This was done as part of the Water Source Improvements Project (referACTEW, 1996a).

The purpose of the Jedda Cave recorder is to monitor one of the most important water sources onthe island, the Jedda cave stream.

The purpose of the Ross Hill Gardens equipment is to record the flows from the springs (Harrison’sNos 1 and 2 and Hewan’s springs) discharging to the centrally placed Ross Hill Gardens pumpstation. Water from this site can be used as backup to the main water supply system from Jedda.The pump is usually started on a monthly basis to ensure that it is operational and to provide water tothe tank at Grant’s Well (used by nearby residents). If required for the main system, water can begravity fed from the Grant’s Well tank to the main storage tank at Jedda.

It was originally proposed that recorders be installed at the other presently used water sources atand near Waterfall (i.e. Waterfall, Freshwater and Jones Springs). However, no equipment wasinstalled at these locations owing to unresolved leasing issues between the Commonwealth and CIRduring the course of the project.

7.2.3 Monitoring equipment

Automatic recorders were installed at the Jedda and Ross Hill Gardens locations in October 1996.Both recorders consisted of a water level and temperature sensor with an associated electronic datalogger, manufactured by Greenspan Pty Ltd (Model PS300 loggers, serial no. PS3262 for JeddaCave and serial no. PS3263 for Ross Hill Gardens). The communication cable of each recorderwas terminated in a sealed terminal box with a small ventilated tube to enable the pressure sensor tobe vented to the atmosphere. Silica gel (desiccant) was provided to control moisture in the system.The terminal box (housing the battery and the recorder’s communication cable termination ) at Jeddawas located at the far end of the underground pump room above the stream. At Ross Hill Gardens,the terminal box was bolted to a post above the pump sump.

Existing corroded steel weir plates were replaced with stainless steel weir plates and gauge heightboards were installed. The gauge boards were set so that a zero reading corresponded with zeroflow over the weir. Installations of the weirs was also completed in October 1996. Details of theinstallations and the initial data collection were reported in a progress report (ACTEW, 1997a).

Further details of the recorders and methods of operation are contained in the Christmas IslandWater Resources Monitoring - Operation Manual (Skinner, 1997). The Shire of Christmas Island isresponsible for the monitoring program and operation of the equipment.

In summary, the recommended monitoring routine is for Shire personnel to visit the site each month,monitor the status and download the logger, obtain a check reading on the staff gauge. Furthercomments about the monitoring program are contained in section 7.7 and Annex S.

7.2.4 Data obtained from Jedda recorder

Continuous water level and temperature records have been obtained for this report from the Jeddawater level and temperature recorder for the following periods:

• 26 October 1996 – 26 February 1998,• 17 October 1998 – 9 November 1998, and• 4 May 1999 – 1 June 1999.

The first gap in the data (between February and October 1998) was caused by failure of therecorder. A new recorder, similar to the original, was purchased and installed in October 1998. Thesecond gap in the data is believed to be due to the recorder being inadvertently turned off during asite visit in November. The recorder was not subsequently turned on until May 1999 after a numberof attempts to establish communications between the recorder and the portable computer. Theexact cause of the communications problem is not known and is still being investigated.


7.2.5 Analysis of Jedda data

Annex J shows a table and a selection of graphs that summarise the data collected at the Jeddacave flow measuring station. The graphs were produced by HYDSYS, the hydrological datamanagement software package that was used for processing, analysis, and archiving of all datafrom the water resources data recorders on the island. Each graph shows the measured depth ofwater, temperature and the calculated flow. The graphs show the maximum and minimum valuesrecorded within the selected time interval (data time resolution). The cumulative rainfall measured atthe Jedda raingauge is also shown on each graph.

The flow is obtained by reference to the rating table or curve (refer to Table J1 and Graph J1,Annex J) which gives the relationship between height of water at the weir plate (measured by therecorder at 10 minute intervals) and the flow through the weir. The rating table and curve arecomposed of two parts. The lower part from gauge height zero to 0.3 m relates to the trapezoidalcross section of the calibrated weir. Above 0.3 m, water overflows the concrete weir walls on eitherside of the calibrated weir. This additional flow was calculated using a broad crested weir formula.The upper part of the table and curve combines the maximum capacity of the trapezoidal weir withthe additional flow for the broad crested weir.

Graph J2 in Annex J shows the data for late 1996, noting that the recorder was not commissioneduntil 26 October. Graphs J3 to J5 show the available data for the years 1997, 1998 and 1999,respectively. Graph J6 summarises the available water level, flow and rainfall data over the fullfour year period. Units for each of the variables are shown on the left side of each graph. Forinstance in Graph J2, the ranges are 0 to 0.5 for water level, 0 to 250 L/s for flow and 24 to 26°C fortemperature. These units were kept the same in each graph to allow for comparison betweengraphs. The time resolution (interval) is one day for the one year graphs and two days for the fouryear graph. The range for rainfall varied between graphs, with the rainfall range in Graph 2 beingfrom 0 to 2,000 mm.

From Graphs J2 to J6 a number of features are evident:• The wide band of data for both the water level and flow is due to frequent starting and

stopping of the Jedda pumps, causing the water level and hence the flow to change. Theflow in these graphs is the flow in the cave stream downstream of the pumps. If one orboth pumps are operating, then any flow that is recorded is overflow. When no pumpsare operating, the total flow in the cave stream is measured. If two pumps are operatingduring low flow periods, then the water can be drawn down below the weir (i.e. belowgauge zero) before the pumps are switched off by a low level float switch.

• From the available data, the level and flow were highest in mid-1999 and then in late1998, following higher than average rainfall. The lowest levels and flows wereexperienced in early 1998 prior to the first recorder malfunctioning. This was at the endof a very dry period experienced on the island.

• The response of the stream to rainfall is lagged by several months. This is particularlyevident at the start of 1997. In Graphs J3 and J7, heavy rainfall occurring in late Januaryand February did not produce higher than normal flows until March-April. The lagbetween heavy rainfall and peak flow is in the order of 3 months.

• The temperature range is reasonably small. Most of the time it was recorded at between25 and 25.5°C. The lowering of the temperature in the months August to October 1997was due to frequent times when the water level was drawn below the level of the waterlevel sensor, which was set approximately 0.14 m below the base of the weir (cease toflow). With no water over the sensor, the temperature sensor was measuring airtemperature that must have been below the water temperature. The minimumtemperature recorded was 22.7°C in mid August 1997 (below the selected temperaturescale in the graphs).

To view the data in more detail, two 3-month graphs are shown. Graphs J7 and J8 show data for theperiods January to March 1998 and April to June 1998, respectively. These two graphs show theresponse of the water level and flow to pumping on a short-term basis and to rainfall on a longerterm basis. In late April and most of May 1997 the water level and flow remain higher than normal asone of the pumps was not operating.


Two graphs showing one month of data each are also included in Annex J. Graphs J9 and J10show, respectively, data for April 1997 and May 1999. In these graphs, the data is plotted to a timeresolution of one hour so nearly all variations are evident. The peak flow in April 1997 was just above50 L/s compared with a peak flow in the recorded May 1999 period of more than 200 L/s. The higherflows in the May 1999 period was a direct result of much higher rainfall being experienced in thepreceding months. Unfortunately, the overall relationship of flow and rainfall in this latter periodcannot be determined owing to the missing data period between November 1998 and May 1999.

Finally, Graph J11 shows the data over a week (7 day) period from 20th to 26th April 1997. Thisindicates a pattern of pumps being (manually) switched on and off at different time of each day. Onthe 21st April, both pumps were switched off in the morning and on again in the afternoon. Thepattern on 20th April indicates both pumps being switched off and then one being switched on shortlyafter in the morning. The second pump was switched on in the afternoon. There are someanomalous water level fluctuations and corresponding flow variations on the night of the 22nd Aprilfollowed by unusual pumping patterns on the following days. The exact cause of these fluctuationsis not known but they were most probably caused by anomalous pumping behaviour. Investigationsof pumping records at this time may be able to locate the cause (not done for this report).

While the patterns due to pumping are interesting, the primary purpose of the automatic recorderwas to help in assessing the total flow within the Jedda stream. This can be obtained by adding thepumped flow to the overflow measured at the weir. The overflow for each month was obtained byintegrating the area under the flow curve for each month (using HYDSYS). The pumped flow isobtained from the Jedda Cave pipeline meter (refer section 7.4). The results of these flowcalculations, expressed as average monthly flows in litres per second are shown in Table 7.

The period from November 1996 to January 1998 had continuous overflow weir data. The months ofFebruary and October 1998 and May 1999 had partial data.

For the period of full record, the highest average flow occurred in April 1997, which is consistent withthe graphs already discussed. The average flows in October 1998 and May 1999 wereapproximately twice and 4 times higher, respectively, than the April 1997 flow.

In addition to the data in Table 7, periodic check readings were made of the staff gauge (obtainedwith the pumps off) during the period February to June 1999. Flow values were calculated from therating curve in Annex J (refer values in italics in Table 7). These manually calculated flows areapproximate only and may tend to overestimate flows in wet periods. For instance, in May 1999, theaverage of the gauge readings obtained in May 1999 was approximately 0.47 m corresponding to aflow of approx. 230 L/s. This value is higher than that obtained from continuous records (185 L/s).The reason for the discrepancy is most probably due to the intermittent check readings and thedifficulty of trying to average a monthly average gauge height reading and hence flow value. At lowflows, which are more critical from a water resources viewpoint, the differences in gauge height aresmall over a period of a month and the discrepancy should be small.

The ability to be able to compute total weir flows from the recorded data and to add these to totalmetered flows to obtain total flows in the Jedda Cave stream, is considered to be a major benefit forwater resources management. It provides a more accurate assessment of total flow than theperiodic readings of gauge height. This implies the necessity to maintain the recorder in goodcondition. At the same time, the manual gauge height readings should continue (at least every twoweeks) as a check on the recorded data and as a back-up when the recorder is not functioning.


Table 7 Average Monthly Flows at Jedda, Nov 1996 - June 1999

Month Pumped Flow Overflow at weir Total Flow

& Year (L/s) (L/s) (L/s)

Nov 96 9.37Dec 96 6.98Jan 97 14.3Feb 97 12.4Mar 97 28.3 19.7 48.7Apr 97 22.2 32.5 54.7May 97 13.6 35.7 49.3Jun 97 21.8 20.7 42.5Jul 97 22.5 14.6 37.1

Aug 97 19.7 14.8 34.5Sep 97 23.5 8.7 32.2Oct 97 26.3 3.2 29.5Nov 97 20.1 7.2 27.3Dec 97 22.3 2.9 25.2Jan 98 19.2 4.3 23.4Feb 98 14.3 7.3 * 21.6 *Mar 98 14.4Apr 98 14.9May 98 15.2Jun 98 15.6Jul 98 15.7

Aug 98 17.8Sep 98 27.4Oct 98 24.9 68.3 * 93.2 *Nov 98 26.7Dec 98 25.4Jan 99 22.5Feb 99 23.3 181Mar 99 17.8 163Apr 99 18.8 290May 99 21.1 164.1 * 185.2 *Jun 99 22.9 172

Notes * indicates months with partial data; blanks indicate missing data

A summary of the flow data from Table 7 and rainfall at the Jedda gauge is shown in Figure 10 insection 5.

From a water resources viewpoint, the minimum flow is very important. From Table 7, the minimummonthly flow was 21.6 L/s in February 1998. The flow may have become lower in the few monthsfollowing February 1998 but any further reduction in flow would probably have been minimal. Thisconclusion is based on the pumped flow increasing from a minimum in February 1998.

It is noteworthy that the combined minimum flow recorded for Jedda in early 1996, after an extensivedrought, was considerably lower than the low flows recorded in early 1998. In January 1996 theJedda flow decreased to 13.6 L/s (refer Figure 11, section 5 of this report and Tables 8 and 9 inFalkland, 1986). Allowing for about a 2-3 month lag between rainfall and Jedda flow, the rainfall forthe 6 months from June to November 1995 was only 219 mm. The rainfall for the corresponding6 month period for July to December 1997 was slightly higher (324 mm).


The data in Table 7 has been used for the analysis of a rainfall-runoff model for the Jedda Cave flow(refer section 5).

7.2.6 Data obtained from Ross Hill Gardens recorder and flow meters

Continuous water level and temperature records are available from the Ross Hill Gardens recorderfor the period 29 October 1996 to 31 March 1998. A limited amount of additional data was availableuntil 15 April 1998 but the data was suspected of being in error. This appears to have been causedby a low battery voltage condition (7.7 volts). This in turn most probably resulted from a failure tochange batteries once the battery voltage decreased below a critical level. It is recommended in theOperation Manual (Skinner, 1997, page 7) that the (rechargeable external) battery be replaced with arecharged battery once the voltage drops to 12.2 volts. After April 1998, the logger ceased tofunction properly. It was withdrawn from service in October 1998 and taken to the manufacturer forchecking and repair.

The (over)flow through the weir of the Ross Hill Gardens pump is the combined flow from thepipelines from the Harrison’s Springs (to the north) and Hewan’s Spring (to the south) minus anywater being pumped to Grant’s Well. There are separate meters on the two incoming pipelines andon the pumping main to Grant’s Well. The two inflow meters were installed as part of the WaterSources Improvement project in 1997. Regular readings of the meters on the pipelines from thesprings commenced in November 1997.

The existing pump meter was replaced with a new one in February 1998 by the Shire and regularreadings commenced in the same month.

Data from the meters is analysed in section 7.2.8.

7.2.7 Analysis of Ross Hill Gardens recorder data

Annex K shows a table and a selection of graphs that summarise the data collected at the Ross HillGardens weir recorder. As with the Jedda data, these graphs were produced with the HYDSYSsoftware package. Each graph shows the measured depth of water and temperature and thecalculated flow. The rainfall measured at the Jedda raingauge is also shown as a cumulative graph.

As for Jedda flows, the Ross Hill Gardens weir flow is obtained from an appropriate rating table orcurve (refer Table K1 and Graph K1, Annex K) measured by the recorder at 10 minute intervals).The rating table is based on the formula for a 90 degree V-notch weir. Above 0.15 m from the baseof the weir, water overflows the weir plate. During the period of record, no flows exceeded thecapacity of the weir. The base of the weir was at a level of 0.005 m (5 mm) on the gauge plate).

Graphs K2, 3 and 4 show the available data for, respectively, 1996, 1997 and 1998. Graph K5summarises the available water level, flow and rainfall data over the full period of record, October1996 – March 1998. Standard ranges for parameters were selected as -0.5 m to 0.5 m for waterlevel (noting that the water in the sump can be well below gauge zero), 0 to 20 L/s for flow and 24 to26°C for temperature. The time resolution (interval) is one day for the one year graphs and two daysfor the four year graph. The range for rainfall varied between graphs, with the rainfall range inGraph K2 being from 0 to 2,000 mm.

From Graphs K2 to K5 a number of features are evident:• The water level generally did not vary greatly and as a result the flow remained

reasonably constant. The intermittent sudden reductions in level to -0.3 m and belowwere due to the pump being turned on resulting in a lowering of the water in the sump.Normally, the pump was run at each visit to check operation of the pump and to providewater to the storage tank at Grant’s Well.

• Some of the fluctuations in water level, and hence flow, were due to obstructions placednear the weir, including pipes to divert the water further downstream. For instance, itwas noted during the October 1998 visit (after records ceased) that a pipe was used todivert water. Such obstructions would have influenced the level and hence the flow onoccasions. In addition, during the construction of the new spring cappings and pipelinesfrom the springs, there were inevitably times when some of the spring flow was divertedaway from the pump sump. There are no records of the duration of such occurrences.


• Despite the fluctuations in water level, there does not appear to be much variation inspringflow resulting from heavy rainfall, a situation that is different from Jedda.

• The temperature remained reasonably constant but not as constant as at Jedda,presumably because of its exposed location. The graphs show average (mean)temperature for each data interval rather than the maximum and minimum values forJedda, so as to remove some scatter. The greater variation is due to the more exposedlocation at Ross Hill Gardens compared with the Jedda Cave site

The weir flow calculated from the recorder data for each month from November 1996 to March 1998was done using HYDSYS. The results of these flow calculations, expressed as average monthlyflows in litres per second are shown in Table 8.

Table 8 Average Monthly Flows at Ross Hill Gardens, Nov 1996 - May 1999

Month & Year Overflow at weir

(L/s)

Nov 96 7.3Dec 96 7.8Jan 97 7.4Feb 97 4.7Mar 97 3.8Apr 97 4.3May 97 5.7Jun 97 4.9Jul 97 4.8Aug 97 4.0Sep 97 3.0Oct 97 5.9Nov 97 5.6Dec 97 5.7Jan 98 4.8Feb 98 4.7Mar 98 4.7

Oct 98 8.3Nov 98 -Dec 98 -Jan 99 10.0Feb 99 10.0Mar 99 10.0Apr 99 11.2May 99 10.3

Additional data is shown in Table 8 for the period October 1998 - May 1999. This data is based onmanual gauge height readings at approximately one to two weeks (refer Annex L). The data hasbeen averaged to obtain a representative gauge height and hence flow for each month (no data wascollected in November and December 1998). As the flow from the springs does not vary rapidly, thismethod of measurement is considered acceptable for future purposes. For this reason, it was notrecommended that the automatic recorder at this site be replaced when it ceased to operate in early1998.

The data from Table 8 is shown graphically with Jedda rainfall in Figure 15.


Figure 15 Monthly Ross Hill Gardens weir flows and Jedda rainfall, 1996-1999

Figure 16 Monthly Ross Hill Gardens weir flows and Grant’s Well rainfall, 1967-1974

0

2

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Jan-96 Jul-96 Jan-97 Jul-97 Jan-98 Jul-98 Jan-99

Time

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Monthly rainfall at Jedda Weir flow (recorder) Weir flow (manual readings)

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Jan-67 Jan-68 Jan-69 Jan-70 Jan-71 Jan-72 Jan-73 Jan-74

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Monthly rainfall at Grant's Well Harrison's Spring FlowsHewans Spring Flow Combined Flow

1


From Table 8 and Figure 15, the highest monthly flow occurred in April 1999 (11.2 L/s) and thelowest was in September 1997 (3.0 L/s). The peak flow was approximately 3 times the lowest flow.This ratio of peak to lowest flow is much lower than for Jedda where it is closer to 10:1 (referTable 7).

As described for Jedda, the minimum flow is very important. Because of the likely disruption to flowsfrom the springs during the period of data collection, the minimum flows shown in Table 8 cannot beviewed as accurate. It is noteworthy that the combined minimum flow recorded for Harrison’s andHewan's Springs in late 1965 and early 1966 was approximately 1 L/s (refer Figure 16, data fromBPC Drawing 67-X9E/X133 and Tables 8 and 9 in Falkland, 1986).

The flows shown in Figure 15 for the period October 1998 to June 1999 are probably under-readingsby an average of 15%, based on more accurate flow meter measurements on the pipelines from thesprings. This difference, which is not major, is further described below.

7.2.8 Data obtained from Ross Hill Gardens meters

Flow meter data is available for the spring pipeline meters from late 1997. Additional flow data fromearly 1998 is available for the meter on the pipeline from the Ross Hill Gardens pump station toGrant’s Well. The full set of data to late June 1999 is provided in Annex L.

In Annex L, average and instantaneous flow rates are shown for the two spring flow meters. Theaverage rate is calculated by subtracting the total flows at successive visits and dividing by theelapsed time between visits. Average flow rates have been measured since November 1997. Theinstantaneous flow rate is obtained by measuring the time taken for a selected volume (e.g.500 litres) to pass through the meter. The instantaneous flow tests were added to the monitoringprogram in October 1998, following the completion of the spring improvements. Instantaneous flowsshould be measured at each visit, and these should be done with the valves fully open, to measurethe full flow. Normally the valves on the inflow pipes should be restricted to some degree so as tocause some overflow at the springs for environmental flows.

The average flow over the period for the two meters were as follows:

• Harrison’s Springs: 2.8 L/s

• Hewan’s Spring: 5.5 L/s

These flows are ‘restricted’ by the valves near the meters being partially closed.

A more accurate guide to the total flows from the springs are the instantaneous flows. Table 9summarises the instantaneous flow data from the springs for the period October 1998 to June 1999,using the data in Annex L.

Table 9 Summary of Instantaneous Flows from Ross Hill Gardens springs

Spring Maximum Minimum Average(L/s) (L/s) (L/s)

Harrison’s (No 1 and No 2) 9.7 8.0 9.0

Hewan’s 3.3 2.0 3.0

Total 12.5 11.0 12.0

The totals for the maximum and minimum flows in Table 9 are not the simple addition of the twoindividual metered flows. The differences between the total springflows and the addition of the twoindividual springflows is due to maximum flows and minimum flows not coinciding at the two springs.

Theoretically, the combined flow from the springs should equal the flow estimated from the height offlow above the weir. A comparison of these two flow estimates is made on the right side of the table


in Annex L. During 1999, a number of simultaneous measurements were made. The combinedmeter flows were always higher than the weir flows, with the range being 0.6 to 3.1 L/s. Thisindicates that the combined meter flows were between 5% and 25% higher than the weir flows. Theaverage difference was 1.7 L/s or 14%. The reason for these discrepancies is most likely due to theweir flow being obtained prior to the valves on the springflow pipelines being fully opened. It isimportant in future that the weir flow measurement (by reading the gauge height) is done after thepipeline valves are fully opened and the sump water level allowed to adjust to the higher flow.

7.2.9 Summary of key results

Flows obtained from the two automatic recorders have provided a valuable insight into the flowvariations due to prior rainfall and other factors, particularly pumping at the Jedda Cave site.

The flow data obtained at Jedda indicates that the minimum flow in the period of observations(October 1996 - May 1999) was approximately 20 L/s in February 1998. Of this flow, approximatelytwo thirds was pumped and one third by-passed the pumps and went through the weir. Thisminimum flow of 20 L/s in the recent monitoring period was substantially greater than the minimumflow of 13.6 L/s recorded in January 1966 (all pumped and no overflow).

The flow data obtained at the Ross Hill Gardens pump station weir (from Harrison’s Springs andHewan’s Spring) indicates that the minimum flow in the period of observations (October 1996 - May1999) was approximately 3 L/s in September 1997. This was greater than the flow of 1 L/s recordedin the early months of 1966.

The Jedda Cave flow has a much greater range than for the Ross Hill Gardens pump well flow. Theratio between maximum and minimum flows is about 10:1 compared with about 3:1 for the Ross HillGardens flow.

7.2.10 Future monitoring requirements

For future flow monitoring at the Jedda and Ross Hill Gardens sites, it is recommended that therecorder (electronic data logger) be continued at the Jedda site, because of the complexity of theflows at that site. With the pump regularly switching on and off, it is very useful to get continuousdata. Combined with the Jedda Cave flow meter records, the total flow within the Jedda Cavestream can be calculated each month, using the method described in this section.

It is not necessary to have a recorder at the Ross Hill Gardens site now that the flow pattern is welldescribed by the available continuous data. However, regular visits are required to obtain the meterreadings and gauge height readings. These two independent flow measurements provide a meansof cross-checking the accuracy of the data.

It is important at Ross Hill Gardens, that the gauge height reading be obtained at each visit after theweir has been checked and any obstructions removed, and after the valves on the inflow pipes fromthe springs have been turned on to full flow and the water in the sump has been allowed to adjust toa new level. During flow measurements, it is important to gauge the total available flow from thesprings by fully opening the valves.

Further details of monitoring requirements at these and other sites are provided in section 7.7.

7.3 Flow and Salinity Recording in Daniel Roux Cave

7.3.1 Background

In the lower Daniel Roux Cave, a discrete freshwater outflow (locally called the ‘gusher’) occurs in aconfined part of the cave system. The exact source of the freshwater outflow is unknown but mostprobably includes some of the island’s area near and around Drumsite. The discharge occursthrough fissured limestone and just before it pours through the cave ceiling it splits into two outflowstreams. The water in the cave near the gusher is tidal. At low tides, there is approximately half ametre of clearance between the water level and the ceiling of the cave. At high tides, the cave ceilingincluding the gusher outlet is completely flooded.


The existence of the gusher has been known for many years and it was the subject of extensiveinvestigations to develop it by the BPC in the 1960s and 1970s. The BPC had undertaken a numberof flow measurements at the gusher in the late 1960s (refer BPC drawing 67-X9E/X33). Details ofthese flow measurements are contained in this section, together with more recent information.

7.3.2 Locations and purpose

Automatic water monitoring recorders were installed at two monitoring locations within Daniel RouxCave. One recorder was situated near the ‘gusher’ (a discrete flow of water from the roof of thecave), approximately 200 m in a direct line from the coastline. The distance via the cave system tothe sea entrance of the cave is further (in the order of 300 m). The second recorder was situated inthe channel system between the gusher and the open sea, approximately 130 m in a direct line tothe coastline. The two sites are referred to, respectively, as ‘DR gusher’ and ‘DR channel’ (thesesites correspond, respectively, to the names DRGUSH and DRCAVE used in the data logger files).

The initial purpose of monitoring these two sites was to measure the degree of saltwater intrusioninto the cave system and to get a better understanding of the freshwater flow through the system bymeasuring the difference in levels at the two sites. Initially, it was intended to establish relative levelsby survey between the two sites. Further discussions and site investigations with Russell Payne ofthe Christmas Island Surveying Company, ruled out the viability of obtaining this information withsufficient accuracy to be useful. It was considered to be an extremely difficult, time consuming, andpossibly dangerous job to survey in the cave using normal survey techniques. However, it wasdecided that it would be worthwhile exploring the use of ‘sonic’ technology to map the cave system.Although this would not provide level information, it would be valuable if in the future there was a needto drill into the cave from the first terrace for the purpose of extracting water.

A more direct way of measuring the long term variation of flow from the gusher would be to designand construct a flow measuring structure to be located underneath the gusher. This structure couldconsist of a receptacle with a V-notch overflow weir. By continually measuring the depth of waterthrough the weir the flow could be calculated (similar to Jedda Cave and Ross Hill Gardens). Thestructure would become drowned during high tide but continual flow measurement can beextrapolated from low tide to low tide. After a satisfactory period of monitoring under the presentregime, it may be an option worth considering to improve the understanding of the flows within thecave. Further recommendations on this aspect will be provided in a later report.

Because of the difficulties associated with the above methods during the course of theinvestigations, it was decided to attempt direct measurement of the gusher flow using the availableweir box and a data recorder, as described later in this section.

7.3.3 Monitoring equipment

The automatic recorder installed at each location in October 1996 consisted of a water level,temperature and salinity (electrical conductivity) sensor with an associated electronic data logger.Both recorders consisted of a water level and temperature sensor with an associated electronic datalogger, manufactured by Greenspan Pty Ltd (Model CP300 loggers, serial no. CP3041 for the originalDR gusher site and serial no. CP3042 for the DR channel site).

As with the Jedda and Ross Hill Gardens recorders, the communication cable of each recorder wasterminated in a sealed terminal box with a small ventilated tube to enable the pressure sensor to bevented to the atmosphere. Silica gel (desiccant) was provided to control moisture in the system.

As the recording sites were distant from the land cave entrance, long (120 m) cables were suppliedwith the sensor/loggers to enable the terminal boxes to be attached to a rock wall near the caveentrance (near base of the first ladder). This meant that Shire staff would need only to go to the caveentrance to interrogate the recorders, download data, and replace batteries and silica gel. The Shirestaff were advised not to attempt to go to the bottom of the cave to inspect the logger/sensors, dueto safety considerations.

Further details of the recorders and methods of operation are contained in the Christmas IslandWater Resources Monitoring - Operation Manual (Skinner, 1997). In summary, the recommendedmonitoring routine is for Shire personnel to visit the site each month, monitor the status and


download the logger. Further comments about the monitoring program are contained in section 7.7and Annex S.

At the Daniel Roux gusher site, attempts were made to measure the flow using a portable ‘weir box’which had been left in the cave since previous measurements were done in the 1970s. This weirbox consists of a shallow rectangular box made from thin galvanised steel with a 90 degree V-notchcut in one end. By holding the weir box under half of the gusher outflow at a time, and reading theheight of the flow through the V-notch, a reasonable estimate of flow could be made. This wasrepeated under the other half of the gusher and the two flow estimates combined to give a total flowestimate.

In October 1998, the weir box was set up on trestles under one half (front outflow) of the gusher andthe level and salinity sensors placed horizontally in the box. The purpose was to try and measurethe height (and hence flow) and salinity over a reasonably long period of time. Conditions forundertaking this work were extremely difficult with a very confined space for setting up the trestlesand weir box. Unfortunately, this set-up lasted only a few days before the force of water from thegusher and possibly the additional action of the rising tide moved the weir box sideways away fromthe gusher. The lesson to be learnt from this experimental flow measurement system is that a lotmore effort including a more permanent structure under the gusher with an outflow pipe would bemore useful in measuring the flow. A pipe flow meter with a data recorder could be installed on theoutflow pipe at a point away from the gusher where it would be easy to read. The meter would needto be capable of working under water (at high tide).

7.3.4 Data obtained from the recorders

Continuous water level, temperature and salinity records are available from the ‘DR gusher’ site forthe following periods:

• 27 October – 22 November 1996, and• 15 October 1998 – 12 May 1999.

Similar records are available from the ‘DR channel’ site for the following periods:• 28 October 1996 – 25 July 1997,• 15 August 1997 – 27 October 1997, and• 3 December 1997 – 10 April 1998.

The large gap in the DR gusher record was due to a malfunction with the recorder. After severalmonths of unsuccessful attempts to communicate with the logger, a new instrument was providedunder warranty by the manufacturer but it was not installed until the final project visit to ChristmasIsland in October 1998. Installation required cutting the original cable at a distance of about 30 mfrom the gusher at the nearest dry location within the cave and reconnecting the new sensor/loggerunit to the cable. Communications were re-established with the new unit by portable computer nearthe cave entrance on 15th October 1998.

The two gaps in the DR channel logger were due to either a problem with turning off the logger at asite visit or loss of the data file on Christmas Island after downloading. Despite these two periods oflost data, there is a long sequence of data from this recorder. Unfortunately, communications withthe recorder could not be established after April 1998. The logger has been left in position and couldbe recovered and returned to the manufacturer for repair at a subsequent visit.

The first gap in the data (between February and October 1998) was caused by failure of therecorder. A new recorder was purchased and installed in October 1998. The second gap in thedata is believed to be due to the recorder being turned inadvertently to off during a site visit inNovember. The recorder was not subsequently turned on until May 1999 after a number of previousunsuccessful attempts had been made to establish communications between the recorder and theportable computer. The exact cause of the communications problem is not known and is still beinginvestigated.


7.3.5 Analysis of DR gusher data

Annex M shows a selection of graphs which summarise the data collected at the DR gusher site. Inaddition, Annex N provides some graphs, which show a comparison between the data from the twoDaniel Roux recording sites (refer section 7.3.6 for analysis). The graphs show variations in waterlevel, temperature and salinity (measured in electrical conductivity or EC units). The data presentedin the graphs are the maximum and minimum values recorded within the selected time interval (datatime resolution).

Graph M1 in Annex M shows a summary of the data collected during the period October 1996 to May1999, noting the large gap between late 1996 and late 1998. Graph M2 shows the data for the firstsegment of data from October to November 1996 while Graph M3 shows the data for the secondsegment of data from October 1997 to May 1999. Graph M4 shows the available data for October19998 after the new sensor/logger was installed. Graph M5 shows data over a 10 day period from15th to 24th October and Graph M6 shows the data over a 3 day period from 16th to 18th October.

From Graphs M1 to M6, a number of features are evident:• Water level is controlled by the tide as shown by the sinusoidal pattern (particularly

evident in Graphs M5 and M6).• The maximum water level range was about 1.4 m during the observation period.• Temperature is very constant, varying only about 0.4°C (from about 25.9 to 26.3°C).

• Water salinity (EC) varied according to tidal movements. The range of values wasbetween about 350 and about 2,200 µS/cm over the recording period. The peaks insalinity occur about 2 hours after the water level peaks (refer Graph M6). It is noted thatthe desirable limit for freshwater is 1,500 µS/cm, so that the water in the cave near thegusher was generally less but sometimes exceeded this limit.

The minimum level of water, seen for the period 15th to 22nd October (Graphs M4 to M6), indicatesthe water level in the weir box, which was set up under the front outflow of the gusher on15th October 1998. During this period, the salinity of the water stayed reasonably constant,indicating it was not affected by the water in the cave to a significant degree. The ‘low tide’ waterlevel provides the means of measuring flow. The level of water in the box was related to the recorderlevel at 1055 am on 15th October. Using this information and the minimum recorded levels asshown in Graph M6, a flow of about 10-11 L/s was estimated during the days 15th-21st October fromhalf the gusher. This flow was similar to manually obtained measurements using the weir box (heldby three people) on 7th October 1998 (water height in weir box = 140 mm, hence flow = approx.10 L/s). After this day, the minimum level dropped substantially and the salinity sensor showed zerovalues at low tide. This occurrence indicated that the weir box was becoming dry and that it musthave moved away from the gusher. Despite this setback, the trial system showed that water leveland salinity of the water at the gusher could be measured if a more permanent arrangement wasmade. This would involve greater expense than was possible during this project.

The fact that the salinity varies with tide at this site, means that there is a direct hydraulic connectionthrough the cave to the sea. Hence, pumping from the cave in this location would not be possiblewithout inducing seawater intrusion, at least at medium to high tides. The only feasible option forobtaining freshwater would be to collect water directly from the gusher. This could be done byconstructing a sump under the gusher with a pipe leading from the sump and down the channeltowards the sea entrance. A borehole could be drilled from the first terrace and a pump installed topump water from the pipeline. The operation of the pump may need to be float switch controlledbecause at high water levels more saline water from the cave would overflow into the sump and mixwith the gusher water

7.3.6 Analysis of DR channel data

Annex N shows a selection of graphs which summarise the data collected at the DR channel site. Italso provides some graphs, which show a comparison between the data from the two Daniel RouxCave recording sites. As for the DR gusher data, the graphs show the water level, temperature andsalinity (measured in electrical conductivity or EC units). The data presented in the graphs are themaximum and minimum values recorded within the selected time interval (data time resolution).


Graph N1 in Annex N shows a summary of the data collected during the period October 1996 to April1998, noting the two small gaps in 1997. Graphs N2, N3 and N4 show the data for 1996, 1997 and1998, respectively. Graphs N5, N6 and N7 show more detailed data for a selected period. Graph N5shows the available data for September 1997. Graph N6 shows data over a 5 day period from 15th

to 19th September and Graph N7 shows the data for a single day (19th September).

Graphs N8, N9 and N10 compare the results from the two sites for November 1997. Graph N8shows the results for both water level and salinity for the month. The other two graphs showseparate comparison of water level and salinity for the 5-day period 9-13 November.

From Graphs N1 to N10 a number of features are evident:• Water level at the DR channel site is controlled by the tide, as for the DR gusher site.

The maximum water level range was about 1.5 m during the observation period. Therange is slightly higher than for the DR gusher site. Graph N9 shows the two water levelgraphs on the same time scale. It is evident that the tidal effects occur at both sites atabout the same time, but the effect on water level is slightly greater at the DR channelsite than at the DR gusher site. The difference in amplitudes of the two responses isabout 15%. It is noted that the levels shown in Graph N9 are on the same scale, but thatthese levels are not inter-related as there has been no survey undertaken.

• Temperature is again very constant, varying only about 0.4°C (from about 25.5 to25.9°C). The difference between the actual temperature readings and those at the DRgusher site maybe due to slight differences in calibration of the two temperature sensors.

• Water salinity (EC) varied according to tidal movements. The range of values was muchhigher than at the DR gusher site. The EC varied between about 600 µS/cm to higherthan 25,000 µS/cm over the recording period. The peaks in salinity occur at about thesame time as the water level peaks (refer Graph N7). The salinity is generally well abovethe desirable freshwater limit (1,500 µS/cm) and the peak values are approximately 50%seawater. This indicates that a very thin layer of freshwater is discharging over salinewater in the form of a ‘wedge’, and that this freshwater wedge moves up and down withthe tide. The salinity sensor, which is fixed in position, is showing higher salinities as itbecomes more immersed in the water (i.e. moves in a relative sense below thefreshwater wedge on each tidal high) and lower salinities at low tide.

The data at this site confirms that it would not be possible to pump from the DR channel systemwithout causing extensive saline intrusion.

7.3.7 Summary of flow and water quality data for the Daniel Roux gusher

Table 10 summarises all data that could be found for flow measurements at the Daniel Roux Cavegusher. These flows relate to the total flow from the two gusher outflows.

In the October 1995 visit, the water levels in the weir box were measured at 140 mm under the frontgusher and 110 mm under the rear gusher. These water levels correspond to flow rates of 10 L/sand 6 L/s, respectively, giving a combined flow of 16 L/s.

In October 1998 (7thOctober), only the front gusher was measured as the tide prevented the weir boxfrom being placed under the rear gusher. The front gusher was measured at 140 mm (10 L/s) in theweir box, as previously mentioned. It was assumed that the rear gusher was similar to themeasurement obtained in 1996 (i.e. 6 L/s) and hence the total was 16 L/s, similar to the October1995 reading. A similar approach was adopted in the 1986 measurements (i.e. only the front outflowwas measured). It was assumed at the time that the rear outflow was about the same as the frontoutflow. This may well be an over-estimate for the rear outflow as found in the 1995 measurement.Hence, the value of 20 L/s shown in Falkland (1986) for the October 1986 measurement may in factbe closer to 16 L/s as found in the October 1995 measurement.

Additional hand written notes in water related files held by the PMCI, obtained during the visit to theisland in 1986, indicated that there were other measurements made in the period 1967-1973. Manyentries (e.g. Jan 1968-May 1968, Aug 1968-Dec 1968 and Feb 1970-Dec 1973) showed a value of12,000 gallons per hour (equivalent to 15.1 L/s). The accuracy of this data is unknown.


Table 10 Summary of the Daniel Roux Cave gusher flows, 1967-1998

Month & Year Flow(L/s)

Source

Jan 1967 21.0 BPC drawing 67-X9E/X33Feb 1967 25.2 BPC drawing 67-X9E/X33Mar 1967 25.2 BPC drawing 67-X9E/X33Apr 1967 26.5 BPC drawing 67-X9E/X33May 1967 20.8 BPC drawing 67-X9E/X33Jun 1967 20.8 BPC drawing 67-X9E/X33Jul 1967 20.8 BPC drawing 67-X9E/X33Aug 1967 19.5 BPC drawing 67-X9E/X33Sep 1967 16.4 BPC drawing 67-X9E/X33Oct 1967 16.4 BPC drawing 67-X9E/X33Nov 1967 17.2 BPC drawing 67-X9E/X33Jun 1968 28.5 BPC drawing 67-X9E/X33Jul 1968 20.2 BPC drawing 67-X9E/X33Jan 1969 25.2 BPC drawing 67-X9E/X33Jul 1969 19.3 BPC drawing 67-X9E/X33Oct 1986 20.0 Falkland (1986)Oct 1995 16.0 Measurement during this projectOct 1998 16.0 Measurement during this project

The minimum flow shown in Table 10 was 16 L/s, which occurred during the very dry period 1965-1967. The minimum flow from all available data (including the unsourced notes) is thusapproximately 15 L/s. This represents a very significant flow and is in fact higher than the minimumflow observed at Jedda Cave of 13.6 L/s (refer section 7.2.5). As such this source is consideredvery reliable and similar to the Waterfall springs, which have shown similar low variation in flows,including during the very dry period in the mid-1960s (refer BPC drawing 67-X9E/X33 and Falkland,1986).

The salinity (EC) of the Daniel Roux gusher water was measured in October 1986 as 530 µS/cm(laboratory test). This result is similar to the EC readings for other sources at the same time(470 µS/cm for Jedda, 500 µS/cm for Waterfall Spring, 500 µS/cm for Harrison’s Springs and520 µS/cm for Hewan’s Spring). The EC readings for the other two springs feeding the Waterfallpumps were higher (780 µS/cm for Freshwater Spring and 720 µS/cm for Jones Spring).

In October 1995 the salinity (EC) of the water obtained from the gusher was 560 µS/cm, asmeasured by a portable salinity meter. The water in the cave near the gusher flow was slightlyhigher at 580 µS/cm.

The salinity (EC) of the gusher was again tested on 13thOctober 1998 and the results was600 µS/cm. This result was consistent with the recorded data from the Greenspan logger(s) at thetime.

All salinity results show a consistency in the data and confirm that the water is of low salinity, similarto the other perched groundwater sources on the island.

7.3.8 Conclusions and future monitoring requirements

The Daniel Roux gusher provides an option for future water resources development on the island.From the monitoring over several years, it appears that the minimum flow is approximately 15 L/s.This is a substantial flow when it is compared with the minimum flow recorded at Jedda of 13.6 L/s.


A number of issues, however, need to be considered before a decision could be made to develop theflow. These include:

• Environmental and heritage values of the cave;

• Environmental impact on the first terrace where a pump station and pipeline to thesettlement would need to be constructed;

• Potential pollution from areas of the island above the cave;

• Potential reduction in flow due to changed hydrogeological properties of the limestonethrough which the water flow to supply the gusher;

• Safety issues related to the development and operation of the water supply system; and

• Technical and economic risks associated with the development of the source.

These issues are beyond the scope of this report but are considered further in the WaterManagement Plan (ACTEW, 1999).

It is recommended to continue the recorder (data logger) at the DR gusher site. The DR channelsite recorder can be removed at the next available opportunity. This could be examined and repairedand kept as a spare for the DR gusher site.

At this stage, it is not recommended that a flow measuring weir be built around the DR gusher. If thesite is seriously considered in the future as a possible source of freshwater then it would beadvisable to build such a weir structure, or another suitable flow measuring device, so thatmeasurements of flow can be estimated from a rating table (similar to Jedda and Ross HillGardens).

Based on experiences with water level recorders and weir boxes, it is considered that a morepermanent structure under the gusher with an outflow pipe would be more useful for measuring theflow. A pipe flow meter with a data recorder could be installed on the outflow pipe at a point awayfrom the gusher where it would be easy to read. The meter would need to be capable of workingunder water (at high tide).

7.4 Water Supply System Flows, Storage and Usage

7.4.1 Background

In the 1970s and early 1980s, the island’s water supply system was operated by the miningcompany and was equipped with extensive metering systems. This was at a time when the needfor, and consumption of, water was at its peak on the island and considerable efforts were made todevelop available sources and to effectively utilise the water that was collected. BPC and PMCI filerecords, reports and drawings indicate the extent of water metering, water usage and measures tocontrol usage. BPC Drawing 65-X9E/X20L (“Diagrammatic Layout of Fresh Water Supply showingRLs, Pumps, Valves etc.”) shows the bulk water supply system with no less than 29 meters for flowmonitoring.

In the late 1980s and early 1990s with the transition of the water supply operation from PMCI to CISCand then to the current Shire of Christmas Island, many of the original meters were either no longeroperating or were redundant due to changes in the system.

With the modifications to the Waterfall Spring and pipework by CIR in the early 1990s, meters wereinstalled to measure flows but these were rarely read. In addition, the main meter on the pipelinefrom Jedda to Drumsite was not functioning.

Despite the lack of some meters, records of daily readings and tank levels were maintained bydedicated personnel within CISC and the Shire. This has enabled a reasonable assessment of thewater supply on the island to be undertaken in recent years.

7.4.2 Improvements to metering

During the course of this project, a number of improvements were made to the metering of flows.These were funded partly by the Water Supply Improvements Project (a component of the


Christmas Island Rebuilding Program) and partly out of the Shire’s budget. The improvementsincluded:

• Fitting a meter to the delivery pipeline from Jedda Cave inside the old chlorinator roomadjacent to the Jedda transfer pump building, and immediately above the cave pumps.This meter, installed in February 1997, measures the total flow from the submersiblepumps in the cave.

• Repairing the existing meter on the pipeline from Jedda to Drumsite in March 1997 andlater relocating it relative to the dirt box. Subsequently, the repaired meter failed and wasreplaced by a new meter in December 1998. This meter measures the total flow fromthe Jedda storage tank (consisting of flows from Jedda Cave, Jane-Up and, if everrequired, Ross Hill Gardens) to the Drumsite tank.

• Fitting meters to the gravity pipelines from Harrison’s Springs and from Hewan’s Springin 1997.

• Fitting a new meter to the pipeline from Ross Hill Gardens pump station to the Grant’sWell storage tank in February 1998.

• Fitting a new meter to the pipeline from Jane-Up to the Jedda storage tank in March1998.

• Fitting an inflow meter at George Fam tank on pipeline from Waterfall in February 1998.

These meter installations now allow a reasonable water balance of the island’s water supply systemto be obtained.

As part of a separate project, consumer meters were installed at all consumer connections.Readings from these meters were analysed in conjunction with the readings from outflow meters onthe main storage tanks to provide a preliminary assessment of water losses in the distributionsystem.

Monitoring and analysis of the bulk water supply system was conducted during the course of theproject. Spreadsheets were developed to store the data on an annual basis and these were given tothe Shire’s Works and Services staff. Training was provided in the data entry procedures, graphgeneration and examination of the data.

The field monitoring sheet was modified to incorporate the new meter readings and other dataincluding storage tank levels. These sheets were developed over several stages in conjunction withShire personnel. It is noted that the storage tank levels, while useful for operational purposes, arenot entered into the spreadsheets of meter data as they are not required for analysis of long termflows in the system.

7.4.3 Additional flow monitoring and analyses

Additional monitoring and analyses, beyond the scope of the project brief, were undertaken duringthe course of the project. These were as follows:

• detailed logging of flows from main storage tanks (Drumsite, George Fam and theHospital tanks);

• data processing and analysis of consumer meter readings; and

• evaluation of the magnitude and distribution of supply system losses.

It was found necessary to include these additional items owing to the large amount of losses fromthe water supply system and the impacts that this had on a number of key elements of the WMP.These key elements included water resources development options, administrative arrangements,water pricing policy and water charging options. In fact, it would not have been possible to developan effective plan without a detailed analysis of the system loss issue. The magnitude andsignificance of the high leakage rates was not made fully apparent until the WMP process was wellestablished.


7.4.4 Available flow meter data

The flow meter data can be divided into four convenient categories as follows:

• Daily readings of flow meters between sources and main storage tanks; also readings,from the outlets of the main storage tanks which feed the distribution systems toconsumers,

• Detailed data logging of flow meters at selected storage tank outflow pipes (Drumsite,George Fam and Hospital tanks). This data assisted greatly in the identification ofsystem losses, and

• Periodic readings of consumer meters.

Analysis of the data for each of these categories is provided in the next sub-sections.

7.4.5 Analysis of daily flows from sources and main storage tanks

The daily meter readings from the main meters maintained by the Shire and its predecessors wereentered into EXCEL spreadsheets. Daily flows were calculated and graphs prepared to summarisethe data on an annual basis and show the linkages between the various flows. Annual graphs wereprepared for all data from 1995 to 1999 and these are shown as Graphs O1 to O5 in Annex O. Thegraph for the first six months of1999 is also shown below as Figure 17.

Figure 17 Meter Flows - Sources and Distribution Tanks, January – June 1999

0

10

20

30

40

50

1-Jan-99 31-Jan-99 2-Mar-99 1-Apr-99 1-May-99 31-May-99 30-Jun-99

Time

Flow

(Li

tres

per

sec

ond)

Jedda Cave Jedda to Drumsite George Fam DrumsitePower Station Hospital Airport


Graphs such as that shown in Figure 17 provide much useful information. For instance, the majorreduction in outflow from the Drumsite tank in early March 1999 was due to rectifying a major leakfed by this storage tank. The leak of approximately 8 L/s had earlier been detected as part of a leakdetection project in late January and early February in a 100 mm AC main near the CIP’s DrumsiteWorkshop (Gugich, 1999). Another major leak repair in August 1997, following an analysis of nighttime flows, caused a reduction in the outflow from the Hospital tank (refer Figure O3 in Annex O). Athird example of reduction in outflow is shown for the George Fam tank in July 1997 after a majorleak was detected and repaired in the Settlement.

Other interesting features evident in the graphs are the switching between operation of the Drumsiteand Power Station tanks (e.g. March and June 1999). More evident is the temporary cessation in theuse of the George Fam tank in May, with the corresponding extra demand placed on the Drumsitetank.

The data collected over the past few years from the sources is summarised in Table 11.

The data in Table 11, shows that the relative contribution from the Jedda Cave source is by far thegreatest in 1998 and the first half of 1999. According to the data, the Jedda Cave flows were 88%and 97% of the total flows, respectively, for these two periods. The latter percentage is probably toohigh because of a suspected under-reading of the flow from Waterfall. This matter will need to beinvestigated further (beyond the scope of this project).

Table 11 Summary of flows from sources 1997-1999

Source

Jedda Cave Jane Up Waterfall TotalYear

ML L/s ML L/s ML L/s ML L/s

1997 690 21.9

1998 609 19.3 7.6 0.2 78 2.5 695 22.0

1999

(to 30 June)

331 21.2 0 0 9.5 0.6 340 21.8

Notes:1. Flows are shown in terms of totals (megalitres or ML) and averages (L/s or litres per second).2. Only very limited pumping occurred from the Ross Hill Gardens and this has not been included in the

above summary. For instance, the total flow for 6 months in 1999 (February – July) was less than0.5 ML or less than 0.1% of the total flow from the other sources.

3. Some of the data are estimates as indicated below.4. 1997 meter data: Jedda Cave meter measured 609 ML for period from 14th Feb (meter installed). This

was factored up on pro-rata basis for whole year. No data was available for Jane Up and Waterfall in1997.

5. 1998 meter data: Jane Up meter measured 5.7 ML for period from 1st April only (meter installed).Waterfall measured 70 ML for period from 10th Feb only (inlet meter to George Fam installed). Bothwere factored up on pro rata basis for whole year.

6. 1999 meter data: the flow from Waterfall is suspected of being under-estimated

In Table 11, the flows from Jedda Cave are those from the meter on the pipeline from the cave itself,which is situated within the transfer pump station, and are not from the meter on the Jedda toDrumsite pipeline. The latter meter, situated on the pipeline about 100 m from the outlet side of theJedda transfer pump, measures all flows from the Jedda Cave, Jane-Up (and, potentially, Ross HillGardens) sources. As, the bulk of the water comes from Jedda Cave and only a very smallproportion from Jane Up (about 1% in 1998 and zero in the first half of 1999), it would be expectedthat the flows through the Jedda Cave meter and Jedda to Drumsite pipeline meters would be almostequal.


Comparisons of the flows through the Jedda Cave and Jedda to Drumsite meter have been made atseveral times during the project. In the second progress report (ACTEW, 1997b), an analysis offlows for the period January to April 1997 showed that the average flows were 25.1 and 21.3 L/s,respectively. The higher flow through the Jedda Cave meter is considered to be correct. Thedifference of 3.8 L/s or 15% of the Jedda Cave flow was found to be caused by under-reading at theJedda-Drumsite pipeline meter. This was established by detailed measurements in May 1997 ofboth meters during a period when only water from Jedda Cave was being pumped and the JeddaTank had been isolated. Details are provided in ACTEW (1997b). Recommendations were made torepeat the tests. The later tests confirmed the earlier results. Measures to improve the meteringwere relocation of the meter further from the ‘dirt box’ to avoid turbulence through the meter, andreplacement of the meter in early December 1998 after failure of the original meter. Analysis of flowdata for the first six months of 1998, prior to problems with the Jedda-Drumsite pipeline meter,indicated that the average flows through the Jedda Cave and the Jedda-Drumsite pipeline meterwere 15.7 and 14.1 L/s, respectively. In addition, an average flow of 0.7 L/s was recorded at theJane Up meter. Thus, there was a difference of 2.3 L/s between the combined flow from JeddaCave and Jane Up and the flow through the Jedda-Drumsite pipeline meter. This differencerepresented 14% of the combined flow from Jedda Cave and Jane Up.

Following replacement of the Jedda-Drumsite pipeline meter, the problem seems to have beenresolved. Average flows through the Jedda Cave, Jane Up and Jedda-Drumsite pipeline meters forthe first 6 months of 1999 were 21.2, zero and 21.4 L/s, respectively. The apparent increase in flowof 0.2 L/s at the Jedda-Drumsite pipeline meter (1% of the Jedda Cave flow) is acceptable and wouldprobably represent slight differences in meter calibration.

The data collected over the past few years from the main distribution tanks is summarised inTable 12. Only the three storage tanks that showed the largest through-flow are shown. Comparedwith the flows from these three main storage tanks, the flows from the other two distribution tanks(Power Station and Airport) are relatively minor. The flows from the Power Station tank were 7.9 MLin 1996, 16.9 ML in 1997, 6.4 ML in 1998, and 1.7 ML in the first 6 months of 1999. These flowsrepresented less than 3% of the total flows in all years. The flows from the Airport tank were 3.1 MLin 1996, 0.9 ML in 1997, 0.8 ML in 1998, and 0.4 ML in the first 6 months of 1999, representing lessthan 0.5% of the total flows in all years.

Table 12 Summary of flows from main distribution tanks, 1996-1999

Distribution tank

Drumsite George Fam Hospital TotalYear

ML L/s ML L/s ML L/s ML L/s

1996 423 13.4 230 7.3 92 2.9 745 23.6

1997 391 12.4 214 6.8 79 2.5 684 21.7

1998 418 13.2 160 5.1 17.6 0.6 596 18.7

1999

(to 30 June)

188 12.0 90 5.8 6.2 0.4 284 18.6

Notes:

1. Flows are shown in terms of totals (megalitres or ML) and averages (L/s or litres per second).

The following comments are made and conclusions drawn from the data presented in Tables 11 and12 and the graphs in Annex O:

• The limited available data in Table 11 from the source meters indicates that total flowfrom sources is approximately 22 L/s during 1998 and 1999.

• For an estimated population of about 1,500 on the island, a flow of 22 L/s is equivalent toabout 1,270 litres per person per day (L/p/d). This is very high and is similar topreviously identified per capita flows (e.g. 1,130 L/p/d in 1985/86: Falkland, 1986).


• The amount of water flowing from the Drumsite tank is about double that from theGeorge Fam tank. The outflow from the Hospital tank is relatively low especially in thelast two years, since a major leak was detected and rectified in the distribution systemfrom that tank in mid-1997 (refer Figure O3, Annex O).

• From Table 12, there has been an overall reduction in flows since 1996. This is partlydue to detection and repair of some leaks and most probably also due to a reduction inthe overall demand for water with the reduction in population in this period.

• Comparison of the total flows in Tables 11 and 12 for 1998 and 1999 provides anindication of possible losses between sources and distribution tanks. In terms ofaverage flows, the differences are 3.3 L/s and 3.2 L/s, respectively. These differencesboth represent approximately 15% of the source flows. . These differences are slightlylower (e.g. 2.9 L/s in 1998) when the outflows from the two minor tanks are taken intoaccount. This reduces the percentage difference to about 13% in 1998. Thesenumerical and percentage differences may represent both systematic meter errors andwater losses (pipeline losses and possible overflows at tanks). It is known that the threeindependent meters near the Jedda and Jane Up sources are internally consistent witheach other in 1999, indicating that these readings are probably correct to within 1%.Hence the problem is either under-reading of one of more of the distribution tank outletmeters and/or actual losses. This matter should be further investigated.

7.4.6 Analysis of continuous flow data from selected tanks

During the course of the project, detailed flow analyses were conducted of the outflows from thethree main storage tanks (Drumsite, George Fam and the Hospital tanks). Initially manual readingsof the outflow meters were taken during the day and night over a selected period. Later, the meterswere fitted with pulse counters and these were connected to data loggers (Data Taker DT5 loggersinstalled in weatherproof boxes).

The purpose of these flow analyses was to gain a more detailed understanding of the diurnalvariations in flows from these storage tanks. In particular, information on minimum night-time flowsfrom the tanks was sought. This information provides an indication of the overall leakage andwastage from the total water supply distribution system (public main pipelines and consumerplumbing). The ratio of minimum night flow to average flow provides a good indication of the amountof leakage and wastage from the system.

Prior to the installation of the data loggers, manual readings were taken periodically during the nightand day over a 13 day period in April and May 1997. Details of these tests have been presented inthe second progress report (ACTEW, 1997b), and a summary is provided here. At each visit, themeter reading was recorded and an instantaneous flow reading obtained by measuring the timetaken for a set volume of water to flow through the meter. Table 13 provides a summary ofmaximum, average and minimum flows recorded manually at the three outlet meters. Maximum andminimum values were from instantaneous flow tests while the average was obtained over the fullperiod (28th April – 10th May 1997).

Table 13 Flows at Drumsite, George Fam & Hospital tanks, 28 Apr-10 May 1997

Flow (L/s)Meter Location

Maximum Average Minimum

Drumsite tank outflow 26.4 13.8 7.0

George Fam tank outflow 16.3 8.3 4.7

Hospital tank outflow 4.3 4.1 3.5


From the data in Table 13, the following conclusions were made at the time (refer ACTEW, 1997b):• maximum flows for Drumsite and George Fam tanks were approximately double the

average flows, while the minimum flows were approximately half the average flows.• very little variation was shown for flows from the Hospital tank. This was an indication of

an almost constant discharge occurring throughout the day and night. As no flows couldbe detected in the areas known to be supplied from the Hospital tank, large leakage wassuspected. It was recommended that metering of the known connections fed by thistank should be provided and detailed monitoring commenced. Subsequently in August1997, a large leak and several minor leaks were detected in the distribution system fedfrom this tank and these leaks were rectified (refer reduction in flow in August 1997, asshown in Figure O3).

• minimum flows in all cases were high. These were recorded at 4:26am, 2:12am and5:25am, respectively, for the three sites (all on separate days). The ratios of minimum toaverage flows were, respectively, 0.51, 0.57 and 0.85 for the Drumsite, George Fam andHospital meters, respectively. The Hospital tank had the worst problem.

• The total of the minimum flows (15.2 L/s) was a very large flow and represents about60% of the average amount of water pumped from Jedda Cave over the first four monthsof 1997 (25.1 L/s). Subsequently, a number of leaks have been detected and repaired(e.g. refer Gugich, 1999).

• the total of the minimum flows mentioned above was equivalent to approximately650 L/p/d, assuming a population of 2,000 on the island at the time. Most of theminimum flows were considered to be losses rather than legitimate usage. Becauseconsumer meter flow data was not then available, the proportion of flow that is being lostthrough leaks and/or wastage within the reticulation system (from the tanks to consumerconnections) and within consumer properties could not be calculated. It wasrecommended that reading of consumer meters be commenced as soon as possible forthis information to be gathered and for remedial measures, including a leak detection andcontrol program, to be implemented.

Following these initial tests in 1997, data loggers and pulse counters were installed at the Drumsite,George Fam and Hospital meters and more detailed data collected. The loggers were set to recordthe meter readings at 2 minute intervals. Data was recorded over periods of several days during1998. The results are shown in the 8 graphs in Annex P. One of these (Graph P1), for the Drumsitetank outflow meter for the period 19-22 June 1998, is shown in Figure 18.

Figure 18 Drumsite tank outflow meter, 19-22 June 1998

0.00

5.00

10.00

15.00

20.00

25.00

19/06/98 0:00 20/06/98 0:00 21/06/98 0:00 22/06/98 0:00 23/06/98 0:00

Date and Time

Flo

w (L

/s)

`


The data shows detailed variations in flows during the day and night. Using Figure 18 as anexample, peaks flows in the morning and afternoon peak are evident. These correspond to highwater usage periods of the day (cooking, showers, etc.). The flow in the middle of the day is lessthan these peaks. The night flows are the most relevant feature from a flow analysis viewpoint.Figure 18 shows minimum night flows between approximately 7.1 and 9 L/s on the three nightsshown. These are significantly high flows at night and are indicative of large leakage and possiblewastage (e.g. taps left on) during this period.

Graphs P1 to P3 show the flows through the Drumsite tank outflow meter during three periods in1998. The minimum night flows varied from approximately 6.3 L/s to just above 10 L/s. Details ofthe flows are summarised in Table 14.

Table 14 Flows from Drumsite, George Fam & Hospital tanks for periods in 1998

Meter Location Period Graph inAnnex P

Flow (L/s)

Maximum Average Minimum

Drumsite tank outflow 19-22 June P1 >21.2 12.4 7.1

“ 22 Jul – 14 Aug P2 >21.2 12.1 6.3

“ 6-17 Oct P3 >21.2 15.4 9.2

George Fam tank outflow 5-19 June P4 (1st part) 8.5 4.4 1.5

19-22 June P4 (2nd part) 9.3 4.2 1.5

“ 22 Jul – 14 Aug P5 21.0 4.9 1.8

“ 6-17 Oct P6 >21.2 6.8 3.0

Hospital tank outflow 22 Jul – 14 Aug P7 8.2 0.3 0

“ 6-17 Oct P8 8.8 1.0 0.6

In Graph P2, the sudden drop and subsequent increase in flow on 27th July 1998 was due to theoutlet valve being turned off. This graph also shows a gradual increase in flows over the period,particularly in minimum (night) flows. Towards the end of the period, the logger was not capable ofstoring the peak flows, which exceeded the capacity of the logger for each 2 minute time interval(254 counts or 21.2 L/s). The same issue occurred for Graphs P1 and P3, particularly the latter.This is the reason for the maximum flows for the Drumsite meter in Table 14 being shown as‘greater than 21.2’ (>21.2).

From the data in Table 14, the following ratios were determined for the storage tank outflow meters:• Drumsite: 0.57, 0.52 and 0.60 for the three periods.• George Fam: 0.35, 0.37 and 0.44 for the three periods.• Hospital: 0 and 0.6 for the two periods.

Graphs P4 to P6 show flow results for the George Fam tank outlet meter. While the normalmaximum flows for each day were approximately 10-15 L/s there were occasional times when thepeak flows exceeded the limit of the logger (21.2 L/s). The average and minimum flows increasedover the periods of record, indicating a worsening leak/wastage problem during the period June toOctober 1998. This is also shown from the increasing ratios of minimum to average flows above.

Graphs P7 and P8 show flow results for the Hospital tank outlet meter. Maximum flows were alwaysless than at George Fam and Drumsite, which is to be expected given the smaller distribution zonefed by the Hospital tank. In the first period (22nd July – 14th August) the minimum flow was generallyat zero indicating no significant leakage in the system (Graph P7). This followed major reductions in


flow due to detection and rectification of leaks, as explained earlier. On a few nights, the minimumflow remained at about 1 L/s. The reason for these occurrences is not known, but could be due tovalves being left open in the distribution system. By the second period (Graph P8), the minimumnight flow had increased to a steady level of about 0.6 L/s. It is noted that the maximum, averageand minimum flows all increased between the two periods, indicating a worsening leakage problem.

Conclusions and recommendations from the above detailed analyses of flows are:• data loggers at selected meters provide a very useful means of analysing flows,

particularly minimum night flows.• leak detection and rectification efforts are required on a regular basis, as short term

‘gains’ can be lost in the medium to longer term as additional leaks occur. An example isthe Hospital tank distribution system that initially showed zero minimum night flows afterleaks were detected and repaired, but that additional leaks were evident within severalmonths.

• it is recommended that periodic data be collected at the data loggers on these three keydistribution tanks (Drumsite, George Fam and Hospital) to check the status of thesystems, by checking the minimum night flows against the average flows.

7.4.7 Analysis of consumer meter data

As part of the project, a detailed analysis of consumer meter data was conducted. Data fromseveral surveys of all consumer meters was compiled into a spreadsheet (Meter ConnectionData.xls), set up specifically for this data. The data was organised according to residential,commercial and public categories. For practical reasons, the residential category was split into sub-categories as follows:

• Drumsite,• Old Poon Saan,• Silver City,• Kampong, and• Settlement.

Most meters were installed in the first half of 1997. The surveys of meter readings were conductedby Shire staff at the following times:

• December 1997,• February 1998,• May 1998, and• September-October 1998,• February 1999, and• May 1999.

The raw data was processed by calculating water usage at each connection over several timeperiods. Average water use for the period from installation of meters until September/October 1998was used in most of the analyses. Most meters were installed in early 1997, so this periodrepresents approximately 18 months. All water users were ranked in each category in terms of theequivalent water use per year and the results are summarised in Figure 19.

The three curves in Figure 19 show the relationship between consumption, expressed as an annualtotal and the percentage of consumers in each category that have lower consumption. For instance,approximately 90% of residential consumers (house or unit with a meter) used less than1,100 kL/year, or approximately 3,000 L/day. For a house of 3 people this is equivalent to1,000 Litres per person per day. The median residential water use (50% of consumers with lowerconsumption, and 50% with higher consumption) was 390 kL/year (or 1,060 L/day). For theresidential sector, the top 20% of consumers used as much water as the other 80%.


Figure 19 Water Consumption Curves for Residential, Commercial and PublicCategories

By comparison with the residential sector results, the following summary is provided of the other twosectors:

• the median water use in the commercial sector was 193 kL/year. In this sector, the top7% of consumers used as much water as the other 93%. The highest water user wasthe Golf Course followed by the CIP Workshop.

• the median water use in the public sector was 364 kL/year. In this sector, the top 8% ofconsumers used as much water as the other 92% did, which is similar to thecommercial sector. The four highest consumers in this sector were the power station,the nursery, the hospital and the school. These four consumers represented 73% of theconsumption in this sector.

A summary of statistics related to the water consumption in each category and for the total of allcategories is shown in Table 15.

From Table 15, it is evident that the residential sector uses the largest proportion of water (74%),followed by the commercial sector (16%). However, the public sector shows the highest averagewater usage (total water usage/number of consumers), followed by the commercial sector.

A preliminary check of the meter readings obtained in February 1999 indicated that the data wassimilar to that shown to September 1998. Thus, similar curves to those shown in Figure 19 wouldbe produced using the more recent data. The data beyond February 1998 is yet to be processed.

Consumption data on Christmas Island indicates that median domestic water consumption is of theorder of 350-400 kL/year, which compares favourably with mainland Australia.

Further discussion of the consumption patterns and the implications for charging policies areconsidered in the accompanying WMP (ACTEW, 1999).

The spreadsheet data used in these analyses has been forwarded to the Shire for their use.

Consumptions for each category were calculated using the addition of average water usage for all consumers in that category. Usage was calculated from date of installation (most in early 1997) to September 1998

0

2,000

4,000

6,000

8,000

10,000

12,000

0 10 20 30 40 50 60 70 80 90 100

% of consumers with lower consumption

Con

sum

ptio

n (k

L/ye

ar)

Residential Commercial Public


Table 15 Water Consumer Statistics by Category, to September/October 1998

CategoryParameter

Residential Commercial PublicTotal

Total water usage (ML/year) 307.9 67.4 42.4 417.7

Total water usage (kL/day) 844 185 116 1,144

Total water usage (L/sec) 9.8 2.1 1.3 13.2

Water usage (% of total) 74% 16% 10% 100%

No of consumers 536 98 29 630

Average water usage perconsumer (kL/year)

574 688 1,463 663

Average water usage perconsumer (L/day)

1,572 1,885 4,000 1,816

Median water usage (kL/year) 384 193 364 -

Note: Residential includes the single meter for Taman Sweetland residential area

Conclusions and recommendations are:• periodic consumer meter data should be collected. It is recommended that this should

continue at three month intervals.• after each set of data is collected, the data should be entered into the consumer meter

spreadsheet and analyses undertaken to check the consistency of the data. Anyanomalies (e.g. higher than normal water usage) should be investigated.

• there is a minor number of cases with meter data anomalies (e.g. some consumers maybe in the wrong category) and these should be checked and amended if necessary bythe Shire.

7.4.8 Assessment of system losses

As part of the investigations, it was necessary to assess the flow within the overall Christmas Islandsystem and to assess losses. The main purpose was to feed this information back into the WMP forthe assessment of various charging policy options. It was also useful to determine the level oflosses when assessing water source options, as one of the options is to reduce such losses leadingto more water available for productive use.

The analysis of flow was made possible by records from meters at sources, meters on the outflowpipes from the storage tanks and consumer meters. Data was available for all meters during part of1997, through 1998 and into the early part of 1999.

The analysis selected data for 1998 for comparison between average flows and an analysis oflosses. The steps are outlined below and the results are shown graphically in Figure 20.

a) From Table 11, the combined average flow from the sources was 22.0 L/s. FromTable 12, the combined average outflow from the three main storage tanks was 18.7 L/s.When the flows from the minor tanks (Power Station and Airport) were added thecombined average outflow was 19.1 L/s. The difference between the flows from thesources and the distribution tanks is 2.9 L/s or about 13% of the combined flows fromsources (as already outlined in section 7.4.5).


b) From Table 15, the combined metered water usage by all consumers averaged over theperiod since the date of first reading (most meters installed in early 1997) untilSeptember/October 1998 was 13.2 L/s. The difference between this combined usageand the outflow from the distribution tanks (5.9 L/s) is a measure of losses in thedistribution systems (between tanks and consumer meters). ‘Losses’ in this contextincludes leakage, use of fire hydrants (for legitimate and unauthorised use) and any un-metered connections to the system. This loss represented about 27% of the combinedflows from sources.

c) From an analysis of the flow data logged at the three main distribution tanks duringselected periods in 1998 (refer section 7.4.6), estimates of minimum night flows weremade. These were 10 L/s from Drumsite tank, 2 L/s from George Fam tank and zerofrom the Hospital tank (as the leaks from the last mentioned tank had been largelyrectified in 1997). Thus, a combined minimum night flow of 12 L/s was evident in late1998. This flow is a measure of losses in the total hydraulic system ‘downstream’ of thedistribution tanks, and includes losses in the distribution system and within consumers’plumbing.

d) From (b) and (c), by subtracting the losses in the distribution system (5.9 L/s) from thetotal losses downstream of the tanks (12 L/s), the losses in the consumer’s plumbing canbe estimated as 6.1 L/s or 28% of the combined flows from sources.

e) Finally, the water remaining for productive use (‘actual consumption’ in Figure 20) is7.1 L/s or 32% of the combined flows from sources.

The results summarised above and shown in Figure 20 indicate that in 1998 only about 32% of thewater supplied from the sources were actually being used for productive use by consumers.

Figure 20 Christmas Island Water Supply Balance, 1998

Distribution of the total supply from sources in 1998 of 22 L/s

7.1 L/s (32%)

6.1 L/s (28%)

2.9 L/s (13%)

5.9 L/s (27%)

Loss - sources to tanks Loss - tanks to consumersLoss - consumer plumbing Actual consumption


There are a number of inherent assumptions in the results summarised in Figure 20. Theseassumptions are:

• All meters accurately recorded flows. This is a reasonable assumption given that nearlyall meters were new. However, errors of between 5% and 10% for individual meters maybe present. At very low flows, consumer meters are likely to under-estimate the amountof water passing through the meter.

• All consumers are metered.• Minor mismatches in periods of meter flows are insignificant to the results. For instance,

the Jane Up meter was installed in April 1998 and hence this flow was averaged over ashorter period than the full year. More importantly, consumer meter readings wereaveraged over the period from installation (most installed in 1997) to September/October1998 (last readings in 1998). It is noted that the average metered water usage for allconsumers was 13.2 L/s for this period. The average combined water usage waschecked for another more defined period and found to be similar. From May 1998 toFebruary 1998, the average combined water usage was 13.5 L/s, which is very similar tothe other value.

• Minimum night flows should be at zero. This is possibly an unrealistic expectation as alldistribution systems will leak to some degree (e.g. toilet cisterns, taps), and there willalways be some legitimate water use during the night. Realistically, it should be possibleto reduce the minimum night flow across the whole system to about 1-2 L/s. Over say6 hours at night, such flows would represent an average water usage for 1,500 people of10-20 litres. If 2 L/s was taken as the upper limit for minimum night flows, then the‘productive use’ plus a small allowable leakage would be 9.1 L/s or 41% of the combinedflows from sources.

While the 32% figure for ‘productive use’ with zero usage at night, or the figure of 41% for productiveuse plus a small minimum night flow, seem low they are not surprising for a water supply systemsuch as that on Christmas Island. It is noted that recent leak analyses in a number of urban centresin the Pacific Islands (Suva in Fiji, Nuku’alofa in Tonga and South Tarawa in Kiribati) have indicatedoverall leakage/wastage rates of 70%, or ‘productive water use’ rates of 30%. While high loss ratesdo occur, it is possible to reduce leakage to much lower levels (say 20%, with an upper limit of 30%),with the introduction of leakage control measures. A reasonable target for Christmas Island isprobably 20%, while more optimistic targets have been mentioned (e.g. 15% in WC/SMEC, 1998). Ifthe 20% target was achieved, this would mean the total losses from the water supply system in 1998would have been about 4.4 L/s.

It is noted that in 1999, some improvements to the leakage situation have occurred, which wouldalter the water supply balance shown in Figure 20. These include:

• a major reduction in outflow from the Drumsite tank in early March 1999 due to rectifyinga major leak fed by this storage tank (refer section 7.4.5). The leak of approximately 7-8 L/s had earlier been detected as part of a leak detection project in late January andearly February in a 100 mm AC main near the CIP’s Drumsite Workshop (Gugich, 1999).The magnitude of this leak was greater than the estimated losses from tanks toconsumers for 1998 (5.9% as shown lower right sector in Figure 20). This indicates thatthese losses may be under-estimated in Figure 20, most probably due to an over-estimation of the losses from consumer connections.

• the detection of a significant leak in the floor of the Drumsite tank during inspections(Adrian Hordyk, personal communication). The amount of the loss was similar to thetotal loss between the flows from the sources and the distribution tanks of 2.9 L/s (refersection 7.4.8 and top right sector of in Figure 20).

This analysis indicates that:

(a) system losses have been a substantial proportion of total water supply, and

(b) leak control efforts can lead to substantial reductions in leakage.

Based on experiences elsewhere, short term improvements in leak reduction need to be supportedby an ongoing commitment in order to sustain these improvements. Effective demand management


and leakage reduction programs require a long term commitment, and are not just a matter ofundertaking a single project. This can best be achieved by developing and sustaining a capabilitywithin the local water supply authority to undertake an ongoing programme of ‘leakage control’(comprising both leak detection and rectification). This means that some staff must be trained in thenecessary techniques for leakage detection and that recurrent budget be supplied to rectify leaksthat are found, or to replace sections of pipeline that are beyond further repair.

7.5 Water Chemistry

7.5.1 Background

Prior to the period of the study, samples from a number of the water sources on the island had beencollected on an intermittent basis. Results of samples obtained in late 1986 are contained inFalkland (1986, Appendix B). Other results are contained in water related files at the Shire office.

During the course of this project, water samples were obtained from some key sites and tested forbasic water chemistry and a range of potential pollutants. The sites selected were Jedda Cave, theprincipal present source of water for the island’s population and pollution monitoring boreholes BH9and BH10 near the present rubbish disposal area.

7.5.2 Results of water chemistry tests

The results of sets of water quality tests in 1968, 1973 and 1986 are shown in Tables Q1, Q2 andQ3, respectively, of Annex Q. Two sets of tests in 1998 are shown in Tables R1 to R2 of Annex R.It is noted that each set of water quality tests has not chosen exactly the same test parameters.Where possible, the sets of tests have been organised in a similar manner to assist withcomparisons between the results.

Salinity

The salinity of water is one of the most important properties, and is often is a major determinant ofwhether island water supplies are potable or not. There are many parameters that can be used as ameasure of salinity, but two of the most common are electrical conductivity (also called conductivityor EC) and chloride (ion concentration). The data for these two salinity parameters from the varioussets of tests are summarised in Tables 16 and 17.

The salinity limit adopted for freshwater (suitable for drinking water) is often taken as the WorldHealth Organisation (WHO) or Australian drinking water guideline value for chloride ion of 250 mg/L(WHO, 1993; NHMRC/ARMCANZ, 1996). This is approximately equivalent to an electricalconductivity (EC) of 1,500 µS/cm. In some islands, a higher value of EC (e.g. 2,500 µS/cm) hasbeen used as an upper limit (e.g. Cocos (Keeling) Islands: Falkland, 1992; Pink & Falkland, 1999),noting that the WHO guidelines are based on taste and not health considerations. This latter value ofEC is approximately equivalent to a chloride ion concentration of 600 mg/L (equal to a previous WHOguideline (WHO, 1971)). A desirable upper limit of 1,500 µS/cm was also defined for the Cocos(Keeling) Islands.

As mentioned in section 2.1, it is recommended for Christmas Island that 1,500 µS/cm be used asan upper limit and a desirable objective be defined as 1,000 µS/cm. This is based largely on acomparison with the salinity of the water supply from current sources which is approximately 500-600 µS/cm (refer Table 16). It could reasonably be argued that as the population has become usedto a salinity value at this level and as the water resources of Christmas Island are more extensivethan in the Cocos (Keeling) Islands, a 1,000 µS/cm upper limit should be adopted.

It is noted from Tables 16 and 17 that the salinity of the present (Jedda, Jane Up, Waterfall and RossHill Gardens) and former (Grant’s Well) water sources are well within the guidelines for salinity.These sources are all from perched groundwater. Other perched groundwater, for example anumber of the monitoring boreholes (refer section 2) and the Daniel Roux cave gusher show similarresults. Basal groundwater, above the transition zone with seawater, also shows similar results, asshown in the upper monitoring tubes in Smithson Bight area monitoring holes (refer section 2.1).


Table 16 Salinity (EC) results (µS/cm) for selected sites

SiteDate

Grant’s Well Jedda Jane-Up Waterfall Ross HillGardens

April 1968 579 541 - 565 -

Oct 1973 356 366 431 457 -

Oct 1986 - 470 400 500 510

June 1998 - 550 - - -

Oct 1998 - 540 - 510 570

Notes 1. Ross Hill Gardens values are averages of Harrison’s Springs and Hewan’s Springs

2. The readings for Oct 1973 are suspected of being too low based on comparison withreadings on other days

Table 17 Chloride ion results (mg/L) for selected sites

SiteDate

Grant’s Well Jedda Jane-Up Waterfall Ross HillGardens

April 1968 16 15 - 20 -

Oct 1973 12 14 14 26 -

Oct 1986 - 46 16 18 22

Oct 1998 - 16 - 21 20

Note: Ross Hill Gardens values are averages of Harrison’s Springs and Hewan’s Springs

Another measure of salinity is total dissolved salts. Tests of water samples from developed sourceshave shown values between 400 and 570 mg/L, with most being less than 500 mg/L. The Australiandrinking water guidelines suggest that values between 80 and 500 mg/L indicate good quality andvalues between 500 and 800 mg/L indicate fair quality. Most water samples are thus in the goodquality category while some are in the upper range of the fair category.

Hardness

The Australian Drinking Water Guidelines (NHMRC/ARMCANZ, 1996) state that a value of 200 mg/Lfor total hardness (as calcium carbonate or CaCO3) should not be exceeded to minimise undesirablebuild-up of scale in hot water systems. Between hardness values of 200 and 500 mg/L, increasingscaling problems occur. Values of hardness above 500 mg/L are likely to cause severe scaling. It isnoted that the guidelines for hardness are not based on health considerations but rather on aestheticor convenience considerations.

Examples of measured hardness values are shown in Table 18, while further details are given inAnnexes Q and R. These values range from about 170 to 310 mg/L, indicating moderate to highlevels. It is well known that Christmas Island water is hard and scale forms on heater elements (e.g.electric kettles and hot water systems). It also causes scaling in pipes and can lead to leaking tapsdue to some scaling of washers.


Table 18 Hardness results (mg/L) for selected sites

SiteDate

Grant’s Well Jedda Jane-Up Waterfall Ross Hill Gardens

April 1968 298 288 - 309 -

Oct 1973 168 195 208 231 -

Oct 1986 - 220 170 250 250

Notes 1. Ross Hill Gardens values are averages of Harrison’s Springs and Hewan’s Springs2. The readings for Oct 1973 are suspected of being too low based on comparison with

readings on other days

Other parameters

Other physical and chemical quality parameters (e.g. pH, turbidity and common specific ions) allmeet guideline values.

Summary

Based on the available physical and chemical analyses (refer Annex Q and Tables R1 and R2 inAnnex R), the basic water chemistry of perched groundwater on Christmas Island meets therequirements of the Australian Drinking Water Guidelines (NHMRC/ARMCANZ, 1996) except forhardness.

7.5.3 Results of testing for chemical pollution

Two sets of water quality tests for a range of potential chemical pollutants were obtained frommonitoring boreholes BH9 and BH10 at the rubbish disposal area in mid-1998. Water samples fromJedda Cave were also tested. The tests covered a range of hydrocarbons (BTEX and TPHs),pesticides (organo-chlorine and organo-phosphate), PCBs, nutrients and heavy metals. The resultsare shown in Tables R1, R3 and R4 in Annex R.

The test results showed there was no sign of chemical pollution at the three sites tested (BH9, BH10and Jedda Cave) except for a higher than guideline value for lead at BH10 in June 1998 (Table R1,Annex R). The test result showed 19 µg/L compared with the Australian Drinking Water Guidelines(NHMRC/ARMCANZ, 1996) value, based on health considerations, of 10 µg/L. The lead level atJedda cave was below the test’s limit of determination (<2 µg/L).

Additional tests for lead and other heavy metals in October 1998 at Jedda and three other sites(Table R2, Annex R) shows that all results were below the limit of determination (<0.5 µg/L). Thisindicates that the result for Jedda in June 1998 may have been an isolated event or possibly an error.

The samples collected and tested in October 1998 from four sites (Jedda Cave, Waterfall Spring,the Ross Hill Gardens pump station (comprising a mixture of water from Harrison’s Springs andHewan’s Spring) and the Daniel Roux Cave gusher) showed low levels of other metals includingarsenic.

7.5.4 Future monitoring

It is important that regular monitoring of water chemistry of the present water sources, somepotential sources and other key sites should be conducted.

For the basal groundwater, for instance at Smithson Bight, no comprehensive tests have been done.However, using conductivity as a reasonable means of comparison between samples, thefreshwater in the basal aquifer in Smithson Bight is similar in quality to the perched water from whereit flows. In the future, it is recommended that representative samples be obtained from selectedSmithson Bight monitoring boreholes and tested for a range of parameters. This should becomepart of an annual water monitoring component.


An ongoing monitoring program is required for the potential chemical pollution at the monitoringboreholes and water supply sources. Details are provided in section 7.7.

7.6 Microbiological Test ResultsData from microbiological tests for the period 1988-1996 were reviewed. These tests wereconducted on water samples collected from the distribution system after chlorination. The tests,which have been usually undertaken at the Water Examination Laboratory in Perth, were normally forbacteria (total coliforms, E. Coli and total plate count and sometimes for faecal streptococci).

Based on available test results stored at the Hospital, the microbiological quality of the water isgenerally good. However, there were some samples showing positive counts for all parameters. Inparticular, occasional samples showed positive E. Coli counts. As the Australian Drinking WaterGuidelines (NHMRC/ARMCANZ, 1996) recommend a zero level of E. Coli, these were obviouslysome non-acceptable results.

As the microbiological quality of water supply can directly impact on public health, it is essential thatthe water delivered to consumers continues to be disinfected. The chlorination systems at Jeddaand Waterfall need to be properly operated and maintained and regular chlorine residual tests needto be continued.

7.7 Water Monitoring Program

7.7.1 Outline of monitoring program during the ProjectAs part of the WMP Project, water resources monitoring systems were installed, procedures writtenfor the use of the equipment (refer Skinner, 1997) and training provided to Shire personnelresponsible for the monitoring. In the initial stages of the project, Mr Ron De Cruz was provided withtraining. Later in the project, training was provided to Mr Jason Tan who had largely taken over thewater monitoring role. These two personnel have played a key role in the success of the monitoringprogram. In addition, valuable assistance with databases for meter readings and other data hasbeen provided by Iris Lim at the Shire offices. Some training in the use of spreadsheets forprocessing data was provided to Iris Lim during the latter part of the project.The list of equipment purchased for the project is shown in Annex S. Some items have beenreplaced during the course of the project due to equipment malfunctions and deterioration. Theseinclude the portable water level measuring reel (‘dipper’) for the salinity monitoring boreholes, andone of the automatic water level recorders (for Jedda Cave).The bulk of the data processing and analysis was undertaken during the course of the project byTony Falkland with assistance from John Skinner and others at Ecowise Environmental in Canberra.The results of analysis have been regularly reported to the Shire staff throughout the course of theproject, and adjustments made to monitoring methods recommended as appropriate.In the final Project visit to the island in October 1998, a summary list of monitoring requirements wasprovided to the Shire. This formed the basis for the latest monitoring requirements, as outlinedbelow and in Annex S.

7.7.2 Current data archives

Most of the present data is stored on a series of EXCEL spreadsheets, which are updated by boththe Shire and Ecowise Environmental as data is collected. Separate spreadsheets are maintainedfor:

• Jedda rainfall – monthly (updated by Ecowise Environmental)• Borehole monitoring data (updated by Ecowise Environmental)• Gauge height readings for Jedda (updated by Ecowise Environmental)• Spring flow meters and gauge height readings for Ross Hill Gardens (updated by

Ecowise Environmental)• Bulk meter readings at various location and hours run data for Jedda pumps (updated by

Shire)


• Consumer meter data (updated by Shire and checked by Ecowise Environmental)• Meter data loggers at Drumsite, George Fam and Hospital tanks (spreadsheets are

updated by Ecowise Environmental when data is available)• Water quality data (updated by Ecowise Environmental).

Once data has been updated and checked, copies of spreadsheets are forwarded to the Shire fortheir information and records.

Data from the water resources data loggers (presently and formerly at Jedda, Ross Hill Gardens andDaniel Roux Cave sites) are archived in HYDSYS, a specialist hydrological data base for time seriesdata. Daily rainfall from the Jedda and Airport sites is also stored in HYDSYS.

Examples of the EXCEL and HYDSYS data are provided throughout this report and theaccompanying annexes in both tabular and graphical form.

7.7.3 Monitoring problems experienced during the ProjectFor future monitoring at sources, electronic data loggers should be avoided where possible, owing tooperational problems with this type of equipment. While a lot of useful data has been collectedduring the course of this project, there have been a number of problems associated with theequipment and its operation. Problems have stemmed from logger malfunctions but sometimesfrom insufficiently frequent visits to the sites to change batteries and silica gel.Problems with the loggers have included electronic faults mainly due to moisture ingress, andcommunication problems with the portable computer, mainly due to physical problems with theconnectors. Connectors have been changed.Low battery voltages and moisture ingress (due to inactive silica gel), due to these items not beingregularly changed, has led to some of the data loss problems. The environments in which theloggers have operated are harsh, especially due to the very high humidity.Other problems have been mainly related to the irregularity of monitoring (e.g. monitoring boreholesare not always done at three monthly intervals). This arises due to staff being heavily occupied onother tasks. There sometimes appears to be a low priority placed on water resources monitoringwhich stems from insufficient resources to cover all the necessary tasks within the Shire.Despite the problems experienced during the course of the monitoring, there is no doubt that muchvery valuable information has been collected and the understanding of the water resources andwater supply system had been greatly enhanced. These achievements are a credit to the staff fromthe Shire (mainly Ron De Cruz, Jason Tan and Lee Swee Chow) who have undertaken themonitoring, often in very difficult circumstances.

7.7.4 Ongoing monitoring program

General

It is essential to continue the water monitoring program established during this project as a long termactivity for the rational assessment, development and management of the island’s water resources.A key issue addressed in the WMP Report (ACTEW, 1999) concerns the role and responsibilities ofthe Administration (Commonwealth) for water resource management; in particular, the allocation ofwater for supply to the island community and also to the environment for conservation of flora andfauna. The national water reform agenda (see COAG, 1994) places emphasis on the importance ofthis function and the need to use water resources on a sustainable basis. These objectives will bedifficult to achieve without commitment to the continuation of the water monitoring program nowdeveloped for Christmas Island.A revised list of monitoring requirements has been prepared, based on operational experience sinceOctober 1998. These requirements and explanations where considered necessary, are providedbelow. A summary of requirements is provided in Annex S for use by the water monitoring agency(currently the Shire of Christmas Island).


Current water sources

(a) Jedda

For future flow monitoring, it is recommended that the recorder (electronic data logger) be continuedat the Jedda site because of the complexity of the flows at that site. With the pump regularlyswitching on and off, it is very useful to get continuous data. Combined with the Jedda Cave flowmeter records, the total flow within the Jedda Cave stream can be calculated each month, using themethod described in this section.

It is important to correctly operate and maintain the Jedda recorder by ensuring:• regular battery checks and changes,• regular silica gel replacements to prevent moisture entering the sensitive electronic

circuitry of the data logger,• regular interrogation and downloading of data from the recorder’s data logger, and• regular check readings of the gauge board, to ensure a correspondence of the gauge

height reading and the logged water level. Gauge board readings need to be made whenboth pumps have been switched off and the flow in the cave has been allowed to adjust(at least 5 minutes after pumping ceases).

Further details of the recorders and methods of operation are contained in the Christmas IslandWater Resources Monitoring - Operation Manual (Skinner, 1997). The recommended monitoringroutine is for the water monitoring personnel to visit the site every four weeks, monitor the status anddownload the logger. Visits to read the gauge board should be every two weeks. This means thatevery second visit should include downloading of the logger.

(b) Ross Hill Gardens

It is not necessary to have a recorder at the Ross Hill Gardens site now that the flow pattern is welldescribed by the available continuous data. However, regular visits are required to obtain the meterreadings and gauge height readings. These two independent flow measurements provide a meansof cross-checking the accuracy of the data.

For Ross Hill Gardens, it is important that the gauge height reading be obtained at each visit after (i)the weir has been checked and any obstructions removed, (ii) after the valves on the inflow pipesfrom the springs have been turned on to full flow and (iii) the water in the sump has been allowed toadjust to a new level. During flow measurements, it is important to gauge the total available flowfrom the springs by fully opening the valves. Visits should be made every two weeks.

(c) Waterfall, Freshwater and Jones SpringsWater monitoring systems should be installed at the three springs feeding the Waterfall pumpstation.

Recommended improvements for the Freshwater and Jones Springs were documented inChristmas Island (Indian Ocean) Water Source Improvements Planning and Design Report, June1997 (ACTEW, 1996a). These recommended improvements included the installation of flow meterson the gravity pipelines and overflow pipes at the spring chambers for flow measurements.

For the Waterfall Spring, recommended improvements should include a flow meter on the pipeline tothe tank and either a flow meter of a measuring weir for overflows. Exact design details are beyondthe scope of this report and would need to be the subject of a further investigation. Clearing of thecurrently overgrown site would need to precede any investigations.Manual readings of flows at the Waterfall Spring should be obtained every two weeks. There wouldbe no need for a data logger at any of these three sites.

Daniel Roux Cave

It is recommended to continue the recorder (data logger) at the DR gusher site, because this is theonly realistic method of getting data from this site. The DR channel site recorder can be removed atthe next available opportunity. This could be examined and repaired and kept as a spare for the DRgusher site.


At this stage, it is not recommended that a flow measuring weir be built around the DR gusher. If thesite is seriously considered in the future as a possible source of freshwater then it would beadvisable to build such a weir structure, or another suitable flow measuring device, so thatmeasurements of flow can be estimated from a rating table (similar to Jedda and Ross HillGardens).

Based on experiences with water level recorders and weir boxes, it is considered that a morepermanent structure under the gusher with an outflow pipe would be more useful for measuring theflow. A pipe flow meter with a data recorder could be installed on the outflow pipe at a point awayfrom the gusher where it would be easy to read. The meter would need to be capable of workingunder water (at high tide).

Monitoring boreholes

(a) Water salinity monitoring boreholes (BH1-BH8)

Every three months, measurements of salinity (electrical conductivity) and water depth at selectedtubes should be made. The selected tubes are specified on a borehole monitoring form which isused currently by the Shire.

It is important to ensure that the portable EC meter is calibrated before each set of three monthlytests (refer to EC meter manual for details).

A small diameter water level sensor and data logger should be purchased and installed on arotational basis at selected groundwater monitoring boreholes to ascertain the groundwater levelmovements in more detail than is possible from manual readings. In particular, it should be deployedat the Smithson Bight monitoring boreholes, on a rotational basis. The estimated cost of a suitablesensor/logger with cable sufficient for the deepest borehole is $5,000.

(b) Pollution monitoring boreholes (BH9-BH11)

Salinity (EC) and water depth measurements should be made every three months. Each year,water samples should be obtained with a bailer and detailed water quality analyses undertaken, asspecified below.

Water meter readings

Water meters should be read at regular intervals as part of the water monitoring program. Keycomponents are listed below:

• Daily flow measurements at the main water supply meters (Jedda Cave, Jedda toDrumsite, Waterfall to George Fam) and at the Jane-Up and Ross Hill Gardens pumpmeters, if the latter pumps are operating. Record data on monitoring form.

• Daily flow measurements at the tank outlet meters (Drumsite, George Fam, Hospital,Power Station and Airport tanks). Record data on monitoring form. Modify list if metersare added or deleted.

• Flow measurements every two weeks at Ross Hill Gardens meters (at pump andpipelines from the two springs). Read meters on pipelines from springs with valves fullyopen (allow a few minutes after opening valves for flow to stabilise). Record data onmonitoring form.

• ‘Instantaneous’ flow measurements every two weeks at Ross Hill Gardens meters onpipelines from the two springs. With stopwatch (or ‘second hand’ of watch), record thetime taken for a known volume of water to flow through the meter. Record volume andtime on monitoring form.

• Flow measurements every three months at all consumer connection meters.Water meter loggers are currently installed at the outlet meters of George Fam, Drumsite andHospital tanks. These can be used periodically to monitor continuous flows. This will giveinformation about minimum night flows and the general status of leaks in the distribution systems fedby these tanks. When in use, download data every month and reset loggers to start again. Ifadditional loggers are installed, these will need to be added to the list.


Water Quality

It is important that regular monitoring of water chemistry of the present water sources, somepotential sources and other key sites should be conducted.

Water quality samples should be obtained and tested at 12 monthly intervals from the following sites:• pollution monitoring boreholes BH9 and BH10 at the current rubbish disposal site;• any future monitoring boreholes at rubbish disposal sites;• Jedda Cave, Waterfall and Ross Hill Gardens flows. Waterfall should be samples at a

location where the combined water from all 3 springs, Waterfall, Freshwater and Jones,can be sampled; and

• monitoring boreholes BH1 and BH4 in the Smithson Bight area (top tube in each hole).The Daniel Roux Cave gusher should be added to this list provided that (a) entry to the cave is safeand (b) this site remains a possible groundwater development option.

The most appropriate sampling time is towards the end of the wet season when water tables arehigh. Samples should be sent to a recognised laboratory in Perth (e.g. AGAL) for testing. Therequired tests should include the following:

• Basic water chemistry (conductivity, TDS, major cations and anions),• Nutrients (nitrate, nitrite, ammonia, orthophosphate, total phosphorous),• Hydrocarbons (TPH and BTEX),• Heavy metals (aluminium, arsenic, cadmium, chromium, copper, mercury, manganese.

lead, selenium and zinc), and• Pesticides (OC and OP).

Results should be circulated to the Shire, the Administration, and the Christmas Island EnvironmentOfficer.

If unacceptable readings are found for any pollutant, then repeat samples should be obtainedimmediately from the affected site(s) and retested. If unacceptable readings are found for anypollutant at a water source (Jedda, Waterfall), then it should be closed until re-sampling and testinghas been undertaken. If this situation was to continue, then the island would have a significantproblem with its water supply, and alternative sources would need to be developed. This mayrequire the imposition of water restrictions, at least as a short to medium term solution untilalternative sources are available. Monitoring should continue at affected sources at 3 monthlyintervals after the first sign of pollution. They should not be re-used (for potable purposes) until atleast two consecutive samples show acceptable water quality.

Chlorination

The chlorination systems at Jedda and Waterfall need to be properly operated and maintained andregular chlorine residual tests to be continued.

Data processing and archiving

In the foreseeable future, the current procedure for data processing, analysis and storage should beused. This requires data to be forwarded on a regular basis to an external agency (currentlyEcowise Environmental) for these tasks to be undertaken.

Analysis and reporting

It is recommended that the data be analysed and quarterly reports be prepared by the externalagency and submitted to the agency responsible for water resources management on the island.This would be similar to procedures already implemented in the Cocos (Keeling) Islands.The monitoring reports should be prepared at the end of March, June, September and Decemberusing data for the previous quarter. These monitoring reports should provide an analysis andsummary of the previous period’s data, provide an assessment of the general status of the waterresources and highlight any necessary corrective action. The December report should be an annualreport and provide a summary of all data for the year making recommendations about any necessarymodifications to the monitoring program in the light of possible changed circumstances.


This reporting system not only enables essential feedback to the island authorities about the statusand sustainable development (use) of water resources but it also provides an opportunity to givemore detailed advice on specific water resource issues as they arise.At some stage in the future, it may be possible to transfer some of the water resources analysisfunction to the appropriate agency on the island.

7.7.5 List of water resources monitoring equipment

The following is a list of the equipment installed and handed over to the Shire for the ongoingmonitoring program:

• water level and temperature sensors and loggers (Greenspan Model PS310), 10 mcable, 2.5 m pressure range - 2 off (Serial Nos PS3262 & PS3263); used at Jedda Caveand Ross Hill Gardens;

• water level, temperature and conductivity sensors and loggers (Greenspan ModelCTP300), 120 m cable, 2.5 m pressure range, 50,000 µS/cm conductivity range - 2 off(Serial Nos CP3041 & CP3042); used at two sites in Daniel Roux Cave);

• Toshiba laptop computer 110CS/810 (Model No PA1224EAV, Serial No 07614340)complete with grey heavy duty plastic ‘pelican’ carry case - 1 off; and

• other accessories (spare batteries for each logger, battery charger, desiccant).

Equipment for monitoring groundwater salinity and level at monitoring boreholes was supplied to theShire, as follows:

• water bailers (Timco - 22 mm dia x 900 long) - 2 off;• conductivity meter (TPS MC84) with 10 m probe, nicad power-pack, hard plastic carry

case) - 1 off; and• water level measuring ‘dipper’ (Glötzl 200 m cable, light & buzzer) - 1 off.

During the October 1998 visit, two replacement loggers were brought to the island to replacemalfunctioning loggers at Jedda Cave and the Daniel Roux Cave gusher site. The replacementinstruments were:

• water level and temperature sensor and logger (Greenspan Model PS310), 15 m cable,2.5 m pressure range (Serial No 004344); used at Jedda Cave. Replaced instrumentwith Serial No 3263; and

• water level, temperature and conductivity sensor and logger (Greenspan ModelCTP300), 30 m cable, 2.5 m pressure range, 50,000 µS/cm conductivity range (SerialNo CP3062); used at gusher site in Daniel Roux Cave). This item was replaced free ofcharge under warranty.

The malfunctioning instruments were removed and taken back for inspection at EcowiseEnvironmental. They were subsequently sent back to the manufacturer, Greenspan, for checkingand repair. The repaired units can be used as replacements for those at Jedda and Daniel Rouxgusher should the need arise.

In early 1999, a replacement water level measuring ‘dipper’ of the same type as the original (Glötzl200 m) was purchased because the original one was no longer operating and the tape had beenbadly stretched.

In addition, three sets of water meter pulse counters and data loggers (Datataker DT5) werepurchased during the project for the Shire. These were set up at the outflow meters from theDrumsite, George Fam and Hospital tanks to record flows. The Shire provided funds for these itemswhich were specified and ordered through Ecowise Environmental.

7.7.6 Costs for ongoing monitoring

Costs for the ongoing monitoring program can be divided into 3 categories as follows:• Category 1: Costs associated with data collection and initial processing on Christmas

Island (currently undertaken by staff of the Works and Services section of the Shire ofChristmas Island)


• Category 2: Costs associated with data analysis and reporting (undertaken by anexternal agency - for this report, this work was done by Ecowise Environmental)

• Category 3: Costs of equipment repairs and periodic replacement.

Costs associated with data collection and initial processing of data on Christmas Island are notincluded in this report. Information has been requested from the Shire but was not available in timefor this report.

The estimated costs for data analysis and reporting to relevant authorities on the island by anappropriate agency are $15,000 per year. These costs would include $2,500 each for three shortquarterly reports at the end of March, June and September, $5,000 for a longer annual report at theend of December and up to $1,000 for ad hoc advice during the year. This is a similar arrangementto that currently used for water resources and water supply monitoring in the Cocos (Keeling)Islands. It is further recommended that the consultant make a visit to the island at two year intervalsto check on equipment at each site, and to discuss current and possible monitoring arrangementswith the water monitoring agency. A visit of between four days and a week, depending on prevailingflight schedules, would be adequate for the purpose. In the future this could possibly be combinedwith a similar visit to Cocos (Keeling) Islands for the same purpose so as to optimise use of timeand resources. The estimated cost of a one week visit for this work is approximately $7,000 (basedon airfare $2,000, accommodation and allowances at $150/day, fees $4,000). Thus, the averagecosts per year including costs for a monitoring visit every two years would be approximately $18,500.

Estimated costs and replacement timetables for major monitoring equipment items are shown inTable 19. The data can be used for developing a budget for programmed future equipmentreplacements. The average cost of replacements per year is approximately $3,000, although thereare some years with expected greater outlays and others with less.

Table 19 Estimated costs and replacement timetables for monitoring equipment

ItemApprox.

Cost(A$)

Year ofpurchase

Estimatedoperational

lifetime(years)

Estimatedremaining

lifetime(years)

Estimated.year for nextreplacement

Salinity (electrical conductivity)meter - TPS WP84 (1 off)

800 1997 5 3 2002

Water level measuring reel (‘dipper’)- Glötzl 200 m (1 off)

2,000 1998 5 5 2003

Automatic water level sensor/logger– Greenspan PS310 - Jedda Cave (1off)

2,200 1999 4 4 2003

Automatic water level sensor/logger– Greenspan CTP300 - Daniel Rouxgusher (1 off)

3,000 1999 3 3 2002

Potable computer, Toshiba 3,000 1996 4 0 2000

Data loggers for flow metermeasurements - Datataker DT5(3 off)

2,000 1997 5 6 2002

There are a number of additional minor items for which funding should also be provided. Theseitems include batteries for the automatic raingauge (six AA batteries every month), salinity meter(one 9 volt battery every year) and water level measuring reel (one 9 volt battery every year). Anallowance of $100 should be allowed for batteries on an annual basis. Other items that needreplacement on a regular basis are standard solution for calibrating the salinity meter ($30 every2 years), replacement connector fittings for salinity monitoring tubes (say $50 every 2 years). Theaverage annual cost per year for minor items is about $150.


It could be expected that minor equipment repairs would add another $400 per year. This wouldmean a total annual average cost of $3,500 for equipment repairs and periodic replacement.

Table 19 shows the portable computer is due for replacement. This is necessary, since problemsare being reported with the screen of the current computer. It is recommended that a new portablecomputer be purchased in the near future, at an estimated cost of $3,000.

The average annual costs for two of the three categories are:• Category 2: (data analysis and reporting): $18,500• Category 3: (equipment repairs and periodic replacement): $3,500• Total $22,000

Costs for Category 1 (data collection and initial processing) can be obtained from the Shire.


8. CONCLUSIONS AND RECOMMENDATIONS

A full synopsis of the conclusions and recommendations emanating from this GIM Report is providedin the Executive Summary.

9. ACKNOWLEDGEMENTS

I particularly thank the water monitoring personnel who have persevered with the various watermonitoring tasks and data processing during the course of this project. These people, from theShire of Christmas Island, include Ron De Cruz, Jason Tan, Lee Swee Chow and Iris Lim.

I would also like to thank the staff of GHD (formerly Works AUSTRALIA) for valuable assistance withbackground information, reports and other assistance during the course of the project, including anumber of visits to the island. These people include Adrian Hordyk, Bryan Edwards, Ian Nelligen andChristine Macintosh.

I would also like to acknowledge the assistance of my colleagues from Ecowise Environmental,particularly John Skinner who was involved with the installation of monitoring equipment and VinceHazell who developed the maps.

Rod Usback, the co-author of the Water Management Plan, provided valuable assistance onChristmas Island with some of the investigations and also with discussions and comments related tothis report.


10. REFERENCES

ACTEW (1995a). Christmas Island (Indian Ocean). Proposal for Management, Protection,Investigation and Monitoring of Water Resources. ACT Electricity and Water in associationwith Douglas Partners, June 1995.

ACTEW (1995b). Christmas Island (Indian Ocean). Proposal for Securing and Monitoring of WaterSources. ACT Electricity and Water, June 1995.

ACTEW (1995c). Christmas Island (Indian Ocean). Proposal for Trial Stormwater RechargeBoreholes. ACT Electricity and Water in association with Douglas Partners. June 1995.

ACTEW (1996a). Christmas Island (Indian Ocean) Water Source Improvements Planning andDesign Report. by Tony Falkland, Denis Baker and John Skinner, ACTEW Corporation,June 1996.

ACTEW (1996b). Christmas Island Water Supply. Chlorination Commissioning and Visit Report,Water Source Improvement Project. by Denis Baker, ACTEW Corporation, November1996.

ACTEW (1996c). Christmas Island Water Supply. Chlorination Manual, Jedda Pump Station,.prepared by Denis Baker, ACTEW Corporation, November 1996

ACTEW (1997a). Water Source Improvements and Water Management Plan, Progress Report, byTony Falkland, Rod Usback, John Skinner and Denis Baker, ACTEW Corporation, April1997.

ACTEW (1997b). Water Management Plan, Second Progress Report, by Tony Falkland and RodUsback, ACTEW Corporation, June 1997.

ACTEW (1999). Water Management Plan, Christmas Island (Indian Ocean). by Tony Falkland,ACTEW Corporation and Rod Usback, Sustainable Environmental Solutions Pty Ltd,November 1999.

Aller L., Benner T., Lehr J.H., Petty R.J. and Hackett G. (1987). A standardized system for evaluatinggroundwater pollution potential using hydrogeologic settings. US Environment ProtectionAgency, EPA/600/2-87/035, Oklahoma, USA.

Appleyard, S.J. (1993). Explanatory Notes for the Groundwater Vulnerability to Contamination of thePerth Basin. Geological Survey of Western Australia, record 1993/6.

ARMCANZ (1996). Generic National Milestones for Actions to Implement the COAG StrategicFramework for Water Reform, 1994, Agriculture and Resource Management Council ofAustralia and New Zealand, 27 September 1996.

Barrett P.J. (1985). Christmas Island Water Resources, Summary Report, Internal report forPhosphate Mining Corporation of Christmas Island, February 1985.

Barrie J. (1967). The Geology of Christmas Island. Bureau of Mineral Resources, Record No1967/37.

Chapman T.G. (1985). The use of water balances for water resource estimation with specialreference to small islands. Bull. 4, Pacific Regional Team, Australian DevelopmentAssistance Bureau.

COAG (1994). Communique, Water Resource Policy (strategic framework for water reform),Council of Australian Governments, Hobart, 25 February 1994.

Doorenbos J. & Pruitt W.O. (1977). Guidelines for Predicting Crop Water Requirements. Irrigationand Drainage Paper, No 24, Food and Agriculture Organisation, United Nations, Rome.

Douglas Partners (1996). Christmas Island Water Supply. Monitoring and Stormwater DisposalBore Installation. prepared by Bron Smolski, December 1996.

Falkland A.C. (1986). Christmas Island (Indian Ocean) Water Resources Study in relation toproposed development at Waterfall. Report HWR 86/19. Hydrology and Water ResourcesSection, Department of Territories.

Falkland A.C. (1992). Review of Groundwater Resources on Home and West Islands. Volume 1,Main Report. prepared for Australian Construction Services, Department of AdministrativeServices by Hydrology and Water Resources Branch, ACT Electricity and Water, ReportNo. HWR92/01.


Falkland A.C. (1993). Hydrology and water management on small tropical islands. Proc. Symp.Hydrology of Warm Humid Regions. International Association of Hydrological Sciences Publ.No. 216, 263-303.

Falkland, A.C. (1994a). Management of freshwater lenses on small coral islands. Proc. WaterDown Under '94 Conference, Adelaide, Australia, November, No. 1, 417-422.

Falkland A.C. (1994b). Christmas Island (Indian Ocean). Dye tracing study to assess impact oflandfill site on present water sources. Hydrology and Water Resources Branch, ACTElectricity and Water.

Falkland A.C. & Woodroffe C. D (1997). Geology and hydrogeology of Tarawa and Christmas Island,Kiribati, Chapter 19, in Geology and Hydrogeology of Carbonate Islands, Developments inSedimentology 54 (editors Vacher, H.L. and Quinn, T.M., Elsevier, Amsterdam).

Gugich J. (1999). Christmas Island Water Supply Leak Detection On-Site Investigation. prepared forGHD Pty Ltd (draft).

NHMRC/ARMCANZ (1996). Australian Drinking Water Guidelines. National Health and MedicalResearch Council, and the Agriculture and Resource Management Council of Australia andNew Zealand.

Pettifer G.R. & Polak E.J. (1979). Christmas Island (Indian Ocean), Geophysical Survey forGroundwater, 1976. Bureau of Mineral Resources, Record No 1979/33.

Pink, B.J. and A.C. Falkland (1999). Cocos (Keeling) Islands, Water Monitoring Annual Report, 1998,prepared for Cocos Island Administration, Cocos (Keeling) Islands by Hydrology Section,Ecowise Environmental, Report No EHYD 99/03.

Polak E.J. (1976). Christmas Island (Indian Ocean), Geophysical Survey for Groundwater, 1973.Bureau of Mineral Resources, Record No 1976/100.

Rivereau J.C. (1965). Notes on Geomorphological Study of Christmas island, Indian Ocean, Bureauof Mineral Resources, Record No 1965/116.

Trueman N.A. (1965). The Phosphate, Volcanic and Carbonate Rocks of Christmas Island (IndianOcean). Journal of the Geological Society, Australia, 12 (2): 261-283.

UNESCO (1991). Hydrology and water resources of small islands, a practical guide. Studies andreports on hydrology No 49. prepared by A. Falkland (ed.) and E. Custodio with contributionsfrom A. Diaz Arenas & L. Simler and case studies submitted by others. Paris, France,435pp.

Skinner, J. (1997). Operation Manual, Christmas Island Water Resources Monitoring. EcowiseEnvironmental.

UNESCO (1991). Hydrology and water resources of small islands, a practical guide. Studies andreports on hydrology No 49. prepared by A. Falkland (ed.) and E. Custodio with contributionsfrom A. Diaz Arenas & L. Simler and case studies submitted by others. Paris, France,435pp.

WC/SMEC (1998). Christmas Island Utilities-Divestment and Future Management Options, WesternAustralia Water Corporation and Snowy Mountains Engineering Corporation, September1998.

Webb T. and Shepherd I. (1997). Pilot Satellite Imagery Processing Study, Christmas Island (IndianOcean) Water Management Plan. Report prepared by Unisearch Limited for ACTEWCorporation.

WHO (1971). International Standards for Drinking Water, 3rd Edition, World Health Organisation,Geneva.

WHO (1993). Guidelines for drinking-water quality. Volume 1, Recommendations. World HealthOrganisation, Geneva.


11. ANNEXES

A. Project Brief 95

B. Summary Details of Boreholes drilled in 1996 97

C. Water Resources Monitoring Boreholes (BH1 to BH8), Details and Data 98

D. Water Resources Monitoring Boreholes (BH1 to BH8), Graphs 122

E. Pollution Monitoring Boreholes (BH9 to BH11), Details and Data 131

F. Monthly and Annual Rainfall Data, Airport, Jan 1973 - May 1999 138

G. Monthly and Annual Rainfall Data, Jedda, Jan 1994 - May 1999 143

H. Monthly and Annual Pan Evaporation Data, Airport, Sep 1972 - Apr 1981and Rocky Point, Settlement, Feb 1968 - Oct 1972 145

I. Monthly Recharge Estimates for period 1986 - 1998 150

J. Jedda Cave flow monitoring, 1996 - 1999 157

K. Ross Hill Gardens weir flow monitoring, 1996 - 1998 164

L. Ross Hill Gardens meter flows and gauge height monitoring, Nov 1997 - June 1999 168

M. Daniel Roux Cave water monitoring, Site 1: Gusher, 1996 - 1999 170

N. Daniel Roux Cave water monitoring, Site 2: Channel to Sea, 1996 - 1998 174

O. Meter Flows - Sources and Distribution Tanks, 1995 - 1999 180

P. Detailed Meter Flows at Distribution Tanks, 1998 186

Q. Water Quality Monitoring Tests, 1968 - 1986 195

R. Water Quality Monitoring Tests, 1998 200

S. Christmas Island Water Monitoring Program, October 1999 205

Christmas Island Groundwater Investigations and Monitoring Report - Annexes, November 1999 page 95

Annex AProject Brief

[The text below is a re-typed copy of Annex A of the Proposal for Management, Protection,Investigation and Monitoring of Water Resources, Christmas Island (Indian Ocean). ACTElectricity and Water in association with Douglas Partners, June 1995.]

Draft Brief for the Management, Protection, Investigation andMonitoring of Water Sources Consultancy on Christmas Island

Water Management and Protection Plan

A Water Management and Protection Plan is to be prepared for Christmas Island, generally alongthe lines of the recommendations made in section 6.3 of the Dye Tracing Study report made by MrTony Falkland of the Hydrology and Water Resources Branch, ACT Electricity and Water, inJanuary 1994.

This plan is to address:

• legislation

• administrative requirements (CISC, ANCA, CI Admin)

• technical investigations and studies

• groundwater quality standards

• groundwater development options

• mechanisms of groundwater allocation and charging

• groundwater protection requirements

• public education and awareness

• opportunities for community involvement

Groundwater Investigation and Monitoring Requirements

A groundwater investigation is to be carried out and a monitoring management system is to beprepared for Christmas Island water supplies, generally along the lines of the recommendationsmade in section 6.4 of the Dye Tracing Study report made by Mr Tony Falkland of the Hydrology andWater Resources Branch, ACT Electricity and Water, in January 1994.

The research program needs to be set up with input from discussions with the consultants andrepresentatives from ANCA, Christmas Island Administration, the Shire Council and ACS shallcomprise of but not necessarily be limited to:

1. Undertake drilling and testing to determine the presence or not of:

• perched groundwater in the high level volcanic rock, and

• the basal groundwater body underlying the Island.

2. Undertake drilling and testing in the vicinity of existing landfill and proposed landfill sites

3. In conjunction with and following drilling, carry out:

• recharge analysis


• locate freshwater flows using satellite imagery

• flow model antecedent flow and rainfall

• aquifer classification and map vulnerability

Note: The recommendations contained in the dye tracing study refer to a two stage study over aperiod of 2-3 years. Consideration should be given to the cost of drilling investigations and thepossibility of doing both stages of drilling in the one mobilisation to Christmas Island.

1. Prepare a monitoring program for:

• weir flows

• pumping and pipeline flows

• storage flows and usage

• monitoring water chemistry

• chlorine and microbiological tests

• on going water level and salinity tests in bore holes

• daily evaporation tests

• flow and salinity recording in Daniel Roux Cave

2. Prepare a processing, monitoring, analysis and reporting program and procedure including asuitable database to allow ongoing control and management of the Christmas Island waterresources. This program should include maximum use of on Island staff, eg CISC, andappropriate training of personnel.

Deliverables

Water Management and Protection Plan:

• Draft plan for joint discussions – ten copies

• Final plan – ten copies

Groundwater investigation reports:

• Draft report – six copies

• Final report – ten copies

Monitoring program:

• Six copies

Training/monitoring manual:

• Six copies

Operating and maintenance manual for monitoring systems:

• Six copies

A Hordyk

9 June, 1995


Annex B

Summary Details of Boreholes drilled in 1996

Borehole Easting Northing Height Description Primary

Number Purpose

(a) Holes drilled as part of the Water Resources Management study

BH1 18628.909 58821.829 156.411 Blowholes area: old road, top WRM

BH2 18298.428 58398.931 98.692 Blowholes area: old road, middle WRM

BH3 18067.851 58068.209 38.124 Blowholes area: old road, bottom WRM

BH4 20125.542 57582.982 165.856 Blowholes area: new road, top WRM

BH5 19422.563 57464.447 97.566 Blowholes area: new road, bottom WRM

BH6 26609.573 62883.614 137.045 Near Ryan Hill, east side of island WRM

BH7 26855.340 65341.356 141.375 Above Jones Spring, east side of island WRM

BH8 26656.151 65943.746 145.655 Below Headridge Hill, east side of island WRM

BH9 25185.752 66410.426 298.090 Rubbish tip (north of airport), NE part EPM

BH10 25188.054 66279.642 296.400 Rubbish tip (north of airport), SE part EPM

BH11 24958.239 66267.777 300.590 Rubbish tip (north of airport), West side EPM

BH12 24356.758 67669.817 151.286 Poon Saan, beside CI Hardware SD

BH13 23887.381 67750.672 88.282 Silver City, near incline SD

(b) Previously drilled holes

WB72 18119.279 58133.965 41.125 Blowholes area: uphill from BH3 WRM

WB73 18508.971 57848.411 15.389 Blowholes area: east of WB72 WRM

Notes:

1. Survey done by Russel Payne, Christmas Island Surveying Company, in late 1996, following drilling

2. Datums are: Horizontal CIG1985

Vertical CIHD1992 (This datum is supposed to be equal to mean sea level)

3. Height in table refers to height above datum of top of protective steel casing (normally 1 m above ground)

4. Purposes: WRM Water Resources Monitoring

EPM Environmental pollution monitoring

SD Stormwater disposal


Annex C

Water Resources Monitoring Boreholes

(BH1 to BH8)

Details and Data


Borehole BH1

Location Blowholes area: old road, top

RL top of casing (m) 156.411

RL ground (m) 155.411

Depth to top of volcanic rock (m) 178.0

Depth to base of hole (m) 192.00

RL top of volcanic rock (m) -22.59

RL base of hole (m) -36.59

Dates of drilling 31-Oct-96 to 4-Nov-96

Purpose Water Resources Monitoring

Comments from drill logs: Hole terminated due to refusal in basalt at 192 m bgl. From airlifting ofsamples after drilling, the basalt appears sufficiently fractured to transmitwater. Originally this borehole was designed to have 5 monitoring tubesinstalled (no. 4 at 164 m bgl and no. 5 at 158 m bgl. However, after installingno 3, the borehole collapsed to 151.2 m bgl and hence only no. 4 wasinstalled (and well above msl).

Monitoring Tube Number

1 2 3 4

Depth below ground level (m) 185.60 176.00 170.00 151.20

RL at base of monitor tube (m) -30.19 -20.59 -14.59 4.23

3-Nov-96

Date & Time 3/11/96 8:00 3/11/96 8:15 3/11/96 8:30 3/11/96 8:45

Depth to water table (m) 152.9 152.9 152.9 152.9

RL of water table (m) 3.51 3.51 3.51 3.51

Conductivity (µS/cm) 2,420

4-Nov-96

Date 4/11/96 8:00 4/11/96 9:16 4/11/96 10:47 4/11/96 10:20

Conductivity (µS /cm) 2,380 1,236 786 669

11-Nov-96

Date & Time 11/11/96 8:49 11/11/96 8:55 11/11/96 9:02 11/11/96 9:12

Depth to water table (m) 155.01 155.07 155.13 152.06


Conductivity (µS /cm) 2,440 1,960 1,757 Dry


17-Nov-96

Date & Time 17/11/96 11:12 17/11/96 11:25 17/11/96 11:37 17/11/96 11:49

Depth to water table (m) 155.04 155.03 155.08

RL of water table (m) 1.37 1.38 1.33

Conductivity (µS /cm) 2,250 1,850 703 Dry

28-May-97

Date & Time 28/05/97 13:30 28/05/97 14:00 28/05/97 14:30 28/05/97 15:00




Temperature 26.2 25.8 25.7

6-Aug-97

Date & Time 6/08/97 13:45 6/08/97 14:05 6/08/97 14:25 6/08/97 14:45





24-Feb-98

Date & Time 24/02/98 8:45 24/02/98 9:05 24/02/98 9:25 24/02/98 9:45





4-Aug-98

Date & Time 4/08/98 13:05 4/08/98 13:30 4/08/98 13:45 4/08/98 14:00

Depth to water table (m) 154.9 154.9 155





29-Oct-98

Date & Time 29/10/98 14:25 29/10/98 14:12 29/10/98 14:12 29/10/98 13:40

Depth to water table (m) 153.1 not measured not measured not measured

RL of water table (m) 3.31

Conductivity (µS /cm) bailer stuck bailer stuck 577 Dry

Temperature 41.1

3-Nov-98

Date & Time 3/11/98 13:45 4/08/98 13:55 4/08/98 14:00 4/08/98 14:05

Depth to water table (m) 153.8




23-Feb-99

Date & Time 23/02/99 13:26 23/02/99 13:02 23/02/99 12:42 23/02/99 12:33

Depth to water table (m)

RL of water table (m)



17-May-99

Date & Time 17/05/99 8:45 17/05/99 8:55 17/05/99 9:20 17/05/99 9:50



Conductivity (uS /cm) 1,780 1,690 416 Dry


Note: RL means Reduced Level (surveyed relative to mean sea level)


Borehole BH2

Location Blowholes area: old road, middle



Depth to top of volcanic rock not intersected

Depth to base of hole 121.00

RL top of volcanic rock (m) not intersected


Dates of drilling 26-Oct-96 to 29-Oct-96


Comments from drill logs: Hole had persistent collapses. Hence, not possible toinstall all tubes at design depths (tube 3 is above watertable).


1 2 3

Depth below ground level (m) 115.85 97.90 93.00

RL at base of monitor tube (m) -18.16 -0.21 4.69

28-Oct-96

Date 28/10/96 28/10/96 28/10/96

Depth to water table (m) 97.2 97.2 Dry

RL of water table (m) 1.492 1.492

29-Oct-96

Date 29/10/97 14:35

Conductivity (µS /cm) 798

1-Nov-96

Date 1/11/96 1/11/96 1/11/96

Conductivity (µS /cm) 788 753 Dry

4-Nov-96

Date 4/11/96 14:57




14-Nov-96

Date & Time 14/11/96 14:40 14/11/96 14:45 14/11/96 14:50

Depth to water table (m) 97.88 97.88


Conductivity (µS/cm) 824 707 Dry

17-Nov-96

Date & Time 17/11/96 10:50 17/11/96 10:55 17/11/96 11:00




30-May-97

Date & Time 30/05/97 8:20 30/05/97 8:40 30/05/97 9:00




Temperature 33.3 34.8

6-Aug-97

Date & Time 6/08/97 12:50 6/08/97 13:25 6/08/97 13:50

Depth to water table (m) 97.44 no water


Conductivity (µS/cm) 628 Dry

Temperature 26.7

2-Apr-98

Date & Time 2/04/98 8:45 2/04/98 9:05 2/04/98 9:25






5-Aug-98

Date & Time 5/08/98 9:30 5/08/98 9:45 5/08/98 10:00



Conductivity (µS/cm) 199.9 587 Dry


9-Oct-98

Date & Time 9/10/98 14:35 9/10/98 14:50 9/10/98 14:55

Depth to water table (m) 97.9 115.8???




30-Oct-98

Date & Time 30/10/98 9:35 30/10/98 9:25 30/10/98 9:05

Depth to water table (m) 97.6 not measured



Temperature 57.5??? 46.6???

23-Feb-99

Date & Time 23/02/99 13:50 23/02/99 13:53 23/02/99 14:07





17-May-99

Date & Time 17/05/99 13:25 17/05/99 13:30 17/05/99 13:40



Conductivity (us/cm) 458 397 Dry



Borehole BH3

Location Blowholes area: old road, bottom









Comments from drill logs: Inserted tube at higher level than designed due topersistent collapses in hole.

Tube No.

1

Depth below ground level (m) 38.30

RL at base of monitor tube (m) -1.18

13-Oct-96

Date & Time 13/10/96 12:00



16-Oct-96

Date 16/10/97 13:20


27-Oct-96

Date & Time 27/10/96


30-Oct-96

Date & Time 30/10/96 12:00



1-Nov-96

Date & Time 1/11/96 12:00



4-Nov-96

Date & Time 4/11/96 14:32




5-Nov-96

Date & Time 5/11/96 9:03




14-Nov-96

Date & Time 14/11/96 15:26




15-Nov-96

Date & Time 15/11/96 22:18




16-Nov-96

Date & Time 16/11/96 5:24


RL of water table (m) -0.128


30-May-97

Date & Time 30/05/97 9:35




Temperature 25.4


6-Aug-97

Date & Time 6/08/97 14:40

Depth to water table (m) Dry


19-Feb-98

Date & Time 19/02/98 10:05




Temperature 26.5

5-Aug-98

Date & Time 5/08/98 8:50




Temperature 37.6

9-Oct-98

Date & Time 9/10/98 15:25




Temperature 25.3

30-Oct-98

Date & Time 30/10/98 10:20




Temperature 48.3???


24-Feb-99

Date & Time 18/05/99 8:37



Conductivity (us/cm) 4,230

Temperature 29.8

18-May-99

Date & Time 18/05/99 8:37



Conductivity (us/cm) 4,230

Temperature 29.8


Borehole BH4

Location Blowholes area: new road, top



Depth to top of volcanic rock 197.50 (??)


RL top of volcanic rock(m)

-32.64 (??)




Comments from drill logs: Borehole collapsed to 196.8 mbgl. Possible intersection of volcanic basement at197.5 mbgl below limestone.


1 2 3 4 5

Depth below ground level (m) 189.00 183.00 177.00 171.00 161.58

RL base of monitor tube (m) -24.14 -18.14 -12.14 -6.14 3.28

26-Oct-96

Date & Time 26/10/97 12:52 26/10/97 10:20



Conductivity (µS/cm) 645

5-Nov-96

Date & Time 5/11/96 10:37 5/11/96 10:24 5/11/96 10:13 5/11/96 10:02 5/11/96 9:50

Depth to water table (m) 164.97 165 165.01 165.03


Conductivity (µS/cm) 626 656 634 629 Dry

29-May-97

Date & Time 29/05/97 8:35 29/05/97 8:45 29/05/97 9:00 29/05/97 9:10 29/05/97 10:10

Depth to water table (m) 165.23 165.19 165.19 164.87 163.9

RL of water table (m) 0.626 0.666 0.666 0.986 1.956


Temperature 25.2 24.7 25.3 25.2


11-Aug-97

Date & Time 11/08/97 13:05 11/08/97 13:10 11/08/97 13:20 11/08/97 13:45 11/08/97 14:05

Depth to water table (m) 164.83 165 164.88 165 164


Conductivity (µS/cm) not enoughwater

not enoughwater

517 493 Dry


1-Apr-98

Date & Time 1/04/98 9:50 1/04/98 10:10 1/04/98 10:30 1/04/98 10:50 1/04/98 11:10

Depth to water table (m) 165.5 165.6 165.3 165.2 no water


Conductivity (µS/cm) 1,120 652 628 598 Dry

Temperature 26.4 24.9 24.9 25.0

4-Aug-98

Date & Time 4/08/98 8:40 4/08/98 9:00 4/08/98 9:15 4/08/98 9:30 4/08/98 9:50



Conductivity (µS/cm) -0.83 -0.62 -0.54 -0.64 Dry

Temperature 38.1 39.9 38.7 39.4

Note: Conductivity readings for 4 Aug 98 are erroneous

8-Oct-98

Date & Time 8/10/98 13:50 8/10/98 13:40 8/10/98 13:30 8/10/98 13:15 8/10/98 12:50

Depth to water table (m) 164.7 not measured not measured not measured not measured


Conductivity (µS/cm) EC probe 580 600 575 Dry

Temperature stuck?? 25.0

28-Oct-98

Date & Time 28/10/98 14:40 28/10/98 14:00 28/10/98 13:30 28/10/98 13:15 28/10/98 13:05



Conductivity (µS/cm) 1,114 577 589 575 Dry

Temperature 33.7 32.1 28.9 26.8


18-Feb-99

Date & Time 18/02/99 8:30 18/02/99 8:40 18/02/99 9:00 18/02/99 9:20 18/02/99 9:40


RL of water table (m) 4.356 Dipper cable broke: measurement at tube 1 is suspect


Temperature 24.5 24.6 24.5 24.5

18-May-99

Date & Time 18/05/99 13:12 18/05/99 13:17 18/05/99 13:35 18/05/99 13:51 19/05/99 9:25



Conductivity (us/cm) 1,048 439 438 430 Dry

Temperature 27.8 26.6 26.0 26.0


Borehole BH5

Location Blowholes area: new road, bottom



Depth to top of volcanic rock 131.9


RL top of volcanic rock(m)

-35.33




Comments from drill logs: Borehole penetrated 2.3m into basalt. Two inflows noticed during drilling at 108mbgl (RL -11.4m) and more substantial at 126.7 mbgl (RL -30.1m)


1 2 3 4 5

Depth below ground level (m) 130.29 124.30 118.30 112.30 106.30

RL base of monitor tube (m) -33.72 -27.73 -21.73 -15.73 -9.73

19-Oct-96

Date & Time 19/10/96 13:17 19/10/96 14:10 19/10/96 15:03 19/10/96 15:45 19/10/96 16:05

Conductivity (µS/cm) 39,400 22,400 20,000 14,490 12,130

4-Nov-96

Date & Time 4/11/96 16:43 4/11/96 16:32 4/11/96 16:21 4/11/96 16:08 4/11/96 15:52




2-Jun-97

Date & Time 2/06/97 8:00 2/06/97 8:30 2/06/97 8:45 2/06/97 9:00 2/06/97 9:10




Temperature 26.5 25.3 25.4 25.8 25.9


12-Aug-97

Date & Time 12/08/97 12:15 12/08/97 13:05 12/08/97 13:25 12/08/97 13:35 12/08/97 13:50



Conductivity (µS/cm) 30,100 19,200 dry 12,980 dry

Temperature 27.1 26.8 dry 26.4 n/a

1-Apr-98

Date & Time 1/04/98 13:15 1/04/98 13:35 1/04/98 13:55 1/04/98 14:15 1/04/98 14:35



Conductivity (µS/cm) 36,800 22,130 not enoughwater

12,750 7,030

Temperature 26.5 25.7 26.4 26.8

26-Aug-98

Date & Time 26/08/98 12:55




Temperature 26.5

29-Oct-98

Date & Time 29/10/98 10:15 29/10/98 10:00 29/10/98 9:45 29/10/98 9:40 29/10/98 9:30



Conductivity (µS/cm) 2,081 2,038 bailer stuck bailer stuck 2,035

Temperature 48.7 53.3 26.4 26.8

3-Nov-98

Date & Time 3/11/98 13:20 3/11/98 13:30 3/11/98 13:40 3/11/98 13:50 3/11/98 14:00

Depth to water table (m) 96 96.3



Temperature 26.5 26.6 26.5 26.8 26.6


18-Feb-99

Date & Time 18/02/99 14:56 18/02/99 14:16 18/02/99 14:05 18/02/99 13:55 18/02/99 13:45

Depth to water table (m) not measured not measured not measured not measured not measured



Temperature 25.7 25.4 25.4 25.3 25.7

18-May-99

Date & Time 18/05/99 9:27 18/05/99 9:37 18/05/99 9:48 18/05/99 10:01 18/05/99 10:15

Depth to water table (m) 96.4 not measured not measured not measured 96.3


Conductivity (us/cm) 11,540 12,740 10,940 6,330 4,740

Temperature 29.1 29.3 29.5 29.8 29.5


Borehole BH6

Location Near Ryan Hill, east side of island





RL top of volcanic rock (m) 13.25

RL base of hole (m) 1.64

Date of drilling 4-Oct-96 to 10-Oct-96


Comments from drill logs: Borehole penetrated 11.6m into basalt.


1 2 3


RL at base of monitor tube (m) 8.04 14.05 20.05

10-Oct-96

Date & Time 10/10/96 12:00 10/10/96 12:00 10/10/96 12:00



Conductivity (µS/cm) 676 Insufficient water Dry

5-Nov-96

Date & Time 5/11/96 14:07 5/11/96 13:57 5/11/96 13:47

Depth to water table (m) Dry 121.73



15-Nov-96

Date & Time 15/11/96 13:00 15/11/96 13:11 15/11/96 13:30

Depth to water table (m) Dry 121.72




3-May-97

Date & Time 3/05/97 17:00 3/05/97 17:07 27/05/97 17:13



Conductivity (µS/cm) not tested not tested Dry

Temperature

27-May-97

Date & Time 27/05/97 7:50 27/05/97 8:10 27/05/97 8:20



Conductivity (µS/cm) Insufficient water 485 Dry

Temperature 26.9

5-Aug-97

Date & Time 5/08/97 7:45 5/08/97 8:30 5/08/97 8:45



Conductivity (µS/cm) not enough water 465 Dry

Temperature 25.4

25-Mar-98

Date & Time 25/03/97 13:20 25/03/97 13:20 25/03/97 13:20

Depth to water table (m) no water 121.70


Conductivity (µS/cm) no water 933 Dry

Temperature 27.1

2-Sep-98

Date & Time 2/09/98 12:55 2/09/98 13:00



Conductivity (µS/cm) no water 606

Temperature 25.8


26-Oct-98

Date & Time 26/10/98 14:40 26/10/98 14:30 26/10/98 14:25



Conductivity (µS/cm) no water 601 Dry

Temperature 26.3

10-Mar-99

Date & Time 10/03/99 9:00 10/03/99 9:17 10/03/99 9:30



Conductivity (us/cm) Dry 448 Dry

Temperature 27.6

20-May-99

Date & Time 20/05/99 8:25 20/05/99 8:30 20/05/99 8:40



Conductivity (us/cm) Dry 439 Dry

Temperature 27.4


Borehole BH7

Location Above Jones Spring, east side of island



Depth to top of volcanic rock 100.0 occurred 31-67, 90-100m, 100m




Date of drilling 24-Nov-96 to 28-Nov-96


Comments from drill logs: No sample recovery except from bit. Complex geology.Volcanics with limestone from 31 – 67 m bgl (RL 109.4 –74.4) and 90-100 m bgl (RL 50.4-40.4); volcanics (basalt?)below 100 m bgl (RL 40.4).


1 2 3


RL at base of monitor tube (m) 36.38 47.98 50.88

28-Nov-96

Date & Time 28/11/96 28/11/96 28/11/96



Conductivity (µS/cm) 1,073 1,273 Dry

29-Nov-96

Date & Time 29/11/96 29/11/96 29/11/96



27-May-97

Date & Time 27/05/97 9:20 27/05/97 9:40 27/05/97 10:00



Conductivity (µS/cm) 908 wet sediment only wet sediment only

Temperature 27.6


5-Aug-97

Date & Time 5/08/97 14:55 5/08/97 15:15 5/08/97 15:40



Conductivity (µS/cm) 1,111 not enough water not enough water

Temperature 27.1

26-Mar-98

Date & Time 26/03/98 9:45 26/03/98 10:05 26/03/98 10:25



Conductivity (µS/cm) 1,265 Dry Dry

Temperature 26.8

2-Sep-98

Date & Time 2/09/98 13:40




Temperature 25.7

26-Oct-98

Date & Time 26/10/98 13:50 26/10/98 13:45 26/10/98 13:40



Conductivity (µS/cm) 1,246 Dry Dry

Temperature 25.8

10-Mar-99

Date & Time 10/03/99 9:45 10/03/99 9:50 10/03/99 9:55



Conductivity (us/cm) 922 Dry Dry

Temperature 30.0

24-May-99

Date & Time 24/05/99 8:30 24/05/99 8:34 24/05/99 8:40



Conductivity (us/cm) 881 Dry Dry

Temperature 26.9


Borehole BH8

Location Below Headridge Hill, east side of island







Date of drilling 4-Nov-96 to 7-Nov-96


Comments from drill logs: Lower section of limestone very fractured. No fracturesobserved in the volcanics. Terminated due to refusal at73.2 mbgl.


1 2 3


RL base of monitor tube (m) 72.66 80.66 96.64

5-Nov-96

Date & Time 5/11/96 12:28 5/11/96 12:32 5/11/96 12:36



7-Nov-96

Date & Time 7/11/96 11:25 7/11/96 12:30 7/11/96 12:45


15-Nov-96

Date & Time 15/11/96 12:40 15/11/96 12:37 15/11/96 12:33


27-May-97

Date & Time 27/05/97 13:20 27/05/97 13:40 27/05/97 14:00



Conductivity (µS/cm) 561 303 not enough water

Temperature 26.7 26.7 n/a


6-Aug-97

Date & Time 6/08/97 9:20 6/08/97 9:35 6/08/97 9:50



Conductivity (µS/cm) 630 not enough water not enough water

Temperature 27.1 for sampling for sampling

26-Mar-98

Date & Time 26/03/98 8:30 26/03/98 8:50 26/03/98 8:10



Conductivity (µS/cm) 757 385 not enough water

Temperature 34.6 33.5 for sampling

2-Sep-98

Date & Time 2/09/98 14:00




Temperature 26.8

26-Oct-98

Date & Time 26/10/98 13:15 26/10/98 13:00 26/10/98 12:50

Depth to water table (m) 51.2 no measurement no water


Conductivity (µS/cm) 639 311 no water


8-Mar-99

Date & Time 8/03/99 8:50 8/03/99 9:00 8/03/99 9:06





20-May-99

Date & Time 20/05/99 9:15 20/05/99 9:20 20/05/99 9:30






Annex D

Water Resources Monitoring Boreholes

(BH1 to BH8)

Contents

Graph D1 Salinity variations at borehole BH1

Graph D2 Water level variations at borehole BH1


















Salinity variations at borehole BH1

0

500

1,000

1,500

2,000

2,500

1-Oct-96 1-Apr-97 30-Sep-97 31-Mar-98 29-Sep-98 30-Mar-99

Time

Ele

ctri

cal C

on

du

ctiv

ity

(uS

/cm

)

Tube 1 (RL base -30.2m) Tube 2 (RL base -20.6m)Tube 3 (RL base -14.6m)

Water level variations at borehole BH1

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00


Time

Wat

er le

vel r

elat

ive

to M

SL

(m

)

Tube 1 (RL base -30.2m) Tube 2 (RL base -20.6m)Tube 3 (RL base -14.6m)





0

500

1,000

1,500

2,000

2,500


Time

Ele

ctri

cal C

ondu

ctiv

ity

(uS

/cm

)

Tube 1 (RL base -18.2m) Tube 2 (RL base -0.2m)


0.00

0.50

1.00

1.50

2.00


Time

Wat

er le

vel r

elat

ive

to M

SL

(m

)

Tube 1 (RL base -18.2m) Tube 2 (RL base -0.2m)





0

5,000

10,000

15,000

20,000


Time

Ele

ctri

cal C

on

du

ctiv

ity (u

S/c

m)

Tube 1 (RL base -1.2m)


-0.50

0.00

0.50

1.00

1.50


Time

Wat

er le

vel r

elat

ive

to M

SL

(m

)

Tube 1 (RL base -1.2m)





0

500

1,000

1,500

2,000

2,500


Time

Ele

ctri

cal C

on

du

ctiv

ity

(uS

/cm

)

Tube 1 (RL base -24.1m) Tube 2 (RL base -18.1m)Tube 3 (RL base -12.1m) Tube 4 (RL base +3.3m)


0.00

0.50

1.00

1.50

2.00

2.50

3.00


Time

Wat

er le

vel r

elat

ive

to M

SL

(m

)

Tube 1 (RL base -24.1m) Tube 2 (RL base -18.1m)Tube 3 (RL base -12.1m) Tube 4 (RL base +3.3m)





0

10,000

20,000

30,000

40,000

50,000


Time

Ele

ctri

cal C

ondu

ctiv

ity

(uS

/cm

)

Tube 1 (RL base -33.7m) Tube 2 (RL base -27.2m)Tube 3 (RL base -21.7m) Tube 4 (RL base -15.7m)Tube 5 (RL base -9.7m)


0.00

0.50

1.00

1.50

2.00


Time

Wat

er le

vel r

elat

ive

to M

SL

(m

)

Tube 1 (RL base -33.7m) Tube 2 (RL base -27.2m)Tube 3 (RL base -21.7m) Tube 4 (RL base -15.7m)Tube 5 (RL base -9.7m)





0

200

400

600

800

1,000


Time

Ele

ctri

cal C

on

du

ctiv

ity

(uS

/cm

)

Tube 2 (RL base +14.05m)


13.00

13.50

14.00

14.50

15.00

15.50

16.00

16.50

17.00


Time

Wat

er le

vel r

elat

ive

to M

SL

(m

)

Tube 2 (RL base +14.05 m)





0

500

1,000

1,500

2,000


Time

Ele

ctri

cal C

on

du

ctiv

ity

(uS

/cm

)

Tube 1 (RL base+36.4m)


36.00

37.00

38.00

39.00

40.00

41.00


Time

Wat

er le

vel r

elat

ive

to M

SL

(m

)

Tube 1 (RL base +36.4m)





0

200

400

600

800

1,000


Time

Ele

ctri

cal C

on

du

ctiv

ity (

uS

/cm

)

Tube 1 (RL base +72.7m) Tube 2 (RL base +80.7m)


93.00

93.50

94.00

94.50

95.00

95.50

96.00

96.50

97.00


Time

Wat

er le

vel r

elat

ive

to M

SL

(m

)

Tube 1 (RL base +72.7m) Tube 1 (RL base +80.7m)


Annex E

Pollution Monitoring Boreholes

(BH9 to BH11)

Details and Data


Borehole BH9

Location Rubbish tip (north of airport), NE part







Dates of drilling 2-Oct-96 to 30-Nov-96 (2 stages)

Purpose Environmental pollution monitoring

Comments from drill logs: Initially drilled to 50 m bgl and tube installed to49.5 m bgl (dry). Later deepened to 91.7 m bgl.Intersected basalt at 87.0 m bgl.

Depth of base of PVC pipe belowground level (m)

90.70

RL at base of PVC pipe (m) 206.39

Depth of screened section of PVCpipe (m)

84.7 - 90.7

30-Nov-96

Date & Time 30/11/96 16:00



1-Dec-96

Date & Time 1/12/96 15:55




27-May-97

Date & Time 27/05/97 15:30



Conductivity (µS/cm) not enough water

Temperature -


4-Aug-97

Date & Time 4/08/97 14:30



Conductivity (µS/cm) not enough water

Temperature -

25-Mar-98

Date & Time 25/03/98 8:55




Temperature 24.6

2-Sep-98

Date & Time 2/09/98 14:10




Temperature 25.2

28-Oct-98

Date & Time 28/10/98 9:15




Temperature 30.9


Borehole BH10

Location Rubbish tip (north of airport), SE part


RL ground (m) 295.4





Dates of drilling 1-Oct-96 to 24-Nov-96 (2 stages)


Comments from drill logs: Initially drilled to 50 mbgl and tube installed to49.5mbgl (dry). Later deepened to 108.8mbgl.Intersected basalt at 107.5mbgl.

Depth of base of PVC pipe below groundlevel (m)

104.50



98.5 – 104.5

23-Nov-96

Date & Time 23/11/96 15:55



24-Nov-96

Date & Time 24/11/96




1-Dec-96

Date & Time 1/12/96 16:47




2-May-97

Date & Time 2/05/97 14:50





27-May-97

Date & Time 27/05/97 15:00




Temperature 25.9

4-Aug-97

Date & Time 4/08/97 13:50




Temperature 26.3

25-Mar-98

Date & Time 25/03/98 12:20




Temperature 31.5

26-Aug-98

Date & Time 26/08/98 13:50




Temperature 26.4

28-Oct-98

Date & Time 28/10/98 8:50




Temperature 36.9


Borehole BH11

Location Rubbish tip (north of airport), West side







Dates of drilling 28-Sep-96 to 30-Sep-96


Comments from drill logs: Hole was drilled through limestone. It is basically dry.This hole was not deepened as were boreholes BH9 &BH10.

Depth of base of PVC pipe belowground level (m)

52.34



46.4-52.3

27-Oct-96

Date 27/10/96



Conductivity (µS/cm) Insufficient water

7-Nov-96

Date 7/11/96



Conductivity (µS/cm) Insufficient water

27-May-97

Date & Time 27/05/97 14:20

Depth to water table (m) 55


Conductivity (µS/cm)

Temperature


4-Aug-97

Date & Time 4/08/97 13:10




Temperature

25-Mar-98

Date & Time 25/03/98 8:40




Temperature

26-Aug-98

Date & Time 26/08/98 13:35




Temperature

28-Oct-98

Date & Time 28/10/98 9:30

Depth to water table (m) No water



Temperature


Annex F

Monthly and Annual Rainfall Data

Airport

Jan 1973 – May 1999


Christmas Island, Indian OceanRainfall (mm) at Christmas Island Airport Daily Read Raingauge (Station 200790)

Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total

1973 254.6 319.8 404.1 108.8 262 430.5 49.4 109.1 106.7 31.6 278.3 351.3 2,7061974 637.6 334 131.6 104.6 66 81.6 108.9 98.6 29 251.8 379.4 478.2 2,7011975 425.2 811.1 354.4 198.8 254.5 31.8 35.6 57.7 346 474.4 103.2 254.2 3,3471976 239.1 121.8 424.6 35.2 71.0 71.2 4.0 6.4 53.2 39.6 145.8 51.2 1,2631977 114.0 313.0 176.6 37.6 313.8 155.6 42.4 2.8 11.4 8.4 13.8 69.6 1,2591978 281.9 206.2 364.4 138.8 528.6 708.4 356.2 163.8 235.2 390.0 269.6 72.2 3,7151979 306.4 90.6 (236.8) (178.8) 327.0 108.2 48.6 60.8 6.2 77.0 72.8 353.6 (1,451)1980 389.8 475.4 36.4 344.0 82.0 101.4 147.6 (25.4) 28.6 200.4 312.2 (2,118)1981 426.2 270.0 289.6 (307.8) ( ) ( ) ( ) ( ) 21.8 67.2 526.5 357.4 (1,959)1982 (194.6) 238.1 313.7 279.7 51.0 31.9 57.8 5.1 44.0 2.2 3.8 214.5 (1,242)1983 192.8 282.8 214.3 512.0 276.5 13.5 24.2 2.2 3.3 21.0 376.3 80.0 1,9991984 342.3 429.2 320.6 370.8 247.3 138.2 52.4 43.0 (108.4) ( ) ( ) ( ) (1,944)1985 ( ) ( ) ( ) 421.6 ( ) ( ) ( ) ( ) ( ) ( ) (125.8) 275.3 (697)1986 378.6 310.6 298.1 292.8 67.8 261.1 105.0 45.4 41.6 24.5 347.5 26.1 2,1991987 275.0 254.6 163.1 37.6 137.5 15.0 7.8 6.4 1.0 16.7 14.1 138.3 1,0671988 194.2 70.0 535.2 18.6 148.9 192.3 34.8 6.3 6.3 105.2 123.4 40.2 1,4751989 347.3 414.8 232.6 268.0 156.7 446.4 261.0 7.6 50.6 5.6 4.9 758.6 2,9541990 450.5 138.6 271.5 53.8 233.3 71.6 67.3 105.0 24.3 1.6 7.6 170.0 1,5951991 197.3 84.4 237.5 570.0 57.8 39.9 12.3 14.8 58.7 0.4 42.8 313.3 1,6291992 273.0 416.5 206.3 305.5 170.2 42.9 210.6 102.6 19.7 118.1 40.6 188.4 2,0941993 137.4 59.6 291.5 285.2 235.2 435.0 100.9 106.6 8.6 10.4 114.7 313.1 2,0981994 186.2 480.6 264.3 191.4 1.2 (2.0) 4.8 (6.2) 3.6 0 16.4 18.8 (1,167)1995 424.8 545.6 212.8 227.6 68.0 366.8 82.4 7.0 38.4 52.8 361.0 393.6 2,7811996 276.2 292.6 104.6 124.4 95.6 29.0 6.2 95.6 11.8 56.2 96.4 130.0 1,3191997 343.2 467.4 67.0 87.2 91.4 20.6 102.0 64.4 13.0 1.2 10.0 12.0 1,2791998 45.6 168.4 463.6 379.8 138.6 447.2 628.2 63.4 36.2 93.4 344.6 474.2 3,2831999 484.2 210.4 532.2 257.4 49.6


SUMMARY OF MONTHLY RAINFALL DATA FOR PERIOD 1973-1998

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMean (1973-98) 297.5 303.8 265.8 224.7 170.1 184.4 106.3 53.4 50.9 78.2 162.2 233.9 2,146Std Dev 129.2 176.8 122.8 156.5 120.5 193.4 140.7 47.5 81.2 123.1 157.5 182.0 820Cv 0.43 0.58 0.46 0.70 0.71 1.05 1.32 0.89 1.60 1.57 0.97 0.78 0.38Max 637.6 811.1 535.2 570.0 528.6 708.4 628.2 163.8 346.0 474.4 526.5 758.6 3,715Min 45.6 59.6 36.4 18.6 1.2 13.5 4.0 2.2 1.0 0.0 3.8 12.0 1,067No. Years 24 25 24 24 24 23 24 22 23 24 24 25 19


Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMean (1994-98) 255.2 390.9 222.5 202.1 79.0 215.9 164.7 57.6 20.6 40.7 165.7 205.7 2,166Std Dev 146.3 155.7 156.6 113.6 50.4 223.1 262.8 36.9 15.7 39.9 174.3 215.4 1,021CV 0.57 0.40 0.70 0.56 0.64 1.03 1.60 0.64 0.76 0.98 1.05 1.05 0.47Max 424.8 545.6 463.6 379.8 138.6 447.2 628.2 95.6 38.4 93.4 361.0 474.2 3,283Min 45.6 168.4 67.0 87.2 1.2 20.6 4.8 7.0 3.6 0.0 10.0 12.0 1,279No. Years 5 5 5 5 5 4 5 4 5 5 5 5 4


Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMean (1986-98) 271.5 284.9 257.5 218.6 123.2 197.3 124.9 52.1 24.1 37.4 117.2 229.0 1,981Std Dev 117.5 170.2 128.1 157.1 68.4 183.7 170.5 42.8 19.1 43.3 139.3 218.5 717CV 0.43 0.60 0.50 0.72 0.56 0.93 1.37 0.82 0.79 1.16 1.19 0.95 0.36Max 450.5 545.6 535.2 570.0 235.2 447.2 628.2 106.6 58.7 118.1 361.0 758.6 3,283Min 45.6 59.6 67.0 18.6 1.2 15.0 4.8 6.3 1.0 0.0 4.9 12.0 1,067No. Years 13 13 13 13 13 12 13 12 13 13 13 13 12


Notes: 1. Records are maintained by the Bureau of Meteorology. Readings are made at 9am and entered for day of reading.2. (Month or year with some or all days missing denoted by brackets). These are not included in averages.

Missing data as follows (refer to original data in S0664Year Month Dates Comment

1979 Mar 26 - 311979 Apr 1-61980 Aug 22-31 also estimated rainfall only from 3-211980 Sep all1981 Apr 28-301981 May all1981 Jun all1981 Jul all1981 Aug all1982 Jan 28-31 some other days estimated1984 Sep 19-301984 Oct all1984 Nov all1984 Dec all1985 Jan all1985 Feb all1985 Mar all1985 May all1985 Jun all1985 Jul all1985 Aug all1985 Sep all1985 Oct all1985 Nov 1-121994 Jun 1-27, 301994 Aug 1-12, 14-15, 18-23, 25, 27-31


Annex G

Monthly and Annual Rainfall Data

Jedda

Jan 1994 – May 1999


Christmas Island, Indian Ocean

Rainfall (mm) at Jedda Raingauge


1994 265.8 532.8 264.0 198.3 41.3 93.8 16.0 12.3 52.0 1.5 11.5 11.3 1,501

1995 536.5 541.0 333.0 244.8 70.3 409.5 104.8 11.0 23.3 123.0 345.5 472.8 3,216

1996 397.0 345.8 231.8 72.8 92.0 21.0 6.5 139.0 13.0 156.0 76.0 282.5 1,833

1997 342.0 434.3 123.8 105.8 110.5 37.8 194.8 94.5 15.3 0.3 1.0 17.8 1,478

1998 31.8 166.8 455.5 549.0 113.5 532.0 669.8 99.3 48.5 225.5 556.8 398.0 3,847

1999 473.0 250.0 500.3 281.0 48.8 145.0 65.2



Mean (1994-98) 314.6 404.1 281.6 234.1 85.5 218.8 198.4 71.2 30.4 101.3 198.2 236.5 2,375

Std Dev 186.5 154.9 123.1 189.1 30.1 235.6 274.4 57.1 18.5 98.8 244.4 213.6 1,088

CV 0.59 0.38 0.44 0.81 0.35 1.08 1.38 0.80 0.61 0.98 1.23 0.90 0.46

Max 536.5 541.0 455.5 549.0 113.5 532.0 669.8 139.0 52.0 225.5 556.8 472.8 3,847

Min 31.8 166.8 123.8 72.8 41.3 21.0 6.5 11.0 13.0 0.3 1.0 11.3 1,478

No. Years 5 5 5 5 5 5 5 5 5 5 5 5 5

Notes: 1. Records are maintained by the Shire of Christmas Island

2. Database assumes readings at 9am and entered for day of reading. Actual readings are often made in the afternoon.

Christmas Island Groundwater Investigations and Monitoring Report - Annexes, November 1999 page145

Annex H

Monthly and Annual Pan Evaporation Data

Airport, Sep 1972 – Apr 1981

and

Rocky Point, Settlement, Feb 1968 – Oct 1972

Contents

Table H1 Monthly and annual pan evaporation (mm) at Airport(Station 200790), 1972-1981

Table H2 Summary of days when data was collected at Airportevaporation pan

Table H3 Monthly and annual pan evaporation (mm) at Rocky Point,Settlement (Station 200790), 1968-1972

Table H4 Summary of days when data was collected at Rocky Point,Settlement evaporation pan


Table H1 Monthly and annual pan evaporation (mm) at Airport (Station 200790), 1972-1981

Month


1972 209.5 197.5 163.1 177.8

1973 159.2 135.4 132.5 142.4 111.3 81.1 137.8 127.8 137.6 153.7 126.8 116.4 1562

1974 113.7 102 130.4 130 125.6 122.6 107.2 92.8 130.8 120.1 112.1 126.9 1414.2

1975 99 78.8 108.5 99.3 101.6 111.9 108.2 113.1 100 101.5 112.4 118 1252.3

1976 132.1 142.6 115.2 146.5 139.7 115.6 128 130.8 137.6 121.8 126.4 135.4 1571.7

1977 140.4 79.6 120 119.4 99.2 80 121.6 141.1 133 152.2 157.6 137.1 1481.2

1978 113.5 114.4 107.2 105.6 84.5 72.6 98.6 102.2 97.5 98.8 104.3 131.8 1231

1979 120.1 102.2 96.1 74.6 90.5 88.2 99.6 101.8 114.6 142.8 136.3 126 1292.8

1980 103.4 119.2 132.8 110 115.2 102.2 96.6 42.4 133.8 107.4 124 1187

1981 105.2 103.4 114.6 81.2

Average (all months) 120.7 108.6 117.5 112.1 108.5 96.8 112.2 106.5 132.6 135.8 127.4 132.6

Average (no months with missing data) 122.7 108.6 120.0 121.9 107.5 98.0 120.6 115.7 132.6 136.1 126.3 133.4

Daily average (no missing data months) 4.0 3.9 3.9 4.1 3.5 3.3 3.9 3.7 4.4 4.4 4.2 4.3

Months with no or missing data


Table H2 Summary of days when data was collected at Airport evaporation pan

Month

Year 1 2 3 4 5 6 7 8 9 10 11 12 Total

1972 30 31 30 31 122

1973 31 28 31 30 31 30 31 31 30 31 30 31 365

1974 31 28 31 30 31 30 31 31 30 31 30 31 365

1975 31 28 30 30 31 30 31 31 30 31 30 31 364

1976 31 29 31 30 31 30 31 31 30 31 30 31 366

1977 31 28 31 30 31 30 31 31 30 31 30 31 365

1978 31 28 31 30 31 30 30 31 30 31 30 31 364

1979 31 28 25 22 31 26 29 31 30 31 28 29 341

1980 31 29 30 30 29 30 28 12 28 30 31 308

1981 30 28 31 27 116


Total missing days

Year No of days

1975 0 (also 1 day accumulated into following day in March) (not include Jan-Aug)

1978 0 (also 1 day accumulated into following day in July)

1979 23 (also 1 day accumulated into following day in Dec)

1980 56 (also 1 day accumulated into following day in July)

1981 0 (also 1 day accumulated into following day in Jan) (no data after 27 April)


Table H3 Monthly and annual pan evaporation (mm) at Rocky Point, Settlement (Station 200790), 1968-1972

Month


1968 175.6 203.6 156.3 195.6 138 104.9 174.8 187 199.8 200.6 1736.2

1969 186.2 135.7 170.2 158 179 165.2 172.4 193.4 194 219.3 207.9 175.8 2157.1

1970 166.4 137.9 153 158.6 134.4 151 170 190.3 195.8 209.6 177.9 156.2 2001.1

1971 140.6 156.7 128.4 151.6 120.5 120.4 169.2 197 194.4 178.7 145.1 155.9 1858.5

1972 174.1 147.5 178.6 189.1 168.3 179.8 187.6 190.1 209.5 197.5 1822.1

Average (all months) 166.8 150.7 166.8 162.7 159.6 150.9 160.8 189.1 196.1 201.0 182.9 162.6

Average (no months with missing data) 166.8 152.1 153.3 168.0 160.6 150.9 175.6 189.1 196.1 198.8 195.5 156.1

Daily average (no missing data months) 5.4 5.4 4.9 5.6 5.2 5.0 5.7 6.1 6.5 6.4 6.5 5.0



Table H4 Summary of days when data was collected at Rocky Point, Settlement evaporation pan

Days when evap data collected Month

Year 1 2 3 4 5 6 7 8 9 10 11 12 Total

1968 27 30 30 27 30 25 31 30 31 30 291

1969 31 27 31 28 31 30 29 31 30 31 30 30 359

1970 31 23 28 30 31 30 31 31 30 30 30 31 356

1971 31 28 31 29 28 30 31 31 30 31 29 31 360

1972 31 29 31 30 31 30 31 31 30 31 305


Total missing days

Year No of days

1968 13 (not include Jan since starts in Feb)

1969 6

1970 8 (also 1 day accumulated into following day in May: OK for monthly total)

1971 4 (also 1 day accumulated into following day in Nov: OK for monthly total)

1972 0 (not include Nov & Dec since ends in Oct)


Annex I

Monthly Recharge Estimates

for period 1986-1998


Sample output from water balance analysis usingWATBAL program

Water Balance Program to compute Recharge to Groundwater using DAILY RAINFALL and AVERAGE MONTHLY EVAPORATION data - allows for interception losses - assumes linear relation between evapotranspiration ratio (EA/ET) and soil moisture content --------------------------------------------------------------------------- RAINFALL & EVAPORATION DATA USED IN WATER BALANCE ------------------------------------------------- Name of Daily Rainfall File : CIAE8698.DAY Title of Rainfall Data : Daily Rainfall, Christmas Is (IO), 1986-98 Name of Monthly Evap File : AIRPORT.EVA Title of Evaporation : Average monthly Pan evap, Airport(1972-81) Pan Factor : .9 No.of Years of Rain Record : 13 First Year of Rain Record : 1986 Last Year of Rain Record : 1998 --------------------------------------------------------------------------- INPUT SOIL AND VEGETATION PARAMETERS ------------------------------------ Interception Store Capacity (ISMAX) in mm = 3 Initial Interception Store Level (IIS) in mm = 3 Soil Moisture Zone Thickness(SMZ) in mm = 2000 Field Capacity(FC)= .25 Wilting Point(WP)= .15 Initial Soil Moisture Content(ISMC) in mm = 400 Deep Rooted Vegetation(eg Coconut Trees) Ratio(DRVR)= 1 Ratio of these roots reaching water table(DRWT)= 0 Crop Factor for Deep Rooted Vegetation(CROPFD)= 1 Crop Factor for Shallow Rooted Vegetation(CROPFS)= 1 Linear Relation of Ea/Et(actual/potential evap) ratio to SMC --------------------------------------------------------------------------- YEAR 1986 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 379 109 44 400 46 291 52 493 198 0 90 198 +0.52 311 96 44 493 50 217 7 492 217 0 94 217 +0.70 298 109 54 492 54 191 5 500 183 0 108 183 +0.61 293 108 29 500 73 190 11 464 226 0 103 226 +0.77 68 98 23 464 62 -17 34 447 0 0 85 0 +0.00 261 89 49 447 38 174 10 494 127 0 87 127 +0.49 105 103 33 494 63 9 22 487 16 0 96 16 +0.15 45 103 25 487 66 -46 29 441 0 0 91 0 +0.00 42 119 23 441 57 -38 83 402 0 0 80 0 +0.00 25 123 10 402 49 -34 115 369 0 0 58 0 +0.00 348 116 28 369 39 281 108 500 150 0 67 150 +0.43


26 120 9 500 86 -69 43 415 16 0 95 16 +0.62 --------------------------------------------------------------------------- 2199 1292 370 683 1134 0 1053 1134 +0.52 ---------------------------------------------------------------------------


YEAR 1987 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 275 109 60 415 46 169 19 496 87 0 106 87 +0.32 255 96 37 496 57 161 7 490 167 0 93 167 +0.66 163 109 30 490 71 62 16 450 102 0 101 102 +0.62 38 108 21 450 58 -42 66 409 0 0 79 0 +0.00 138 98 30 409 55 52 48 459 2 0 85 2 +0.01 15 89 13 459 51 -49 67 410 0 0 64 0 +0.00 8 103 6 410 43 -41 111 369 0 0 49 0 +0.00 6 103 6 369 27 -27 145 342 0 0 33 0 +0.00 1 119 1 342 19 -19 168 323 0 0 20 0 +0.00 17 123 8 323 13 -4 178 319 0 0 21 0 +0.00 14 116 12 319 8 -7 184 313 0 0 21 0 +0.00 138 120 30 313 26 82 146 395 0 0 56 0 +0.00 --------------------------------------------------------------------------- 1067 1292 255 473 359 0 728 359 +0.34 --------------------------------------------------------------------------- YEAR 1988 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 194 109 32 395 39 123 90 499 19 0 71 19 +0.10 70 99 26 499 66 -22 17 452 25 0 92 25 +0.36 535 109 41 452 61 433 17 487 398 0 102 398 +0.74 19 108 10 487 77 -68 43 420 0 0 86 0 +0.00 149 98 32 420 42 75 73 489 6 0 74 6 +0.04 192 89 38 489 49 106 9 493 101 0 87 101 +0.53 35 103 12 493 75 -52 37 442 0 0 86 0 +0.00 6 103 6 442 55 -55 86 387 0 0 61 0 +0.00 6 119 6 387 38 -37 132 350 0 0 44 0 +0.00 105 123 20 350 35 50 131 399 0 0 56 0 +0.00 123 116 25 399 47 51 94 451 0 0 72 0 +0.00 40 120 24 451 62 -45 73 406 0 0 85 0 +0.00 --------------------------------------------------------------------------- 1475 1296 270 646 549 0 916 549 +0.37 --------------------------------------------------------------------------- YEAR 1989 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 347 109 53 406 45 249 34 490 165 0 98 165 +0.48 415 96 50 490 45 320 4 500 310 0 95 310 +0.75 233 109 51 500 55 127 10 486 141 0 106 141 +0.61 268 108 50 486 57 161 4 486 161 0 107 161 +0.60 157 98 41 486 53 62 12 500 49 0 94 49 +0.31 446 89 50 500 38 358 5 497 361 0 88 361 +0.81 261 103 47 497 54 160 5 479 178 0 101 178 +0.68 8 103 8 479 68 -68 56 411 0 0 76 0 +0.00 51 119 10 411 64 -23 83 388 0 0 74 0 +0.00 6 123 6 388 39 -39 134 348 0 0 45 0 +0.00


5 116 5 348 21 -21 162 328 0 0 26 0 +0.00 759 120 56 328 33 670 64 497 501 0 88 501 +0.66 --------------------------------------------------------------------------- 2954 1292 426 571 1866 0 997 1866 +0.63


YEAR 1990 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 451 109 74 497 35 342 1 495 343 0 109 343 +0.76 139 96 21 495 63 54 28 500 49 0 84 49 +0.35 272 109 48 500 59 165 6 472 193 0 107 193 +0.71 54 108 26 472 62 -34 51 437 0 0 88 0 +0.00 233 98 35 437 46 152 45 482 107 0 81 107 +0.46 72 89 25 482 58 -11 21 471 0 0 83 0 +0.00 67 103 28 471 58 -18 48 452 0 0 86 0 +0.00 105 103 41 452 52 12 34 464 0 0 93 0 +0.00 24 119 12 464 71 -58 68 406 0 0 83 0 +0.00 2 123 2 406 48 -48 120 357 0 0 50 0 +0.00 8 116 6 357 25 -23 155 334 0 0 31 0 +0.00 170 120 34 334 34 102 117 437 0 0 68 0 +0.00 --------------------------------------------------------------------------- 1595 1292 351 611 693 0 962 693 +0.43 --------------------------------------------------------------------------- YEAR 1991 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 197 109 35 437 66 96 21 500 33 0 101 33 +0.16 84 96 34 500 59 -8 11 472 20 0 92 20 +0.24 238 109 35 472 60 142 32 498 116 0 95 116 +0.49 570 108 51 498 55 464 4 476 486 0 106 486 +0.85 58 98 16 476 70 -27 30 449 0 0 85 0 +0.00 40 89 22 449 45 -27 68 422 0 0 67 0 +0.00 12 103 11 422 45 -44 102 378 0 0 57 0 +0.00 15 103 12 378 29 -27 135 351 0 0 41 0 +0.00 59 119 22 351 23 13 153 364 0 0 45 0 +0.00 0 123 0 364 30 -30 152 335 0 0 30 0 +0.00 43 116 14 335 16 13 168 347 0 0 30 0 +0.00 313 120 37 347 58 218 63 500 66 0 95 66 +0.21 --------------------------------------------------------------------------- 1629 1292 290 556 720 0 846 720 +0.44 --------------------------------------------------------------------------- YEAR 1992 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 273 109 41 500 64 168 10 494 174 0 105 174 +0.64 416 99 54 494 44 318 4 497 315 0 98 315 +0.76 206 109 45 497 62 99 5 500 96 0 107 96 +0.47 306 108 61 500 47 198 2 496 202 0 108 202 +0.66 170 98 33 496 63 74 6 489 82 0 96 82 +0.48 43 89 22 489 59 -37 29 451 0 0 80 0 +0.00 211 103 36 451 60 115 22 467 99 0 96 99 +0.47 103 103 30 467 53 19 53 486 0 0 83 0 +0.00 20 119 17 486 76 -73 50 413 0 0 93 0 +0.00 118 123 18 413 51 50 104 463 0 0 68 0 +0.00


41 116 14 463 74 -47 55 416 0 0 88 0 +0.00 188 120 34 416 68 86 41 479 23 0 102 23 +0.12 --------------------------------------------------------------------------- 2094 1296 404 720 991 0 1125 991 +0.47


YEAR 1993 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 137 109 32 479 72 33 13 487 25 0 104 25 +0.18 60 96 23 487 65 -29 18 458 0 0 89 0 +0.00 291 109 39 458 60 192 24 500 150 0 99 150 +0.52 285 108 56 500 51 179 5 477 202 0 106 202 +0.71 235 98 45 477 50 140 10 482 135 0 95 135 +0.58 435 89 34 482 52 349 9 471 360 0 86 360 +0.83 101 103 31 471 65 5 22 474 3 0 95 3 +0.03 107 103 24 474 69 14 25 485 2 0 93 2 +0.02 9 119 8 485 79 -79 55 406 0 0 88 0 +0.00 10 123 10 406 47 -46 117 361 0 0 56 0 +0.00 115 116 11 361 33 71 136 431 0 0 44 0 +0.00 313 120 30 431 73 210 36 479 162 0 103 162 +0.52 --------------------------------------------------------------------------- 2098 1292 342 717 1039 0 1059 1039 +0.50 --------------------------------------------------------------------------- YEAR 1994 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 186 109 51 479 55 80 9 498 62 0 106 62 +0.33 481 96 63 498 32 385 2 500 383 0 95 383 +0.80 264 109 41 500 64 160 11 467 193 0 104 193 +0.73 191 108 38 467 67 87 11 493 61 0 105 61 +0.32 1 98 1 493 74 -74 46 419 0 0 75 0 +0.00 2 89 2 419 42 -42 104 376 0 0 44 0 +0.00 5 103 4 376 30 -30 140 347 0 0 34 0 +0.00 6 103 4 347 19 -17 162 330 0 0 23 0 +0.00 4 119 4 330 13 -13 177 317 0 0 17 0 +0.00 0 123 0 317 8 -8 187 309 0 0 8 0 +0.00 16 116 6 309 5 5 191 314 0 0 12 0 +0.00 19 120 15 314 7 -3 187 311 0 0 22 0 +0.00 --------------------------------------------------------------------------- 1176 1292 229 415 698 0 645 698 +0.59 --------------------------------------------------------------------------- YEAR 1995 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 425 109 50 311 33 342 69 500 153 0 83 153 +0.36 546 96 62 500 33 450 2 493 457 0 95 457 +0.84 213 109 43 493 61 109 15 465 138 0 103 138 +0.65 228 108 35 465 62 130 24 442 153 0 98 153 +0.67 68 98 29 442 44 -5 73 437 0 0 73 0 +0.00 367 89 61 437 22 284 30 500 221 0 83 221 +0.60 82 103 23 500 75 -15 14 466 19 0 97 19 +0.23 7 103 7 466 64 -64 68 402 0 0 71 0 +0.00 38 119 11 402 53 -26 102 376 0 0 64 0 +0.00 53 123 8 376 53 -8 108 368 0 0 61 0 +0.00


361 116 45 368 42 274 69 500 142 0 87 142 +0.39 394 120 43 500 73 278 11 486 291 0 116 291 +0.74 --------------------------------------------------------------------------- 2781 1292 417 615 1574 0 1032 1574 +0.57


YEAR 1996 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 276 109 33 486 71 172 11 481 177 0 104 177 +0.64 293 99 41 481 55 197 8 474 204 0 96 204 +0.70 105 109 29 474 60 15 51 489 0 0 90 0 +0.00 124 108 27 489 75 23 15 477 35 0 102 35 +0.28 96 98 12 477 72 11 31 468 20 0 84 20 +0.21 29 89 11 468 59 -41 49 428 0 0 70 0 +0.00 6 103 4 428 51 -49 97 379 0 0 55 0 +0.00 96 103 29 379 33 33 112 412 0 0 62 0 +0.00 12 119 9 412 48 -46 112 366 0 0 58 0 +0.00 56 123 19 366 28 9 146 375 0 0 47 0 +0.00 96 116 31 375 37 28 113 404 0 0 68 0 +0.00 130 120 43 404 52 35 67 438 0 0 95 0 +0.00 --------------------------------------------------------------------------- 1319 1296 289 642 436 0 931 436 +0.33 --------------------------------------------------------------------------- YEAR 1997 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 343 109 56 438 46 241 26 500 179 0 102 179 +0.52 467 96 77 500 19 372 1 500 372 0 96 372 +0.80 67 109 26 500 74 -33 19 448 19 0 100 19 +0.28 87 108 19 448 65 3 53 451 0 0 84 0 +0.00 91 98 34 451 51 6 39 456 0 0 86 0 +0.00 21 89 9 456 53 -42 68 415 0 0 62 0 +0.00 102 103 42 415 41 19 68 434 0 0 83 0 +0.00 64 103 31 434 47 -13 70 421 0 0 78 0 +0.00 13 119 10 421 53 -49 103 371 0 0 62 0 +0.00 1 123 1 371 33 -33 146 339 0 0 34 0 +0.00 10 116 5 339 18 -13 168 325 0 0 23 0 +0.00 12 120 9 325 12 -9 179 317 0 0 21 0 +0.00 --------------------------------------------------------------------------- 1279 1292 319 512 571 0 831 571 +0.45 --------------------------------------------------------------------------- YEAR 1998 --------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 46 109 10 317 12 23 175 340 0 0 23 0 +0.00 168 96 26 340 36 107 96 446 0 0 62 0 +0.00 464 109 67 446 40 356 6 499 304 0 107 304 +0.66 380 108 68 499 39 272 2 500 271 0 108 271 +0.71 139 98 23 500 68 47 14 457 91 0 91 91 +0.65 447 89 58 457 27 362 18 492 327 0 85 327 +0.73 628 103 65 492 37 526 5 500 519 0 102 519 +0.83 63 103 23 500 72 -31 19 451 17 0 95 17 +0.28 36 119 17 451 63 -43 78 408 0 0 79 0 +0.00 87 123 30 408 49 8 95 416 0 0 79 0 +0.00


345 116 41 416 65 239 26 482 172 0 106 172 +0.50 474 120 60 482 57 357 10 500 340 0 117 340 +0.72 --------------------------------------------------------------------------- 3276 1292 488 564 2040 0 1053 2040 +0.62


13 YEAR AVERAGES ---------------- RAIN ET EI SMC1 ES XCESS AVSMDEF SMC2 GWR TL EA NETR RECHARGE (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) RATIO --------------------------------------------------------------------------- 1919 1293 342 594 975 0 937 975 +0.51

Explanations for the column headings in the listing above are:

RAIN monthly rainfall (addition of daily values)

ET monthly potential evaporation

EI monthly interception loss

SMC1 soil moisture content at start of month

ES monthly evaporation from soil moisture store

XCESS rainfall minus evaporation losses above (EI + ES)

AVSMDEF average soil moisture deficit for the month

SMC2 soil moisture content at end of month

GWR gross recharge to freshwater lens

TL transpiration due to deep rooted vegetation

EA sum of all evaporation losses (EI + ES + TL)

NETR net recharge to freshwater lens (GWR - TL)

RECHARGE RATIO ratio of NETR to RAIN


Annex J

Jedda Cave flow monitoring

1996 - 1999

Contents

Table J1 Jedda Cave weir rating table

Graph J1 Rating curve for Jedda Cave trapezoidal weir

Graph J2 Water level, flow & temperature variations at Jedda Cave andcumulative rainfall at Jedda rain gauge, 1996




Graph J6 Water level and, flow variations at Jedda Cave and cumulative rainfallat Jedda rain gauge, Oct 1996 - June 1999

Graph J7 Water level, flow & temperature variations at Jedda Cave andcumulative rainfall at Jedda rain gauge, Jan - Mar 1997

Graph J8 Water level, flow & temperature variations at Jedda Cave andcumulative rainfall at Jedda rain gauge, Apr – Jun 1997

Graph J9 Water level, flow & temperature variations at Jedda Cave andcumulative rainfall at Jedda rain gauge, Apr 1997

Graph J10 Water level, flow & temperature variations at Jedda Cave andcumulative rainfall at Jedda rain gauge, May 1999

Graph J11 Water level, flow & temperature variations at Jedda Cave andcumulative rainfall at Jedda rain gauge, May 1999


Table J1 Jedda Cave weir rating table

Location: Jedda Cave weir, downstream of pumps Type of weir: stainless steel trapezoidal Rating Table: version 1.02 (01/09/1996 to Present) Cease to flow = 0.0 m; G.H. = Gauge height

G.H. (m) Flow (L/s) G.H. (m) Flow (L/s) G.H. (m) Flow (L/s)

0 0 0.20 42.8 0.40 155 0.01 0.4 0.21 46.4 0.41 163 0.02 1.15 0.22 50.2 0.42 172 0.03 2.13 0.23 54.1 0.43 181 0.04 3.31 0.24 58.1 0.44 190 0.05 4.67 0.25 62.3 0.45 200 0.06 6.20 0.26 66.6 0.46 216 0.07 7.88 0.27 71.1 0.47 234 0.08 9.72 0.28 75.5 0.48 252 0.09 11.7 0.29 80.2 0.49 270 0.10 13.8 0.30 85.0 0.50 290 0.11 16.1 0.31 89.7 0.12 18.5 0.32 94.5 0.13 21.1 0.33 99.5 0.14 23.8 0.34 105 0.15 26.6 0.35 110 0.16 29.6 0.36 118 0.17 32.7 0.37 127 0.18 35.9 0.38 136 0.19 39.3 0.39 145

Jedda Rating Curve HYRATAB V63 Output 02/07/1999

Discharge (L/s) (linear scale)

Leve

l

(M

etre

s)

0 50 100 150 200 250 300 -0.2

0.05

0.3

0.55StationVarFromVarTo

JEDDA 100 143

Jedda Cave weir, downstream of pumps, Christmas IslandStream Water Level in MetresStream Discharge in Litres/Second

1

1

1

1

1

1

1

1

1

1

Table 1.02 Jedda Cave CTF= 0.0000


Graph J1 Rating curve for Jedda Cave trapezoidal weir


Graph J2 Water level, flow & temperature variations at Jedda Cave and cumulative rainfall at Jedda rain gauge, 1996


Jedda, 1996 data HYPLOT V90 Output 02/07/1999


PeriodInterval

Plot StartPlot End

1 Year1 Day 00:00_01/01/1997

00:00_01/01/1996 1996

0

0.1

0.2

0.3

0.4

0.5

1

1 JEDDA Jedda Cave,Christmas 100.00 Max & Min Level (Metres) JEDDA

0

50

100

150

200

250

2

2 JEDDA Jedda Cave,Christmas 143.00 Max & Min Discharge (L/s) JEDDA

24

24.4

24.8

25.2

25.6

26

3

3 JEDDA Jedda Cave,Christmas 450.00 Max & Min WaterTemp (DegC) JEDDA

0

400

800

1200

1600

2000

4

4 JEDDARAI Jedda (daily), CI 10.00 Cumulative Rainfall (mm) JEDDARAI



PeriodInterval

Plot StartPlot End

1 Year1 Day 00:00_01/01/1998

00:00_01/01/1997 1997

0

0.1

0.2

0.3

0.4

0.5

1


0

50

100

150

200

250

2


24

24.4

24.8

25.2

25.6

26

3


0

400

800

1200

1600

2000

4







PeriodInterval

Plot StartPlot End

1 Year1 Day 00:00_01/01/1999

00:00_01/01/1998 1998

0

0.1

0.2

0.3

0.4

0.5

1


0

50

100

150

200

250

2


24

24.4

24.8

25.2

25.6

26

3


0

1000

2000

3000

4000

5000

4




PeriodInterval

Plot StartPlot End

1 Year1 Day 00:00_01/01/2000

00:00_01/01/1999 1999

0

0.1

0.2

0.3

0.4

0.5

1


0

50

100

150

200

250

2


24

24.4

24.8

25.2

25.6

26

3


0

400

800

1200

1600

2000

4



Graph J6 Water level and, flow variations at Jedda Cave and cumulative rainfall at Jedda rain gauge, Oct 1996 - June 1999

Graph J7 Water level, flow & temperature variations at Jedda Cave and cumulative rainfall at Jedda rain gauge, Jan - Mar 1997

Jedda, 1996-1999 data HYPLOT V90 Output 02/07/1999

1996 1997 1998 1999

PeriodInterval

Plot StartPlot End

4 Year2 Day 00:00_01/01/2000

00:00_01/01/1996 1996

0

0.1

0.2

0.3

0.4

0.5

1


0

50

100

150

200

250

2


0

2000

4000

6000

8000

10000

3


Jedda, Jan - Mar 1997 HYPLOT V90 Output 02/07/1999

Jan Feb Mar

PeriodInterval

Plot StartPlot End

3 Month3 Hour 00:00_01/04/1997

00:00_01/01/1997 1997

0

0.1

0.2

0.3

0.4

0.5

1


0

50

100

150

200

250

2


24

24.4

24.8

25.2

25.6

26

3


0

200

400

600

800

1000

4



Graph J8 Water level, flow & temperature variations at Jedda Cave and cumulative rainfall at Jedda rain gauge, Apr – Jun 1997

Graph J9 Water level, flow & temperature variations at Jedda Cave and cumulative rainfall at Jedda rain gauge, Apr 1997

Jedda, Apr - Jun 1997 HYPLOT V90 Output 02/07/1999

Apr May Jun

PeriodInterval

Plot StartPlot End

3 Month3 Hour 00:00_01/07/1997

00:00_01/04/1997 1997

0

0.1

0.2

0.3

0.4

0.5

1


0

50

100

150

200

250

2


24

24.4

24.8

25.2

25.6

26

3


0

100

200

300

400

500

4


Jedda, April 1997 data HYPLOT V90 Output 02/07/1999

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

PeriodInterval

Plot StartPlot End

1 Month1 Hour 00:00_01/05/1997

00:00_01/04/1997 1997

0

0.1

0.2

0.3

0.4

0.5

1


0

50

100

150

200

250

2


24

24.4

24.8

25.2

25.6

26

3


0

40

80

120

160

200

4



Jedda, May 1999 data HYPLOT V90 Output 02/07/1999

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

PeriodInterval

Plot StartPlot End

1 Month1 Hour 00:00_01/06/1999

00:00_01/05/1999 1999

0

0.1

0.2

0.3

0.4

0.5

1


0

50

100

150

200

250

2


24

24.4

24.8

25.2

25.6

26

3


0

10

20

30

40

50

4


Graph J10 Water level, flow & temperature variations at Jedda Cave and cumulative rainfall at Jedda rain gauge, May 1999

Jedda, 20-26 Apr 1997 HYPLOT V90 Output 02/07/1999

20 21 22 23 24 25 26

PeriodInterval

Plot StartPlot End

7 Day15 Minute 00:00_27/04/1997

00:00_20/04/1997 1997

0

0.1

0.2

0.3

0.4

0.5

1


0

50

100

150

200

250

2


24

24.4

24.8

25.2

25.6

26

3


0

10

20

30

40

50

4


Graph J11 Water level, flow & temperature variations at Jedda Cave and cumulative rainfall at Jedda rain gauge, May 1999


Annex K

Ross Hill Gardens

Weir flow monitoring

1996 - 1998

Contents

Table K1 Ross Hill Gardens weir rating table

Graph K1 Rating curve for Ross Hill Gardens V-notch weir

Graph K2 Water level, flow & temperature variations at Ross Hill Gardens andcumulative rainfall at Jedda rain gauge, 1996



Graph K5 Water level, flow & temperature variations at Jedda Cave andcumulative rainfall at Jedda rain gauge, Oct 1996 – Mar 1998


Table K1 Ross Hill Gardens weir rating table

Location: Ross Hill Gardens pump sump Type of weir: stainless steel 90 degree V-notch Rating Table: version 1.01 Cease to flow = 0.005 m; G.H. = Gauge height

G.H. (m) Flow (L/s)

0 0 0.01 0.01 0.02 0.08 0.03 0.21 0.04 0.44 0.05 0.75 0.06 1.20 0.07 1.77 0.08 2.47 0.09 3.32 0.10 4.32 0.11 5.48 0.12 6.81 0.13 8.32 0.14 10.0 0.15 11.9 0.16 14.9

Graph K1 Rating curve for Ross Hill Gardens V-notch weir

Jedda Rating Curve HYRATAB V63 Output 02/07/1999

Discharge (L/s) (linear scale)

Leve

l

(M

etre

s)

0 50 100 150 200 250 300 -0.2

0.05

0.3

0.55StationVarFromVarTo

JEDDA 100 143

Jedda Cave weir, downstream of pumps, Christmas IslandStream Water Level in MetresStream Discharge in Litres/Second

1

1

1

1

1

1

1

1

1

1

Table 1.02 Jedda Cave CTF= 0.0000


Graph K2 Water level, flow & temperature variations at Ross Hill Gardens and cumulative rainfall at Jedda rain gauge, 1996


Ross Hill Gardens, 1996 HYPLOT V90 Output 03/07/1999


PeriodInterval

Plot StartPlot End

1 Year1 Day 00:00_01/01/1997

00:00_01/01/1996 1996

-0.5

-0.3

-0.1

0.1

0.3

0.5

1

1 ROSSHILL Rosshill Gdns weir 100.00 Max & Min Level (Metres) ROSSHILL

0

4

8

12

16

20

2

2 ROSSHILL Rosshill Gdns weir 143.00 Max & Min Discharge (L/s) ROSSHILL

24

24.4

24.8

25.2

25.6

26

3

3 ROSSHILL Rosshill Gdns weir 450.00 Mean WaterTemp (DegC) ROSSHILL

0

400

800

1200

1600

2000

4




PeriodInterval

Plot StartPlot End

1 Year1 Day 00:00_01/01/1998

00:00_01/01/1997 1997

-0.5

-0.3

-0.1

0.1

0.3

0.5

1


0

4

8

12

16

20

2


24

24.4

24.8

25.2

25.6

26

3


0

400

800

1200

1600

2000

4




Graph K5 Water level, flow & temperature variations at Ross Hill Gardens and cumulative rainfall at Jedda rain gauge, Oct 1996 – Mar 1998



PeriodInterval

Plot StartPlot End

1 Year1 Day 00:00_01/01/1999

00:00_01/01/1998 1998

-0.5

-0.3

-0.1

0.1

0.3

0.5

1


0

4

8

12

16

20

2


24

24.4

24.8

25.2

25.6

26

3


0

1000

2000

3000

4000

5000

4


Ross Hill Gardens, 1996-1998 HYPLOT V90 Output 03/07/1999

1996 1997 1998

PeriodInterval

Plot StartPlot End

3 Year2 Day 00:00_01/01/1999

00:00_01/01/1996 1996

-0.5

-0.3

-0.1

0.1

0.3

0.5

1


0

4

8

12

16

20

2


24

24.4

24.8

25.2

25.6

26

3


0

2000

4000

6000

8000

10000

4



Annex L

Ross Hill Gardens

Meter flows and gauge height monitoring

Nov 1997 – June 1999


ROSS HILL GARDENS METER & GAUGE HEIGHT READINGS Hewans Springs Harrisons Springs Pump Ross Hill Total

Reading Flow Reading Flow Reading Flow GaugeBoard

Inst. Flow Difference

Date Total Avg Instantaneous Total Avg Instantaneous Total Avg frommeters

kL kL L/sec L secs L/sec kL kL L/sec L secs L/sec kL kL L/sec m L/sec L/sec L/sec (%)

25-Nov-97 3,240.6 5,859.3 28-Nov-97 3,758.0 517.4 2.00 6,831.1 971.8 3.75 30-Nov-97 4,117.0 359.0 2.08 7,503.2 672.1 3.89 5-Dec-97 4,970.0 853.0 1.97 9,127.9 1,624.7 3.76 20-Dec-97 7,539.8 2,569.8 1.98 13,617.1 4,489.2 3.46 27-Dec-97 8,621.7 1,081.9 1.79 15,688.6 2,071.5 3.43 31-Dec-97 9,583.6 961.9 2.78 16,858.7 1,170.1 3.39 3-Jan-98 10,249.5 665.9 2.57 17,733.6 874.9 3.38 6-Jan-98 10,962.2 712.7 2.75 18,678.8 945.2 3.65 10-Jan-98 11,796.5 834.3 2.41 19,776.1 1,097.3 3.18 15-Jan-98 12,989.5 1,193.0 2.76 21,266.0 1,489.9 3.45 24-Jan-98 15,183.7 2,194.2 2.82 23,865.3 2,599.3 3.34 2-Feb-98 17,324.7 2,141.0 2.75 26,463.7 2,598.4 3.34 5-Feb-98 18,050.5 725.8 2.80 27,339.3 875.6 3.38 12-Feb-98 19,698.5 1,648.0 2.72 29,336.4 1,997.1 3.30 49.0 49.0 0.08 12-Mar-98 25,895.6 6,197.1 2.56 36,680.9 7,344.5 3.04 60.0 11.0 0.00 16-Mar-98 26,818.8 923.2 2.67 37,721.2 1,040.3 3.01 1-Apr-98 30,504.5 3,685.7 2.67 41,716.4 3,995.2 2.89 68.0 8.0 0.01 22-Apr-98 35,393.3 4,888.8 2.69 46,945.1 5,228.7 2.88 102.0 34.0 0.02 9-May-98 39,578.4 4,185.1 2.85 51,601.6 4,656.5 3.17 107.0 5.0 0.00 25-May-98 43,401.8 3,823.4 2.77 56,217.6 4,616.0 3.34 128.0 21.0 0.02 4-Oct-98 76,264.2 32,862.4 2.88 138,189.2 81,971.6 7.19 0.135 9.3 9-Oct-98 77,182.7 918.5 2.13 50 23.30 2.15 140,144.9 1,955.7 4.53 400 41.30 9.69 0.125 7.5 14-Oct-98 78,087.1 904.4 2.09 142,504.8 2,359.9 5.46 571.0 443.0 0.04 0.130 8.3 16-Oct-98 78,425.0 337.9 1.96 80 40.00 2.00 143,585.0 1,080.2 6.25 200 22.90 8.73 571.0 0.0 0.00 0.130 8.3 26-Nov-98 86,109.1 7,684.1 2.17 166,713.2 23,128.2 6.53 698.0 127.0 0.04 31-Dec-98 98,308.2 12,199.1 4.03 190,420.2 23,707.0 7.84 731.0 33.0 0.01 13-Jan-99 98,321.6 13.4 0.01 190,448.4 28.2 0.03 765.0 34.0 0.03 0.140 10.0 1-Feb-99 103,765.7 5,444.1 3.32 300 92.00 3.26 199,245.7 8,797.3 5.36 500 54.13 9.24 805.0 40.0 0.02 0.140 10.0 12.50 2.50 20 1-Mar-99 111,519.8 7,754.1 3.21 300 94.00 3.19 213,829.9 14,584.2 6.03 500 54.24 9.22 859.0 54.0 0.02 0.135 9.3 12.41 3.11 25 10-Mar-99 113,998.6 2,478.8 3.19 300 96.00 3.13 219,487.4 5,657.5 7.28 500 62.00 8.06 886.0 27.0 0.03 0.140 10.0 11.19 1.19 11 18-Mar-99 116,129.5 2,130.9 3.08 300 96.00 3.13 223,925.2 4,437.8 6.42 500 54.42 9.19 896.0 10.0 0.01 0.140 10.0 12.31 2.31 19 1-Apr-99 119,835.1 3,705.6 3.06 300 99.13 3.03 231,011.5 7,086.3 5.86 500 55.69 8.98 921.0 25.0 0.02 0.140 10.0 12.00 2.00 17 6-Apr-99 121,156.8 1,321.7 3.06 300 98.79 3.04 233,512.6 2,501.1 5.79 500 54.35 9.20 930.0 9.0 0.02 0.148 11.6 12.24 0.64 5 19-Apr-99 124,765.9 3,609.1 3.21 300 99.88 3.00 242,345.5 8,832.9 7.86 500 52.50 9.52 976.0 46.0 0.04 0.145 11.2 12.53 1.33 11 28-Apr-99 126,864.8 2,098.9 2.70 300 100.34 2.99 247,224.9 4,879.4 6.27 500 52.67 9.49 1,036.0 60.0 0.08 0.145 11.2 12.48 1.28 10 10-May-99 129,974.1 3,109.3 3.00 300 100.33 2.99 255,242.3 8,017.4 7.73 500 52.80 9.47 1,060.0 24.0 0.02 0.145 11.2 12.46 1.26 10 27-May-99 134,281.9 4,307.8 2.93 300 101.65 2.95 265,662.8 10,420.5 7.09 500 55.80 8.96 1,099.0 39.0 0.03 0.138 9.8 11.91 2.11 18


2-Jun-99 135,851.1 1,569.2 3.03 300 102.66 2.92 269,282.1 3,619.3 6.98 500 62.12 8.05 1,111.0 12.0 0.02 0.140 10.0 10.97 0.97 9 8-Jun-99 137,367.1 1,516.0 2.92 272,696.2 3,414.1 6.59 1,111.0 0.0 0.00 16-Jun-99 139,366.3 1,999.2 2.89 277,372.6 4,676.4 6.77 1,137.0 26.0 0.04 23-Jun-99 141,105.8 1,739.5 2.88 281,314.7 3,942.1 6.52 1,148.0 11.0 0.02 Average 2.78 3.0 5.54 9.0 0.02 9.86 12.09 1.70 14


Annex M

Daniel Roux Cave Water Monitoring

Site 1: Gusher

1996-1999

Contents

Graph M1 Water level, temperature & salinity variations at Daniel Roux gushersite, summary of data collected between October 1996 and May 1999

Graph M2 Water level, temperature & salinity variations at Daniel Roux gushersite, 27 October – 22 November 1996

Graph M3 Water level, temperature & salinity variations at Daniel Roux gushersite, 15 October 1998 – 12 May 1999

Graph M4 Water level, temperature & salinity variations at Daniel Roux gushersite, October 1998

Graph M5 Water level, temperature & salinity variations at Daniel Roux gushersite, 15-25 October 1998

Graph M6 Water level, temperature & salinity variations at Daniel Roux gushersite, 16-18 October 1998


Graph M1 Water level, temperature & salinity variations at Daniel Roux gusher site, summary of data collected between October 1996 and May 1999

Graph M2 Water level, temperature & salinity variations at Daniel Roux gusher site, 27 October – 22 November 1996

Daniel Roux gusher, 1996-1999 HYPLOT V90 Output 04/07/1999

1996 1997 1998 1999

PeriodInterval

Plot StartPlot End

4 Year2 Day 00:00_01/01/2000

00:00_01/01/1996 1996

0

0.5

1

1.5

1

1 DRGUSH Daniel Roux 'gusher' 100.00 Max & Min Level (Metres) DRGUSH

25

25.4

25.8

26.2

26.6

27

2

2 DRGUSH Daniel Roux 'gusher' 450.00 Max & Min WaterTemp (DegC) DRGUSH

0

500

1000

1500

2000

2500

3

3 DRGUSH Daniel Roux 'gusher' 825.00 Max & Min EC (uS/cm) DRGUSH

Daniel Roux gusher, Oct-Nov 96 HYPLOT V90 Output 04/07/1999

1-4 5-8 9-12 13-16 17-20 21-24 25-28 29-1 2-5 6-9 10-13 14-17 18-21 22-25 26-29

PeriodInterval

Plot StartPlot End

2 Month2 Hour 00:00_01/12/1996

00:00_01/10/1996 1996

0

0.5

1

1.5

1


25

25.4

25.8

26.2

26.6

27

2


0

500

1000

1500

2000

2500

3



Daniel Roux gusher, Oct 98-May 99 HYPLOT V90 Output 04/07/1999

Oct Nov Dec Jan Feb Mar Apr May

PeriodInterval

Plot StartPlot End

8 Month8 Hour 00:00_01/06/1999

00:00_01/10/1998 1998

0

0.5

1

1.5

1


25

25.4

25.8

26.2

26.6

27

2


0

500

1000

1500

2000

2500

3


Graph M3 Water level, temperature & salinity variations at Daniel Roux gusher site, 15 October 1998 – 12 May 1999

Graph M4 Water level, temperature & salinity variations at Daniel Roux gusher site, October 1998

Ecowise Environmental HYPLOT V90 Output 21/06/1999

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

PeriodInterval

Plot StartPlot End

1 Month1 Hour 00:00_01/11/1998

00:00_01/10/1998 1998

0

0.5

1

1.5

1


25

25.4

25.8

26.2

26.6

27

2


0

500

1000

1500

2000

2500

3



Daniel Roux gusher, 15-25 Oct 98 HYPLOT V90 Output 04/07/1999

15 16 17 18 19 20 21 22 23 24

PeriodInterval

Plot StartPlot End

10 Day20 Minute 00:00_25/10/1998

00:00_15/10/1998 1998

0

0.5

1

1.5

1


25

25.4

25.8

26.2

26.6

27

2


0

500

1000

1500

2000

2500

3


Graph M5 Water level, temperature & salinity variations at Daniel Roux gusher site, 15-25 October 1998

Daniel Roux gusher, 16-18 Oct 98 HYPLOT V90 Output 04/07/1999

16 17 18

PeriodInterval

Plot StartPlot End

3 Day6 Minute 00:00_19/10/1998

00:00_16/10/1998 1998

0

0.5

1

1.5

1


25

25.4

25.8

26.2

26.6

27

2


0

500

1000

1500

2000

2500

3


Graph M6 Water level, temperature & salinity variations at Daniel Roux gusher site, 16-18 October 1998


Annex N

Daniel Roux Cave Water Monitoring

Site 2: Cave (Channel to Sea)

(and comparisons with Site 1)

1996-1998

Contents

Graph N1 Water level, temperature & salinity variations at Daniel Roux channelsite, summary of data collected between October 1996 and April 1998

Graph N2 Water level, temperature & salinity variations at Daniel Roux channelsite, 1996



Graph N5 Water level, temperature & salinity variations at Daniel Roux gushersite, September 1997

Graph N6 Water level, temperature & salinity variations at Daniel Roux gushersite, 15-19 September 1997

Graph N7 Water level, temperature & salinity variations at Daniel Roux gushersite, 19 September 1997

Graph N8 Water level & salinity (no temperature) variations at Daniel Rouxchannel (cave) site and gusher site, November 1996

Graph N9 Water level variations at Daniel Roux channel (cave) site and gushersite, 9 – 13 November 1996

Graph N10 Salinity variations at Daniel Roux channel (cave) site and gusher site, 9- 13 November 1996


Graph N1 Water level, temperature & salinity variations at Daniel Roux channel site,

summary of data collected between October 1996 and April 1998

Graph N2 Water level, temperature & salinity variations at Daniel Roux channel site, 1996

Daniel Roux channel, 1996-1998 HYPLOT V90 Output 04/07/1999

1996 1997 1998

PeriodInterval

Plot StartPlot End

3 Year2 Day 00:00_01/01/1999

00:00_01/01/1996 1996

0

0.4

0.8

1.2

1.6

2

1

1 DRCAVE Daniel Roux Cave 100.00 Max & Min Level (Metres) DRCAVE

25

25.2

25.4

25.6

25.8

26

2

2 DRCAVE Daniel Roux Cave 450.00 Max & Min WaterTemp (DegC) DRCAVE

0

10000

20000

30000

40000

50000

3

3 DRCAVE Daniel Roux Cave 825.00 Max & Min EC (uS/cm) DRCAVE

Daniel Roux channel, 1996 HYPLOT V90 Output 04/07/1999


PeriodInterval

Plot StartPlot End

1 Year12 Hour 00:00_01/01/1997

00:00_01/01/1996 1996

0

0.4

0.8

1.2

1.6

2

1


25

25.2

25.4

25.6

25.8

26

2


0

10000

20000

30000

40000

50000

3







PeriodInterval

Plot StartPlot End

1 Year12 Hour 00:00_01/01/1998

00:00_01/01/1997 1997

0

0.4

0.8

1.2

1.6

2

1


25

25.2

25.4

25.6

25.8

26

2


0

10000

20000

30000

40000

50000

3




PeriodInterval

Plot StartPlot End

1 Year12 Hour 00:00_01/01/1999

00:00_01/01/1998 1998

0

0.4

0.8

1.2

1.6

2

1


25

25.2

25.4

25.6

25.8

26

2


0

10000

20000

30000

40000

50000

3




September 1997


15-19 September 1997

Daniel Roux channel, Sep 1997 HYPLOT V90 Output 04/07/1999

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

PeriodInterval

Plot StartPlot End

1 Month1 Hour 00:00_01/10/1997

00:00_01/09/1997 1997

0

0.4

0.8

1.2

1.6

2

1


25

25.2

25.4

25.6

25.8

26

2


0

10000

20000

30000

40000

50000

3


Daniel Roux channel, 15-19 Sep 97 HYPLOT V90 Output 04/07/1999

15 16 17 18 19

PeriodInterval

Plot StartPlot End

5 Day10 Minute 00:00_20/09/1997

00:00_15/09/1997 1997

0

0.4

0.8

1.2

1.6

2

1


25

25.2

25.4

25.6

25.8

26

2


0

10000

20000

30000

40000

50000

3



Daniel Roux channel, 19 Sep 97 HYPLOT V90 Output 04/07/1999

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

PeriodInterval

Plot StartPlot End

1 Day2 Minute 00:00_20/09/1997

00:00_19/09/1997 1997

0

0.4

0.8

1.2

1.6

2

1


25

25.2

25.4

25.6

25.8

26

2


0

10000

20000

30000

40000

50000

3



19 September 1997

Graph N8 Water level & salinity (no temperature) variations at Daniel Roux channel (cave) site

and gusher site, November 1996

Daniel Roux, both recorders, Nov 96 HYPLOT V90 Output 04/07/1999

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

PeriodInterval

Plot StartPlot End

1 Month1 Hour 00:00_01/12/1996

00:00_01/11/1996 1996

0

0.4

0.8

1.2

1.6

2

1


0

10000

20000

30000

40000

50000

2


0

0.4

0.8

1.2

1.6

2

3


0

10000

20000

30000

40000

50000

4



Graph N9 Water level variations at Daniel Roux channel (cave) site and gusher site,

9 – 13 November 1996

Graph N10 Salinity variations at Daniel Roux channel (cave) site and gusher site,

9 - 13 November 1996

Daniel Roux, water level, 9-13 Nov 96 HYPLOT V90 Output 04/07/1999

9 10 11 12 13

PeriodInterval

Plot StartPlot End

5 Day10 Minute 00:00_14/11/1996

00:00_09/11/1996 1996

0

0.4

0.8

1.2

1.6

2

1


-0.4

0

0.4

0.8

1.2

1.6

2


Daniel Roux, salinity, 9-13 Nov 96 HYPLOT V90 Output 04/07/1999

9 10 11 12 13

PeriodInterval

Plot StartPlot End

5 Day10 Minute 00:00_14/11/1996

00:00_09/11/1996 1996

0

5000

10000

15000

20000

25000

1


0

5000

10000

15000

20000

25000

2



Annex O

Meter Flows – Sources and Distribution Tanks

1995-1999

Contents

Graph O1 Meter Flows - Sources and Distribution Tanks, 1995







0

5

10

15

20

25

30

35

40

1-Jan-95 2-Mar-95 1-May-95 30-Jun-95 29-Aug-95 28-Oct-95 27-Dec-95

Time

Flo

w (

Lit

res

per

sec

on

d)

George Fam Drumsite Power Station Hospital Airport Total (tanks)



0

5

10

15

20

25

30

35

40

1-Jan-96 1-Mar-96 30-Apr-96 29-Jun-96 28-Aug-96 27-Oct-96 26-Dec-96

Time

Flo

w (

Lit

res

per

sec

on

d)

George Fam Drumsite Power Station Hospital Airport Total (tanks)



0

5

10

15

20

25

30

35

40


Time

Flo

w (

Lit

res

per

sec

on

d)

Jedda Cave Jedda to Drumsite George Fam DrumsitePower Station Hospital Airport Total (tanks)



0

10

20

30

40

50


Time

Flo

w (

Lit

res

per

sec

on

d)

Jedda Cave Jedda to Drumsite Total inflow to tanks George FamDrumsite Power Station Hospital Airport

Christmas Island Groundwater Investigations and Monitoring Report - Annexes, October 1999 page 186

Annex P

Detailed Meter Flows at Distribution Tanks, 1998

Contents

Graph P1 Drumsite tank outflow meter, 19-22 June 1998

Graph P2 Drumsite tank outflow meter, 22 July – 14 August 1998

Graph P3 Drumsite tank outflow meter, 6-17 October 1998

Graph P4 George Fam tank outflow meter, 5-22 June 1998

Graph P5 George Fam tank outflow meter, 22 July – 14 August 1998

Graph P6 George Fam tank outflow meter, 6-17 October 1998

Graph P7 Hospital tank outflow meter, 22 July – 14 August 1998

Graph P8 Hospital tank outflow meter, 6-17 October 1998


Graph P1 Drumsite tank outflow meter, 19-22 June 1998

Drumsite Outlet Meter, Christmas Island, June 1998

0.00

5.00

10.00

15.00

20.00

25.00

19/06/98 0:00 20/06/98 0:00 21/06/98 0:00 22/06/98 0:00 23/06/98 0:00

Date and Time

Flo

w (

L/s

)

`


Graph P2 Drumsite tank outflow meter, 22 July – 14 August 1998

Drumsite Outlet Meter, Christmas Island, July-August 1998

0.00

5.00

10.00

15.00

20.00

25.00

22/07/98 0:00 26/07/98 0:00 30/07/98 0:00 3/08/98 0:00 7/08/98 0:00 11/08/98 0:00 15/08/98 0:00

Date and Time

Flo

w (

L/s

)


Graph P3 Drumsite tank outflow meter, 6-17 October 1998

Drumsite Outlet Meter, Christmas Island, October 1998

0.00

5.00

10.00

15.00

20.00

25.00

6/10/98 0:00 8/10/98 0:00 10/10/98 0:00 12/10/98 0:00 14/10/98 0:00 16/10/98 0:00 18/10/98 0:00

Date and Time

Flo

w (

L/s

)


Graph P4 George Fam tank outflow meter, 5-22 June 1998

George Fam Outlet Meter, Christmas Island, June 1998

0.00

2.00

4.00

6.00

8.00

10.00

5/06/98 0:00 8/06/98 0:00 11/06/98 0:00 14/06/98 0:00 17/06/98 0:00 20/06/98 0:00 23/06/98 0:00

Date and Time

Flo

w (

L/s

)

5 min logging interval 2 min logging interval

`


Graph P5 George Fam tank outflow meter, 22 July – 14 August 1998

George Fam Outlet Meter, Christmas Island, July-August 1998

0.00

5.00

10.00

15.00

20.00

25.00

22/07/98 0:00 26/07/98 0:00 30/07/98 0:00 3/08/98 0:00 7/08/98 0:00 11/08/98 0:00 15/08/98 0:00

Date and Time

Flo

w (

L/s

)

`


Graph P6 George Fam tank outflow meter, 6-17 October 1998

George Fam Outlet Meter, Christmas Island, October 1998

0.00

5.00

10.00

15.00

20.00

25.00

6/10/98 0:00 8/10/98 0:00 10/10/98 0:00 12/10/98 0:00 14/10/98 0:00 16/10/98 0:00 18/10/98 0:00

Date and Time

Flo

w (

L/s

)


Graph P7 Hospital tank outflow meter, 22 July – 14 August 1998

Hospital Tank Outlet Meter, Christmas Island, July-August 1998

0

2

4

6

8

10

22/07/98 0:00 26/07/98 0:00 30/07/98 0:00 3/08/98 0:00 7/08/98 0:00 11/08/98 0:00 15/08/98 0:00

Date and Time

Flo

w (

L/s

)

`


Graph P8 Hospital tank outflow meter, 6-17 October 1998

Hospital Tank Outlet Meter, Christmas Island, October 1998

0

2

4

6

8

10

6/10/98 0:00 8/10/98 0:00 10/10/98 0:00 12/10/98 0:00 14/10/98 0:00 16/10/98 0:00 18/10/98 0:00

Date and Time

Flo

w (

L/s

)

`


Annex Q

Water Quality Monitoring Tests, 1968-1986

Contents

Table Q1 Water chemistry tests, 1968





Samples collected on 4 April 1968

Samples tested at Chemical Branch, State Laboratories, Melbourne, Victoria

Grant’s Jedda Cave Waterfall

Parameter Unit Well at Weir Spring

Sample No. 760 761 759

Calcium mg/L 116 112 114

Magnesium mg/L 2 2 6

Hardness (calculated as CaCO3) mg/L 298 288 309

Sodium mg/L 9 8 12

Potassium mg/L 1 1 1

Chloride mg/L 16 15 20

Sulphate mg/L 5 2 2

Carbonate mg/L 0 0 0

Bicarbonate mg/L 356 336 342

Nitrate mg/L 0 0 Trace

Fluoride mg/L 0 0 0.1

Silicate mg/L 2 3 5

Phosphate mg/L 0.1 0.1 0

Iron – total mg/L 0.1 2.5 0.2

Iron – soluble mg/L 0.1 0.1 0.1

Total Dissolved Salts (calculated) mg/L 507 479 508

pH 7.4 7.6 7.6

Conductivity @ 25OC uS/cm 579 541 565



Samples collected between 26th and 29th October 1973

Samples tested at AMDEL Computer Services (ref Polak, 1976)

Grant’s Jedda Cave Jane Up Waterfall

Parameter Unit Well at Weir Spring

Sample No. 7414001 7414002 7414003 7414004

Calcium mg/L 64 73 80 81

Magnesium mg/L 2 3 2 7

Hardness (as calculated as CaCO3) mg/L 168 195 208 231

Sodium mg/L 9 10 10 17

Potassium mg/L <1 2 1 2

Chloride mg/L 12 14 14 26

Sulphate mg/L 4 4 3 3

Carbonate mg/L 0 0 0 0

Bicarbonate mg/L 212 242 261 277

Nitrate mg/L <1 <1 <1 8

Phosphate mg/L 0.01 <0.01 0.01 0.01

Total Dissolved Salts (tested) m/L 194 235 208 280

Total Dissolved Salts (calculated) mg/L 195 225 208 281

pH 8.0 7.6 7.6 7.7

Conductivity @ 25OC uS/cm 356 366 431 457



Samples collected between 1st and 7th October 1986

Samples tested at Water Quality and Investigations Laboratory, Lower Molonglo, Canberra (ref Falkland, 1986)

Jedda Cave Waterfall Freshwater Jones Ross Hill Gardens

Parameter Unit at Weir Jane-Up Spring Spring Spring Harrison's Hewan's

Springs Spring

Calcium mg/L 84 64 90 130 100 99 83

Magnesium mg/L 3.4 1.6 5.4 13 10 3.2 7.1

Hardness (calculated as CaCO3) mg/L 220 170 250 380 290 260 240

Sodium mg/L 26 7 13 26 27 18 18

Potassium mg/L 0.97 0.31 1.2 3.4 2.2 0.69 1.50

Chloride mg/L 46 16 18 41 40 20 24

Sulphate mg/L 7.1 2.7 5.0 7.4 8.6 3.8 4.7

Carbonate mg/L 0 13 12 0 8.5 4.6 14

Bicarbonate mg/L 300 270 280 290 370 300 280

Hydroxide (OH) mg/L 0 0 0 0 0 0 0

Total Dissolved Salts (Calc) mg/L 468 375 424 511 566 448 432

Total Alkalinity as (CaCO3) mg/L 244 242 246 239 319 250 250

Turbidity ntu 0.60 0.20 0.35 0.08 0.15 0.15 0.97

pH 7.4 7.4 7.7 7.4 7.6 7.5 7.6

Conductivity @ 25OC uS/cm 470 400 500 780 720 500 520

Total phosphate mg/L 0.065 0.060 0.045 0.130 0.160

Total Iron mg/L 0.21 0.17 0.06 0.16 0.21

Total Manganese mg/L 0.04 0.05 0.09 0.08 0.09


Table Q3 Water chemistry tests, 1986 (continued)

Samples collected between 1st and 7th October 1986

Samples tested at Water Quality and Investigations Laboratory, Lower Molonglo, Canberra (ref Falkland, 1986)

Tap Tap Tap Daniel Borehole Freshwater Cave Seawater off

Parameter Unit (VQ3 (House (Mine Office Roux WB30 at Smithson Bright Lost Lake

Settlement) Settlement) Drumsite) Cave #1 #2 Cave

Calcium mg/L 110 92 110 86 22 120 80 440

Magnesium mg/L 9.0 5.6 2.4 12 0.74 13.0 19.0 1200

Hardness (calculated as CaCO3) mg/L 310 250 280 260 58 350 280 6000

Sodium mg/L 20 16 26 15 15 95 220 16100

Potassium mg/L 2.00 1.4 0.56 1.3 3.40 4.60 6.50 90

Chloride mg/L 27 22 15 17 15 170 270 18800

Sulphate mg/L 6.1 4.8 3.0 5.0 0.12 26 39 2600

Carbonate mg/L 0 0 7.5 4.9 0 0 0 29

Bicarbonate mg/L 350 320 300 320 85 370 300 86

Hydroxide (OH) mg/L 0 0 0 0 0 0 0 0

Total Dissolved Salts (calculated) mg/L 524 462 464 461 141 799 935 39345

Total Alkalinity as (CaCO3) mg/L 284 261 250 269 70 304 248 118

Turbidity (ntu) ntu 0.26 0.35 0.30 0.30 3.4 0.10 0.10 0.10

Pangai-Hihifo 7.3 7.7 8.0 7.7 7.7 7.4 7.4 8.1

Conductivity @ 25OC uS/cm 615 540 760 530 180 1100 1420 48000

Total Phosphate mg/L 0.060 0.045 0.115 0.070 0.055 0.060

Total Iron mg/L 0.31 0.09 0.14 16.7 0.08 0.11

Total Manganese mg/L 0.03 0.09 0.08 1.1 0.05 0.08


Annex R

Water Quality Monitoring Tests, 1998

Contents

Table R1 Water Quality Tests (chemistry, nutrients & metals), June 1998

Table R2 Water Quality Tests (salinity & metals), October 1998

Table R3 Water Quality Tests (potential pollutants), May 1998

Table R4 Water Quality Tests (potential pollutants), June 1998


Table R1 Water Quality Tests (chemistry, nutrients & metals), June1998

Samples collected by Shire on 4 June 1998

Tests organised by SGS Laboratory, Perth and reported on 24 June 1998

Sample Description Rubbish Tip Bore BH10 Jedda Cave

Laboratory Number Unit

98W07039 98W07040Conductivity @25OC µS/cm 580 550

Iron (unfiltered) mg/L 0.11 0.008

Potassium mg/L <0.1 <0.1

Total phosphorus mg/L 2.4 0.105

Total Kjeldahl nitrogen mg/L 0.44 0.033

Nitrite (as nitrogen) mg/L 0.003 0.003

Nitrite (as nitrogen) mg/L 0.72 0.405

Ammonia as nitrogen mg/L 0.015 0.008

Arsenic mg/L <0.002 <0.002

Cadmium mg/L <0.0002 <0.0002

Chromium mg/L <0.002 <0.002

Copper mg/L 0.003 <0.002

Lead mg/L 0.019 <0.002

Zinc mg/L 0.04 0.06


Table R2 Water Quality Tests (salinity & metals), October 1998

Samples collected between 13th and 17th October 1998

Samples tested at Ecowise Environmental Laboratory, Canberra

Jedda Cave Waterfall Ross Hill Daniel Roux

Parameter Unit at Weir Spring Gardens Cave gusher

Sample No. 174636 174638 174637 174635

Date of Sampling 14 Oct 17 Oct 14 Oct 13 Oct

Chloride mg/L 16 21 20 17

Conductivity @ 25OC µS/cm 540 510* 570 600

Silver µg/L <0.5 <0.5 <0.5 <0.5

Aluminium µg/L <10 50 <10 <10

Arsenic µg/L <1 <1 <1 <1

Barium µg/L <1 <1 <1 3

Beryllium µg/L <1 <1 <1 <1

Cadmium µg/L <0.1 <0.1 <0.1 <0.1

Cobalt µg/L 4 0.7 3 3

Chromium µg/L 2 7 3 3

Copper µg/L <0.5 <0.5 2 <0.5

Iron µg/L 360 63 340 330

Manganese µg/L <0.5 <0.5 <0.5 <0.5

Mercury µg/L <0.05 <0.05 <0.05 <0.05

Molybdenum µg/L <0.5 <0.5 <0.5 0.5

Nickel µg/L 0.6 <0.5 <0.5 <0.5

Lead µg/L <0.5 <0.5 <0.5 <0.5

Antimony µg/L 0.6 <0.5 <0.5 0.7

Selenium µg/L 1 <1 1 1

Thorium µg/L <1 <1 <1 <1

Thallium µg/L <1 <1 <1 <1

Uranium µg/L <1 <1 <1 <1

Vanadium µg/L <1 <1 <1 1.5

Zinc µg/L <1 <1 <1 <1

Note: * Conductivity for Waterfall shown as 210 µS/cm on results sheet: this value is uncharacteristically lowand is most likely a transcription error. The value is most likely to be 510 µS/cm.


Table R3 Water Quality Tests for potential pollutants, May 1998

Samples collected by Shire (May 1998)


Sample Description Unit

Rubbish Tip BoreBH10

Rubbish Tip BoreBH9

Jedda Cave

Laboratory Number 98W06197 98W06198 98W06199

Benzene mg/L <0.001 <0.001 <0.001

Toluene mg/L <0.001 <0.001 <0.001

Ethyl Benzene mg/L <0.001 <0.001 <0.001

Xylene mg/L <0.002 <0.002 <0.002

Dieldrin µg/L <0.001 <0.001 <0.001

Aldrin µg/L <0.001 <0.001 <0.001

Chlordane (total isomers) µg/L <0.001 <0.001 <0.001

Chlorpyrifos µg/L <0.002 <0.002 <0.002

DDT (total isomers) µg/L <0.001 <0.001 <0.001

Heptachlor µg/L <0.001 <0.001 <0.001

Aroclor 1242 mg/L 0.2 0.2 0.2

Aroclor 1254 mg/L 0.2 0.2 0.2

Aroclor 1260 mg/L 0.2 0.2 0.2

Arcolor 1262 mg/L 0.2 0.2 0.2

C6-9 mg/L 0.2 0.2 0.2

C10-14 mg/L 0.2 0.2 0.2

C15-28 mg/L 0.4 0.4 0.4

C29-36 mg/L 0.4 0.4 0.4


Table R4 Water Quality Tests for potential pollutants, June 1998

Samples collected by Shire on 4 June 1998


Sample Description Unit

Rubbish Tip Bore BH10 Jedda Cave

Laboratory Number 98W07039 98W07040

Benzene mg/L <0.001 <0.001

Toluene mg/L <0.001 <0.001

Ethyl Benzene mg/L <0.001 <0.001

Xylene mg/L <0.002 <0.002

Dieldrin µg/L <0.001 <0.001

Aldrin µg/L <0.001 <0.001

Chlordane (total isomers) µg/L <0.001 <0.001

Chlorpyrifos µg/L <0.002 <0.002

BHC (each isomer) µg/L <0.001 <0.001

Heptachlor µg/L <0.001 <0.001

DDT (total isomers) µg/L <0.001 <0.001

Endosulfan µg/L <0.005 <0.005

Lindane (µg/L) µg/L <0.001 <0.001

HCB (µg/L) µg/L <0.001 <0.001

PCBs (as Aroclor 1254) mg/L 0.2 0.2

C6-9 mg/L 0.2 0.2

C10-14 mg/L 0.2 0.2

C15-28 mg/L 0.4 0.4

C29-36 mg/L 0.4 0.4

Note from laboratory: No evidence of the following:

- organochlorine (OC) pesticides

- organophosphate (OP) pesticides

- polychlorinated biphenyls (PCBs)

- benzene, toluene, ethylbenzene and xylene (BTEX)

- total petroleum hydrocarbons (TPHs)


Annex S

Christmas Island Water Monitoring Program

October 1999


Christmas Island Water Monitoring Program by Shire of Christmas Island

October 1999 [This water monitoring program is an update of a program provided to the Shire of

Christmas Island in October 1998]

1. Data Collection (a) Daily

• flow measurements at the main water supply meters (Jedda Cave, Jedda to Drumsite,Waterfall to George Fam) and at the Jane-Up and Ross Hill Gardens pump meters, if thelatter pumps are operating. Record data on monitoring form.

• flow measurements at the tank outlet meters (Drumsite, George Fam, Hospital, PowerStation and Airport tanks). Record data on monitoring form. Modify list if meters are addedor deleted.

• pump hours and water levels in main water tanks. Record data on monitoring form.

• Jedda raingauge. Record data on monitoring form.

(b) Every two weeks• flow measurements at Ross Hill Gardens meters (at pump and pipelines from the two

springs). Read meters on pipelines from springs with valves fully open (allow a fewminutes after opening valves for flow to stabilise. Record data on monitoring form.

• ‘instantaneous’ flow measurements at Ross Hill Gardens meters on pipelines from thetwo springs). With stopwatch (or ‘second hand’ of watch), record the time taken for aknown volume of water to flow through the meter. Record voume and time on monitoringform.

• gauge height readings at Ross Hill Gardens. Remove any obstructions at flowmeasuring weir and allow flow to stabilise from springs for a few minutes before takingreading. Record data on monitoring forms.

• gauge height readings at Jedda Cave. Take reading with both pumps OFF. If one orboth pumps are ON, then switch OFF and allow flow in cave to stabilise for a few minutesbefore taking reading. Record data on monitoring forms.

• chlorine residual tests at selected locations (decided by Shire).

(c) Every four weeks• water source data loggers: monitor and download data from Greenspan data loggers at

Jedda and Daniel Roux Cave using a portable computer loaded with SMARTCOMsoftware. While at these sites:- Check data has been downloaded OK, end logging and begin logging again (to

clear memory).- Take check reading of gauge height (at Jedda).- Check battery voltage (by reviewing the download file, or using a multi-meter) and

replace with a fully charged battery if the voltage is less than 10 volts. TheSMARTCOM manual says that the battery voltage should not fall below 8 volts forreliable operation. The extra 2 volts (between 10 and 8 volts) should enableanother 4 weeks of operation. If in doubt, replace battery at each visit.

- Change silica gel with freshly charged silica gel.- Record data and observations on monitoring forms.


Make sure computer is fully charged and date/time correct before visits. Full details forchecking loggers at visits are provided in Operation Manual, Christmas Island WaterResources Monitoring. by John Skinner, Ecowise Environmental, 1997.

• water source meters and gauge height at Ross Hill Gardens: read gauge height andwater meters (with valves fully open), as per two weekly visits.. Walk pipelines to Hewan’sand Harrison’s springs and check if any overflow at springs. If no overflow, partially closevalves near water meters to slow the flows to the pump station.

• water quality tests (for bacteria) at selected sites of water supply system (testing atChristmas Island Hospital).

(d) Every three months• monitoring boreholes: measure salinity (electrical conductivity or ‘EC’) and water level at

selected tubes (as specified on special monitoring form). Make sure to calibrate the ECmeter before each set of three monthly tests (refer to EC meter manual).

• flow measurements at all consumer connection meters.

(e) Annual• water quality sampling at the following sites:

- pollution monitoring boreholes BH9 and BH10 at the current rubbish disposal site- any future monitoring boreholes at rubbish disposal sites- Jedda Cave, Waterfall and Ross Hill Gardens flows. Waterfall should be sampled

at a location where the combined water from all 3 springs, Waterfall, Freshwaterand Jones, can be sampled

- monitoring boreholes BH1 and BH4 in the Smithson Bight area (top tube in eachhole)

- Daniel Roux Cave gusher (provided that the entry to the cave is safe and that thissite is still seen as a possible groundwater development option).

Sampling to be done at end of ‘wet season’ when water table is high and sent to a NATAregistered laboratory for testing on the mainland. Sample bottles to be supplied byselected testing laboratory to suit the tests identified below. The list of tests to beperformed should be similar to past tests and include:- basic water chemistry (conductivity, TDS, major cations and anions)- nutrients (nitrate, nitrite, ammonia, orthophosphate, total phosphorous)- hydrocarbons (TPHs, BTEX)- heavy metals (aluminium, arsenic, cadmium, chromium, copper, lead, mercury,

manganese, selenium and zinc)- pesticides (organo-chlorine, OC and organo-phosphate, OP)

• water supply checks and discussions with consumers (start with consumers with highestreadings): regular and ongoing

(f) Other• Water meter data loggers: Loggers are currently at the outlet meters of George Fam,

Drumsite and Hospital tanks. These can be used periodically to monitor continuous flows.This will give information about minimum night flows and the general status of leaks in thedistribution systems fed by these tanks. When in use, download data every month andreset loggers to start again. If additional loggers are installed, these will need to be addedto the list.

• silica gel inspection & replacement at the junction box in Daniel Roux Cave (bycavers: need screwdriver and replacement gel (note that this is not a Shire function due tocave condition, but if someone is going down the cave for recreation, it may be possible toask them to do this task: estimated time 5 minutes, once at the site)


2. Data processing• record all data on appropriate forms at field sites (as specified above).• store all data sheets in appropriate monitoring folder.• enter the daily water meter data into Excel spreadsheet (Meters98.xls) each month.

• enter the connection meter data into Excel spreadsheet (Meter Connection.xls) every 3 months

• enter the borehole data into Boreholes.xls every 3 months

• send by fax/email to Tony Falkland, Ecowise Environmental each month: - copy of daily water meter/tank level/Jedda rainfall recording sheets. - computer files from water source data loggers (Jedda and Daniel Roux Cave gusher).- inspection/monitoring sheets for visits to Jedda, Ross Hill Gardens and Daniel Roux Cave

(with gauge height readings, comments, etc.).- any data collected from the meter data loggers. - any comments or queries on monitoring procedures or problems.

• send by fax/email to Tony Falkland, Ecowise Environmental every 3 months:- same data as above (for each month), plus- borehole data (copy of original sheet plus updated Boreholes.xls). - connection meter data (Meter Connection.xls).

3. Monitoring equipment at Shire• Electrical conductivity (salinity) meter (TPS WP84)• Conductivity calibration solutions (512, 5020, 15000 µS/cm) in 0.5 L bottles

• Water level measuring device (200 m reel, Glötzl)• Special electric ‘fishing reel’ and bailer for groundwater monitoring• Water level and temperature logger at Jedda Cave (Greenspan Model PS300, replaced in Oct

1998)• Water level, salinity and temperature logger at Daniel Roux Cave (Greenspan Model CTP300,

replaced bottom section to gusher in Oct 1998)• Water meter loggers (Datataker DT5) with pulsers to suit Kent type water meters (3 off, at

Drumsite, George Fam and Hospital tanks)• Portable computer (Toshiba) with software (Smartcom and Smartute for Greenspan loggers;

Dt5win for water meter loggers)• Multi-meter (for battery tests)• Tools (hacksaw, drill brace, drill bits)

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