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Report No.: 37/2005A

Anthony Knapton

Natural Systems Division

Alice Springs

._1• N o rthern Territory G overnment 0.,p::utonenl cf l'v.Jtura !lc•curcc:s, E r-nrun,.,,,..I and lhc A•i.

Groundwater Modelling of the Oolloo Dolostone

Department of Natural Resources, Environment & The Arts Natural Systems

Technical Report No. 37/2005A

Preliminary Groundwater Modelling

of the Oolloo Dolostone

A report prepared by NRETA

Author:

Anthony Knapton

Department of Natural Resources, Environment & The Arts, Alice Springs

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Department of Natural Resources, Environment & The Arts

Natural Resources

Technical Report No. 37/2005A

Copyright and Disclaimer

© 2004 Northern Territory Government

To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of Northern Territory Government.

PO Box 496, Palmerston, NT, 0831, Australia

Important Disclaimer

The Northern Territory Government advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional , scientific and technical advice. To the extent permitted by law, the Northern Territory Government (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it.

Cover Image: The bedded unit of the Oolloo Dolostone, Dorisvale Rd; Outcrop of the basal Cretaceous sandstone in the Daly River 1 Okm downstream from Black Bull Yard; Daly River at Bee Boon Crossing; Crystal Falls on the Douglas River; Outlet channel of the spring that originates from a pool on top of a gravel bar along the Daly River and Screen shot of a simulation from the FEFLOW modelling package.

© 2005 Department of Natural Resources, Environment and the Arts


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Executive Summary

Background

The Oolloo Dolostone is a major aquifer in the Daly River catchment. Impacts on the groundwater

resource from extraction or changes to the natural recharge regime could have considerable

impact on the dry season flows in the Daly River. Groundwater modelling is used here to

determine the validity of the conceptual model developed for the Oolloo Dolostone aquifer system.

This report presents the development of a numerical groundwater model to provide a method to

assess the impacts of development (both due to clearing and extraction) on the groundwater

system and the flows in the Daly River.

Conceptual Model of the Oolloo Oolostone

The conceptual model was developed by the Water Resources section of NRETA from the

available groundwater and surface water data and observations. It can be summarized as:

• The aquifer may be represented as a single semi-unconfined to semi-confined layer as the

groundwater levels coincide with the base of the Cretaceous sediments.

• The dolostone aquifer was expected to have greatest permeability in the dolostone aquifer is

within the weathered zone, confined to the upper 100 metres from the surface. For the

purposes of this exercise the aquifer was considered to have a constant thickness below the

groundwater table (ie a single layer of variable transmissivity was used instead of varying

hydraulic conductivity and aquifer thickness).

• Transmissivity estimate of 10,000 m2/d, based on the limited pumping test data.

• Storage coefficient estimate of 0.04. This is considered a reasonable estimate as previous

experience (Jolly, pers comm.) indicates that this value should be between 0.01 and 0.07.

• The main influence of the Cretaceous sediments is to reduce the recharge to the Oolloo

Dolostone aquifer. This is based on the subdued response of hydrographs for bores located in

areas with the Cretaceous cover (eg RN7595). The recharge was therefore divided into two

areas, outcropping dolostone and areas with Cretaceous cover.

• Initial estimates of the steady state annual recharge over the two areas were 150 mm/yr

(0.41 mm/d) for the outcropping dolostone and 40 mm/yr (0.11 mm/d) for the Cretaceous

cover. Recharge was estimated using the potential recharge model developed for the

Katherine rainfall record (Jolly et al, 2000). The recharge model estimates the soil moisture

deficit and evapotranspiration to derive the potential recharge due to deep drainage.

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• The dominant discharge from the aquifer is through the streambed and via springs. Discharge

mainly occurs in the lower reaches of the Daly River from approximately 27 km downstream of

Dorisvale Crossing through to the Douglas River (Tickell, 2002b).

• Over the long term the dry season discharge to the river via spring flows range from 5 to

15 cumecs.

• Evapotranspiration from the riparian zone is estimated at approximately 3 mm/day, which

equates to a total usage of 0.2 cumecs. Assuming th is is all derived from groundwater this is a

relatively small component of the water balance (Tickell, 2002b ).

Model Calibration Results

Based on the conceptual model developed, cal ibration of both the steady state model and the

transient model to the observation data was possible. Relatively good fits were obtained for both

the head and discharge data available.

Conclusions

Initial modeling of the Oolloo Dolostone indicates that the conceptual model is valid . However,

further refinement is required before the groundwater model can be implemented to assess the

effects of groundwater pumping on discharge to the river. The major areas where refinement is

required relate to the improved representation of recharge, spring inflows and wet season river

heights in the model.


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I Groundwater Modelling of the Oolloo Dolostone I

Contents

Executive Summary ...... .... ................................... ... .... ........................ ......... ... .......... ............ ..... ...... .. iii l Introduction ............... .............. ....................... ...... ... ... .. ...................... ....... ................................... 1

1.1 Background ... ..... ... .......... ........ .... .. ............ ..... ........ ................... .. ... ... ................................... 1 1.2 Objectives ......... ....... ... .. ...... ........ ... ........... .. ........... ....... ... .. ........... ..... ......... ... ......... .... ....... ... I 1.3 Model Steps ....... ..... .......... ............ .. ............ .......... ... ........ .............. ...................... ... ..... .. ....... I 1.4 Location ........ .. .. ........ ..... .... ...... ....... ....... ..... .. ........ .. ....... .. ............... ................. ... ... .... ........... 2 1.5 Climate ................... ... ...... ..... ....... .. ........ ..... ..... .. .. ............. ................................ ..... ..... ... ....... 2 1.6 Geomorphology ......... .... ....... ............. ....... .. ....... ............... .......... .. ... ....... ... .. ......................... 4

1.6.l Topography ........... ... .. ....... ............... .................................... ... ... .................................. 4 2 Hydrogeological Setting and Conceptual Model .......... ............................. .... .......................... .... 6

2.1 Hydrogeology ........ .... ....... ..... ........................ ........ .. ................................ .......... ................... 6 2.1 . l Cretaceous Rocks .. .. ....... .......... .. ......... .. ........ .. .................................................. .. .. .... ... 6 2.1.2 Oolloo Dolostone ............................... .. .. .......... ......... .. .. ............................................... 6 2. 1.3 Jinduckin Formation ..... .......... ... ... .. ...... .... ..... ... .... .. ..................... ......................... ........ 8

2.2 Observation Data ....................... .................... .......... .. ......................... .................................. 8 2.2. l Rainfall and Potential Recbarge ............... .... ........ ................ .............. ........ ... .......... ... .. 8 2.2.2 Observation Bores ..... .. ......... ......... ............ .......... ... .. ................ ...... .. ........... .. .. .. .. .. .. ... 10 2.2.3 Groundwater Level Hydrographs ................... .... .. ...... ..... ............. ..... ...... .... .. ..... ..... .. . 11 2.2.4 Potentiometric Head Distribution ............... .. .... ...... ....... ...................... ....... .... .. .. .. ... ... 11 2.2.5 River Gauging Data ....... ...... .... .. ...... .. ..... ... ... .... ...... .. .... .. ... ............... ... .. ... .. .... ...... .. .... 13

2.3 Conceptual Model .......... ... ......... .......... ........... ... ... ........ .................................................. ... 16 3 Model Design .... ................................... ......................... .. .. .. ... .. ..... ....... ....... ...... ...... ... ...... ....... ... 18

3.1 Model Specifications .......... ......... ......................... .. ... .. ................................ ... ..... ........ ....... 18 3.2 Layers ........ .......... .............. .... .. ........... ................ .. .. ..... ..... .............. ...... ................. .... ......... 18 3.3 Boundary Conditions ......... ....... .. ... .............................. .... .............. .. ..... ... ..................... ...... 18

3.3. l Recharge (Specified Flux) ................. ......... .... .... .. .. ........ ............... ...... .... ...... .... ......... 18 3.3.2 Transfer (Cauchy) Boundary ...... ............... .. ... .... ....... ............................... ....... ... .. ... .. . 18

3.4 Hydraulic Parameters ............... ....... ... ... ........ ............ .... ............ ............... .. .... ................. ... 19 3.4.1 Transmissivity Distribution .. .... .. ......... ........ .... .. .. .. .. ... .. ... .............. ... .... ....... ..... ... ...... . 20 3.4.2 Recharge Distribution .... ...... .. ................................ ................................ ........ ... .. .. .... . 21

3.5 Numerical Model Implementation ...... ...... ............ ... .......... ................... .. ... .. ...... ................ 23 3.5. l Numerical Model Code .... .... ......... ........ ........ ... ..... .... ... ...... .. .... .... .... ... .. ........ ........... .. 23 3.5.2 Spatial Discretisation .. ..... .... ... ...................... ....... ...... .......... ........ .. .. .. ... .... ........... .. ..... 23 3.5.3 Temporal Discretisation ... ..... ........ .... .... ......... ... .......... .... .... ............... ... .... ...... .. .... ..... 24

3.6 Steady State Model Development ................ ..... .......... ..... ..... .. ... ... ........ .............. ........ .. .. ... 25 3. 7 Steady State Model Calibration ....... .... ..... ..... ................. ... ..... .. .. .. ...................................... 25 3.8 Transient Model Development ................ .. .......... .. .......................................... ...... ........ ..... 27 3.9 Transient Model Calibration ...... ... ............. ........ ............... ......... ............. .. ... .... ............... ... 27 3.10 Calibrated Model Results ........ .. ...... ... ... ........ ................... .................. ....... ..... ........ .. ...... .. .. 28

3.10. l Groundwater Level Hydrograpbs ...... ............. ......... ... .. ... .. ......................................... 28 3.10.2 Groundwater Discharge Hydrograpbs ............ ........ ... .............. ............ .................... ... 30

3.11 Sensitivity Analysis ................... ........... .............. ...... .......... .............................................. .. 31 4 Model Validation ... ............... ... ....... ......................................... .............. ... ............................ ... ... 33

4.1 Stable Isotope vs Particle Tracking as an Estimate of Residence Time ............................. 33 4.1.1 14C Ageing to Estimate Groundwater Residence Time .... .... ........ .. .. ............ .... ... ....... 33 4.1.2 Storage vs Discharge to Estimate Groundwater Residence Time .... .. .... ............ ........ 33 4. 1 .3 Particle Tracking to Estimate Groundwater Residence Time .......... ... ... .. .................. 34

5 Conclusions .................... ........ ... ................. ......... .. ......... ....... ...... ...................... ........................ . 36 6 Recommendations ..... .. .................... ............. .. .. ... .... .. .. ..... .............. .. .. ... ..... .............. .. ... ... .......... 37


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7 References ............................................. ........................................... .................. ..... ........... ........ 3 8 Appendix A Oolloo Monitoring Bores .............................................................. ..... ... ... .... ....... ....... 39 Appendix B Oolloo Dolostone Pumping Test Data .................. ...................... .. ............................ .41


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I Groundwater Modelling of the Oolloo Dolostone I

List of Figures

Figure 1 Figure 2

Figure 3 Figure 4 Figure 5 Figure 6

Figure 7 Figure 8 Figure 9 Figure 10 Figure 11

Figure 12 Figure 13

Figure 14

Figure 15 Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Study Area Location ................................... .............................. ..... .................. .. ............... 3 Variation in the monthly average rainfall across the Daly Basin from Katherine in the southeast to Adelaide River in the northwest. ......... ..................... ..... .............................. .4 3sec (90 metre) Shuttle Radar Topographic Model of the study area showing drainage.5 Simplified geology of the Daly Basin .. ............................................................................ 7 Geological cross-section of the Oolloo Dolostone ... ......... ................ ............................... 8 Relationship between rainfall at Katherine and potential recharge modified from Jolly, (2000) ............................................................................................................................... 9 Location of observation bores and bores used to calibrate model... ............................... I 0 Typical hydrographs across the study area ..................................................................... 11 Groundwater level contours for the late dry season 2002 (Tick ell, 2002b) ..... ..... ..... .... 12 Current Gauging Station Locations ................. .. ..... ........................................................ 13 Average monthly late dry season flows (cumecs) in the Daly River, estimating the groundwater discharge to the river from the aquifer. .................................... ................. 14 Transfer boundary conceptualization for a losing stream (Diersch, 2004) .................... 19 Distribution of transmissivity across the study area based on the mapped occurrence of the massive (Zone 1) and bedded (Zone 2) Oolloo Dolostone (Tickell, 2002) ....... ....... 21 Recharge zones, Zone 1 and Zone 3 represent the higher recharge rates associated with the outcropping Oolloo Dolostone, Zone 2 is the lower recharge rate in areas where Cretaceous cover exists .................. ................................................. ... .. ... ....................... 22 Model mesh geometry showing refinement along drainage features ........ ..................... 24 Comparison of modelled heads vs observed heads for RN7597. The response from the calibrated model are in blue (RunlO) ...... ....................................................................... 28 Comparison of modelled heads vs observed heads for RN8660. The response from the calibrated model are in blue (RunlO) ..... ....................................... ..... ............................ 29 Comparison of modelled heads vs observed heads for RN2 l 7 l 7. The response from the calibrated model are in blue (Run 10) .............................. ... ...................................... 29 Comparison of modelled discharge vs observed discharge along the Daly River from Dorisvale to Mt Nancar .. ...... .............. ...... ..... ... ... ... ............................ .... ...... ... ....... ........ 30 Comparison of modelled discharge vs observed discharge along the Daly River just upstream of Stray Creek .................... ...... .. .... ........ ......................................................... 31 Sensitivity analysis for variations in the transmissivity for the massive and bedded Oolloo dolostone units and storage coefficient. ............................................................ .32 Particle tracking results from the calibrated transient model. "X" markers at the head of the particle tracking indicate a time of one year, whilst " T " indicates a travel time of 50 years ......... ....................................... .. ....... ............................................... ................... 35

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Groundwater Modelling of the Oolloo Dolostonc

List of Tables

Table I

Table 2 Table 3

Gauged flows along the Daly River for Oct/Nov 1970, 1982, 2000 (Jolly, 2002) and September 200 I (Tickell, 2002a) ................................................................................... 14 Hydraulic Parameters ......................................... ....... ................................... ................. . 20 Selected steady state calibration run input parameters, outputs in the form of discharge to streams and RMS errors for hydraulic head data. Runl3 is considered to be the calibrated model. ............... .... .................... ..... .. .... .. .... ... .. ...... ........ ............ ........ ... ........ .. 26

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1 Introduction

1. 1 Background

The Oolloo Dolostone is a major aquifer in the Daly Basin. It represents the source of the majority

of the baseflow in the Daly River. The impending development of nearby horticultural districts

reliant on water from the Oolloo Dolostone aquifer, now represents a threat to the environmental

flow regime of the river. Changes to the aquifer recharge regime may also be associated with land

clearing and development.

1. 2 Objectives

The objective of this preliminary modelling is to validate the conceptual model developed for the

recharge, groundwater flow and discharge mechanisms for the Oolloo Dolostone aquifer

developed by NRETA. The modelling will then form the basis for recommendations for the future

refinement of the model and to conduct detailed modelling studies, such as extraction scenario

modelling.

A groundwater model has been developed based on a conceptual hydrogeological model

proposed by Tickell (2002b ). This work has provided affirmation of a viable hydrogeological model

and a tool to be applied under various development scenarios to assess aquifer and springflow

impacts.

This report presents the model's basis for development and identifies areas in which data

deficiencies exist.

1. 3 Model Steps

The groundwater model was developed using the following steps:

1) Conceptual model development;

2) Numerical model implementation;

3) Steady state model development;

4) Calibration of the steady state model;

5) Extension of the calibrated steady state model to the transient domain;

6) Calibration of the model to the transient hydrologic data from 1987 to 2005 including

rainfall/recharge data, water levels hydrographs and streamflow data;

7) Sensitivity analysis of the calibrated model to determine what are the key assumptions which

have a significant impact on the model;


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8) Model validation.

1.4 Location

The study area for the groundwater modelling comprises the full extent of the Oolloo Dolostone

some 230 km to the south-southeast of Darwin (Figure 1 ). The Oolloo Dolostone covers an area

of 4,600 km2 and is bounded approximately by the latitudes 13.75° S and 14.90° S and the

longitudes 132.22° E and 131.12° E. The Katherine River and Daly River are the major drainage

flowing through the region, tributaries include the Flora River, Fergusson River, Stray Creek and

Douglas River.

Katherine is the closest major centre and is approximately 40 km to the east of the study site.

1.5 Climate

The study area falls within the wet-dry tropics, that is, there are two distinct seasons. The wet

season is from December to April and the dry season spans the remainder of the year. Annual

rainfall increases to the northwest from an average of 980 mm at Katherine to 1, 156 mm at Oolloo

Crossing and 1,328 mm at Adelaide River. The variation in monthly rainfall at each of these sites

is presented in Figure 2.


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I _ _____ _

Figure 1 Study Area Location

- - - - - - - - - - - - - - -

o Towns

-- Major Roads

-- Major Drainage

Oolloo Dolostone

Q Jinduckin Formation

0 Tindall limestone

Q Daly River Catchment

LOCATION MAP N°' to Scalt

TENNANT CREEK

0 10 20 40 60 80 100 Kilometres

- - - - - -


~ 250 E

~ 200 ~ .: 150 co

Ck: :?:- 100 .= c ~ 50

0

Groundwater Modell ing of the Oolloo Dolostone

Average Monthly Rainfall

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

Month

a Adelaide River · 66yrs • Oolloo Crossilg • 44yrs o Katherine· 119yrs

Figure 2 Variation in the monthly average rainfall across the Daly Basin from Katherine in the

southeast to Adelaide River in the northwest.

1.6 Geomorphology

The major drainage within the study area shows a rectangular drainage pattern, where both the main

stream and its tributaries exhibit right-angle bends, indicating that geological structures (ie faulting and

jointing) have strongly influenced the development of the drainage, especially where the drainage

incises the Oolloo Dolostone. The Daly River is orientated sub-parallel to the strike of the Daly Basin.

The ephemeral drainage shows a more dendritic pattern.

1.6.1 Topography

The study area varies in topography from approximately 29 to 236 metres above Australian Height

Datum (Figure 3). The low lying areas are along the main drainage, and the highest topography is

located along the flanks. Topography is relatively rugged on the dissected flanks of the plateaux,

where steep gullies have been incised into the soft Cretaceous rocks. In contrast the areas where the

Oolloo Dolostone is exposed have low undulating topography with generally sparse outcop.

Date printed 22 November 2005 Date Last Modi fied: 22 November 2005

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'-~------


-- Ephemeral Drainage

- Major Drainage

Oolloo Aquifer Extents

Elevation (mAHD)

High: 236.4

Low : 28.7

s

0 3.5 7 14 21 28 35 Kilometres

Figure 3 3sec (90 metre) Shuttle Radar Topographic Model of the study area showing drainage.

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2 Hydrogeological Setting and Conceptual Model

2.1 Hydrogeology

The study area is within the Daly River catchment (Figure 1 ). The major liydrogeological feature of

the region is the Cambrian-Ordovician Daly Basin comprising the Tindal Limestone, Jinduckin

Formation and the Oolloo Dolostone. Early Cretaceous rocks overlie much of the Oolloo Dolostone.

The surface geology of the Daly Basin is depicted in Figure 4. A geological cross-section depicting

the stratigraphic relations of the Cretaceous sands and clays, Oolloo Dolostone and Jinduckin

Formation is also presented in Figure 5. The unit of interest in this study is the, Oolloo Dolostone,

which, is the upper unit of the Daly River Group and the major aquifer with respect to base flows in the

Daly River. The hydrogeology of the study area is described in detail by Tickell, (2002b) and is

summarized below.

2.1.1 Cretaceous Rocks

The beds are sub-horizontal and consist predominantly of clay, claystone and sandy clay with lesser

sandstone, sand and clayey sand. Outcrop is generally sparse due to the soft nature of the rock but in

places silicification has altered them to porcellanite and quartzite which outcrop reasonably well. The

thickest accumulations are preserved along the axis of the Daly Basin running from the north side of

the King River, through Florina Station and then following the north east side of the Daly River as far

as Stray Creek (Tickell , 2002b). The main influence of the Cretaceous sediments is to reduce the

recharge to the Oolloo Dolostone aquifer. This assertion is based on the lithology of the unit, which is

predominantly clay/clayey sand and the subdued response of groundwater hydrographs for the bores

located in areas with the Cretaceous cover (eg RN7595 - Figure 8).

2.1.2 Oolloo Dolostone

The Oolloo Dolostone is the uppermost formation in the Cambrian-Ordovician Daly Basin, a largely

undeformed sequence of shallow water carbonate rocks. Outcrop is generally poor due to the

extensive cover of Cretaceous rocks. The main exposures occur at the northwestern and

southeastern ends of the basin (Tickell , 2002b). The transmissivity of the Oolloo Dolostone has been

estimated at 10,000 m2/d from pumping test data (Tickell, 2002b), which is also presented in

Appendix B. Jolly, (2000), used a storage coefficient of 2% in storage calculations of the Oolloo

Dolostone aquifer. It has been suggested that the storage coefficient could be between 1 % and 7%

and is probably closer to 4% (Jolly pers comm., 2005).





Two broad units, an upper massive one and a lower well-bedded one are apparent in both gamma

logs and in outcrop. A contrast in the permeability of the two units is expected, due to the differences

in the lithology and from pumping test data.

The massive unit is a medium grained crystalline, pale pink, gray or cream coloured dolostone. It is a

hard, coarsely fractured rock, often showing abundant solution pits and cavities. Sedimentary

structures have mostly been destroyed by recrystallization (Tickell, 2002b).

N

·-<r' s

Northom Territory Govommont It_ ... _ ,......,_ "-1.-. ..... -~ ....... ,_ .......

Figure 4 Simplified geology of the Daly Basin



Oolloo Groundwater Model

Simplified Geology

- Drainage Cretaceous

Daly Basin D Oolloo Bedded CJ Oolloo Massiw CJ Tindall D Jinducki n


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South west North east

g 200

M 150 M

100

50

0

·50

-100

-150

-200

0 2 4 6 8 10 Km

Horizontal scale

Figure 5 Geological cross-section of the Oolloo Dolostone

The bedded unit underlies the massive unit (Figure 5). The unit is typified as fine to medium

crystalline ooid grainstone, dolostone, sandy dolostone and dolomitic sandstone. Sparse silty laminae

occur throughout the section and discrete regionally continuous silty and shaly dolostone beds up to

3 metres thick are spaced at intervals of about 20 metres. In outcrop the rocks are typically well

bedded with beds ranging from 10 to 50 centimetres thick. Beds are continuous over outcrops that

are up to several hundred metres in extent (Tickell, 2002b).

2.1.3 Jinduckin Formation

The Jinduckin Formation underlies the bedded unit of the Oolloo Dolostone. Aquifers are only

sparsely developed in this formation. The bulk of the formation is shale and siltstone with little

fractured porosity. Minor cavernous and fractured rock aquifers are developed in the thicker dolostone

beds. There are few aquifers in the upper part of the formation directly beneath the Oolloo Dolostone.

2.2 Observation Data

2.2.1 Rainfall and Potential Recharge

Rainfall data is available in the Katherine area from the Katherine Post Office site , DR014902. Data is

available from 1887 to present. The methodology for determining the potential recharge to the

aquifers in the Katherine region, based on these rainfall records, was developed by Jolly et al., (2000).

The potential recharge record derived from this work was used as a basis for the recharge to the

Oolloo aquifer system. Date printed 22 November 2005 Date Last Modified: 22 Novembcr 2005

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Groundwater Modelling of the Oolloo Dolostooe

The potential recharge was calculated from the daily rainfall record, using estimates for the end of dry

season soil moisture deficit and daily losses (evapotranspiration etc). A soil moisture deficit of 150

mm and wet season evapotranspiration (ET) of 5mm/day were chosen. It was also assumed that

there was little surface runoff from the ground overlying the limestone aquifers (Jolly et al., 2000).

Daily potential recharge is calculated using the following expression:

where

If Else if Else if Else if

SMDd + PPTd- ET <= -150 then SMDd + PPTd - ET <= 0 then PPTd-ET > 0 then PPTd - ET <= 0 then

SMD = soi l mois ture deficit (mm) PPT = daily rainfall (mm) ET = daily evapotranspiration (mm) d = day since beginning of record

SMDd+,= -150 SMDd+1= SMDd+ PPTd- ET SMDd+1 = SMDd + PPTd- ET SMDd+,= 0

d+I where l = number of days since previous SMDd value R = daily recharge

The calculated potential recharge record was extended to 2004, and to reduce the computational

effort during the model simulations the monthly potential recharge was used, derived from summation

of the calculated daily data. The relationship between the monthly rainfall and monthly potential

recharge from 1962 to 2004 is presented in Figure 6.

Cl) Cl ... RI ~ u Cl)

~

800

600

!e 400 .E E ni-0:: >. ~ 200 -c 0 ::E

0

Rainfall

• Pote ntial Recharge

1970 1975

J I 1 I

1980 1985 1990 1995 2000 2005 Date

Figure 6 Relationship between rainfall at Katherine and potential recharge modified from Jolly, (2000).




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2.2.2 Observation Bores

24 bores within the Oolloo groundwater model extent have time series water level data. The list of

bores is provided in Appendix A Oolloo Monitoring Bores. RN007595, RN08660 and RN021717

were selected to provide a basis for the transient calibration.

0 5 10

RN0252 • RN025285

N025286e

~~021830

s

20 30 Kilometres

RN033033 • RN033034 •

RN007595 •

RN032751 • RN032750 •

RN026555 •

• Model Obs Bores

• Observation Bores

Major Drainage

~ Oolloo Extent

RN033132 RN033133

RN033131 •

RN033039 • RN006660 •

Figure 7 Location of observation bores and bores used to calibrate model

Date printed 22 November 2005 Date Last Modified: 22 ovembcr 2005


Department of Natural Resources. Environment and The Arts

Groundwater Modelling of !be Oolloo Dolostone

2.2.3 Groundwater Level Hydrographs

RN7595 is located in an area with considerable Cretaceous cover, the subdued response to the

seasonal recharge events is interpreted to be due to lower recharge rate through the Cretaceous

layer. The obvious deviation from the response observed in the other hydrographs is attributed to this

reduced I buffered recharge regime, as opposed to a differing diffusivity (the ratio of transmissivity to

storage coefficient and describes the ability of an aquifer to transmit water).

RN8660 is located in the southeastern portion of the study area and shows a very strong response to

recharge events. This is interpreted to be due to a relatively high diffusivity (T/S). If it is assumed that

the transmissivity is relatively constant for the aquifer material then a lower specific yield than the rest

of the system is indicated. This may also be reflected in the topographic relief in this area, perhaps

suggesting a more competent aquifer material (ie the bedded Oolloo unit).

RN21717 is located in the northwest of the study area in the massive Oolloo unit. This area has been

mapped as having minimal Cretaceous cover, and the response to recharge events reflects this. The

response indicates strong seasonal influences, although not as strong as the response observed in

the southeast of the study area.

130

120

110

100 Qj > Ill ..J 90 ... .so ~~ 80 ci E c:-'i5 70 c: J!I (/)

60

50

40

30

1970

- RN7595 .,._, RN8660

...._ RN21717

1975 1980 1985

Figure 8 Typical hydrographs across the study area

2.2.4 Potentiometric Head Distribution

1990 1995 2000 2005 Date

The groundwater levels for November 2002 were collated and contours of the head distribution are

presented by Tickell, (2002). The head distribution provides some indication of the distribution of Date printed 22 November 2005 Dale Last Modified: 22 November 2005

S1a1us: FINAL Page 11

Depanmenl of Natural Resources, Enviroamem and The Ans

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transmissivity across the study area. The area to the south of the Katherine River shows relatively

high groundwater gradient (1 in 400 or 0.0025), supporting the conceptualization that lower

transmisivities exist here. The area to the northwest of Stray Creek also shows a relatively high

gradient (1 in 400 to 1 in 800 or 0.0025 and 0.00125), although the majority of the discharge occurs in

this part of the system, making a similar correlation a bit more difficult. The central portion of the study

area between Stray Creek and the Katherine River exhibits a very low gradient (1 in 4000 or 0.00025),

suggesting a relatively high transmissivity.

0 2 4 8 12 16 20

Kilometres

• Observation Bores

Major Drainage

- Groundwater Contours

c:> Oolloo Extent

Figure 9 Groundwater level contours for the late dry season 2002 (Tickell, 2002b)

Date printed 22 November 2005 Date Last Modified: 22 ovcmber 2005


Dcpanment of Natural Resources, Environment and The Ans


2.2.5 River Gauging Data

Stream discharge hydrographs are available at various locations along the Daly River. Continuous

gauging data exist at Dorisvale Crossing (G8140067) and Mt Nancar (G8140040). The locations of

the long term river flow stations are depicted in Figure 10.

0 5 10 20 30 Kilometres

Figure 10 Current Gauging Station Locations

G81 0060

G8 0008

The difference between the dry season flows at Dorisvale and Mt Nancar have been used to estimate

the discharge from the aquifer to the river, as the upstream component is common to both flow

measurements. The late dry season discharge to the river is generally of the order of 10 cumecs

(Jolly et al., 2000), corresponding to the period during the SO's and early 90's.


SIBtus: FINAL Page 13

Depanment of Natural Resources, Environment and The Ans


I I I I I I I I I I I I I I I I I I I I _I

-l/j u Cl)

E

100

:I 10 .£.

1970

Figure 11

\ . \

1975

.. i •. ~ . : .

1980

•• • . . . • . .

1985


. . ,. . ' . . . . . . . . . . . . \ . . . \ ~ .

•

1990 1995 Date

. . • :

.. . .. ; .

Dorisvale Flow

Mt Nancar Flow

~ Difference

2000 2005

Average monthly late dry season flows (cumecs) in the Daly River, estimating the

groundwater discharge to the r iver from the aquifer.

Jolly, (2002) presented below average, average and above average flow gaugings along the Daly

River for Oct/Nov 1970, 1982 and 2000 (Table 1 ). The data enables the calculation of discharge to

the river between the various gauging locations. The discharge between Dorisvale and Stray Creek

for the three measurement times is approximately 2.4, 4.8 and 6.7 cumecs. The corresponding

discharge from between Dorisvale to Mt Nancar is approximately 5. 7, 14.3 and 15.5 cumecs. The

percentage contribution of discharge upstream of Stray Creek to the total discharge between

Dorisvale and Mt Nancar is therefore, 42.1 %, 33.6% and 43.2%. There appears to be a relatively

consistent relationship between the total discharge from Dorisvale to Mt Nancar and the discharge

upstream of Stray Creek where discharge upstream of Stray Creek is approximately 30-40% of the

tota l flow in the Dorisvale - Mt Nancar section of the Daly River. A comprehensive survey of 100 sites

of the dry season inflows to the river along the section between Dorisvale and Douglas River in early

September 2001 is presented in Tickell, (2002a). The flows measured at various locations are

presented for comparison in Table 1. The contribution upstream of Stray Creek to the total flow

between Dorisvale and Mt Nancar is approximately 38%, in line with the previous assessment.

Table 1 Gauged flows along the Daly River for Oct/Nov 1970, 1982, 2000 (Jolly, 2002) and September

2001 (Tickell, 2002a)

Location Station

Date printed 22 November 2005 Diiie Last Modified: 22 Novcmber 2005

Flow in early Flow in early Flow in early Flow in


Department of Natural Resources, Environment and The Ans

November 1970

(cumecs)

Sum of Flora GS8140301 + 4.2* River and GS8140044 Katherine River Flows

Daly River at GS8140067 2.8 Doris vale Crossing

Daly River 5.2 near Stray Creek

Daly River at GS8140038 5.9 Oolloo Crossing

Douglas River GS8140063 0.26

Daly River at GS8140042 7.7 Bee Boom Crossing

Daly River at GS8140041 8.2 Gourley

Daly River at GS8140040 8.5 Mount Nancar

*indicates estimated value

#values derived from Tickell, (2002a)

Date printed 22 November 2005 Dace Last Modified: 22 November 2005



November November September 1982 2000 2001

(cumecs) (cumecs) (cumecs) 5.74* 7.1*

5.1 8.5 12#

9.9 15.2 20#

13 20.8 26#

0.66 1.2

16.9

17.2

19.4 24* 33#



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Groundwater Modelling oftbe Oolloo Dolostone

2.3 Conceptual Model

The conceptual model for the Oolloo Dolostone was developed by the Water Resources section of

NRETA from the available data and observations outlined in the previous sections. The conceptual

model for the Oolloo dolostone system can be summarized as:

• The aquifer may be represented as a single semi-unconfined to semi-confined layer as the

groundwater levels coincide with the base of the Cretaceous sediments.

• The dolostone aquifer was expected to have greatest permeability in the dolostone aquifer is

within the weathered zone, confined to the upper 100 metres from the surface. For the purposes

of this exercise the aquifer was considered to have a constant thickness below the groundwater

table (ie a single layer of variable transmissivity was used instead of varying hydraulic conductivity

and aquifer thickness).

• Aquifer transmissivity of 10,000 m2/d, based on the limited pumping test data, which is

summarized by Tickell, (2002b).

• Aquifer storage coefficient was 0.04. This is considered a reasonable estimate as previous

experience (Jolly, pers comm.) indicates that this value should be between 0.01 and 0.07.

• The main influence of the Cretaceous sediments is to reduce the recharge to the Oolloo Dolostone

aquifer. This is based on the subdued response of hydrographs for bores located in areas with the

Cretaceous cover (eg RN7595). The recharge was therefore divided into two areas, outcropping

dolostone and areas with Cretaceous cover.

• Initial estimates of the steady state annual recharge over the two areas were 150 mm/yr

(0.41 mm/d) for the outcropping dolostone and 40 mm/yr (0.11 mm/d) for the Cretaceous cover.

Recharge was estimated using the potential recharge model developed for the Katherine rainfall

record (Jolly et al, 2000). The recharge model estimates the soil moisture deficit and

evapotranspiration to derive the potential recharge due to deep drainage.

• The dominant discharge from the aquifer is through the streambed and via springs. Discharge

mainly occurs in the lower reaches of the Daly River from approximately 27 km downstream of

Dorisvale Crossing through to the Douglas River (Tickell, 2002b)

• Over the long term the late dry season discharge to the river via spring flows range from 5 to 15

cumecs, with an average discharge rate of 10 cumecs, with approximately 30% or 3 cumecs

discharging near Stray Creek.



Department of Natural Resources, Environment and The ArtS


• Evapotranspiration from the riparian zone is estimated at approximately 3 mm/day, which equates

to a total usage of 0.2 cumecs. Assuming this is all derived from groundwater this is a relatively

small component of the water balance (Tickell , 2002b).




I I I I I I I I I I I I I I I I I 1. I!

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1:

Groundwater Modelling of the Oolloo Dolostooe

3 Model Design

3. 1 Model Specifications

The model encompasses the mapped occurrence of the Oolloo Dolostone aquifer and covers an area

of 4637 km2•

3.2 Layers

It was considered that the aquifer could be approximated as a single layer system, with spatially

variable transmissivity.

3.3 Boundary Conditions

The entire surface of the model is a variable flux boundary describing the recharge to the aquifer. The

conceptual model assumes that the dominant mechanism for discharge of groundwater from the

system is through spring flow to the rivers. Based on this assumption the discharge to the rivers has

been implemented using a transfer boundary. The boundaries for the rest of the model domain are

no-flow.

3.3.1 Recharge (Specified Flux)

Recharge was applied to the entire model based on the surface geology. In areas were the

Cretaceous unit occurred the recharge rate was reduced by a factor of 3-4. Also, the groundwater

table has been modelled to be in direct connection to the recharge from the surface (ie no time lag has

been introduced to simulate the time for the deep drainage to travel through the Cretaceous unit,

which, can be up to 100 metres thick).

3.3.2 Transfer (Cauchy) Boundary

The discharge along the river was simulated using transfer (Cauchy) boundary condition. The transfer

boundary is similar to the RIV package used by MODFLOW (Anderson and Woessner, 2002). The

transfer boundary condition (Figure 12) describes a reference hydraulic head which has an imperfect

hydraulic contact with the groundwater body caused by a colmation layer (related to the stream bed

conductance) . Additionally to the reference head for the Transfer boundary condition you have to

assign a transfer rate (leakage) to describe the hydraulic properties of the colmation layer (Diersch,

2004).

Date printed 22 November 2005 Dale Last Modified: 22 November 2005




jg] = modeling area K1 ,,. conductivity of model area

1i: =reference hydraulic head 1(11 • conductivity of colmation layer •

h = hydraulic head

Figure 12 Transfer boundary conceptualization for a losing stream (Diersch, 2004).

The flux through the colmation layer as shown above can be described using the Darcy equation:

The transfer rate (¢~: )can be estimated by:

The reference hydraulic ( h: ) was initially determined from the 3 second (90 metre) digital terrain

model. It was found during steady state calibration that the reference heads were too high by

approximately 10-15 metres. It is expected that the elevations derived were of the banks of the river.

It is suggested that further work is required to obtain more accurate river height data.

3.4 Hydraulic Parameters

The hydraulic parameters of interest in the steady state model were the transmissivity and recharge

rate and the reference hydraulic heads and the transfer out rate associated with the Transfer

Boundary condition. The methodology for the choice of values for the major hydraulic parameters are

discussed below, and the range of values employed are summarized in Table 2.

• Transmissivity was initially defined as being consistent across the model with an estimated initial

value of 10,000 m2/d. However, it was found that zoning of the transmissivity was necessary. The

head distribution presented in section 2.2.4 provides some indication of the distribution of Date printed 22 November 2005 Date Last Modified: 22 November 2005

S1a1Us: FINAL Page 19





transmissivity across the study area and the likely magnitude of variation expected. The area to

the south of the Katherine River shows relatively high groundwater gradient (1 in 400 or 0.0025),

suggesting lower transmissivities in this area. The area to the northwest of Stray Creek also

shows a relatively high gradient (1 in 400 to 1 in 800 or 0.0025 and 0.00125). The central portion

of the study area between Stray Creek and the Katherine River exhibits a very low gradient (1 in

4000 or 0.00025), suggesting a relatively high transmissivity. Although the head distribution is

also a factor of the recharge rate, it is expected that the transmissivity in the southern and northern

areas are an order of magnitude lower than the central region.

• Recharge was initially zoned according to the occurrence of the Cretaceous cover. Higher

recharge rates were applied where the dolostone unit outcropped. Lower recharge rates

(approximately 3-4 times lower) were applied to areas with Cretaceous cover. Initial estimates of

the annual recharge over the two areas were 140 mm/yr (0.38 mm/d) for the outcropping

dolostone and 40 mm/yr (0.11 mm/d) for the Cretaceous cover.

• Transfer Rate describes the connection between the Transfer Boundary and the model and in this

instance is considered to be controlled by the surficial geology. That is, the lowest transfer rate

was assigned where the Cretaceous cover occurs. The southern area was assigned a rate of

1000 d-1, the northern area of exposed dolostone was assigned 10,000 d-1 and the area around

Stray Creek assigned 1,000,000 d-1.

Table 2 Hydraulic Parameters

Source

Pumping Tests

Modelled

Values

Transmissivity

[m2/d]

2 - 28,440

Ave= 5,578

1,000-25,000

3.4.1 Transmissivity Distribution

Storage Transfer Rate Coefficient

d"1

N/A N/A

0.01 - 0.07 1,000-1 ,000,000

The variations in the groundwater gradient appear to be related to the two different units mapped in

the Oolloo Dolostone. That is the lower gradients occur in the massive unit and the higher gradients

appear to correspond with the bedded unit. The transmissivity distribution (Figure 13) is based on the

mapped occurrence of the two units of the Oolloo Dolostone as described by Tickell, (2002b), where

Zone 1 and Zone 2 correspond to the massive and bedded units respectively. Date printed 22 November 2005 Date Last Modified: 22 November 2005



s

0 5 10 20 Kilometres

30


Transmlssivity Zones

0 Zone 1 (Bedded Unit)

Zone 2 (Massive Unit)

<:::) Oolloo Extent

Figure 13 Distribution of transmlssivity across the study area based on the mapped occurrence of the

massive (Zone 1) and bedded (Zone 2) Oolloo Dolostone (Tickell, 2002).

3.4.2 Recharge Distribution

As discussed previously, the steady state recharge to the model was zoned depending on the

occurrence of the Cretaceous unit. In areas where the Cretaceous layer was absent (Zone1 and

Zone3) higher recharge rates were applied (-1 50 mm/yr), in areas where the Cretaceous cover exists

(Zone2) the recharge was reduced by approximately 3-4 times (-40 mm/yr). Date printed 22 November 2005 Date Last Modified: 22 November 2005

Status: FINAL Page 2 1



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s

0 5 10 20

Kilometres 30


Recharge Zones

Q zone1

Q zone2

Q zone3

<::::) Oolloo Extent

Figure 14 Recharge zones, Zone 1 and Zone 3 represent the higher recharge rates associated with the

outcropping Oolloo Dolostone, Zone 2 is the lower recharge rate in areas where Cretaceous

cover exists.



Ocpanmeat of Natural Resources, Environment and The Ans


3.5 Numerical Model Implementation

3.5.1 Numerical Model Code

Finite element modelling code was employed to simulate the groundwater system. Finite elements

provide greater flexibility in the mesh design than the rectilinear grids employed by finite difference

code, and allows for refinement of the mesh around points such as bores and linear features such as

rivers. The code is limited because the software requires a licence to run - unlike the core code for

Modflow which is "freeware" from the US Geological Survey.

The finite element package FEFLOw® vS.11 from WASY was used to simulate the saturated flow

processes (Diersch, 2004). FEFLOw® is a fully three dimensional finite-element package capable of

simulating unsaturated and saturated flow and contaminant transport. FEFLOw® also has built-in

mesh-design, problem editing and graphical post processing display modules that allow rapid model

development, execution and analysis. A 32-bit PC laptop under Windows XP was used as the

platform for the numerical simulations (transient simulations over 18 years typical took 5-10 minutes).

3.5.2 Spatial Discretisation

The superelement, mesh and model were developed with the FEFLOvv® package using the automatic

Triangle option (Shewchuk, 2002). This feature offers the ability to define the local variation of mesh

density by allowing for the refinement of the mesh around specified point and line features.

Refinement of the model mesh was defined along the major drainage features within the model extent.

The resultant mesh used in the modelling is presented in Figure 15 and comprises 8433 elements

and 4379 nodes.







- Major Drainage

(> Finite Element Mesh

0 5 10 20 30 Kilometres

Figure 15 Model mesh geometry showing refinement along drainage features.

3.5.3 Temporal Discretisation

The model was initially developed as a steady state model, which is time independent. The transient

simulation uses the automatic time step control in FEFLOw®, which employs the forward Adams

Bashforth I backward trapezoid time integration scheme (Diersch, 2004) using a minimum possible

time step of 0.001 days. Model inputs such as recharge were applied on a monthly basis.


S1atus: FINAL Page 24



3.6 Steady State Model Development

The initial conceptual model described in section 2.2 was implemented using a single semi

unconfined layer with inputs from regional/diffuse recharge (implemented as source/sink on the upper

slice of the model) and outputs, as discharge along the river features using the transfer boundary

condition applied at the nodes along the rivers.

The steady state model initially used a single value across the entire model domain for the

transmissivity. These were then adjusted to more closely represent the mapped occurrence of

massive and bedded units in the Oolloo Dolostone.

The 1987 late dry season water levels were considered as "average" and constituted a reasonable

approximation of the system in steady state.

3. 7 Steady State Model Calibration

The dependent variables considered in the steady state calibration process were the hydraulic heads

and the groundwater discharge along the section upstream of Stray Creek and the total discharge to

the Daly River from between Dorisvale and Douglas River. The steady state water levels are

considered to be during 1987. The discharge to the Daly River was estimated from the difference in

flow between Dorisvale and Nancar.

The measure of the "goodness" of fit of the heads is the root mean square error (RMS error) where:

n

I (hobo.(i)- h model(i))2

RMS error= /cl

n

and

RMS error is the root mean square error (metres)

h obs{.i) is the i1h observed water level (metres)

hmoc1et(iJ is the i1h modelled water level (metres)

n is the number of observations

The target for calibration was to adjust the transmissivity and recharge rates to minimise the overall

RMS error and provide a discharge from the transfer boundary, in line with the estimate of 10-

12 cumecs (section 2.2.5).

As stated previously the steady state model has been calibrated against the observed heads on site

for the late dry season of 1987. The resulting calibrated model parameters are indicated by Run13 Date printed 22 November 2005 Date Last Modified: 22 November 2005






(Table 3) with hydraulic conductivities for Zone 1 = 25,000 m2/d and Zone 2 = 2500 m2/d and a RMS

error value of 1.0 metres.

Table 3 Selected steady state calibration run input parameters, outputs in the form of discharge to

streams and RMS errors for hydraulic head data. Run13 is considered to be the calibrated

model.

Run Trans. Trans. Recharge Recharge Bndry Discharge Discharge RMS Zone1 Zone2 Zone1 & 3 Zone2 Elev @Stray along Daly Error (m2/d) (m2/d) (mm/d) (mm/d) Creek River (m)

!cumecs} {cumecs}

Run1 25,000 5000 0.55 0.055 -10 1.87 9.17 4 .3 Run2 25,000 5000 0.55 0.055 -12 1.91 9.19 2.5 Run3 25,000 25,000 0.55 0.055 -12 1.82 9.83 2.2 Run4 25,000 25,000 0.55 0.055 -10 1.86 9.90 3.6 Runs 25,000 25,000 0.55 0.055 0 1.82 9.83 13.2 Run6 25,000 25,000 0.55 0.055 -5 1.82 9.83 8.3 Run7 25,000 25,000 0.55 0.055 -7 1.86 9.90 6.4

Run8 25,000 25,000 0.55 0.055 -15 1.82 9.83 2.7

Run9 25,000 25,000 0.55 0.055 -20 1.82 9.83 7.2 Run10 25,000 2500 0 .55 0.055 -12 1.94 8.95 3.6

Run11 25,000 2500 0.55 0.01 -12 2.33 9.84 3.9 Run12 25,000 2500 0.55 0.01 -15 2.35 9.87 1.3 Run13 25L000 2500 0.45 0.15 -15 3.04 10.25 1.0

Run14 25,000 2500 0.45 0.20 -1 5 2.87 10.52 1.6 Run15 25,000 2500 0.40 0.20 -15 2.69 9.92 1.4 Run16 25,000 2500 0.40 0.40 -15 4.49 13.67 5.0 Run17 25,000 2500 0.55 0.20 -15 3.23 11.74 2.2 Run18 25,000 25,000 0.55 0.20 -15 3.15 12.79 1.4 Run19 25,000 25,000 0.55 0.30 -15 4.11 14.77 2.2

Run20 25,000 25,000 0.55 0.30 -15 4.81 15.34 2.2 Run21 25,000 25,000 0.45 0.15 -15 2.86 11 .14 2.0

Run22 10,000 2500 0.45 0.15 -15 1.91 8.82 1.8 Run23 25,000 1000 0.45 0.15 -15 3.24 10.10 3.3 Run24 25,000 25,000 0.26 0.26 -15 3.56 9.93 2.6

The results of the calibrated steady state model (highlighted - Run13) provides a reasonable fit to the

selected observation data, with the RMS error for the observed versus modelled heads of 1.0 metres.

This is an error of approximately 1-2% considering the head distribution across the site ranges from 20

-110 metres above Australian Height Datum.

One of the major controls on the calibration turned out to be the proportioning of the discharge along

the Daly River. It can be seen from Table 3 that in order to obtain approximately 30% of the discharge

from upstream of Stray Creek, the transmissivity requires zoning with Zone 1 having a transmissivity

of approximately 10 times that of Zone 2.





Observed vs Steady State Modelled Heads

80 • Steady-Run1

• Steady-Run2

Steady-Run3

70 RN7595 x Steady-Run4

JC Steady-Runs

• Steady-Run6 • + Steady-Run7

0 60 ::c < .§.

. Steady-Runs

- Steady-Run9

Steady-Run10 "C

"' 50 Ci> Steady-Run11

::c "C

Steady-Run12

~ RN20614 '"*-Steady-Run13 Ci>

"C 40 0

:IE

Steady-Run 14

• Steady-Run15

Steady-Run16

. Steady-Run17

30 - Steady-Run18

• Steady-Run19

Steady-Run20

20 • Steady-Run21

20 30 80 x Steady-Run22

JC Steady-Run23 40 50 60 70

Observed Head (mAHD) Steady-Run24

3.8 Transient Model Development

The model was converted from a steady state model to a transient model. The main addition to the

model was storage coefficient and the time variable recharge (section 2.2.1 ).

3.9 Transient Model Calibration

As with the steady state calibration process the dependent variables considered were the hydraulic

heads and the groundwater discharge along the section upstream of Stray Creek and the total

discharge to the Daly River from between Dorisvale and Douglas River. The transient model was

modified to minimize the difference between the observed heads and the modelled heads at the 3

observation bores (RN7595, RN8660 and RN21717), which, are considered typical of the groundwater

response in the aquifer system.

Date printed 22 November 2005 Date Last Modified : 22 November 2005





3.10 Calibrated Model Results

3.10.1 Groundwater Level Hydrographs

The resultant calibrated hydrographs for RN7595, RN8660 and RN21717 are presented in Figure 16,

Figure 17 and Figure 18.

The resultant average annual recharge rate for Zone1 , Zone2 and Zone3 respectively are 0.95 mm/d,

0.32 mm/d and 0.74 mm/d, which, is approximately twice the steady state calibrated recharge rates

(approximately 0.41 mm/d for Zone1 & Zone3 and 0.11 mm/d for Zone2). It should be noted,

however, that the second half of the simulation is during a period of relatively high rainfall and

therefore the average over the 20 years would be expected to be greater. If the period from 1987 to

1997 is used to estimate the recharge, the average annual rates for Zone1 , Zone2 and Zone3

respectively are 0.52 mm/d, 0.17 mm/d and 0.40 mm/d in line with the steady state and conceptual

model recharge rates.

Cl> > Cl>

...I so Ill :::c

90

80

70

:i: <( -c E c- 60 :J 0 ...

C>

50

40

+++ ~ . -••

1980

Observat ion Data RN7595 Run1

Run10

Run13

Run18 • •

.. ++..,. t +

1985 1990 1996 2001 Date

Fig ure 16 Comparison of modelled heads vs observed heads for RN7597. The response from the

calibrated model are in blue {Run10).

Date printed 22 November 2005 Dale Last Modified: 22 November 2005



Cl> > Cl> ..J ... -s~ ns <(

~E c;, 0 ...

<.!)

130

120

11 0

100

90

80

1980

+++ Observation Data Run1 - Run10 Run13

••• Run18

1985

I I

Groundwa1er Modelling of1he Oolloo Dolosione

I RN8660

I I I

+ I I

1990 1995 2000 2005 Date

Figure 17 Comparison of modelled heads vs observed heads for RN8660. The response from the I calibrated model are in blue (Run10) .

Cl> > 3 ... -sC ns ::J: ~ <( ,, E

70

60

50

c-;, 40 0 ...

<.!)

30

20

+++ + + -••

1980

RN21717 Observation Data Run1 Run10 Run13 Run18

1985 1990 1995 2000 2005 Date

Figure 18 Comparison of modelled heads vs observed heads for RN21717. The response from the

calibrated model are in blue (Run10).

Date primed 22 November 2005 Date Last Modified: 22 November 2005

Sta1us: FINAL Page 29

Deparlment ofNa1urul Resources, Environment and The Arts

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3.10.2 Groundwater Discharge Hydrographs

The modelled and observed discharge to the river between Dorisvale and Mt Nancar are presented in

Figure 19. The modelled response shows a reasonable fit to the observed data, except in the late

80's to early 90's, where the modelled response is lower. It is interpreted that this is due to the use of

rainfall data from Katherine to simulate the recharge pattern in the northwestern portion of the study

area, where, in section 1.5 it was shown that the average rainfall increases to the northwest, also

rainfall events in the northwest of the study area, may not have been recorded in the southeast of the

study area or poor dry season river flow data at gauging stations G810067 and G8140040.

The results from Run18 have been added to demonstrate the effects of a constant transmissivity

across the model.

100

Discharge along Daly River from Dorisvale to Mt Na near

10

0.1

1980

Run18

- Run10 ......._... Observed Flows

1985 1990 Date

Discharge underestimated - associated with underestimated recharge in northwest of the study area.

1995 2000 2005

Figure 19 Comparison of modelled discharge vs observed discharge along the Daly River from

Dorisvale to Mt Nancar.

The modelled and observed discharge to the river upstream of Stray Creek are presented in Figure

20. Again the modelled response shows a reasonable fit to the observed data, except in the late 80's

to early 90's, where the modelled response is lower.




'---~-


Discharge upstream of Stray Creek

0.1

1980

Run18

- Run10 ......_. 30% Discharge to Daly River

1985 1990 Date

Discharge underestimated - associated with underestimated recharge in northwest of the study area.

\

1995 2000 2005

Figure 20 Comparison of modelled discharge vs observed discharge along the Daly River just

upstream of Stray Creek.

3. 11 Sensitivity Analysis

The sensitivity analysis was completed by adjusting the transmissivity and storage coefficients in the

transient model (hence the increased RMS value of 2.5 metres from the steady state calibrated RMS

error of 1.0 metres). The RMS error (simulated groundwater levels versus observed groundwater

levels) was used to determine the effects of changing the hydraulic parameters on the model output.

The results of this process are presented in Figure 21 .

One of the conclusions to be drawn from this method of presenting the sensitivity analysis is that the

transmissivity and storage coefficient derived during the parameters derived from the calibration

process can be considered to be optimized. This is indicated by the error minima at a parameter

multiplication factor of 1.

Date printed 22 November 2005 Date Las1 Modified: 22 November 2005


Depenment of Natural Resources, Environment end The Arts


I I I I I I I I I I I I I I I I I I I I 11

10.0

9.0

8.0

7.0 ...

6.0 e ... w 5.0 Cl)

~ 4.0

~ ·~ "'-' I'..

~

3.0

2.0

1.0

0.0 0.1

Sensitivity Analysis

"' I "\ // ' I\.

'\ ~ "\ /. ---..._ i'.. i\ - ~-,,....

1

Multiplication Factor

I If

J v

/ ./

I _......

10


~ Transmissi~ty Zone1

- Transmissi~ty Zone2

-.-storage Coefficient

Figure 21 Sensitivity analysis for variations in the transmissivlty for the massive and bedded Oolloo

dolostone units and storage coefficient.

Date printed 22 November 2005 Date Last Modified: 22 Novcmber2005


Deparuncnt of Natural Resources, Environment and The Arts


4 Model Validation

4. 1 Stable Isotope vs Particle Tracking as an Estimate of Residence Time

4.1.1 14C Ageing to Estimate Groundwater Residence Time

Tickell, (2004) and Herczeg, (2004), presented the results of a carbon 14 survey conducted in late

July and mid August of 2003 (two samples were obtained in early September 2002).

"The corrected results indicate that the water is modem. The (14C) model age

estimates give mostly negative ages, and are expressed here as modern which

means that they must contain some bomb-fallout 14C making them less than 50

years old. This means that recharge is very rapid and that all groundwater ages with

the exception of G8145619, G8145130 (samples taken at springs) and RN32751 are

less than 50 years old."

(Herczeg, 2004)

4.1.2 Storage vs Discharge to Estimate Groundwater Residence Time

Assuming the conceptual model employed in the numerical modelling (section 2.3), the estimated

turnover time for the basin can be estimated by dividing the average discharge rate per year by the

total storage of the aquifer. The storage of the aquifer S is estimated as:

S=A x bxs

where:

S is the groundwater stored in the aquifer

A is the area of the aquifer= 4637 km2 (4.637 x 109 m2)

b is the aquifer thickness = 100 m

sis the specific yield of the aquifer= 0.04

s = 4.637 x 109 x 100 x 0.04

S = 1.8548 x 1010 m3

the aquifer discharges on average approximately 10 m3/sec = 3.78x108 m3/yr

the estimate of the turnover time is the groundwater stored divided by the discharge

1.8548 x 1010 m3 / 3.78 x 108 m3/yr

= 49 years






Groundwater Modelling o f the Oolloo Dolostone

4.1.3 Particle Tracking to Estimate Groundwater Residence Time

The particle tracking computation methods are based on the Darcian velocity distributions determined

from the steady state head distribution (Anderson and Woessner, 2002).

where

vd = darcy velocity

K = hydraulic conductivity

& = specific yield

az = groundwater gradient a

This technique can provide point related information about groundwater age in the form of isochrones,

which are often used to delineate well capture zones. It should be noted that particle tracking

simulates advective transport and neglects to include dispersion processes.

The hydraulic head determined from the steady state simulation is independent of porosity, however,

as noted above, to determine the particle track of the plume migration using the Darcy velocity a

porosity is required, a porosity of 0.04 and an aquifer thickness of 100 meters was employed.

The simulations have been presented in isochrones (the distance covered by a "particle" for a given

time) to show the migration of a water "particle". The results are presented in Figure 22 "X" markers

at the head of the particle track indicate a time of one year, whilst "'Y " indicates a travel time of

50 years.

The particle tracking indicates that the residence time of the groundwater in the Oolloo Dolostone is

generally younger than 100 years as evidenced by the particle tracks originating near the Katherine

River. Water recharging closer to Stray Creek shows residence times of the order of a decade or so.

It could therefore be argued that an average residence time of -50 years is a reasonable assertion.

This estimate is in line with the previous analytical estimates.

Dille printed 22 November 2005 Drue Last Modified: 22 November 2005



T

+ T

+

• • •

0 5 10 20 30

Kilometres

• •

Groundwater Modelling oflhe Oolloo Dolostone

• +

• +

lsocrone Marker

1 yr

+ 10 yrs

• 20 yrs

t 40 yrs

T 50 yrs

Particle Track

- Major Drainage

~ Oolloo Extent

Figure 22 Particle tracking results from the calibrated transient model. "X" markers at the head of the

particle tracking indicate a time of one year, whilst " ~ " indicates a travel time of 50 years.



Depanrnent of Nat11r11I Resources, Environment and The Ans


I I I I I I I I I I I I I I I I I I I I l) ___ _


5 Conclusions

• Initial modeling of the Oolloo Dolostone indicates that the conceptual model is valid. However,

further refinement is required before the groundwater model can be implemented to assess the

effects of groundwater pumping on discharge to the river. The major areas where refinement is

required relate to the improved representation of recharge, spring inflows and wet season river

heights in the model.

• Recharge events for the model area need to take into account the variable nature of the rainfall

across the study area. There is an increase in average rainfall going towards the coast, it is also

suggested that some rainfall events in the northwest of the study area may not be represented in

the records from the southeast of the study area.

Da1e printed 22 November 2005 Status: FINAL Page 36

Depanmcnt of Natural Resources, Environment and The Ans Dale Last Modified: 22 November 2005

Groundwater Modelling of the Oolloo Dolostoae

6 Recommendations

• Inclusion of gauged stream heights to be used for the transfer boundary, this will provide a closer

simulation of the recharge/discharge processes occurring during the wet and dry seasons. This

would involve:

o Survey groundwater monitoring sites to obtain actual stream heights

• An upgrade of dry season river flow data contained in Hydsys for gauging stations G8140040 and

G8140067 located on the Daly River is required to remove discrepancies between Hydsys flows

(generated from river heights and rating curves) and actual gauged flows.

• Include rainfall data from the northwest of the study area and determine the relationship to

potential recharge, as has been completed for the Katherine region.

• Locate springs and define actual spring zones in river (rather than making entire river bed a

spring/discharge)

• Include assessment in the variation in recharge rate associated with natural vegetation and

cleared in areas where development is occurring/expected.

• Scenario modelling - what do we see as the future developments- land clearing, groundwater

pumping.

• Riparian evapotranspiration could be included, although this is only a small component of the

water balance.

• Identify sites where additional groundwater level data is required;

Date printed 22 November 2005 Date Last Modified: 22 Novernbes- 2005






7 References

Anderson, M. P. and Woessner, W. W., (2002) Applied groundwater modelling: simulation of flow and

advective transport, Elsevier (USA)

Diersch, H.-J .G., (2004), FEFLO~ 5.1 Users Manual, WASY - Institute for Water Resources

Planning and System Research, Berlin, Germany.

Herczeg, A., (2004), 14C Ages for Groundwaters in the Daly River Region, Northern Territory, CSIRO

Land and Water

Jolly, P.J ., (2002), Daly River Catchment Water Balance, NTG Report No. 10/2002

Jolly, P.J., George, D., Jolly, I., and Z Spiers, (2000), Analysis of Groundwater Fed Flows for the

Flora, Katherine, Douglas and Daly Rivers, NTG Report No. 36/2000

Tickell , S.J., (2002a), A Survey of Springs along the Daly River, NTG Report No. 06/2002

Tickell , S.J., (2002b), Water Resources of the Oolloo Dolostone, NTG Report No. 17/2002

Tickel, S.J., (2003), Carbon Dating of Groundwaters in the Oolloo Dolostone Aquifer, NTG Report No. 21/2004




LI _ _____ _


Appendix A Oolloo Monitoring Bores

Station Easting Northing Completion Rlmp Completed SWLRL Monitoring Monitoring

Date (mAHD) SWL (mAHD) Commenced Ceased

(mBGL)

RN007509 133802.3 8413500 29/01 /1971 107.5 58.2 49.3

RN007595 133706.1 8413432 18/02/1971 110.3 57.7 52.6 3/05/1974 Present

RN008660 170461 8362829 22/11/1974 120.7 16.3 104.4 24/10/2000 Present

RN020614 87747.5 8466984 19/12/1980 42.8 16.18 26.6 22/08/1985 Present

RN021717 100642.2 8451881 20/10/1982 71 .4 22108/1985 Present

RN021830 92661.0 8435917 28/10/1982 56.2 11 .2 45.0 21/08/1985 Present

RN021833 100969.5 8452407 18/11/1982 73.1 7/03/1986 7/05/1987

RN025285 97488.6 8439119 20/05/1988 46.0 12.8 33.2 26/07/1988 Present

RN025286 94939 8436873 24/05/1988 47.6 12.5 35.1 26/07/1988 Present

RN025287 102309.2 8442830 27/05/1988 75.4 39.4 36.0 26/07/1988 Present

RN026555 150299.3 8372294 27/06/1988 83.1 13 70.1 6/09/2000 22/02/2001

RN030803 173765.1 8388082 19/10/1996 109.8 49.7 60.1 20/04/2002 Present

RN031101 92484.7 8457804 16/06/1997 42.0 2.68 39.3 28/01/1999 Present

RN032750 156367.3 8393206 1/09/2000 122.6 61.31 61 .3 24/10/2000 Present

RN032751 142749.3 8399793 6/09/2000 68.2 9.75 58.4 9/10/2000 Present

RN033033 110576 8434338 14/06/2001 70.9 13.7 57.2 16/04/2002 Present

RN033034 110616.8 8429468 20/06/2001 68.9 19.6 49.3 16/04/2002 Present

RN033035 113103.6 8441191 26/06/2001 85.5 16.6 68.9 16/04/2002 Present

RN033039 178468 8367454 1/08/2001 102.1 12.9 89.2 16/04/2002 Present

RN033130 189239 8378588 8/08/2001 135.8 58.9 76.9

RN033131 174367.4 8373019 10/08/2001 84.1 11.8 72.3

RN033132 174370.9 8373000 13/08/2001 85.1 12.2 72.9 8/10/2001 Present

Date printed 22 November 2005 Status: FINAL Department of Natural Resources, Environment and The Arts Date Last Modi fied: 22 November 2005 Page 39

---------------------

- - - - - - - -RN033133 174667.5 8372605 15/08/2001

RN033308 136723.8 8420625 13/11/2001

Note: Coordinates are in GDA94 MGA Zone 53


Status: FINAL Pagc40

-85.5

- -6.3

42.5

-79.2

- -8/10/2001

17/04/2002

Department ofNatural Resources, Environment and The Arts

- - - - -Groundwater Modelling of the Oolloo Dolostonc

Present

Present

- -


Appendix B Oolloo Dolostone Pumping Test Data

Screen Screen I Recommended Depths Slots I Diameter T Storage Test Rate Obs.

RN. Area Formation. Rate (Usec.) (mBGL) O~en Hole . (mm) (m2/d) Coefficient Test !):~e (Usec) Bore South of 120 min.

7595 Dorisvale Rd. Massive 53 - 87.5 open hole 19 constant rate 42.8 South of 180 min.

7838 Dorisvale Rd. Massive 66.7-125 open hole constant rate 10.9 360 min.

8014 Massive 30.5 - 103.5 open hole 125 constant rate 0.75 South of

8015 Dorisvale Rd. Bedded 3.5 0 - 47 slots 152 5 x ? min steps 583 3 x 150 min

47 - 71.45 open hole steps 533 300 min. constant rate 1422 300 min.

8109 DouglaslDaly Bedded 25 19.5 - 52.7 open hole 193 constant rate 25 South of 1000 min.

8660 Dorisvale Rd. Bedded 4 36.4 - 60 slots 117 constant rate 9 South of 1400 min.

8661 Dorisvale Rd. Bedded 6 34.8 - 58 slots 117 116.5 constant rate 12 4 x 100 min.

20628 Douglas/Daly Bedded 50 40.2 - 81.2 open hole 178 1490 7.50E-03 steps 37 - 56 20614 1440 min

2150 constant rate 56 5540 Jolly(1984) 56

480 min. 21671 Douglas/Daly Massive 5 44.6 - 51.0 slots 152 35 constant rate 11.4 21672 Douglas/Daly Bedded 10 57 -68 slots 152 2590 3 x 30 min 2.5 - 6.6

68-78 open hole 3x100min 7.4 - 15 with extended last step 10 480 min.

21673 DouglaslDaly Bedded 7 40.6 - 47 open hole 140 constant rate 7 21834 DouglaslDaly Massive 40 97_5 - 99.7 screens 152 350 5.00E-05 2 x 30min. Steps 21717

60 min. constant 105.7-110 152 689 rate 50

1430 min. 3320 constant rate 80

103 Jolly(1984) 30

Date printed 22 November 2005 Status: FINAL Departmcn1 of Natural Resources, Environment and The Arts Date Last Modified: 22 November 2005 Page41

- - - - - - - - - - - - - - - - - - - -

- ----------- - - - - - - - - - - -28956 Douglas/Daly Bedded

South of 30404 Dorisvale Rd Bedded

South of 30451 Dorisvale Rd Massive



30949 Douglas/Daly Bedded

31101 Douglas/Daly Bedded


33308 Douglas/Daly Massive

7626 Douslas/Dal~ Bedded


0.2

1.5

10

60

100

70

80

0.75

Status: FINAL Page42

80-98 slots 152

31 - 35 screens 154 16.6

20.8

69- 75 slots 140 244

screens & 78-119 slots 206 8054

79 - 95.1 screens 203 14972

28440

39.5 - 73.0 slots 202 16368

14483

33.1 - 99.4 slots 203 2304

5530

94.6-100.94 screens 206 3326 100.94 -119.01 slots 206

61.1-218.8 open hole 152 23700

78.7 - 91.0 slots 152 2


- - - - - - -Groundwater Modelling of the Oolloo Dolostone

36 min. constant rate 0.5 3 x 100 min. steps 0.5 - 2 1440 min constant rate 2.5 4 x 100 min. step test with Aug-14 extended last step to1440 min. 10 3 x 100 min. step test with 65 - 100 extended last step 30- 75

3 x 60 min. steps 3 x 100 min. steps 30-90 30803 1440 min constant rate 90 4 x 100 min. steps 70-118 1440 min constant rate 110 4 x 100 min. step test with 30 - 65 30948 extended last step 70 30949

1470 min constant rate 4 x 100 min. step lest with 100

extended last step to 1440

min. 3 x 100 min. step test 6- 18 1440 min constant rate 1.25

preliminary groundwater modelling i of the oolloo...

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