final report vol2-river basin study

Version 2

NORTH WEST IRRIGATION SECTOR PROJECT ADB Loan No. 2035 - CAM (SF) AFD Grant No. CHK 3003.01

RIVER BASIN AND WATER USE STUDIES, PACKAGE 2

Boribo and Dauntri Sub-basins

Final Report

Volume 2: Boribo Sub-basin

5 December 2006

Prepared for MINISTRY OF WATER RESOURCES AND METEOROLOGY by PRD Water & Environment in association with DHI Water & Environment

North West Irrigation Sector Project River basin and water use studies, Package 2

Version 2

Revisions Version 1: Summary expanded

New section 4.4: Water availability

Table 4.7 skipped, Table 8.2 changed

Version 1a: Section 4.4 expanded

A large part of Section 6.3 (water quality) shifted to new Appendix 5

Some wrong figures replaced in Appendix 3

Version 2: Section 3.5: Reference added to Appendix 3; short comment added about a new regulator at Bamnak

New Section 4.5 (allocation of manageable flows), with explanation of manageable flows, and estimates of water availability downstream of candidate sub-projects

Section 8.4: Livestock analysis revised

Acknowledgement The Package 2 Team expresses its sincere thanks to the staff members from the Provincial Departments, the district officers, and the many individual persons who have kindly taken time out to share their knowledge for the purpose of the present study. MOWRAM, the PMO, the PIUs and the TA Consultant have provided valuable guidance and shared data and knowledge, including results from monitoring programmes and previous related studies. MRC has kindly made data and GIS layers available for the purpose of the study.


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Summary The Northwest Irrigation Sector Project (NWISP) is being implemented by MOWRAM, with assistance from Asian Development Bank (ADB) and Agence Française de Développement (AFD). It has the overall objective of supporting the effort of the Royal Government of Cambodia to reduce poverty in rural areas of northwest Cambodia through enhanced agricultural production. The immediate objectives are to improve the use of water resources and to take advantage of the potential for irrigated agriculture.

One activity of the NWISP is a series of river basin and water use studies, which have the over-all objective 'to provide a framework leading eventually to institutional means for installing a scientifically informed approach for management of water quantity and quality in the target river basins'.

The river basin and water use studies will provide a part of the basis for subsequent master planning, and for design and feasibility studies of irrigation schemes to be conducted later on under the NWISP.

Package 2 of these studies covers Dauntri Sub-basin in Battambang and Pursat Provinces, and Boribo Sub-basin in Pursat and Kg Chhnang Provinces (and with a small corner in Kg Speu Province).

The present 'Final Report, volume 2' describes the water balance and water uses in Boribo Sub-basin.

The work has been based on data and information available from the Commune Database, MOWRAM, MRC and others, as well as comprehensive field surveys conducted under the present study. The analyses have been supported by numerical river basin modeling of water balance and water quality.

A summary of the average water balance and the present water utilization is shown in the following table.

Boribo Sub-basin (St. Bamnak, St. Boribo, and St. Thlea Maam) Area: 1,499 km2 (39 percent of which is more than 100 m above mean sea level) Cultivated (rice) area (2005): 288 km2, of which wet season irrigated: 109 km2 (actual), 239 km2 (potential) dry season irrigated (2 crops per year): 20 km2 (actual), 72 km2 (potential) Population (2004): 52,774

Annual water balance, present conditions, 4 out of 5 years

Rainfall Evaporation Storage and losses

Water availability

Domestic uses

Irrigation uses

Livestock uses

Outflow

m3/s m3/s m3/s m3/s m3/s m3/s m3/s m3/s

54.1 35.0 -0.3 19.4 - 1.1 - 18.3

l/s/km2 l/s/km2 l/s/km2 l/s/km2 l/s/km2 l/s/km2 l/s/km2 l/s/km2

36.1 23.3 -0.2 12.9 - 0.7 - 12.2

'-' means 'less than 0.05'


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Boribo Sub-basin has 2 schemes that have been identified as candidate sub-projects under the NWISP. The estimated manageable water availability is summarized below.

Water availability at candidate sub-projects

Bamnak Tram Mneash Tram Mneash alone,

low estimate (a) To share with

Bamnak, high estimate (a)

m3/s m3/s m3/s

J 0,7 0,7 1,3

F 0,3 0,3 0,6

M 0,1 0,1 0,3

A 0,1 0,1 0,1

M 1,2 1,3 2,5

J 2,7 2,7 5,5

J 5,8 5,6 11,3

A 12,1 12,0 24,1

S 16,6 16,5 33,1

O 12,7 12,6 25,3

N 4,1 4,0 8,1

D 1,6 1,6 3,2

The water availability is the estimated availability in 4 out of 5 years under present conditions The estimate includes present withdrawals for irrigation; and present and future withdrawals for domestic and livestock The estimate excludes any future expansion of irrigation withdrawals (a) The water availability at Tram Mneash is influenced by the implementation of the Bamnak scheme and on the operation

of the Bamnak diversion. The low and high estimates are based on assumptions about the future operation. Please refer to text for details

No allocation has been made for in-stream demands

North West Irrigation Sector Project River basin and water use studies, Package 2 i

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Contents Acronyms and abbreviations..................................................................................................................vii Study tasks ........................................................................................................................................... viii Terminology............................................................................................................................................ix Names .....................................................................................................................................................ix Location map............................................................................................................................................x 1 Introduction .........................................................................................................................1 2 Geography ...........................................................................................................................2

2.1 Data ........................................................................................................................2 2.2 Population, administrative boundaries ...................................................................2 2.3 Elevations, land use, soils ......................................................................................4 2.4 Irrigation.................................................................................................................7

3 Hydrology............................................................................................................................9 3.1 Data ........................................................................................................................9 3.2 River network and catchment delineation ..............................................................9 3.3 Rainfall and evaporation ......................................................................................12 3.4 Streamflow ...........................................................................................................13 3.5 Regulation ............................................................................................................17

4 Water uses and water balance............................................................................................19 4.1 Water uses ............................................................................................................19 4.2 Water balance.......................................................................................................20 4.3 Candidate sub-projects .........................................................................................31 4.4 Water availability .................................................................................................34 4.5 Allocation of manageable flows...........................................................................37

5 Morphology, floods and drought .......................................................................................41 5.1 Data ......................................................................................................................41 5.2 Morphology..........................................................................................................41 5.3 Floods and drought...............................................................................................44

6 Aquatic environment .........................................................................................................46 6.1 Data ......................................................................................................................46 6.2 Pollution loads......................................................................................................46 6.3 Water quality........................................................................................................51 6.4 Implications of irrigation development ................................................................54

7 Fisheries.............................................................................................................................59 7.1 Thlea Maam/Kompong Lor River........................................................................59 7.2 Boribo River.........................................................................................................60

8 Socio-economics................................................................................................................61 8.1 Data ......................................................................................................................61 8.2 Socio-economic context .......................................................................................61

North West Irrigation Sector Project River basin and water use studies, Package 2 ii

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8.3 Water utilization...................................................................................................67 8.4 Economic analysis................................................................................................76 8.5 Water user groups ................................................................................................84

References..............................................................................................................................................86

Appendix 1: Thematic maps ..................................................................................................................87 Appendix 2: Data files ...........................................................................................................................90 Appendix 3: Water management structures ...........................................................................................92

St. Boribo...........................................................................................................................92 St. Bamnak .......................................................................................................................93 St. Thlea Maam ................................................................................................................94

Appendix 4: Water balance tables..........................................................................................................95 Appendix 5: Water quality simulations................................................................................................127

A5.1 General ...............................................................................................................127 A5.2 Present conditions ..............................................................................................128 A5.3 Implications of irrigation development ..............................................................131

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Figures 2.1: Communes in Boribo Sub-basin 2.2: Land elevations in Boribo Sub-basin 2.3: Land elevation distribution in Boribo Sub-basin 2.4: Land use in Boribo Sub-basin 2.5: Irrigation schemes in Boribo Sub-basin 3.1: River network, Boribo Sub-basin (detailed and simplified) 3.2: Catchment boundaries 3.3: Comparison of catchment boundaries from different studies 3.4: Observed and rated discharge at Boribo 3.5: Rated discharge plot. Boribo versus Bac Trakoun 3.6: Rated discharge at Bac Trakoun versus that of Peam 3.7: Discharge relation between Bac Trakoun and Peam 3.8: Average monthly rainfall versus runoff, Maung Russey 3.9: Average monthly rainfall versus runoff, Kg.Tralach 3.10: The Bamnak Diversion 3.11: Diversion structures at Bamnak 4.1: MIKE Basin model of the Boribo Sub-basin 4.2: Schematic representation of sub-catchments 4.3: Rated and observed discharge at Boribo 4.4: Simulated and observed/rated discharge at Boribo 4.5: Water availability in April, present conditions 4.6: Specific water availability in April, present conditions 4.7: Water availability in September, present conditions 4.8: Specific water availability in September, present conditions 4.9: Specific water availability, yearly average, present conditions 4.10: Effective drainage area of Boribo Sub-basin 4.11: Schematization of candidate sub-projects 5.1: Examples of bank erosion, St. Boribo and St. Bamnak 5.2: Erosion 5.3: Accretion 6.1: Amount of annual BOD load by sub-catchment 6.2: Location of the sub-catchments of the Boribo Sub-basin 6.3: Amount of annual Total Nitrogen load by sub-catchment 6.4: Amount of annual Total Phosphorous load by sub-catchment 6.5: Total specific runoff and estimated base-flow for Boribo 6.6: Calculated concentrations at Kg Preah Kokir

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6.7: Simulated discharge at the outlet of St. Boribo 6.8: Simulated discharge at the outlet of St. Thlea Maam 6.9: Calculated concentrations at the outlet of St. Boribo 6.10: Calculated concentrations at the outlet of St. Thlea Maam 8.1: Household wealth 8.2: Structure of household cash income 8.3: Main sources of drinking water in Pursat 8.4: Irrigated cropping areas in Boribo Sub-basin 8.5: Present and future extractive water demands 8.6: Value added by water to livelihoods A5.1: Average concentration of BOD for 2000 and 2001 A5.2: Maximum concentration of BOD for 2000 and 2001 A5.3: Average concentrations of NH4 for 2000 and 2001 A5.4: Maximum concentrations of NH4 for 2000 and 2001 A5.5: Average concentrations of NO3 for 2000 and 2001 A5.6: Maximum concentrations of NO3 for 2000 and 2001 A5.7: Average concentration of BOD for the candidate sub-projects A5.8: Maximum concentration of BOD for the candidate sub-projects A5.9: Difference in BOD concentrations between the candidatesub- projects and the present situation A5.10: Average concentrations of NH4 for the candidate sub-projects A5.11: Maximum concentrations of NH4 for the candidate sub-projects A5.12: Difference in NH4 concentrations between the candidate sub-projects and the present situation A5.13: Average concentrations of NO3 for the candidate sub-projects A5.14: Maximum concentrations of NO3 for the candidate sub-projects A5.15: Difference in NO3 concentrations between the candidate sub-projects and the present situation A5.16: Difference in total-phosphorus concentrations between the sub-candidate projects and the present situation

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Tables 2.1: Administrative units with area and population 2.2: Land use 2.3: Forest cover 2.4: Irrigation schemes 3.1: Distribution of annual rainfall 3.2: Pan evaporation 4.1: Estimate of future domestic demand 4.2: Summary water balance, present conditions 4.3: Water balance for increased domestic consumption 4.4: Water balance in case of an assumed climate change 4.5: Water balance for a 50% - 50% distribution at Bamnak 4.6: Water balance for the lower part of Thlea Maam 4.7: Estimated water availability at Bamnak 4.8: Estimated water availability at Tram Mneash 4.9: Manageable flows downstream of candidate sub-projects 4.10: Rainfall deficit, Boribo sub-basin 4.11: Irrigable areas 5.1: Cultivation areas affected by floods and drought 5.2: Occurrence of floods and drought 6.1: Estimated BOD load reaching the river in each subcatchment 6.2: Estimated nitrogen load reaching the river in each subcatchment 6.3: Estimated phosphorus load reaching the river in each subcatchment 8.1: Summary socio-economic indicators 8.2: Cultivated areas 8.3: Irrigated crop areas 8.4: Future demands for irrigation 8.5: Present livestock water demands 8.6: Change in livestock population, Cambodia 8.7: Projected livestock water demands 8.8: Projected domestic consumption demands 8.9: Crop budget summary 8.10: Crop budgets for NE Thailand 8.11: Livestock value 8.12: Average tariff and unit production costs 8.13: Net benefits of domestic water supply

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8.14: Gross value of the potential fish yield 8.15: Water User Groups A2.1: Time series data A2.2: Data tables A4.1: Summary water balance, base situation A4.2: Summary water balance, increase in domestic water use A4.3: Summary water balance, climatic change. A4.4: Summary water balance, candidate project 50%-50% distribution A4.5: Summary water balance, candidate project 100%-0% distribution A4.6: Water balance on monthly basis, base situation A4.7: Water balance on monthly basis, increase in domestic water use A4.8: Water balance on monthly basis, climatic change A4.9: Water balance on monthly basis, candidate project 50%-50% A4.10: Water balance on monthly basis, candidate project 100%-0%

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Acronyms and abbreviations ADB : Asian Development Bank

AFD : Agence Française de Développement

CNMC : Cambodia National Mekong Committee

DoE : (Provincial) Department of Environment

EIA : environmental impact assessment

FWUC : farmer's water user community

GW : groundwater

IWRM : integrated water resources management

MAFF : Ministry of Agriculture, Forestry and Fisheries

MCM : million cubic metres

MoE : Ministry of Environment

MOWRAM : Ministry of Water Resources and Meteorology

MRC : Mekong River Commission

NWISP : North West Sector Irrigation Project

PDAFF : Provincial Department of Agriculture, Forestry and Fisheries

PDWRAM : Provincial Department of Water Resources and Meteorology

PIU : Project Implementation Unit (of the NWISP)

PMO : Project Management Office (of the NWISP)

PRA : participatory rural appraisal

RGC : Royal Government of Cambodia

ToR : terms of reference

WQ : water quality

WUC, WUG : water user community, water user group

WUP-FIN : Finnish component of MRC's Water Utilization Programme

WUP-JICA : Japanese component of MRC's Water Utilization Programme

North West Irrigation Sector Project River basin and water use studies, Package 2 viii

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Study tasks No. Item Reference

Inception phase – Collection of information

1 Collection of general data and information (cross-cutting)

2 Collection of hydro-meteorological and hydraulic data and information Vol1 Sect 4.1

3 Field surveys, inspection of monitoring stations, flood damage assessment (cross-cutting)

4 Consultation meetings at province, commune and village level (cross-cutting)

5 Basic thematic maps Vol2&3 App 1

6 Approach to hydrological analysis Vol1 Sect 5.3, Vol1 App 2

7 Technical workshop with MOWRAM/PDWRAM (reported separately)

Hydrological studies and modelling

8 Review of river monitoring network Vol1 Sect 9.1

9 Hydrological analysis Vol2&3 Ch 4

10 Morphological analysis Vol1 6.2, Vol2&3 Sect 5.2

11 Flood characteristics Vol1 Sect 6.3, Vol2&3 Sect 5.3

12 Fish, fish habitats and fish migration Vol1 Sect 7.2, Vol2&3 Ch 7

13 Support to selecting candidate NWISP subprojects Vol1 Sect 9.2, Vol2&3 Sect 4.3

Analysis of water uses

14 Remote sensing analysis and field survey (cross-cutting)

15 Forestry and land use survey Vol1 Sect 2.3, Vol2&3 Sect 2.3

16 Field surveys of water uses Vol1 Sect 5.2, Vol2&3 Sect 4.1

17 Inventory of water users committees

18 Quantification of consumptive and non-consumptive water uses Vol1 Sect 5.2, Vol2&3 Sect 4.1

19 Economic analysis of water utilization Vol1 Ch 8, Vol2&3 Ch 8

20 Economic analysis of long-term development opportunities Vol1 Sect 8.4

Water balance

21 Water balance for the sub-basins Vol2&3 Sect 4.2, Vol2&3 App 4

22 Assessment of trends in water availability and demand (same)

23 Assessment of impacts of each subproject on downstream water uses Vol2&3 Sect 4.3, Vol2&3 App 4

24 NWISP candidate sub-projects Vol2&3 Sect 4.4

Environmental aspects

25 Existing WQ data and classification Vol1 Sect 7.3

26 Point and non-point sources Vol1 Sect 7.4, Vol2&3 Sect 6.2

27 Aquatic environment in representative reaches Vol2&3 Sect 6.3

28 Environmental flows in representative reaches, and assessment of enforcement Section 9.6

29 Evaluation of fish passages Vol2&3 Ch 7

Reports – progress meetings - workshops

30 Inception report (reported separately)

31 Sub-basin reports (reported separately)

32 Surface water and groundwater maps Vol2&3 Sect 4.2 (no GW maps)

33 Response to data shortcomings (cross-cutting)

34 Project completion report (reported separately)

35 Project completion workshops (reported separately)

36 Weekly progress statements (reported separately)

37 Liaison with RGC and provincial agencies and community representatives (cross-cutting)

38 Knowledge-sharing with designated counterpart staff (cross-cutting)

North West Irrigation Sector Project River basin and water use studies, Package 2 ix

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Terminology Following a discussion at the Inception Workshop in Pursat on 11 July 2006, and with a view to the terminology applied in the Terms of Reference, the following suggestions are made:

Terms used in the present study:

Catchment: The general term for an area from where the surface flow proceeds towards a specific location (like a cross-section of a river or canal, or a lake or reservoir). A catchment is delineated by a catchment boundary. It can be a river basin or a part of a river basin. Same as drainage area

Catchment boundary: The boundary of a catchment (or a river basin or a sub-catchment). The surface flow of rain falling on each side of the boundary will proceed towards different locations. A review of catchment boundaries is a part of the present study

River basin: The catchment of a whole river (with its tributaries). In the present study, this term is used both for the Mekong Basin and the Tonle Sap Basin. (In some other studies, the Tonle Sap Basin is referred to as a sub-basin of the Mekong Basin)

Study area (Package 2): The Daun Try/Svay Don Keo and the Boribo/Thlea Maam Sub-basins

Sub-area: An area that is a part of another area

Sub-basin: The catchment of a tributary, and hereby a part of river basin. The present study deals with the Daun Try/Svay Don Keo Sub-basin and the Boribo/Thlea Maam Sub-basin

Sub-catchment: A catchment that is explicitly a part of a larger catchment. In the present study, an irrigation scheme will receive water from a sub-catchment, and sub-catchments are used as units for the river basin modelling of water balance and water quality

Terms not used in the present study:

Drainage area or drainage basin: Same as a catchment (or a sub-catchment)

Watershed: (1) in English, same as a catchment boundary; (2) In American English, same as a catchment. Watershed management can cover different aspects of water-related management within a watershed, depending on the circumstances

Names Most rivers change their names along their course, often within short distances.

Different spellings are used for many rivers, streams and locations, for example Pursat/Pouthisat, Bamnak /Bomnork, Daun Try/Dauntry/Dauntri, Boribo/Baribour, etc.

St. Thlea Maam is also named St. Kompong Lar. MOWRAM applies the former name for data storage, while the latter name is commonly used in the area. Also, St. Thlea Maam has been used as the name for the adjacent St. Ou Srang in Pursat River Basin

St. Daun Try is also named St. Muong.

North West Irrigation Sector Project River basin and water use studies, Package 2 x

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Location map

1 450 000

1 400 000

1 350 000

300 000 350 000 400 000 450 000 500 000

300 000 350 000 400 000 450 000 500 000

1 500 000

1 450 000

1 400 000

1 350 000

1 500 000

North West Irrigation Sector Project River basin and water use studies, Package 2 1

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1 Introduction The Northwest Irrigation Sector Project (NWISP) is being implemented by MOWRAM, with assistance from Asian Development Bank (ADB) and Agence Française de Développement (AFD). It has the overall objective of supporting the effort of the Royal Government of Cambodia to reduce poverty in rural areas of northwest Cambodia through enhanced agricultural production. The immediate objectives are to improve the use of water resources and to take advantage of the potential for irrigated agriculture. It is intended to establish ten to twelve rehabilitated and sustainably operational small to medium-scale irrigation systems and other water control infrastructure.

The NWISP is managed by a Project Management Office (PMO) within MOWRAM, assisted by a TA Consultant (BCEOM/ACIL/SAWAC). The assistance by the TA Consultant includes guidance and supervision of the studies outlined in the present report.

One activity under the NWSIP is the 'River Basin and Water Use Studies, Package 2', covering Dauntri Sub-basin in Battambang and Pursat Provinces, and Boribo Sub-basin in Pursat and Kg Chhnang Province. This work is being carried out by PRD Water & Environment in association with DHI Water & Environment.

The scope of the river basin and water use studies is specified in the Terms of Reference prepared by MOWRAM. The overall objective is 'to provide a framework leading eventually to institutional means for installing a scientifically informed approach for management of water quantity and quality in the target river sub-basins'.

The aim is not a master plan nor a set of feasibility studies for selected sub-projects. Rather, the work will serve as a part of the basis for subsequent master planning and preparations for individual projects.

The Final Report comes in 3 volumes:

1 Methodology and general findings

2 Boribo Sub-basin

3 Dauntri Sub-basin

Data tables and thematic maps are submitted separately. Basic documentation has been indexed and compiled on a CD.

A report about Boribo Sub-basin was discussed at a workshop in Pursat on 19 September 2006. The present report is based on guidance received at the workshop as well as from the TA Consultant.


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2 Geography

2.1 Data This section relates to ToR, Task 1: Collection of general data and information

The physical geopgraphic description has been based on

• Land cover maps 1992/93, 1996/97 and 2002

• Satellite images (RADARSAT-1) 1998, 2000, 2002 and 2005 (showing topographical features and land use)

• Aerial photos (available for a part of the area only)

• Administrative boundaries: Country, province, district, commune and village (villages as point coverage)

• Topographical maps 1:50,000 and 1:100,000

• Digital Elevation Model with 50 m resolution

• Soil coverage digitized from 1,000,000 scale map

Various demographic information origins from the 2004 Commune Database. The commune is the basic unit for a substantial part of the geographic, agricultural and socio-economic data.

2.2 Population, administrative boundaries This section relates to ToR, Task 1: Collection of general data and information

Related data (submitted electronically) Area-population.xls Area and population (2002-04) within the study area; buffaloes,

cows, horses, goats, pigs, and poultry; families using fertilizer; by province, district and commune

In Boribo Sub-basin, the population density was 46 persons/km2 in 2004 and the population growth was 2.4 percent/year from 2002 to 2004.

There are no major urban settlements (such as provincial towns) in the study area. This influences the future population growth, which is expected to be much higher in urban areas than in rural areas.

Commune boundaries, areas and population are shown in the following figure and table.


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Figure 2.1: Communes in Boribo Sub-basin

Table 2.1: Administrative units with area and population, Boribo Sub-basin

Province District Commune Area (km2) Area within sub-basin (km2)

Population within sub-basin (2004)

Kg Chhnang Baribour Anhchanh Rung 68,2 26,6 1.810 Khon Rang 31,5 0,3 57 Kampong Preah Kokir 59,8 13,3 460 Melum 52,4 25,7 1.726 Phsar 36,1 20,9 2.916 Pech Changvar 55,7 14,0 836 Tuek Phos Chieb 350,2 84,0 1.413 Krang Skear 592,1 229,0 4.329 Pursat Kandieng Kanhchor 85,4 10,1 1.030 Krakor Ansa Chambak 213,7 3,1 91 Boeng Kantuot 46,9 23,7 2.803 Chheu Tom 190,8 172,2 9.516 Kampong Pou 74,0 45,0 3.602 Ou Sandan 85,2 59,3 3.156 Sna Ansa 87,6 14,0 724 Svay Sa 195,8 189,2 5.752 Tnaot Chum 169,1 145,1 9.092 Phnum Kravanh Prongil 1133,1 405,9 3.158 Sampov Meas Roleab 204,4 0,1 6 Kg Speu Aural Trapeang Chour 17,7 17,7 297 Total 1499,2 52.774

Data: Commune Database 2004 and GIS analysis


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2.3 Elevations, land use, soils This section relates to ToR, Task 1: Collection of general data and information

Related data (submitted electronically) Landuse.xls Land use within each sub-basin (2005), and forest cover within each

sub-basin (1993, 1997, 2002, 2005), and rate of change Geology.xls Geological classification of each sub-basin Protectedareas.xls Protected areas in each sub-basin

Elevations

The land elevation in the sub-basin is illustrated below. The highest elevation in Boribo Sub-basin is around 1,755 m (according to the 50 x 50 m resolution DEM). Cambodia's highest peak, Phnom Aoral (1,784 m), is located on the sub-basin boundary. 1

1 The 'Lonely Planet Guide' lists the height of Phnom Aoral at 1,813 m


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Figure 2.2: Land elevations in Boribo Sub-basin

Figure 2.3: Land elevation distribution in Boribo Sub-basin

0-20 m (17.1 pct)

20-50 m (16.3 pct)

50-100 m (27.6 pct)

> 500 m (10.2 pct)

200-500 m (10.3 pct)

100-200 m (18.6 pct)

Phnom Aoral (1,784 m)


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Land use and soils

The present land use (2005) is shown in the following figure, which provides an important characterization of the sub-basin: The major part is forest - evergreen, semi-evergreen or deciduous (shedding the leaves annually). There is some rainfed paddy area, and only small parts of other land use. Additional information is given in Tables 2.2 and 2.3.

Figure 2.4: Land use in Boribo Sub-basin

Data: Interpretation from Landsat ETM (2005)

Table 2.2: Land use (2005)

Land use Area (km2) Evergreen forest 235

Semi-evergreen forest 215

Deciduous forest 663

Other forest 52

Grassland 34

Dry season rice 0

Rainfed rice 288

Village 7

Water 4

Total 1.499


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Table 2.3: Forest cover (1993-2005)

Forest cover Rate of change 1993 1997 2002 2005 1993-97 1993-2002 1993-2005 km2 km2 km2 km2 percent percent percent Evergreen forest 235 235 235 235 0,0 0,0 0,0 Semi-evergreen forest 18 18 215 215 0,0 13,1 13,1 Deciduous forest 714 711 654 663 -0,2 -4,0 -3,4 Other forest 265 238 43 52 -1,8 -14,8 -14,2 Non-forest 267 298 351 334 2,1 5,7 4,5

Total 1.499 1.499 1.499 1.499 0,0 0,0 0,0

'0,0' means 'less than 0,005'

2.4 Irrigation This section relates to ToR, Task 1: Collection of general data and information

Related data (submitted electronically) Irrigation.xls Wet and dry season irrigated areas (actual and potential)

Many of the schemes were registered and evaluated under the so-called Halcrow study in 1994, conducted for the Mekong Committee (today's MRC). Some of them, including most candidate sub-projects, were re-visited and evaluated under NWISP in 2003. These studies are still relevant. When using them, however, it is noted that in some cases, both the scheme and the commune(s) have changed their names. The UTM coordinates provide the best identification.

Irrigation schemes are shown in the following table and figure. Additional information (including coordinates and water source) are included in the corresponding electronic file.

Table 2.4: Irrigation schemes in Boribo Sub-basin

District Name Commune Existing Potential Status Wet (ha) Dry (ha) Wet (ha) Dry (ha)

Krokor Bomnork Cheur Tom 900 300 2.300 800 CS, 2

Krokor Tram Mnas Dam Thnoat Chu 830 70 1.100 100 CS, 2

Krokor Thlea Maam Boeung Kan 873 50 1.700 100 2

Krokor Kampong Lar Kampong Po 250 20 300 150 2

Krokor Cham Kar Krouch Svay Sar 120 0 350 0 2

Krokor Trapeang Kantuot Boeng Kantuot 0 0 2

Boribo Lum Hach Pict Sangv 7.945 1.535 18.165 6.051 2

Total 10.918 1.975 23.915 7.201

Status: CS = candidate sub-project; 1 = poor; 2 = medium; 3 = good state of maintenance


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Figure 2.5: Irrigation schemes in Boribo Sub-basin

An overview of water management structures is given in Appendix 3.


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3 Hydrology

3.1 Data This section relates to ToR, Task 2: Collection of hydro-meteorological and hydraulic data and information

Related data (submitted electronically) [email protected] Daily, monthly and annual rainfall at Battambang (8 years), Kg

Chhnang (55 years), Pursat (60 years), Krakor (36 years), Kravanh (10 years), Svay Donkeo (6 years), Talo (6 years), Bamnak (15 years) and Boeung Khnar (7 years)

R@Pursat-12-05 Daily and monthly rainfall data from Pursat 1912-2005 (53 years), with summary statistics

[email protected] Monthly rainfall data from 16 stations from 2001-2004 (4 years), with summary statistics

[email protected] Monthly rainfall data from Battambang, Pursat and Kg Chhnang, from 1939, 1996, and 2001-05 (7 years)

[email protected] Daily and monthly evaporation at Pochentong 2000-04 and Siem Reap 1996-2000

[email protected] Daily water level at Kg Chhnang 1995-2004 (10 years) [email protected] Daily water level at Prek Kdam 1995-2004 (10 years) [email protected] Daily and monthly flow at Prek Kdam 1964-73 (10 years) [email protected] Daily water level and calulated flow at Boribo (St. 590101) Jun 98 -

Dec 05 (7.5 years) [email protected] Daily water level and calulated flow at Maung Russey (St. Dauntry)

(St. 5501101) Jun 01 - Dec 02 (1.5 years) [email protected] Flow records from St. Boribo (91 months), St. Dauntri (19 months),

and St. Pursat (72 and 58 months)

3.2 River network and catchment delineation This section relates to ToR, Task 9: Hydrological analysis

The river network has been established on the basis of satellite (RADARSAT-1) images; aerial photos (where available); and topographical maps 1:50,000 and 1:100,000. In addition, several reconnaissance visits have been made to locations where there was doubt about the network.

In addition to the detailed network, which forms the basis for the catchment delineation, a simplified network (of main rivers and streams) has been derived as a basis for the hydrological analysis.

Results are shown below, together with an overview of the study area catchments and adjacent catchments.

A comparison has been made between the catchment boundaries established in this way and catchment boundaries from other studies:

• Sub-Basin Profiles of the Tonle Sap, ADB website, http://www.adb.org/ Projects/ Tonle_Sap/atlas/default.asp;

• Ly Sarann, Someth Paradis, Seng Bunrith, And Men Nareth: Potential of Water Resources of Pursat Basin for Irrigation Development. Proceedings of


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the 2nd International Symposium on Sustainable Development in the Mekong River Basin, Phnom Penh, 16th – 18th September 2006, p. 77; and

• TA 4756-CAM, Tonle Sap Lowland Stabilization Project: Water Availability Report, September 2006

Figure 3.1: River network, Boribo Sub-basin (detailed and simplified)

Figure 3.2: Catchment boundaries

A sample result of the comparison are shown below. The boundaries complied well, except for one small area, where it was found that the surface runoff is intercepted by an elevated road.

50 km

Tonle Sap Basin boundary

Thlea Maam - Boribo St. Pursat

Daun Try - Svay Don Keo

St. Battambang

St. Sangker

St Thlea Maam

St Bamnak

St Boribo


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Figure 3.3: Comparison of catchment boundaries from different studies

Approximate topographical divide (not extremely well defined, due to the flat land)

Elevated road without culverts, expectedly intercepting the surface runoff

TA 4756-CAM, Tonle Sap Lowland Stabilization Project: Water Availability Report, September 2006

Present study


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3.3 Rainfall and evaporation This section relates to ToR, Task 9: Hydrological analysis

Related data (submitted electronically) [email protected] Daily, monthly and annual rainfall at Battambang (8 years), Kg

Chhnang (55 years), Pursat (60 years), Krakor (36 years), Kravanh (10 years), Svay Donkeo (6 years), Talo (6 years), Bamnak (15 years) and Boeung Khnar (7 years)





Rainfall

The long-term record from Pursat has been chosen as the basis for the water balance analysis presented in this study. The rainfall in Boribo/Thlea Maam Sub-basin has been estimated as the rainfall in Pursat plus 3 percent.

Hereby, the analysis builds on (i) 53 years of 'good' data (which is fully acceptable); (ii) a relatively safe estimate of the 4-out-of-5 years rainfall; (iii) another relatively safe estimate of the variation along the Great Lake; and (iv) a less safe assumption that the rainfall is homogenous within the sub-basin.

The resulting estimate of rainfall in the study area is shown below.

Table 3.1: Distribution of annual rainfall, Boribo Sub-basin (mm/year or mm/month)

1986 4 of 5 yrs Average 1995 Year 897 1.156 1.360 2.143

Jan 0 3 4 0

Feb 0 4 5 25

Mar 5 37 43 36

Apr 20 68 80 74

May 85 131 154 245

Jun 130 115 136 176

Jul 96 122 143 294

Aug 206 159 187 230

Sep 156 207 243 436

Oct 111 198 233 404

Nov 48 97 114 190

Dec 40 16 19 32

Data: Estimated as Pursat plus 3 percent


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Evaporation

Evaporation data are sparse. The following figure and related table are based on 9 station-years of 'accepted' data from two different stations - Battambang and Pochentong, which are located on each side of the study area. There was no overlap between the 'accepted' records, but the difference between the stations remained within 5 percent on an over-all average basis. The average variation from one year to another on a monthly basis was +/- 24 percent.

Table 3.2: Pan evaporation (mm)

J F M A M J J A S O N D Year

Lowest 112 110 114 137 120 115 116 83 97 105 83 93 1,543

Average 130 135 167 163 154 143 151 139 128 124 125 133 1,691

Highest 156 184 217 203 200 167 167 171 155 147 150 183 2,000

Data: Battambang (1996-2000) and Pochentong (2001-04) (9 years)

The actual evaporation will be less than the pan evaluation values, depending on the so-called pan coefficient and also on the vegetation cover (that varies very much over the year in the study area). In view of the uncertainties, a conservative estimate of 0.7 times the pan evaporation has been applied.

3.4 Streamflow This section relates to ToR, Task 9: Hydrological analysis

Related data (submitted electronically) [email protected] Daily water level and calulated flow at Boribo (St. 590101) Jun 98 -

Dec 05 (7.5 years) [email protected] Daily water level and calulated flow at Maung Russey (St. Dauntry)

(St. 5501101) Jun 01 - Dec 02 (1.5 years)

Stung Boribo

There is no back water effect at the measurement site, wherefore the type of the rating curve is Q = f(H), where H is the water level at Boribo. This type is suggested by Le van Sanh (June 02). The correlation coefficient is 0.97. The rating curve has the formula (JICA 2004):

( )22588.056.23 −⋅= BoriboHQ

Rating curve for Stung Boribo at Boribo

Q=f(H), data from 1998,1999, 2001

0.00

0.50

1.00

1.50

2.00

2.50

0.00 20.00 40.00 60.00 80.00 100.00 120.00

Q [m3/s]

Gau

ge h

eigh

t [m

]


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Stung Pursat

There is no indication that Bac Trakoun station is subject to back water effects. Further Carbonnel and Guiscafre suggest that the rating curve is of the type Q=f(H), where H is the water level at Bac Trakoun. The correlation coefficient is very good, 0.99. The formula reads (JICA 2004):

The rating curve formulas for the stations above are applied for generation of discharge. As an example, the rated discharge at Boribo is presented in the following figure.

Figure 3.4: Observed and rated discharge at Boribo

The fluctuations in the rated discharge in the recession period and dry season are not immediately explainable. The sudden changes results from sudden changes in water level, which could be a results of some control in the river system.

The generated discharges from all three stations are applied for model calibration and general analysis in the study.

The discharges at two stations in a catchment may be correlated. The more uniform the catchment is with regards to topography, soil characteristics and vegetation cover, the more likely are the discharges of the sub-catchments to be correlated.

( )20856.05.25 −⋅= BakTrakounHQ

Rating curve Stung Pursat at Bak Trakoun

Q=f(H), data from 1998,1999, 2001

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.00 100.00 200.00 300.00 400.00 500.00 600.00

Q [m3/s]

Gau

ge h

eigh

t [m

]

Observed and rated discharge at Boribo, Stung Boribo

0

20

40

60

80

100

120

140

160

180

200

01/01/98 01/01/99 01/01/00 31/12/00 01/01/02 01/01/03 01/01/04 01/01/05 01/01/06

Dis

char

ge [m

3/s]

Rated discharge

Observed discharge


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Discharges from different catchments are not likely to be well correlated. An example of this is shown below, where the daily discharge at Boribo is correlated with the discharge at Pursat. The year selected is 2001. It is seen from the plot that there is no correlation.

Figure 3.5: Rated discharge plot for 2001. Boribo versus Bac Trakoun

If two stations within the same catchment are selected then a correlation can be expected. In Figure 4.15 the rated discharge at Peam (upper part of Stung Pursat) is plotted against the rated discharge at Bac Trakoun (lower part of Stung Pursat). Although there is some scatter in the data, there seems to be a trend between the two data sets. There are several ways to plot the discharges. In Figure 4.16 the square root of the product of the two discharges are plotted against the discharge at Peam. The correlation is acceptable.

Figure 3.6: Rated discharge at Bac Trakoun Figure 3.7: Discharge relation between versus that of Peam, year 2001 Bac Trakoun and Peam, year 2001

Rated discharge at Boribo versus rated discharge at Bac Trakoun, year 2001

0

100

200

300

400

500

600

0 10 20 30 40 50 60 70

Daily discharge at Boribo [m3/s]

Dai

ly d

isch

arge

at B

ak T

rako

un [m

3/s]

Rated discharge at Bac Trakoun versus rated discharge at Peam, year 2001

y = 0.0004x2 + 0.1179x + 2.8326R2 = 0.7595

0

50

100

150

200

250

0 100 200 300 400 500 600

Daily discharge at Bac Trakoun [m3/s]

Dai

ly d

isch

arge

at P

eam

[m3/

s]

Discharge relation between Bac Trakoun and Peam, rated daily data year 2001

y = 0.5874x - 1.8781R2 = 0.9529

0

50

100

150

200

250

0 50 100 150 200 250 300 350

Sqrt(Q_BacTrakoun * Q_Peam)

Dai

ly d

isch

arge

at P

eam

[m3/

s]


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In conclusion, the streamflow analysis - drawing comprehensivlely on the previous JICA studies - provide a acceptable (and useful) understanding of the flow in the downstream part of St. Boribo, which is believed to provide a valid basis for describing the rainfall-runoff conditions in the Boribo Sub-Basin.

Rainfall versus discharge

The runoff in a catchment is clearly a result of the amount of rainfall. However, in terms of establishment of a relation between the rainfall and runoff, the outcome may be more of less successful. The reasons are several: The selected rainfall station(s) may not be representing the entire catchment, the infiltration rate may be unevenly distributed throughout the catchment, and there may be flow regulation and storage occurring, just to mention a few.

The relation between the rainfall and runoff is likely to be better on bi-weekly or monthly time scale rather on a daily scale. One source of uncertainty in the present study is that the discharges are mostly rated and that the number of rainfall stations are few and of different quality.

Examples of relations between rainfall and runoff is seen in the figures below, where the average monthly rainfall is plotted against the average monthly runoff at Maung Russey and at Boribo respectively. There is no clear tendency, but the data suggest that threshold values of rainfall exist in order to generate substantial runoff. One problem with this kind of plots is that the seasonal development of e.g. soil saturation is embedded in the data. Hence a moderate rainfall in the late monsoon period may give a higher runoff than a similar amount of rainfall occurring in the beginning of the monsoon.

Figure 3.8: Average monthly rainfall Figure 3.9: Average monthly rainfall versus runoff, Maung Russey versus runoff, Kg.Tralach

Rainfall versus runoff - Maung Russey

0

5

10

15

20

25

30

35

40

45

0 50 100 150 200

Average monthly rainfall at Maung (mm/month)

Ave

rage

mon

thly

runo

ff at

Mau

ng(m

3/s)

Rainfall versus runoff - Boribo

0

5

10

15

20

25

30

0 100 200 300

Average monthly rainfall at Kg.Tralach (mm/month)

Ave

rage

mon

thly

run

off a

t Bo

ribo

(m3/

s)


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3.5 Regulation This section relates to ToR, Task 9: Hydrological analysis

Overview

An overview of regulation is shown in Appendix 3. For details, please refer to the thematic 'Sub-basin map', submitted separately.

The Bamnak Diversion

The Bamnak Diversion distributes water from the St. Bamnak catchment between the two downstream catchments of St. Boribo and St. Thlea Maam (also named St. Kompong Lar).

About 300 m downstream of the Boribo/ThleamMaan junction a diversion channel built under the Khmer Rouge period conveys water to the Thleam Maam catchment. This channel usually conveys water from August and onwards in the monsoon, but is left dry the remaining part of the year. Prior to 2002, however, most of the flow was diverted to Thleam Maan catchment and only a smaller part to Boribo.

The sudden change in flow distribution has created significant erosion on the Bamnak/Boribo channel.

Figure 3.10: The Bamnak Diversion controls the flow distribution between the Boribo and Thlea Maam rivers. (Photo 5 July 2006)

Pursat


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Nearby structures comprise a bridge on the Khmer Rouge channel; a destroyed Khmer Rouge gate located downstream of the Khmer Rouge channel (but on the old Bamnak river course); and an old overflow weir built by Sihanouk in the 1960’ies, around 100 m downstream (and still on the old Bamnak).

Figure 3.11: Diversion structures at Bamnak

Restoration of the regulator

The flow distribution between St. Boribo and St. Thlea Maam is quite significant to the present and future water users in both catchments, as it will be clearly exemplified in the following chapter. Particulalry in St. Boribo, present water uses depend on inflow from upstream (i.e. from the Bamnak Sub-catchment) in February, March and April (whereas in January, the availability and the demand more or less balance each other, and in the rest of the year, the water availability exceeds the present demand, even in the absence of an inflow from St. Bamnak) 2. Also, the flow distribution affects the water availability for the Tram Mneash candidate sub-project on St. Thlea Maam.

Restoration of the regulator would provide a tool for orderly and predictable operation, which would, expectedly, be a benefit for all downstream water users, assuming that a small but reliable flow can be equally valuable as a higher but less reliable flow.

2 Please refer to Table 4.9

Old channel (with diversion structures)

Diversion structures, built in the 60-ies and upgraded in 1977, now degraded

New channel, originally a buffalo cart road, developed gradually via a flood season channel to all-year flow 1980-94, so that the flow tends to bypass the diversion


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4 Water uses and water balance

4.1 Water uses This section relates to ToR, Task 18: Quantification of consumptive and non-consumptive water uses



Agriculture-2006.xls PRD survey Jul-Aug 2006: Cultivation practices; cropping cycles; labour input; livestock; use of fertilizers and pesticides; farmgate prices; obstacles to cultivation

Domesticdemand.xls Present and projected domestic water demand in each sub-basin

An attempt has been made to illustrate the possible development of domestic demand. The following assumptions have been made:

• The actual long-term population growth within the sub-basin, including the effect of migration, will be between nil and 2 percent per year

• The unit demand will increase by between 1 and 2 l/p/d per year

If so, as seen in the table below, the future domestic demand will be somewhere between 3 and 6 times the present demand.

This is still a small part of the available water in the area, but the increase must be kept in mind in connection with the predicted increased demand for other purposes, particularly irrigation.

For long-term planning, a 'strategic priority allocation' could be considered, perhaps of 60-80 l/p/d. This is believed to be a realistic level, although it cannot be safely predicted when it will be reached.

Table 4.1: Estimate of future domestic demand, Boribo Sub-basin

Year Population Unit demand Total demand High

estimate Low estimate

High estimate

Low estimate

High estimate

Low estimate

2 pct/yr nil l/p/d l/p/d Mm3/year Mm3/year

2004 52,774 52,774 23 23 0.4 0.4

2009 58,267 52,774 33 28 0.7 0.5

2014 64,331 52,774 43 33 1.0 0.6

2019 71,027 52,774 53 38 1.4 0.7

2024 78,419 52,774 63 43 1.8 0.8

2029 86,581 52,774 73 48 2.3 0.9

2034 95,593 52,774 83 53 2.9 1.0

Data: The present unit demand of 23 l/d is from TSBMO (Mar 03); the present pupolation is from the Commune Database; other values are estimates


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Agricultural water uses

Agricultural water uses are by far the largest in terms of volume, and play an important role in terms of social and economic value, including livelihoods.

Today, the agricultural water uses are limited both by the raw water availability and by infrastructural constraints. In the course of time, however, as the infrastructural constraints are gradually removed, the raw water availability will become the sole limiting factor.

Distribution of water uses

Spatial and monthly distributions of present and future domestic demand, livestock demand and irrigation demand are inlcluded in Appendix 2.

4.2 Water balance This section relates to ToR, Task 21: water balance for the sub-basins

Related data (submitted electronically) B-W-balance-4of5yrs.xls Boribo Sub-basin, calculated water balance, present conditions, with

water uses and availability, in 4 out of 5 years, whole sub-basin and details

B-W-balance-scenarios.xls Boribo Sub-basin, calculated water balance, alternative scenarios: Increased domestic consumption, 50-50 and 100-0 diversion at Bamnak, and impact of climate change

MIKE Basin set-up

Water balances have been calculated using the MIKE Basin modeling system. Please refer to Appendix 3 for a general description. The set-up for the present study is shown in the following figure.


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Figure 4.1: MIKE Basin model of the Boribo Sub-basin

The model is divided into 17 sub-catchments with associated river network as well as water uses. The sub-catchments follow largely internal catchments divides, and are thus derived on basis of physical boundaries. An exemption is the delineation between sub-catchment C67 and C68, which is located at the proposed site for candidate sub-project Tram Mneash. In some cases the topographical information was insufficient for a sub-catchment delineation, instead the average distance to tributaries has been used.

The catchment contains one very important diversion point located at Bamnak. The river water from the upstream part of the catchment divides here into a portion flowing into the Thlea Maam catchment and another part into the Boribo Sub-basin. The history of the flow distribution is unclear as there are no exact information on how this diversion point has been controlled in the past. For model purposes the flow distribution at this location must therefore be assumed.

The figure below shows in schematic form the connection between the subcatchments and their areas.


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Figure 4.2: Schematic representation of sub-catchments

Catchments given by a number (eg. C14) and an area in km2 (eg. 55). Bamnak catchment shown with green color, Boribo Sub-basin with yellow color, and Tlhea Maam shown with red color

Rainfall-runoff model calibration

In the Thlea Maam- Boribo there is only one station in which discharges have been observed. This station is located at Boribo, and represents therefore only approximately half of the catchment outflow. As this is the only discharge measurement location, calibrated parameters from the rainfall-runoff module are assumed to be valid for the Thlea Maam part of the catchment.

The discharge available for model calibration at Boribo are few, but nevertheless usable. The data cover mainly 2001, but a few data have been made in 1998 and 1999. Based on the discharge data and associated water level observations it has been possible to construct a rating curve for the station. This rating curve can be applied to derive a rated discharge by using the observed water levels. In principle the rating curve should be checked from time to time using new measurements of discharge. This is not possible in the present case due to lack of data, hence the rated discharge produced for the period 1998 to 2005 is subject to uncertainty.

C1455

C13129

C1142

C1587

C1079

C18131

C957

C824

C1756

C16165

C19141

C610

C748

C5156

C68100

C67110

C2111


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The rainfall-runoff results have been compared with the discharge observations as well as the rated discharge. The water levels from 2002 -2005 give rise to a slightly different runoff pattern than the years 1998-2001. Since the discharge observations fall in the period 1998-2001, emphasis has been on this period in the model calibration. The figures below show the rated and observed discharge for the entire period 1998-2005, and the simulated and observed/rated discharge for the period 1998-2001.

The calibrated parameters have been applied for the entire Boribo Sub-basin.

Figure 4.3: Rated and observed discharge at Boribo for 1998-2005

Observed and rated discharge at Boribo, Stung Boribo

0

20

40

60

80

100

120

140

160

180

200

01/01/98 01/01/99 01/01/00 31/12/00 01/01/02 01/01/03 01/01/04 01/01/05 01/01/06

Dis

char

ge [m

3/s]

Rated discharge

Observed discharge


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Figure 4.4: Simulated and observed/rated discharge at Boribo, 1998-2001

Water uses

The water uses that have been accounted for in the model are domestic, irrigation and livestock water uses.

The principle in the MIKE Basin model is that the water uses in a given sub-catchment draws water from a particular node, in this case the catchment nodes. Hence all the water uses in a catchment takes water from the same catcment node, which is always located in the downstream end of the catchment. Since the sub-catcments are based on physical boundaries and the water uses are based on commune data, it has been necessary to calculate the fractional contribution of each commune to each of the sub-catchments. The commune data (eg. number of persons) are then assumed to be evenly distributed in the communes.

Domestic water uses: It has been assumed that each person presently consumes 23 l/d in the catchment. It is estimated that this unit demand will increase in future at a rate of 1-2 l/p/d per year. One of the scenario simulations made is to predict the effect of increased domestic consumption 25 years ahead. For this simulation the unit domestic water demand is 73 l/p/d.

This is a hidden box


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Irrigation water uses: Data for rain fed irrigation area, wet season irrigation area, dry recession irrigation area and dry season irrigation area are available in the commune data base. These data have been used for the estimation of the irrigation areas in each of the sub-catchments. The present state of the irrigation systems suggest that there are no return flows from the paddy fields. Hence the rain fed irrigation areas can simply be taken out of the calculations, as the water use in there areas does not affect and is not affected by the river flows.

In the present MIKE Basin model, the wet season irrigation, the dry recession irrigation and the dry season irrigation areas have been included. It is assumed that the wet season irrigation takes place between july and November, the dry recession irrigation between December and February, and the dry season irrigation between March and June. It is assumed for all categories that the water demand for irrigation is 2 l/s/ha, and that the paddy fields are evenly distributed in the communes. It is further assumed that there are no return flows from the paddy fields.

Water balance, present conditions

The MIKE Basin model has been used to compute a water balance for the sub-basin on a monthly and annual basis, considering the rainfall, evaporation, inflow, outflow, storage/losses and water uses.

Results are shown in the table below (while detailed water balances for each sub-catchment are presented in Appendix 2).

It is seen from this table that the water uses in general constitute a small fraction of the available water, at least on a yearly basis and during the wet season. In the driest months – February to April, the water uses are of the same magnitude as the available water. In April there are almost no outflows from the catchment. Both presently (in some years) and in the future there is therefore competition for water in the driest months of the year. Proper planning of the water allocation is therefore inevitable, if the situation is to be improved.

Another remark to the numbers in table is that in the wet season (June to November) as well as a part of the recession period (December), there is plenty of available water for irrigation water use or other uses. Presently most water in this period flows into the Great Lake, where it naturally serves other purposes.

The numbers in the table are based on precipitation data that represent a ‘4 out of 5 years’ situation, or 80 % reliability. This means that in 1 out of 5 years (on the average), the water availability is expected to be less than shown in the table.

The figures below show

• the water availability for each sub-catchment in the month of April given as runoff [m3/s] and specific runoff [l/s/km2];

• the same, but for the month of September; and

• the yearly averaged specific runoff [l/s/km2] for each sub-catchment.

Subcatchments which have a higher specific runoff than the lowest value receive flows from upstream catchments.


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Table 4.2: Summary water balance for Boribo sub-basin, present conditions

Rainfall Evapora-tion

Storage and losses

Water availability

Domestic uses

Irrigation uses

Livestock uses

Outflow from catchment

m3/s m3/s m3/s m3/s m3/s m3/s m3/s m3/s

January 1,7 10,8 -11,8 2,7 - 0,6 - 2,1 February 2,5 4,0 -2,8 1,3 - 0,6 - 0,7 March 20,4 20,4 -0,8 0,8 - 0,5 - 0,2 April 38,4 38,4 -0,7 0,7 - 0,5 - 0,1 May 73,4 57,5 10,9 4,9 - 0,5 - 4,4 June 65,0 53,8 0,7 10,6 - 0,5 - 10,1 July 68,4 47,1 -2,6 23,8 - 1,7 - 22,1 August 89,2 41,7 -0,6 48,1 - 1,7 - 46,4 September 115,9 32,9 17,5 65,4 - 1,7 - 63,7 October 111,3 36,3 24,6 50,5 - 1,7 - 48,7 November 54,6 43,4 -6,4 17,7 - 1,7 - 15,9 December 8,8 33,7 -31,1 6,2 - 0,6 - 5,6

Yearly 54,1 35,0 -0,3 19,4 - 1,1 - 18,3

l/s/km2 l/s/km2 l/s/km2 l/s/km2 l/s/km2 l/s/km2 l/s/km2 l/s/km2 l/s/km2

January 1,1 7,2 -7,9 1,8 - 0,4 - 1,4 February 1,7 2,7 -1,9 0,9 - 0,4 - 0,5 March 13,6 13,6 -0,5 0,5 - 0,3 - 0,2 April 25,6 25,6 -0,4 0,4 - 0,3 - 0,1 May 48,9 38,4 7,3 3,3 - 0,3 - 2,9 June 43,4 35,9 0,4 7,1 - 0,3 - 6,7 July 45,6 31,4 -1,7 15,9 - 1,2 - 14,7 August 59,5 27,8 -0,4 32,1 - 1,2 - 30,9 September 77,3 22,0 11,7 43,6 - 1,2 - 42,5 October 74,3 24,2 16,4 33,7 - 1,2 - 32,5 November 36,4 28,9 -4,3 11,8 - 1,2 - 10,6 December 5,8 22,5 -20,8 4,1 - 0,4 - 3,7

Yearly 36,1 23,3 -0,2 12,9 - 0,7 - 12,2

mm mm mm mm mm mm mm mm

January 3 19 -21 5 - 1 - 4 February 4 6 -5 2 - 1 - 1 March 36 36 -1 1 - 1 - 0 April 66 66 -1 1 - 1 - 0 May 131 103 19 9 - 1 - 8 June 112 93 1 18 - 1 - 17 July 122 84 -5 43 - 3 - 39 August 159 74 -1 86 - 3 - 83 September 200 57 30 113 - 3 - 110 October 199 65 44 90 - 3 - 87 November 94 75 -11 31 - 3 - 27 December 16 60 -56 11 - 1 - 10

Yearly 1139 737 -5 408 - 22 - 386

Values calculated by MIKE Basin representing a '4 out of 5 years' availability. '-' means ''less than 0.5 m3/s', less than 0.05 mm', or 'less than 0.05 l/s/km2'.


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Figure 4.5: Water availability in April (m3/s), present conditions

Figure 4.6: Specific water availability in April (l/s/km2), present conditions


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Figure 4.7: Water availability in September (m3/s), present conditions

Figure 4.8: Specific water availability in September (l/s/km2), present conditions


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Figure 4.9: Specific water availability, yearly average (l/s/km2), present conditions

Water balance, future conditions

Apart from the implications of irrigation development (which is described in a separate section below), water balances have been calculated for two development scenarios:

• Increased domestic demand - a development that is certain to take place, although it is uncertain how fast; and

• climate change - illustrated by tentaive (and quite uncertain) assumptions as described in Section 4.8.

Increased domestic demand: The water balance assumes an increase of 2 l/p/day per year. This corresponds to a high-end estimate of this development. With a simulation that predicts the situation 25 years ahead, this value amounts to 73 l/p/day. The increased domestic water use is adopted in the MIKE Basin model with all other conditions being unchanged as compared with present conditions. Hereby, the calculations describe the water availability in 4 out of 5 years.

Climate change: The assumed changes are a decrease of 2 % in the rainfall and and an increase in evaporation of 2%. These changes have been imposed on the rainfall and evaporation series that were used for the base situation simulation. No other changes have been considered. The net difference in water availability as compared with the base situation is app. 8 %, but the effect is more pronounced in the pre-monsoon and recession period than in the dry season.

Results are shown in the tables below. Detailed water balances for each sub-catchment are presented in Appendix A.


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Table 4.3: Water balance for increased domestic consumption


Storage and losses

Water availability

Domestic uses

Irrigation uses

Livestock uses

Outflow to the Great

Lake [m3/s] [m3/s] [m3/s] [m3/s] [m3/s] [m3/s] [m3/s] [m3/s]

January 1,67 10,77 -11,81 2,70 0,04 0,61 0,01 2,03

February 2,50 3,99 -2,82 1,33 0,04 0,61 0,01 0,66

March 20,43 20,43 -0,80 0,80 0,04 0,52 0,01 0,22

April 38,36 38,36 -0,67 0,67 0,04 0,52 0,01 0,09

May 73,38 57,54 10,90 4,94 0,04 0,52 0,01 4,36

June 65,04 53,79 0,65 10,61 0,04 0,52 0,01 10,03

July 68,38 47,11 -2,57 23,84 0,04 1,75 0,01 22,03

August 89,23 41,69 -0,61 48,14 0,04 1,75 0,01 46,34

September 115,91 32,94 17,54 65,43 0,04 1,75 0,01 63,63

October 111,32 36,27 24,57 50,48 0,04 1,75 0,01 48,68

November 54,62 43,36 -6,40 17,66 0,04 1,75 0,01 15,85

December 8,76 33,68 -31,11 6,19 0,04 0,61 0,01 5,52

Yearly 54,13 34,99 -0,26 19,40 0,04 1,05 0,01 18,29

Table 4.4: Water balance in case of an assumed climate change


Storage and losses

Water availability

Domestic uses

Irrigation uses

Livestock uses

Outflow to the Great

Lake [m3/s] [m3/s] [m3/s] [m3/s] [m3/s] [m3/s] [m3/s] [m3/s]

January 1,67 10,33 -11,20 2,54 0,01 0,61 0,01 1,90

February 2,08 3,80 -2,96 1,25 0,01 0,61 0,01 0,61

March 20,01 20,01 -0,76 0,76 0,01 0,52 0,01 0,21

April 37,53 37,53 -0,60 0,60 0,01 0,52 0,01 0,05

May 72,13 58,37 10,55 3,21 0,01 0,52 0,01 2,66

June 63,38 55,04 0,10 8,24 0,01 0,52 0,01 7,69

July 67,13 47,95 -1,86 21,04 0,01 1,75 0,01 19,27

August 87,56 42,53 -0,35 45,38 0,01 1,75 0,01 43,60

September 113,41 33,77 17,07 62,57 0,01 1,75 0,01 60,79

October 108,82 37,11 23,92 47,79 0,01 1,75 0,01 46,02

November 53,37 44,20 -6,91 16,08 0,01 1,75 0,01 14,31

December 8,34 33,49 -30,97 5,82 0,01 0,61 0,01 5,19

Yearly 52,95 35,34 -0,33 17,94 0,01 1,05 0,01 16,86


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4.3 Candidate sub-projects This section relates to ToR, Task 23: Assessment of impacts of each sub-project on downstream water uses; and Task 24: NWISP candidate sub-projects

Related data (submitted electronically) B-W-balance-4of5yrs.xls Boribo Sub-basin, calculated water balance, present conditions, with

water uses and availability, in 4 out of 5 years, whole sub-basin and details


There are 2 candidate sub-projects in the Boribo-Thlea Maam Sub-basin: Bamnak (or Bomnork) and Tram Mneash.

Bamnak (Bomnork)

Bomnork (code KK3, map 5833 IV) Boribo - Thlea Maam - Srang Sub-basin Pursat Province, Krakor District, Chheu Tom and Svay Char Communes 410 295 E, 1 359 550 N 1,750 ha (wet season)/ 50 ha (dry season)

Tram Mneash

Tram Mneash (code KK51, map 5833 IV) Boribo - Thlea Maam - Srang Sub-basin Pursat Province, Krakor District, Thnot Chum Commune 393 868 E, 1 375 032 N 1,200 ha (wet season)/ 60 ha (dry season)

The two candidate projects have been examined using the MIKE Basin model. The water demand has been assumed at 2 l/s/ha and the return flows have been assumed at nil. While return flows are likely to occur in the future, using no return flow is on the conservative side with regards to water availability.


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Since it is difficult to predict the water distribution at the Bamnak diversion, two different assumptions have been applied:

• A 50% - 50% distribution between Thlea Maam and Boribo; and

• a 0% - 100% distribution between Thlea Maam and Borobo (so that the entire flow goes to Boribo).

The two scenarios have been selected because it is expected that the future distribution - which is utterly uncertain - will be within the interval of a 0 - 50 percent diversion. A diversion rate higher than 50 percent is regarded as unlikely.

A 50% - 50% distribution at Bamnak: A summary water balance for this scenario is seen in the following table. The scenario has a significant effect on the water balance. On a yearly basis, the net outflow from the catchment is reduced by app. 14 %. The outflows during the dry months is less as compared with the base situation, and the driest month (April) appears to be critical.

Table 4.5: Water balance for a 50% - 50% distribution at Bamnak

Rainfall Evapo-ration

Storage and losses

Water availability

Domestic uses

Irrigation Livestock Outflow

[m3/s] [m3/s] [m3/s] [m3/s] [m3/s] [m3/s] [m3/s] [m3/s]

January 1,67 10,77 -11,81 2,70 0,01 0,83 0,01 1,84

February 2,50 3,99 -2,82 1,33 0,01 0,83 0,01 0,47

March 20,43 20,43 -0,83 0,83 0,01 0,74 0,01 0,06

April 38,36 38,36 -0,77 0,77 0,01 0,74 0,01 0,00

May 73,38 57,54 10,90 4,94 0,01 0,74 0,01 4,17

June 65,04 53,79 0,65 10,61 0,01 0,74 0,01 9,84

July 68,38 47,11 -2,57 23,84 0,01 7,65 0,01 16,16

August 89,23 41,69 -0,61 48,14 0,01 7,65 0,01 40,47

September 115,91 32,94 17,54 65,43 0,01 7,65 0,01 57,76

October 111,32 36,27 24,57 50,48 0,01 7,65 0,01 42,81

November 54,62 43,36 -6,40 17,66 0,01 7,65 0,01 9,98

December 8,76 33,68 -31,11 6,19 0,01 0,83 0,01 5,33

Yearly 54,13 34,99 -0,27 19,41 0,01 3,64 0,01 15,74

All flow at Bamnak distributed to St. Boribo: All conditions under this scenario are the same as the previous scenario, except the flow distribution at Bamnak. This scenario assumes that all flows upstream of the Bamnak diversion is diverted into the Boribo Sub-basin, and nothing into the Thlea Maam catchment. The idea is shown in the figure below, in which the area that drains into the Boribo Sub-basin under such circumstance is shown with red color.


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Figure 4.10: Effective drainage area of Boribo Sub-basin (red color) assuming a 100 % flow distribution towards Boribo at Bamnak

The summary water balance (for the entire catchment as a whole) for this scenario is identical to the previous scenario, hence it is not presented. However, there are pronounced effects at the two outlets of the catchments. To illustrate this, the water balance for sub-catchment 2 (the downstream part of Thlea Maam) is shown below for the base situation, the present and previous scenario. (Sub-catchment 2 has been selected as an example because the effects are particularly visible and significant in this area).

All months are affected by the change in flow diversion at Bamnak. The outflow from catchment 2 of the 100%-0% scenario is app. 25 % lower than the outflows from the 50%-50% scenario. This is a significant change, and it means that the driest months are close to zero outflow.

The flow diversion at Bamnak is a significant control for the diversion of water into the two catchments. Therefore, an analysis of the optimal water allocation into the two catchments can develop into a set of rules for this diversion.

Table 4.6: Water balance for the lower part of Thlea Maam (sub-catchment 2)

Runoff Rainfall Inflow Domestic Irrigation Livestock Outflow m3/s m3/s m3/s m3/s m3/s m3/s m3/s

Present conditions, 4 out of 5 years

Jan 0,20 0,13 1,24 - 0,10 - 1,34

Feb 0,10 0,17 0,60 - 0,10 - 0,60

Mar 0,05 1,50 0,29 - 0,10 - 0,23

Apr 0,03 2,83 0,18 - 0,10 - 0,11

May 0,37 5,44 2,29 - 0,10 - 2,55

Jun 0,79 4,80 4,93 - 0,10 - 5,62

Jul 1,76 5,05 10,18 - 0,40 - 11,55

Aug 3,56 6,59 21,53 - 0,40 - 24,69

Sep 4,84 8,56 29,60 - 0,40 - 34,04

Oct 3,74 8,22 22,62 - 0,40 - 25,96

Nov 1,31 4,03 7,30 - 0,40 - 8,20

Dec 0,46 0,64 2,87 - 0,10 - 3,23


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Runoff Rainfall Inflow Domestic Irrigation Livestock Outflow Candidate sub-projects plus a 50% - 50% distribution at Bamnak Jan 0,20 0,13 1,07 - 0,10 - 1,17

Feb 0,10 0,17 0,43 - 0,10 - 0,43

Mar 0,05 1,50 0,12 - 0,10 - 0,06

Apr 0,03 2,83 0,02 - 0,10 - 0,00

May 0,37 5,44 2,12 - 0,10 - 2,38

Jun 0,79 4,80 4,76 - 0,10 - 5,45

Jul 1,76 5,05 6,03 - 0,40 - 7,40

Aug 3,56 6,59 17,38 - 0,40 - 20,54

Sep 4,84 8,56 25,45 - 0,40 - 29,89

Oct 3,74 8,22 18,47 - 0,40 - 21,81

Nov 1,31 4,03 3,15 - 0,40 - 4,05

Dec 0,46 0,64 2,70 - 0,10 - 3,06

Candidate sub-projects, all water from Bamnak diverted into Boribo Jan 0,20 0,13 0,78 - 0,10 - 0,87

Feb 0,10 0,17 0,32 - 0,10 - 0,31

Mar 0,05 1,50 0,09 - 0,10 - 0,03

Apr 0,03 2,83 0,02 - 0,10 - 0,00

May 0,37 5,44 1,53 - 0,10 - 1,79

Jun 0,79 4,80 3,43 - 0,10 - 4,11

Jul 1,76 5,05 4,89 - 0,40 - 6,25

Aug 3,56 6,59 13,06 - 0,40 - 16,22

Sep 4,84 8,56 18,87 - 0,40 - 23,31

Oct 3,74 8,22 13,84 - 0,40 - 17,18

Nov 1,31 4,03 2,82 - 0,40 - 3,72

Dec 0,46 0,64 1,95 - 0,10 - 2,30

'-' means 'less than 0.005'

The estimated water availability at the two candidate sub-projects is shown in the following figure. The availability at the Tram Mneash site is affected by upstream withdrawals and can be affected by the Bamnak diversion, in case that the diverted water reaches the location.

4.4 Water availability This section relates to ToR, Task 24: NWISP candidate sub-projects

Related data (submitted electronically) Subprojects.xls Water availability for candidate sub-projects, and irrigable areas

On the basis of the analyses described above, the present section elaborates on the water availability for candidate sub-projects in the sub-basin.

The two candidate sub-projects are located upstream and downstream of each other, as shown in the figure below. The water availability for the downstream one,


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Tram Mneash, is influenced by the implementation of the upstream one, Bamnak, and on the manageable Bamnak Diversion.

In consequence, the water availability can conveniently be presented as

1 Water available for the Bamnak scheme; and

2 water available to share between the Bamnak scheme and the Tram Mneash scheme.

Hereby, the water available for Bamnak is included in the water available to share between the schemes.

Figure 4.11: Schematization of candidate sub-projects

Not all the water available at each location should be used for irrigation. As estimated in Section 4.1, the domestic demand may increase by a factor 3-6 within a period of 30 years. Also, livestock breeding may increase. However, these demands are small in comparion with the over-all water availability. Today, between them, they are estimated at around 0.02 l/s/km2, or around 0,027 m3/s for the entire sub-basin. A 5-fold increase would amount to 0.13 m3/s. They have been included in the availability estimates in proportion to the catchment area of each scheme, not because they are significant but in order not to forget about them.

The estimated awater availability is shown in the following tables.

St. Bamnak catchment

St. Thlea Maam catchment

Bamnak scheme and Bamnak Diversion

Tram Mneash scheme

Flow to the Great Lake

Flow to St. Boribo


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Table 4.7: Estimated water availability at Bamnak

Inflow Other uses Manageable m3/s

(1)

m3/s

(2)

m3/s (3) =

(1) - (2)

J 0,7 0,03 0,7

F 0,3 0,03 0,3

M 0,2 0,03 0,1

A 0,1 0,03 0,1

M 1,3 0,03 1,2

J 2,8 0,03 2,7

J 5,8 0,03 5,8

A 12,1 0,03 12,1

S 16,7 0,03 16,6

O 12,8 0,03 12,7

N 4,2 0,03 4,1

D 1,6 0,03 1,6

Catchment area: 392 km2 The water availability is the estimated total availability in 4 out of 5 years under present conditions, including present withdrawals for irrigation; present and future withdrawals , domestic and livestock; and excluding any future expansion of irrigation withdrawals

Table 4.8: Estimated water availability at Tram Mneash

Inflow From Bamnak

Other uses Tram Mneash alone

To share with Bamnak

m3/s (1)

low estimate m3/s (2)

high estimate m3/s (3)

m3/s (4)

low estimate m3/s (5) =

(1)+(2)-(4)

high estimate m3/s (6) =

(1)+(3)-(4)

J 0,7 0 0,7 0,03 0,7 1,3

F 0,3 0 0,3 0,03 0,3 0,6

M 0,2 0 0,1 0,03 0,1 0,3

A 0,1 0 0,1 0,03 0,1 0,1

M 1,3 0 1,2 0,03 1,3 2,5

J 2,8 0 2,7 0,03 2,7 5,5

J 5,6 0 5,8 0,03 5,6 11,3

A 12,0 0 12,1 0,03 12,0 24,1

S 16,5 0 16,6 0,03 16,5 33,1

O 12,6 0 12,7 0,03 12,6 25,3

N 4,0 0 4,1 0,03 4,0 8,1

D 1,6 0 1,6 0,03 1,6 3,2

Catchment area: 394 km2 (excluding the Bamnak catchment)

(2), (5): Assuming all water from Bamnak is diverted into St. Boribo

(3), (6): Assuming all water from Bamnak is diverted into Thlea Maam and subtracting an allocation for domestic + livestock upstream of Bamnak (6): Water available to share between Bamnak and Tram Mneash The water availability is the estimated total availability in 4 out of 5 years under present conditions, including present withdrawals for irrigation; present and future withdrawals for domestic and livestock; and excluding any future expansion of irrigation withdrawals


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4.5 Allocation of manageable flows Manageable flow (or water availability) The manageable flow is the water that can technically be withdrawn for off-stream uses at a given river section. The manageable flow is determined as the upstream generation of water (by net rainfall and storage exchange) minus upstream off-stream uses. The manageable flow is available to share between • off-stream uses at the given river section • off-stream uses downstream; and • in-stream (non-consumptive) uses downstream. The allocation can depend on the value generated, observation of exsiting water uses, and other aspects.

Downstream water uses

The following table lists the estimated manageable flows downstream of each candidate sub-project.

The table indicates that the water uses in St. Boribo depend on inflow from upstream (i.e. from the Bamnak Sub-catchment) in February, March and April, whereas in January, the availability and the demand more or less balance each other. In the rest of the year, there is a positive water availability.

In St. Thlea Maam, the marigin between availability and consumption is small in February, March and April, whereas the marin is clearly positive in the rest of the year.

Table 4.9: Manageable flows downstream of candidate sub-projects

Bamnak Tr Mneash St. Boribo St. Thlea

Maam St. Thlea

Maam m3/s m3/s m3/s

J -0,01 0,54 0,30

F -0,26 0,22 0,10

M -0,29 0,06 0,00

A -0,34 0,00 -0,04

M 0,48 1,07 0,63

J 1,51 2,41 1,47

J 4,30 5,05 3,06

A 8,70 10,79 6,64

S 11,82 14,87 9,19

O 9,12 11,34 6,99

N 3,18 3,59 2,15

D 0,62 1,36 0,81

Values are water generated in 4 out of 5 years minus present off-stream uses, extracted from MIKE Basin baseline simulation (Appendix 4, Table A4.6) Inflow from upstream not included Negative values indicate that inflows from upstream are relied upon to serve present demand Values include present estimated withdrawals for irrigation, domestic use and livestock


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In-stream water uses

Environmental flows (and other in-stream demands) have not been included in the analysis. An allocation of (for example) 2 l/s/km2 (or 3.0 m3/s for the entire sub-basin) would exceed the present water availability from December through June and is simply not possible to achieve. On the other hand, 2 l/s/km2 is around the flow required on the average for the entire Mekong Basin to keep the saline sea water out of the Mekong Delta. It is an open question, however, how the contributions to this flow should be functionally allocated within the Mekong Basin, considering that much more water is available elsewhere.

Areas that can be irrigated with the available water

The area that can be irrigated with the manageable flow will change from one month to another, and will depend on the withdrawal demand. The withdrawal demand, in turn, depends on the crops, the cultivation routines, the direct rainfall, and the water losses in the irrigation system (conveyance losses, seepage and infiltration).

Today, during an average rainy season, the farmers can raise one purely rainfed crop, although the yield is affected by water stress (which means that the water availability is less than ideal). This indicates a present withdrawal demand of somewhere around 0,5 l/s/ha minus direct rainfall - which would allow the farmers to cultivate their present wet season rice crops, with the present yield, in years with rainfall less than average.

Short- and medium-term rice varieties require more water than long-term varieties, and dry season paddy cultivation requires more water that wet season cultivation, whereas many crops other than rice require less water.

The area that can be irrigated with a given amount of water can be calculated as the rainfall deficit divided by the flow that is available. The rainfall deficit is the difference between the irrigation demand and the direct rainfall. It is shown in the following table for assumed withdrawal demands of 0.5, 1 and 2 l/s/ha. The former value is an indication of present practices in the wet season, while the latter value indicates possible future practices in the dry season.

Withdrawal demands According to MOWRAM's design manual for irrigation schemes (draft, Dec 03) Crop water requirement: 1,700 m3/mth (December) to 2,300 m3/month (April), or 0.6-0,9 l/s/ha, assuming a crop factor 1.1 for paddy and including percolation 2 mm/day Over-all system efficiency: Varying between 60 percent to schemes up to 50 ha and 51 percent for schemes above 400 ha This gives a withdrawal demand of between 1.1 and 1.7 l/s/ha in December to April The MOWRAM Manual notes that 'experience in other countries has indicated that crop yields are not significantly reduced if water supplied is within 85-90% of optimum'.


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Table 4.10: Rainfall deficit, Boribo sub-basin

Withdrawal demand 0.5 l/s/ha 1 l/s/ha 2 l/s/ha Rainfall Demand Deficit Demand Deficit Demand Deficit

(1) (2) (3) = (4) (5) = (6) (7) =

(2) - (1) (4) - (1) (6) - (1)

mm mm mm mm mm mm mm

J 3 134 131 268 265 536 533

F 4 122 118 244 240 488 484

M 37 134 97 268 231 536 499

A 68 130 62 259 191 518 450

M 131 134 3 268 137 536 405

J 115 130 15 259 144 518 403

J 122 134 12 268 146 536 414

A 159 134 0 268 109 536 377

S 207 130 0 259 52 518 311

O 198 134 0 268 70 536 338

N 97 130 33 259 162 518 421

D 16 134 118 268 252 536 520

Note: Values are for 4 out of 5 years

The corresponding irrigable areas are shown in the following tables.

Table 4.11a: Irrigable areas (a), withdrawal demand 0.5 l/s/ha

Bamnak Tram Mneash alone to share

Low estimate

High estimate

ha ha ha

J 1.355 1.370 2.725

F 628 641 1.269

M 351 367 718

A 283 306 590

M 114.476 115.377 229.853

J 48.463 48.734 97.198

J 129.245 125.221 254.466

A n/a n/a n/a

S n/a n/a n/a

O n/a n/a n/a

N 32.883 31.412 64.294

D 3.577 3.602 7.179

n/a: Cultivation not limited by water availability (irrigation supplies not required)


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Table 4.11b: Irrigable areas (b), withdrawal demand 1 l/s/ha


Low estimate

High estimate

ha ha ha

J 670 677 1.347

F 309 315 624

M 147 154 301

A 91 99 190

M 2.443 2.462 4.905

J 4.907 4.934 9.841

J 10.564 10.235 20.798

A 29.798 29.415 59.213

S 82.581 81.889 164.470

O 48.788 48.199 96.986

N 6.609 6.313 12.922

D 1.675 1.687 3.362

Table 4.11c: Irrigable areas (c), withdrawal demand 2 l/s/ha


Low estimate

High estimate

ha ha ha

J 333 337 670

F 153 156 309

M 68 71 139

A 39 42 81

M 826 833 1.659

J 1.754 1.764 3.518

J 3.724 3.608 7.332

A 8.610 8.499 17.109

S 13.843 13.727 27.570

O 10.090 9.969 20.059

N 2.544 2.430 4.974

D 812 817 1.629

The allocation of a finite amount of water between upstream and downstream schemes is a matter of give and take. In the so-called Halcrow Study (1993-95), it is recommended to prepare a master plan for 'the interconnected catchments that discharge into the south-west shore of the Great Lake' (Halcrow, Dec 03, p. 3).


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5 Morphology, floods and drought

5.1 Data This section relates to ToR, Task 2: Collection of hydro-meteorological and hydraulic data and information

Information about morphological processes was collected in July-August 2006 in connection with the present study.

5.2 Morphology This section relates to ToR, Task 10: Morphological analysis

Bank erosion and accretion takes place along the alluvial reaches of rivers and streams, sometimes as a gradual process that proceeds for years in a predictable way, and sometimes rather abruptly. In the present study area, the erosion rate is generally slow to moderate.

Bank erosion can cause damage to property, buildings and infrastructure (including irrigation infrastructure), while accretion can increase the flood risk and affect fish habitats and mish migration.

Figure 5.1: Examples of bank erosion, St. Boribo and St. Bamnak (5 July 2006)


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Figure 5.2: Erosion


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Figure 5.3: Accretion


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5.3 Floods and drought This section relates to ToR, Task 23: Assessment of impacts of each sub-project on downstream water uses; and Task 24: NWISP candidate sub-projects

Related data (submitted electronically) Agriculture-2006.xls PRD survey (Jul-Aug 06): Cultivation practices; cultivation areas;

cropping cycles; labour input; livestock; use of fertilizers and pesticides; farm gate prices; obstacles to cultivation

Flooded areas in 1999, 2000, 2001 and 2002 are shown in a thematic map (submitted separately).

Effects of floods and drought exist over most of the sub-basin, to an extent that depends on the cultivation cycle. Normally, a drought is regarded as a drought only if it occurs during cultivation. The effects vary from one village to another, over short distances, often within each commune.

In general, drought problems are much more widespread and more frequent.

The following tables show drought-affected areas and the general occurrence of floods and drought in the sub-basin.

Table 5.1: Cultivation areas affected by floods and drought

Province District Commune 2005, flood Drought 2004, flood Drought ha ha ha ha

Pursat Bakan Snam Preach 137 55 Trapeangchong 192 62 Boengbatkandol 418 88 Boeng Khnar 1813 125 Metuek 218 85 Outapoang 5 2042 106 Svaydaunkeo 511 27 Khnar Totueng 1234 70 Rumlech 163 97 Talor 436 160

Kg. Chhnang Boribo Anchanh Rung 65 …. Pich Changvar 50 …. Po Pel 48 …. Psar 63 32 10 Trapeang Chan 126 36 20 Punley 25 32 Melum 141 88 20 Khon Rang 142 102 20 Chak 135 18 Chnok Tru 98 … 30 Kampong Koki … … 20

Total 898 0 7472 995

Data: District Agriculture Offices


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Table 5.2: Occurrence of floods and drought

Province District Commune Village Flood Drought K.Chnang Boribo Melum Toul Thlok 2000 Every year

K.Chnang Boribo Anchanrong Anchanrong 0 Every year

K.Chnang Boribo Anchanrong Andong Rovieang 0 Every year

K.Chnang Boribo Anchanrong Andong Rovieang 2000 Every year

K.Chnang Boribo Anchanrong Steung Thmey 2000 Every year

K.Chnang Boribo Melum Melum 2000 Every year

K.Chnang Boribo Melum Toul Roka 2000 Every year

K.Chnang Boribo Psar Kbal Thnol 2000 Every year

K.Chnang Boribo Psar Psar 2000 Every year

Pousat Krokor Boeng Kantot Ou Anchanh 2000 Every year

Pousat Krokor Bomnork Toul Tbeng 0 Every year

Pousat Krokor Cheu Tom Bomnork 0 Every year

Pousat Krokor Cheu Tom Cham Thmey 0 Every year

Pousat Krokor Cheu Tom Cheu Tep 0 Every year

Pousat Krokor Cheu Tom Cheu Tom 0 Every year

Pousat Krokor Cheu Tom Phteak Chek 0 Every year

Pousat Krokor Cheu Tom Tang Lvear 0 Every year

Pousat Krokor Svay Sor Toul Andet 0 Every year

Data: 22 household surveys in Boribo Sub-basin 2006

Flood damage: Damage to crops, livestock and infrastructure

Drought damage: Damage to crops and livestock disease

For details, please refer to data table Agriculture-2006.xls


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6 Aquatic environment

6.1 Data This section relates to ToR, Task 25: Exisiting WQ data and classification

Data used in the evaluation and assessment of the aquatic environment is mainly from the commune database 2004 as presented in the previous chapters regarding population and livestock estimates.

Besides this also satellite images from LandSat 2005 have been used in the analysis including data on landuse from 1993, 1997 and 2002.

No water quality data have been available for the studied sub-catchments. Only data from Tonle Sap Lake have been available to a limited extent.

6.2 Pollution loads This section relates to ToR, Task 26: Point and non-point sources




BOD

In the figure below the load of BOD is shown for each sub-catchment.


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Figure 6.1: Amount of annual BOD load by sub-catchment

From this figure it can be seen that the BOD load reaching the receiving waters will be biggest in sub-catchments covering the lower stretches of the Boribo Sub-basin and especially in the districts of Krakor and Boribor.

The figure also show the distribution of receiving water load between domestic and non-point load. This shows clearly that in all sub-catchments the non-point load is the highest.

In Table 6.1 below the estimated pollution load of BOD to each subcatchment of the river is presented. The total load, the load for non-point pollution sources and domestic load has been calculated.

Table 6.1: Estimated BOD load reaching the river in each subcatchment

Name Area BODTotal BODNonPoint BODDomestic km2 kg kg kg

Catchment2 111,2 63303 58005 5298

Catchment5 155,7 39882 38579 1304

Catchment6 9,7 6764 6529 235

Catchment7 48,0 34073 33006 1067

Catchment8 23,9 18451 17857 594

Catchment9 57,2 35214 33634 1580

Catchment10 79,9 37181 35602 1579

Catchment11 42,1 12351 12126 225

Catchment13 128,7 17731 17268 463

Catchment14 55,1 10125 9897 228

Catchment15 87,0 19619 18867 752


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Catchment16 165,3 43909 42142 1768

Catchment17 56,2 20335 19595 740

Catchment18 130,7 78315 73741 4575

Catchment19 140,8 114018 107486 6532

Catchment67 110,3 71665 66080 5585

Catchment68 99,6 48303 44824 3479

For identification of location of the different subcatchments please refer to Figure 7.8 below

Figure 6.2: Location of the sub-catchments of the Boribo Sub-basin

Nitrogen

The highest contribution of nitrogen to the receiving waters originates in the sub-catchments covering the districts of Krakor and Boribor.

Substantial differences in the receiving water load between the upper and lower stretches of the Boribo Sub-basin can be seen. Compared to the BOD load there is indications that the proportion of nitrogen load from non-point sources might be even more pronounced.


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Figure 6.3: Amount of annual Total Nitrogen load by sub-catchment

In Table 6.2 below the estimated pollution load of total-nitrogen to each subcatchment of the river is presented. The total load, the load for non-point pollution sources and domestic load has been calculated.

Table 6.2: Estimated nitrogen load reaching the river in each subcatchment

Name Area N_Total N_Nonpoint N_Domestic km2 kg kg kg

Catchment2 111,2 39861 39861 942

Catchment5 155,7 34432 34432 295

Catchment6 9,7 3862 3862 41

Catchment7 48,0 19276 19276 187

Catchment8 23,9 10323 10323 102

Catchment9 57,2 20343 20343 281

Catchment10 79,9 25384 25384 303

Catchment11 42,1 13324 13324 49

Catchment13 128,7 23207 23207 124

Catchment14 55,1 12145 12145 56

Catchment15 87,0 19898 19898 174

Catchment16 165,3 43487 43487 389

Catchment17 56,2 19052 19052 153

Catchment18 130,7 47457 47457 818

Catchment19 140,8 69249 69249 1086

Catchment67 110,3 39692 39692 961

Catchment68 99,6 32455 32455 653

For identification of location of the different subcatchments please refer to Figure 7.8


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Phosphorus

The phosphorus load shows a similar pattern as for nitrogen when indicating the pressure of human impact.

Again the highest overall phosphorus load to the river system is generated in Krakor and Boribor districts.

Figure 6.4: Amount of annual Total Phosphorous load by sub-catchment

In Table 6.3 below the estimated pollution load of total-phosphorus to each subcatchment of the river is presented. The total load, the load for non-point pollution sources and domestic load has been calculated.


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Table 6.3: Estimated phosphorus load reaching the river in each subcatchment

Name Area PtotTotal PtotNonPoint PtotDomestic km2 kg kg kg

Catchment2 111,2 4650 4398 252

Catchment5 155,7 2078 2024 54

Catchment6 9,7 455 443 12

Catchment7 48,0 2370 2313 57

Catchment8 23,9 1445 1410 35

Catchment9 57,2 2167 2094 74

Catchment10 79,9 2283 2204 79

Catchment11 42,1 916 906 11

Catchment13 128,7 740 727 13

Catchment14 55,1 561 553 8

Catchment15 87,0 1341 1311 30

Catchment16 165,3 2733 2665 69

Catchment17 56,2 1585 1550 35

Catchment18 130,7 5144 4918 225

Catchment19 140,8 11519 11176 343

Catchment67 110,3 4720 4451 269

Catchment68 99,6 3051 2890 160

For identification of location of the different subcatchments please refer to figure 7.8

The results above are first estimates on pollutant loads entering the river. The results may only give an indication on how the relative differences in concentration may look like and which catchments may contribute relatively more than others to pollution levels expected in the river system.

The plan plot showing pollutant loads entering the river system discriminates between nonpoint and point types of sources. In general the plots indicate that nonpoint sources in general are far more important than point sources (e.g. domestic sources from population). However this cannot be verified but compared to the above load amount generated it seems reasonably. However, a number of local conditions may affect the transport and retention of different sources types and it is important to obtain monitoring data covering both low flow and high flow periods in order to verify that this is also actually the case.

6.3 Water quality This section relates to ToR, Task 27: Aqautic environment in representative reaches

The different water uses require a raw water quality that is adequate for the particular use, whether domestic, fisheries, industrial, or for agriculture. And most water uses generate a return flow, the water being released as sewage from households, businesses and industries, or as tailwater from irrigation systems and mines.

A MIKE Basin Water Quality model was setup for the Boribo study area based on the water balance. The water balance is based on down stream discharges calculated from the water level measurements and Q/h relations which are


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available for 1998 – 2005. The Q/h relation is primarily based on measured discharge data from 2001. Calculated discharges have been translated into area specific runoffs as input for the MIKE Basin model.

The applied area specific runoff and estimated base-flow are presented the below figure.

Figure 6.5: Total specific runoff and estimated base-flow for Boribo study area in 2001.

Water quality simulations This section presents the results from the water quality simulations. Two types of simulation results are presented.

• Time series plot for a selected location in the river

• Plan plot showing average and maximum concentrations

Below is shown the simulated concentrations of BOD, total-nitrogen and total phosphorus.

These simulations indicated relative high concentrations of BOD, ammonia, and total phosphorus in February-March (dry season), and relatively high levels of nitrate and partly BOD and total phosphorus in the rainy season.

BOD

The simulated average concentration of BOD during the present conditions show that the concentration levels will increase in the lower reaches of the Boribo Sub-basin. The calculations indicate that an up to three times increase might occur in the lower reaches of the northern river arm. However the calculation indicate using the assumptions given above that the present quality conditions should be good. During periods with low flow the simulations indicate more or less the same pattern and concentration level.

Boribo Runoff [l/s/km^2]baseflow [l/s/km^2]

Jan2001

Feb2001

Mar2001

Apr2001

May2001

Jun2001

Jul2001

Aug2001

Sep2001

Oct2001

Nov2001

Dec2001

0

10

20

30

40


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Figure 6.6: Calculated concentrations at the outlet of St. Boribo (Kg Preah Kokir): BOD, ammonia, nitrate and total phosphorous

Ammonia

The average annual concentrations of ammonia in the main part of the catchment in general meets the requirements for good quality except some short stretches in the northern river arm. However, the calculations indicate that in periods with low flow during the dry season the quality conditions regarding ammonia might be poor as the levels found in the lower reaches of the northern river arm might be five to six times higher than the upper reaches.

N140|BOD [mg/l]

2000 2001

0.5

1.0

1.5

2.0

2.5

N140|NO3 [mg/l]

2000 2001

0.40

0.50

0.60

0.70

N140|NH4 [mg/l]

2000 2001

0.10

0.20

0.30

0.40

0.50

N140|P_tot [mg/l]

2000 2001

0.05

0.10

0.15

0.20

0.25


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Nitrate

Regarding nitrate the average concentrations indicates that good quality conditions will occur in all river stretches. The calculations indicate however that during the rainy season the quality conditions in the lower reaches will be decreasing showing concentration levels of approx. 2 times higher than the upper reaches.

6.4 Implications of irrigation development This section relates to ToR, Task 23: Assessment of impacts of each sub-project on downstream water uses

The impact of the candidate sub-projects on the water quality conditions will be evaluated in the following.

The comparison have been made under the assumption that all pollution loads and retention in the system will be similar to the present situation, so that the only change that will occur will be the reduced water flow due to the newirrigation scheme.

Figure 6.7: Simulated discharge for reference scenario (black) and the candidate sub-projects (blue) at node 140 at the outlet of St. Boribo

Figure 6.8: Simulated discharge for reference scenario (black) and the candidate sub-projects (blue) at node 11 at the outlet of St. Thlea Maam


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The figures show clearly that the discharge through the two river arms will be reduced during the rainy season for the candidate project and also that the discharge in the dry season will be very low.

Similar types of simulation have been made as for the present situation.

Below is shown the simulated concentrations of BOD, ammonium, nitrate and total phosphorus in the two arms of the river.

These simulations indicate that relative small changes will take place in the concentrations of BOD, ammonium, nitrate and total phosphorus the southern arm of the river. The biggest changes will be in the level of total-phosphorus in the end of the dry season and for nitrate in July-August.

In the northern arm the changes will be more pronounced. The simulations indicate that the concentrations of the simulated compounds might increase by a factor of 2 in the end of the dry season. In the wet season no significant changes will occur.

BOD

The simulated average concentration of BOD for the candidate project with 50-50% diversion of water have been calculated. The concentration show a similar situation as for the present situation but with slightly higher values in the lower reaches. Figure 7.24 show the simulated differences in concentration levels between the candidate project and the present situation. These calculations indicate that the levels in the lower reaches will increase between 0 – 0.5 mg/l in the average situation.

Ammonium

The simulated concentrations of ammonium show an increase in concentration level in the lower reaches and in average an increase between 0 – 0.07 mg/l. The biggest increase will occur in the northern branch.


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Figure 6.9: Simulation results for the outlet of St. Boribo at Kg Preah Kokir: BOD, ammonia, nitrate and total phosphorous. Simulated concentrations for reference scenario (black) and the candidate sub-projects (red) at node 140

N140|NO3 - Candidate project [mg/l]N140|NO3 - reference [mg/l]

2000 2001

0.40

0.50

0.60

0.70

N140|NH4 - Candidate project [mg/l]N140|NH4 - reference [mg/l]

2000 2001

0.10

0.20

0.30

0.40

0.50

0.60

N140|BOD - Candidate project [mg/l]N140|BOD - reference [mg/l]

2000 2001

0.5

1.0

1.5

2.0

2.5

3.0


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Figure 6.10: Simulation results for the outlet of St. Thlea Maam: : BOD, ammonia, nitrate and total phosphorous Simulated concentrations for reference scenario (black) and the candidate sub-projects (red) at node 11 at the northern outlet

N11|P_tot - Candidate project [mg/l]N11|P_tot - reference [mg/l]

2000 2001

0.10

0.20

0.30

0.40

0.50

N11|NH4 - Candidate project [mg/l]N11|NH4 - reference [mg/l]

2000 2001

0.2

0.4

0.6

0.8

1.0

N11|BOD - Candidate project [mg/l]N11|BOD - reference [mg/l]

2000 2001

1.0

2.0

3.0

4.0

5.0


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Nitrate

The simulated concentrations of nitrate for the candidate project show that the concentrations in the lower reaches of the Boribo Sub-basin will increase between 0 – 0.07 mg/l. The biggest increases will be seen around the diversion and in the outer part of the northern branch.

Total phosphorus

The simulated concentrations of total-phosphorus show a similar pattern as the other compounds and with increases of 0 up to 0.03 mg/l

Conclusion

The simulations conducted so far indicate that the quality conditions could be good and this seems to be in accordance with recent water quality monitoring programs, undertaken by MOWRAM, MRC and WUP-FIN, that the general pollution level is fairly low at present. The simulations conducted for the candidate project indicate an increase in the concentrations but overall it is not expected to change the water quality conditions to any great extent. So the proposed irrigation schemes will generally result in a reduction in water quality as less water will be available for dilution of the pollutants.

In the future, in the likely case of crop diversification and the related increased use of pesticides and fertiliser, it is important to prevent serious environmental impacts in general, and contamination of edible fish in particular.


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7 Fisheries Boribo Sub-basin comprises two parts: One associated with Boribo river and another one associated with Thlea Maam / Kompong Lor river. The two areas are linked by a man-made canal at Bamnak (built in 1967). The fishery in Boribo Sub-basin can be described seperately for each of these areas.

7.1 Thlea Maam/Kompong Lor River With the current situation, the linkage of different fishery ecologically compartments are significantly disturbed by a number of blocking structures.

Kampong Lor River is currently blocked by two existing water regulators. One is at its downstream close to the lake, in Kampong Lor village. The other one is at its upstream part, at the Thlea Maam regulator. During high water level, the regulator downstream seems not to be a barrier to the fish migration, because of a general flood over the area. Therefore fishes are able to bypass the structure during the upstream migration. In contrast to this, the one upstream seems to be an important barrier to the fish migration. Both of the two structures are problematic concerning the upstream fish migration early in the migration period that starts in the beginning of the rainy season (June to August).

This Thlea Maam regulator is probably one of the main causes of fishery changes observed by the local communities in this area. In the dry season, no fishing activities were reported by the local communities. The main river stream downstream this regulator has changed its morphology and apparently lost fish pools (deep part of river that serves as fish refuge area during dry season). In rainy season, especially at the begining of the season, fishing practice is reactive. This activity coincides with the period of up-stream migration. During this period, the immediate downstream part of this up-stream regulator structure has become a good site for fishing by the local communities. These are apparently fishes from the Tonle Sap lake which seems to attempt to migrate up-stream but is blocked by the regulator.

The blocking of the regulator has made fishery in the rice field in these areas downstream of the regulator significant. Interviews under the present study revealed that approxiately 2kg of fishes can be caught by a farmer per day during rainy season, especially begining of the season.

Upstream of the regulator, the fishery becomes less significant. However, observation on the morphology of the river of this part has indicated that many fish pools could exist along the main stream. These pools could serve as fish refuge areas during the dry season. In rainy season, rice field fishery is reported as common by the local communities.

Finally, it is also important to note that, while the Thlea Maam regulator seems to have a major impact on fishery in the sub-basin, this could be rectified if a fish passage is included within the regulator structure and operation. The improved structure for fish passage would also significantly contribute to the fishery in the upstream areas.


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All future irrigation subprojects, that involve blocking the river, must consider including fish passage, and the interaction/passageway between different ecologically fish related compartments must be maintained. Beside, the amount of water in the irrigation canal will probably increase and more permanent, thus- some additional benefit to the local people, who usually fully exploit the canal for fishing. Moreover, irrigated systems will be operated to help overcome water shortage in the wet season. This should benefit the natural fisheries as they prevent drought conditions in the fields.

7.2 Boribo River Under the current situation, it is observed that the fishery associated with this river is less disturbed by the blocking structures along the main river. Only one possible blocking could be in the past (before 2000), at the Prekchik 17 April Dam. This dam was washed out by the 2000 and 2001 floods. Currently the dam is not forming any potential impact on fish migration.

Before 2000, the dam isolated the catchment area above the dam from migrating fish species, developing a permanent water body upstream of the dam. Thereby, fishery was practically divided upstream and downstream of this dam.

According to reports by local communities, flood water in the reservoir upstream of the dam is now abandoned of fishes. The area used to be a fishing ground for all fishermen from all around the dam site. The reservoir upstream of the dam created a refuge for riverine fish in the dry season. To survive during the dry season, fish is locally, laterally migrating in the river to deeper water. Locally migrating species can adapt to reservoir condition.

Fishing is reported significantly dropping after the dam collapsed. Rehabilitation of the dam will reinstate an upstream reservoir and its fishery. Without exception, the fishermen interviewed in areas around the dam are supporting the proposed rehabilitation of the dam in anticipation of returning lucrative reservoir fisheries.

Further upstream, at Bam Nak area, the river course has been severely disturbed by the Bam Nak diversion weir. Morphological development and changes are significant in this area. The Bam Nak weir itself seems to have isolated the upstream catchment (Bam Nak sub-basin) from its downstream fishery. The fishery upstream of this weir seems to have relied only on the local fishery. After the break though in the 1990s, the river have rejoined its course. No blocking of fish migration is observed after this period. The fish can use this newly cut-through river as its migration route up-stream or downstream.

The rehabilitation of the Bam Nak weir may involve in blocking also this newly cut-through river course, thus could also significantly impact the aquatic diversity and fishing yield upstream of the weir. Aquatic diversity and fishing yield downstream of the weir could also be impacted if migrating fish species would have been denied access to their spawning grounds located upstream of the weir. A possible mitigation measure to avoid blocking off fish migration by weirs is the construction of fishways.


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8 Socio-economics

8.1 Data This section relates to ToR, Task 1: Collection of general data and information



Cultivation-livestock.xls Cultivation areas and livestock (2005), by province, district and commune


Data and information is available from

• government reports, official publications by various ministries, consultant reports, and other relevant available literature

• previous studies carried out by ADB and WUP-FIN;

• secondary data from a variety of sources including the National Institute of Statistics and the Ministry of Agriculture, Forestry, and Fisheries (MAFF), commune databases and various projects; and

• surveys conducted under the present study in July-August 2006.

8.2 Socio-economic context This section relates to ToR, Task 19: Economic analysis of water utilization

The Boribo-Thlea Maam Sub-basin straddles three of the poorest provinces in Cambodia - Pursat, Kampong Chhnang and Kampong Speu. Prevailing socio-economic conditions within the sub-basin are described briefly below.

Population and population growth rates

The Boribo Sub-basin has an estimated population of around 52,774 which is projected to grow at an average annual rate of around 1.2% (compared with the national rate of 2.5%). The growth in population will require future investment in water and sanitation, power and transport systems.

Income and poverty

Pursat and Kampong Chhnang are two of the poorest provinces in Cambodia. It is estimated that around 40% of the population live below the consumption-based poverty line (MRC, 2003) in both provinces. Average gross household cash income among households surveyed in the Boribo-Thlea Maam Sub-basin is US$682 per year (or US$131 per person) compared to average national GDP per capita in 2004 of around US$363 (ADB, 2006).


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The figure below clearly shows the dependency of households in the sub-basin on their land as their main source of wealth 3 and highlights their vulnerability to the impacts of drought and severe floods which affect both crop and livestock productivity. Livestock – although not often sold or traded – are clearly an important store of value, providing some form of security to households in times of need.

The structure of cash income is very similar, with at least half of all cash income generated from actual sales of livestock, paddy and poultry. Note that the income levels shown below do not account for the costs associated with undertaking these income-generating activities. When these are considered, a very different picture emerges.

Income and wealth

For the purposes of this report, the distinction is made between cash income and wealth. Cash income is money that the household receives in return for goods and services that it provides. Wealth is the value of household goods (e.g. crops) and services (i.e. labour) that could be converted into direct cash value if sold.

Also, although a large share of production is for subsistence, using economic prices for all crops, livestock and fisheries is justified on the basis that farmers would otherwise need to acquire these products in the market.

Employment

Over 80% of the populations of Pursat and Kampong Chhnang are engaged in agriculture as the primary source of employment (MRC, 2003). This figure is believed to be a lot higher in the study area where there are no major towns offering employment in industry or services. Among the 68 households interviewed, 100% stated their main occupation as farming.

Seasonal migration is a common phenomenon with around 30-40% of households in the study area having at least one member employed in either Phnom Penh or market towns along the Thai border for up to 8 months of the year. Women working in garment factories in Phnom Penh are able to earn US$30 per month while men working in the Thai border areas earn up to US$60 per month, providing an important source of supplementary cash income to households.

3 Here income is used in the economic sense and does not necessarily refer to cash income. Furthermore, livestock is valued at its stock value (i.e. as an asset) rather than as a flow value


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Figure 8.1: Household wealth

Source: project survey data

Figure 8.2: Structure of household cash income

Source: project survey data

Access to water and sanitation

Safe water is defined by UNICEF as a supply of water through household connection, public standpipe, protected dug well, protected spring or rainwater collection, with a minimum quantity of 20litres/person/day within one hour of people’s residences (UNICEF, 2002).

The sub-basin population has poor access to safe water and sanitation facilities. At the time of the last census in 1998, it was estimated that less than 20% of the population in each of Pursat and Kampong Chhnang provinces had access to a safe

Household gross income (2005)

1.76%

1% 8%

79%

10%

Paddy cultivation

Livestock

Fisheries

Paid work

Off-farm

Average gross cash income per household per year

44%

1%

0.1%

45%

2%8%

Paddy

Livestock

Poultry

Fisheries

Off-farm

Other on-farm


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water supply (MRC, 2003) and less than 12% had access to proper sanitation facilities (MRC, 2003). The main sources of drinking water for the population of Pursat are shown below.

Figure 8.3: Main sources of drinking water in Pursat

Source: UNDP, 2006

Domestic water consumption within the Boribo Sub-basin is characterized by a large span between urban households with piped water supply and rural households with shared or no water supply. The distribution is the limiting factor in all areas that are not covered by public supplies directly to each household.

The majority of the sub-basin population harvests rainwater during the wet season which is stored in large jars. This is supplemented with water collected from nearby rivers and streams.

Water quality has not been reported as a problem but with growing populations of both humans and livestock, and increasing applications of chemical fertilizers and pesticides in agriculture, poor water quality may become an issue, especially in the dry season.

Health

The health of people living in the Boribo Sub-basin is generally poor due to low levels of access to clean water and sanitation. Diarrhea is common among children.

Almost half of all children in Pursat and Kampong Chhnang Provinces are malnourished (MRC, 2003). The MAFF (2005) estimates per capita rice requirements to be 143 kg per year, equivalent to 744 kg of rice per household per year in the sub-basin. According to project survey data, rice yields are around 736 kg/ha, or 1.13 tonnes per household year, suggesting that poor diet, rather than food or rice shortages, is the main cause of malnutrition among children.

Main source of drinking water - Pursat Province

1%2%

40%

5%0%4%

48%

PipedTube / piped wellProtected dug wellUnprotected dug wellSpring / river / streamBoughtOther


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Land holdings

Findings from village surveys reveal that the average cultivated area per household is around 1.5 hectares. The small size of land holdings, poor quality soils and lack of water limit the types and quantity of crops that can be grown and deny farmers the opportunity to benefit from economies of scale. Generally, households devote most of their cultivated area to wet season paddy.

Literacy

Education and training standards are extremely low by developing country standards. Literacy in Pursat and Kampong Chhnang provinces is around 80% for men but much lower (60%) for women. Less than 20% of the population complete primary school and less than 10% are educated to a secondary school level (MRC, 2003).

Low levels of education limit the options available to households to diversify their livelihoods away from subsistence farming, again making them extremely vulnerable to factors affecting agricultural productivity.

Physical infrastructure

The physical infrastructure serving villages in the Boribo Sub-basin is relatively undeveloped and roads are poorly maintained. Most of the roads and cart tracks become impassable during the wet season, isolating many rural communities and limiting opportunities to market surplus agricultural produce. Rivers and streams are thus important transport conduits in the wet season, allowing people to travel between villages located near waterways.

Plans to rehabilitate the railway between Phnom Penh and Poipet as an integral part of the Greater Mekong Subregion (GMS) southern economic corridor (one of 11 flagship programs under the GMS subregional economic cooperation) are underway. The railway (which will eventually link Singapore to Kunming) passes through Bamnak in Boribo basin and could be beneficial to residents in the Boribo basin by:

• Providing a means for farmers (in collaboration) to transport surplus produce to markets in Phnom Penh, Battambang and Poipet

• Creating an opportunity for the development of tourism to the Cardamom mountains

The railway line is expected to be completed by 2015 (ADB, 2006).

Summary

The residents of Boribo basin are predominantly poor rice farmers. They engage in subsistence rice cultivation during the wet season and typically find off-farm work during the dry season when water shortages severely limit the feasibility of a second rice crop. However, low levels of education and literacy, limit the off-farm opportunities available to most households. Rural households do not have access to safe water supplies and consequently suffer poor health which also affects their agricultural productivity. Livestock raising is an important source of wealth but livestock health depends on the availability of sufficient water for drinking and fodder. Apart from water shortages during the dry season, agricultural productivity is constrained by small landholdings and poor soil quality.


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Summary socio-economic indicators for Boribo Sub-basin are presented in the table below.

Table 8.1: Summary socio-economic indicators for Pursat, Kampong Chhnang and the study area

# Provincial estimates are sourced from MRC Social Atlas (1998 census data unless otherwise indicated); sub-basin data comes from project surveys and commune databases

IndicatorBoribo /

Thlea MaamPursat

Province#

Kampong Chhnang

Province#Demographics

Population 52,774 360,400

Population growth rate (% p.a.) 2.4

Population density (persons/km2) 46 28.4 75.7

Migrant population (%) 2.8 3.9

Health & welfareInfant mortality rate (per 1,000 live births)

104 91

Proportion of population aged 0-14 (%)

47.2 44.5

Child malnutrition (%) 48.6 47.6

Ave household size 5.2 5.2 5GDP per capita (US$) 161

Ave household landholdings (ha) 1.5

% of population living below consumption-based poverty line

40.7 44.6

% of population with access to safe water supply

12.3 19.3

% of population with access to sanitation

11.7 6

Ave household livestock holdings (cows, buffaloes, pigs)

4

Education82.5 (male) 76.5 (male)59.5 (female) 53.7 (female)

Primary attainment rate (%) 16.7 15.2Lower secondary attainment rate (%)

8 5.4

Employment

Labour force participation rate (%) 74.2 76.4

Agricultural Employment (%) 100 82.6 85.5Industrial Employment (%) 2.1 1.7Services Employment (%) 15.3 12.8Unemployment (%) 3.5 3.1

Literacy rate (%)


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8.3 Water utilization This section relates to ToR, Task 19: Economic analysis of water utilization

This section provides a snapshot of knowledge about current water use in the Boribo Sub-basin. It identifies and quantifies (as far as possible) the water uses and services by socio-economic sector thereby providing some insight into the relative socio-economic importance of water uses to the sub-basin residents. The economic importance of each water use is analysed in section 8.4.

Irrigated agriculture and forestry

Water is essential to the agricultural sector for irrigation, drinking water for livestock and cleaning. It is estimated that 19 % of the total sub-basin area is under cultivation (Table 8.2) and that 38 % of the total cultivated area is irrigated.

Table 8.2: Cultivated areas in Boribo Sub-basin

Total Wet paddy Dry paddy Other crops Basin area (ha) 149,900

Cultivated area (ha) 28,800 28,800 1,975 45

Percent of basin area 19 19 0.3 0.03

Irrigated area (ha) 10,900 1,975

Percent of total cultivated area 38 7

Source: Cultivated area by land use analysis (2005) (Table 2.2); distribution of cultivated area estimated from data contained in the commune database and collected from local authorities; irrigation areas according to Table 2.4

Rice cultivation is relatively limited, representing no more than 5-10 percent of the commune area in the majority of the communes, with some higher coverage in the lower reaches. Wet season paddy is the predominant crop (see Figure 8.4) with only relatively small areas of irrigated dry season paddy. In many localities, farmers grow other crops (Table 8.3) such as vegetables, sugar palm, and various fruit. Livestock rising generally is important, with most farmers raising chickens, pigs and ducks for consumption and sale, and oxen or buffalo for draught power. For non-rice crops, a large variety of cropping systems are used, some of which involve supplementary irrigation. (Apart from vegetables, very small areas of non-rice crops are fully irrigated). For instance, maize is grown under rain-fed conditions along river floodplains, where the soil receives an annual replenishment of silt, to maintain fertility. The crop is planted at the beginning of the wet season rains, and harvested prior to the floods in September. Supplementary crops are grown primarily for subsistence use while corn is grown to provide pig fodder.

Drought has become an annual occurrence, and is often accompanied by pest infestations, giving farmers little incentive to cultivate during the dry season. While severe flooding is less of an issue, when it does occur the impacts are devastating, with farmers reporting crop losses of between 50-90%, particularly in those communes bordering The Great Lake.


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Figure 8.4: Irrigated cropping areas in Boribo Sub-basin

Data from commune database and district authorities

Table 8.3: Irrigated crop areas

Irrigated agriculture is the largest user of water in the Boribo Sub-basin (as in Cambodia as a whole), presently consuming around 32.8 million m3 per annum. Most agriculture is rainfed with only around 7% of the total land area receiving any form of irrigation. However, where irrigation is possible, the benefits are substantial. The total potential irrigable area is estimated to be around 23,915 in the wet season and 7,201 ha in the dry season. At present, only 46% and 27% of irrigation potential is being exploited in the wet and dry season respectively.

Demands for irrigation water can be expected to increase over time as more food is required to support a growing population. It is difficult to predict exactly how much additional water will be required as much depends on the mix of crops

Irrigated cropping areas (2005)

5% 1%

94%

Wet

Dry

TotalSupplementary

District Commune

Wet Dry Corn Potato Bean Sugar Cane Pineapple Vegetable Total

Boribo Anchanh Rung 4,076 0 0 8 1 1 1 9 19Boribo Pich Changvar 1,445 320 65 0 0 0 0 0 65Boribo Psar 2,027 280 0 3 0 1 0 12 16Boribo Melum 1,724 200 0 4 0 1 0 9 14Boribo Khon Rang 1,858 0 0 6 0 1 1 10 17Boribo Kampong Koki 280 240 0 11 0 1 1 11 24Tuek Phos ChiebTuek Phos Krang SkearKrokor AnsaChambak 2,080 35 …. …. …. …. …. …. ….Krokor Snar Ansar 502 2 …. …. …. …. …. …. ….Krokor Ou Sandann 1,020 …. …. …. …. …. …. …. ….Krokor Boeng Kantout 833 …. …. …. …. …. …. …. ….Krokor Tnoat Chum 1,538 …. …. …. …. …. …. …. ….Krokor Kampung Po 1,149 2 …. …. …. …. …. …. ….Krokor Cheu Tom 1,549 …. …. …. …. …. …. …. ….Krokor Svay Sor 1,531 30 …. …. …. …. …. …. ….Kandieng KanhchorPhnum Kravanh ProngilSampov Meas RoleabAural Trapeang ChourTotal 21,612 1,109 65 32 1 3 2 51 154

Other Irrigation Crops (Ha)Paddy (ha)


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grown, technological uptake and water-use efficiency. Access to markets, agricultural extension and the terms of trade offered to farmers will also impact agricultural productivity.

Future demands for irrigation water (Table 8.4) are estimated based on the following assumptions:

• The full development of potential irrigation areas such that water utilization is limited by the water availability rather than by distribution capacity

• Improvements in water and land-use efficiencies

• A partial shift towards crops that are less water-consuming and more valuable than rice

Table 8.4: Future demands for irrigation in Boribo basin

Present (million m3) Future (million m3) Irrigation demands 32.8 113.2

During the course of the household surveys, farmers cited the main obstacles to cultivation as:

• Lack of water (100%)

• Lack of capital (29%)

• Lack of seed (19%)

• Lack of technology (14%)

• Low yields (5%)

It is thus believed that an inability to manage water flows around the considerable variability in rainfall is likely to a serious constraint to agricultural growth in the sub-basin. The long dry season and irregular rainfall during the wet season place considerable constraints on crop production, and on farmer confidence and ability to invest. Water resources management and control are a basic requirement for increasing agricultural productivity, reducing risk of crop failure, and reducing rural poverty (CNMC, 2003).

Impacts of irrigation development on agricultural water demands and water availability

Potential impacts of irrigation development on agricultural water demands include:

• Reduced total demand because of improved water-use efficiencies (i.e. reduced leakage from canals, etc) thereby contributing to water availability

• Increased total demand because of improved access to water for irrigation and potential for expanding both the cultivated area and the cultivation period. The change in demand will depend largely on the price of water for irrigation vis-à-vis the value of household returns to agricultural production.

• Reduced water availability through increased use of chemical fertilizers and pesticides on an expanded and/or intensified cropping area


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Forestry

78 percent of the Boribo Sub-basin is covered by evergreen, semi-evergreen or deciduous forest (PRD Interpretation from Landsat ETM (2005). Agronomically, natural forest may be the largest consumer of water in the basin. The forest receives all of its required water from annual rainfall and by tapping residual soil moisture plus water from shallow aquifers during the dry season. Overall water consumption decreases in land denuded of forest and cultivated with annuals, but there will be an accompanying change in seasonal flows into the mainstream and possible long-term climate change effects (Nesbitt, 2005).

Livestock

Livestock is regarded as both a source of income and as a livelihood safety net to be sold in response to shocks such as illness or expenses associated with marriage or death. Animal sales are a major source of income for subsistence farmers who see them as ‘banks’ for accumulation of wealth. Based on information from project surveys, over 70% of all households raise cows, and over 60% of all households raise pigs. Chickens are generally a source of protein for farmers, and there are no known commercial poultry farms.

Estimates of water consumption by large animals range from 50 to 120 litres of water per animal per day. Table 5 shows present livestock water demands based on both low and high estimates of daily water consumption.

Table 8.5: Present livestock water demands in the Boribo Sub-basin (2005)

* Livestock numbers are based on a combination of project surveys and information contained in commune databases

Table 8.6 shows recent over-all changes in livestock population for Cambodia as a whole. More localised (but short-term) data are available from the Commune Database. In the recent past, the number of buffaloes has been decreasing, possibly reflecting a shift from using animal-drawn implements to machinery for crop cultivation. However, the increased number of cattle and pigs across the basin has offset this decline. The general increase in large animal numbers is a reflection of improved crop production and of the general welfare of farmers. Higher rice grain yields for example, have resulted in associated increases in the quantity of stubble made available for grazing both cattle and buffaloes. Pigs on the other hand are fed with rice bran, a bi-product of milling. Increased grain production results in the support of a greater number of pigs, chickens and ducks.

Table 8.6: Change in livestock population, Cambodia

Head

Daily water demand per

animal (m3) - LOW

Total annual water

demands (m3) -LOW

Daily water demand per animal (m3) -

HIGH

Total annual water

demands (m3) - HIGH

Water demands(m3/s) - LOW

Water demands (m3/s) - HIGH

Buffalo 18,050 0.05 329,413 0.12 790,590 3.813 9.150Cows 11,085 0.05 202,301 0.10 404,603 2.341 4.683Pigs 14,993 0.03 164,173 0.05 273,622 1.900 3.167Poultry 131,023 0.01 478,234 0.02 956,468 5.535 11.070Total 175,151 1,174,121 2,425,283

Livestock Change 1991 - 2001 (% per year)

Buffalo -2.4Cows 2.2Pigs 1.7Chickens 5.5Ducks 3


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Source: UNFAO, 2002. ‘Selected Indicators of food and agriculture development in Asia', quoted by MoE (Apr 05)

Based on the information in Table 8.6, it is possible to project future livestock demands, assuming that:

• Animal population growth rates will remain more or less stable over the next 10 years

• Livestock productivity among subsistence farmers will not be heavily impacted by the spread of animal diseases such as avian influenza

• Possible changes in market prices will not influence the holding patterns of subsistence farmers in Boribo Sub-basin

The figures in Table 8.7 are based on conservative (low) estimates of daily livestock water demands.

Table 8.7: Projected livestock water demands to 2030

Domestic consumption

Today, in the project area, with its large rural population, domestic water uses are limited by the infrastructure (withdrawal capacity and distribution capacity), and also, in some places and in part of the year, by the immediate raw water availability.

Information from the household surveys revealed the following:

• Most households in the study area collect and store rainwater in large 225 litre jars during the wet season. Each household will have between 3 and 5 jars. The harvested rainwater is used for drinking and cooking only and will last until around Feb/March.

• Bathing and washing is done in nearby rivers and ponds.

2005 population

2030 population

2030 annual water demand

(m3)

2030 water demands

(m3/s)Buffalo 18,050 7,220 131,765 0.004Cows 11,085 17,182 313,567 0.010Pigs 14,993 21,365 233,947 0.007Poultry 131,023 311,180 1,135,806 0.036Total 175,151 356,946 1,815,085


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• Those households living within 100 metres of rivers and streams tend to fetch drinking water from the nearest source. Households who have to collect water from streams or rivers generally spend about 1 hour per week doing so.

• During the dry season households will either purchase water from delivery trucks (around 10,000 riel per load = 1,250 litres) in more built up areas, or fetch water from rivers in rural areas. Those households who cannot afford to pay for water are able obtain it from the nearest pagoda or community well.

Estimated daily water consumption in the Boribo Sub-basin is around 50 litres per person, or a total of 2.6 million litres per day. This is high in comparison with estimates of per capita consumption for Cambodia as a whole – 20.7 litres per person per day in rural areas and 65.1 litres per person per day in urban areas (MRC Jun 03).

Demands for domestic water are expected to increase over the coming years as a result of:

• Population growth, including the impacts of migration. Net migration may be negative, since there are no significant urban centres (such as provincial towns) in the study area. The possibility exists that at a certain stage, the population of the study area will stagnate, and, later on, decrease, reflecting an anticipated shift of livelihood opportunities from rural to urban areas, as well as new agricultural technologies with a much higher labour efficiency.

• Increased per capita demand because of better education about the benefits of water for good hygiene

• Improved lifestyles with more widespread use of water-using technologies and an expanded coverage of piped water supplies direct to each household

Assuming a conservative population growth rate of 1.2% per annum (low) and a more typical one of 2.4% (high) as well as an increase in per capita demands of between 1 and 2 litres per day per year until 2015, consumption levels are projected to be around the levels shown in Table 8. Based on these assumptions, domestic demand in 25 years’ time will be somewhere between 3 and 5 times the present demand. This is still a small part of the available water in the area, but the increase must be kept in mind in connection with the predicted increased demand for other purposes, particularly irrigation. When managing water allocation, priority should be given to domestic uses as a basic human right.

Table 8.8: Projected domestic consumption demands

2005 2030 (low) 2030 (high) Population 52,774 71,964 88,313

Daily per capita consumption (litres)* 23 49 75

Total annual demand (mm3) 0.44 1.29 2.42

* assumes an increase of 1 litre per capita per day under the low growth scenario and 2 litres per capita per day under the high growth scenario. The present unit demand of 23 l/d is from TSBMO (Mar 03); the present population is from the Commune Database; other values are estimates

Fisheries

Fisheries in the Boribo Sub-basin (like elsewhere in the Mekong basin) is enormously important both commercially and for subsistence livelihoods. Fish provide a vital source of nutrients to the people of the Tonle Sap and the


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surrounding area (Ahmed et. al., 1998) and are also an important component of households’ cash economy. Fish provide self-employment, wage employment (for men and women in the fishing lots on Tonle Sap Lake), direct nutrition, indirect nutrition, and other livelihood needs (by cash sale or barter for other produce).

Both subsistence and commercial fishing takes place in the Boribo-Thlea Maam basin. While most households are involved in subsistence fishing in the wet season (10 days per month in the wet season), only a very small number of villagers do any kind of commercial fishing. Around 30% of total fish catch is either sold or exchanged for rice.

No data on fisheries productivity was available for the Boribo basin, therefore values have been derived from studies by the MRC Fisheries Program which estimates that average consumption of fish and other aquatic products (OAP) in the Lower Mekong Basin as a whole is about 36 kg/person/year. Households in the Boribo basin each consume around 2kg of fish per week (20kg/person/year), or a total at present of 1,000 tonnes per year for the sub-basin. With a growing population (and assuming no change in diet), future demands are expected to rise to around 1,500 tonnes per year by 2030 (under a conservative population growth rate).

Actual production estimates vary widely, and are subject to a number of methodological debates centred around whether catch or consumption should be used as the basis for measuring yield. The estimated fish yield of the Great Lake and the Tonle Sap river itself is as high as 139-190 kg/ha/year (by Van Zalinge et al 2001). Annual fish productivity in the Cambodian floodplains is estimated to be around 243kg/ha. This is a high-end estimate based on work near Phnom Penh by Dubeau et al 4 (see Beecham and Cross, 2005).

The productivity and sustainability of fisheries – and hence their ability to meet rising demands - depends on a number of factors including:

• fishing practices

• total fishing effort

• river flows

• barriers to migration

• access to, and from floodplain habitats; and

• the floodplain area that is inundated in the wet season, which in turn depends on the annual maximum flood height..

There is, as yet, no standard functional form for evaluating the impact of changes in river flow levels to changes in fisheries productivity but recent advances have, however, been made in modelling how fisheries productivity may be affected by changes in hydrological flow levels using indicators relating to habitat availability and migration (Beecham & Cross, 2005).

4 Dubeau, P., Poeu, O. and Sjorslev, J. (2001) Estimating fish and aquatic animal productivity /yield per area in Kampong Tralach: An integrated approach. http://www.mekonginfo.org/


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Preserving the Mekong fishery is central to food security in the region. The wild fishery is particularly important for the poorest rural households, making significant contributions to their nutrition, food security and income (MRC, 2003).

Industry

There are no significant industrial activities in the Boribo Sub-basin at present. There is some light industry in the form of rice milling and brick making. Rice milling demands negligible amounts of water (for cleaning) while brick-making requires around X m3 per tonne. The scale of brick production in the Boribo Sub-basin is relatively minor (around 2 family-run operations), with production for only local consumption.

Some sand extraction takes place in the dry season in the lower parts of the rivers, at places where the transport of the excavated sand is practical. Each operation can extract around 5m3 per day in the dry season. The sand sells for around US$2 per m3. These operations are typically run by outsiders who draw on cheap, local labour.

Future industrial development in the area is limited by the poor infrastructure network and generally low levels of education among sub-basin residents. It is not therefore expected to impact, or be impacted upon by, water availability.

Navigation

The roads and tracks in the study area are generally very poor and virtually impassible during the wet season. Many villagers thus rely on waterborne transport when they need to travel beyond their own village in the wet season.

Irrigation development in the sub-basin is not expected to impact upon river navigability during the wet season.

Tourism and recreation

Pursat province is the gateway to the Cardamom mountains and, together with its location not far from Phnom Penh, offers significant tourism potential. However, the poor condition of the access road (impassable during the wet season) and extremely limited tourist facilities are reflected in the low number of visitors to the region. Peak visitation rates are during Khmer and Vietnamese New Year holidays.

As mentioned earlier, the proposed railway development from Phnom Penh to Poipet could stimulate tourism activity around the Cardamom mountains. The impacts upon water resource availability, at least in the next 20 years, are believed to be negligible.

Micro-hydropower

The general topography of the Boribo-Thlea Maam Sub-basin supports the development of run-of-river micro-hydropower schemes. At present there is only one known scheme in operation in the sub-basin. It is located near Chrak La Eang waterfall and its low capacity (2-3kW) allows it to serve only a small number of households. It is believed that there is significant potential for further micro-hydropower development, although more particularly on the other side of the catchment (personal communication, Teang Sokhom, 17 October 2006). The development of such schemes will not affect water availability and their location in


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the upper catchment areas should protect them against the potential impacts of downstream irrigation development.

Maintenance of aquatic ecosystems for livelihood support and environmental sustainability

Apart from the direct use value that rivers provide in the form of water for irrigation, livestock, domestic and industrial consumption and fisheries production, they are also important for the maintenance of aquatic ecosystems. Riverine ecosystems in Cambodia support a highly diverse aquatic animal and plant community, many of which are valuable foods and medicines for rural households.

A number of households in Boribo basin, for example, collect water hyacinth for domestic consumption during the wet season.

Summary

Agriculture is presently the biggest user of water in the Boribo Sub-basin and is likely to expand its share of water demand significantly if the basin’s irrigation potential is fully exploited (fig. 4). Domestic and livestock demands are almost insignificant by comparison (in terms of volume), although they are important in value. With the available data, it is not possible to quantify industrial demands but these are negligible at present and expected to continue to be so. Instream demands (such as fisheries and ecology) are also difficult to quantify, not least of all because the relationships between productivity and water flows are generally not yet well understood.


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Figure 8.5: Present and future composition of major extractive water demands in Boribo Sub-basin

8.4 Economic analysis This section relates to ToR, Task 19: Economic analysis of water utilization

This section attempts to quantify, in monetary terms, the value of water uses in the Boribo Sub-basin. In turn, such an analysis should provide decision-makers with some insight into the relative magnitude of costs and benefits associated with irrigation development and the significance of any water-use trade-offs that may arise.

Economic valuation approach

In order to compare and quantify the economic value of water uses in such a way that the analysis can be used to guide decision-makers towards an economically optimal allocation of water, it is important that the values assigned to the different water uses are comparable (i.e. valued in common units) and that all items can be valued at their value in use or opportunity cost to society.

Opportunity costs

... are the benefits foregone by using a limited resource for one purpose instead of for its next best alternative use (Gittinger, 1996)

The general approach is taken to recognise that water is one of a number of inputs into a process and each input makes a contribution to the final value of the output. Wherever possible, the analysis has attempted to convert the value of water use to a value per m3.

Typically, an economic analysis of water use requires some estimation of the contribution water makes to an industrial process using indicators such as contribution to national GDP/GNP, employment (share of labour force employed by activity), value-added activities and contribution to export earnings) to measure the significance of each activity (WFD CIS Guidance, 2004). However, given the

Present and future composition of extractive water demands in the Boribo Basin

0

20

40

60

80

100

120

Livestock Irrigation Domestic

Mill

ion

cubi

c m

etre

sPresentFuture


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largely subsistence nature of ‘economic activity’ within the study area, such an analysis is more difficult to conduct – and less meaningful - not least of all because the data to substantiate such indicators is rarely available below the national level. Furthermore, these indicators do not give a complete picture of the relative economic importance of each of these activities. For example, they rarely account for informal economic activities (such as subsistence agriculture and non-motorised water transport); roles in poverty reduction; indirect links that arise as a result of the primary activity (e.g. servicing of trucks used to transport produce to market), and the social and environmental impacts of the activities.

The approach adopted here is therefore to quantify the benefits of water at a household level which is justified by the overall poverty alleviation objective of the project.

Markets generate the relative values of all traded goods and services as prices which makes them very useful for comparison as not only are they co-measurable but also some indication of their current relative scarcity value is provided (Hanley and Spash, 1993). However, the use of market prices alone is sometimes not sufficient for analysing the real trade-offs to society as they do not always reflect the total economic value (TEV) of a particular good or service.

Total Economic Value (TEV)

is used to define features in terms of their direct and indirect use and non-use values (see figure 1 below). Using the concept of TEV allows us to include values for benefits that may not have market prices (i.e. they are generally not bought or sold, e.g. ecological services and heritage value) and to examine the environmental and social impacts of development options

In order to make resource allocation decisions based on economic values, what we really want to measure is the net economic benefit obtained from a good or service. For individuals, this is measured by the amount that they are willing to pay, rather than the amount they might actually pay. The amount individuals are willing to pay for something will change if its usefulness or quality changes. Also, if the price or quality of a good changes, that is considered to be a substitute for the original good, willingness to pay for the original good will change.

Sometimes, consumers will be willing to pay more than the market price for a particular good or service because its private value to them is much higher. This may be because the resource has a non-use value that is not typically expressed in the market place or conveys some form of positive externality.

Externalities

are unintended, unpriced impacts of developments. They may be positive where benefits are realised or negative where costs are borne by third parties

The economic benefits of domestic, industrial and agricultural water demands are generally straightforward to quantify, as their values are expressed in the market place. However, economic benefits of environmental water demands are more difficult to quantify, as their values are generally not expressed through market processes.


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All monetary values are expressed in terms of net benefits (i.e. revenues minus costs). This is to account for the fact that prices (set by local, regional and sometimes global markets) are not necessarily good indicators of the true value of a good or service because they do not always account for the value of resources used up in the production of goods and provision of services.

In summary, net benefits for water-dependent activities in the sub-basin were calculated using various approaches as follows:

• By estimating the production costs (including externalities wherever possible) associated with an activity and subtracting these from gross revenues (i.e. gross sales value at point of first sale, or farmgate prices)

• Household survey and commune data was used as far as possible to estimate the net benefits

• In each case, the marginal relationship between water (as an input) and the value of output (i.e. the net benefit) was established to allow further examination of how these values might be expected to change with changes in water availability.

Irrigated agriculture

The value of water used for irrigation can be broadly estimated by determining the net value of irrigated crop harvests. Wet season paddy is the principal crop grown with only relatively small areas of dry season paddy and other supplementary crops receiving any form of irrigation.

The valuation approach can be summarised as follows:

• Although a large share of production is for subsistence, using economic prices for all irrigated crops is justified on the basis that farmers would otherwise need to acquire these products in the market.

• Values are calculated per hectare and per household on the basis of the net profits to farmers once production costs have been accounted for.

• Crop production costs were not widely available for supplementary crops and thus estimates of the approximate returns to production were based on limited information from reports containing farm production budgets. Using this information, production costs are estimated at around 75% for fruit and vegetables. This takes into account both the direct costs of crop production and the opportunity cost of family labour and land.


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Table 8.9: Crop budget summary for Boribo Sub-basin

These findings are consistent with those from other studies including Sareth (2002) who found that gross family income (Gross income minus cash and in-kind costs) equalled US$131 per ha in Takeo province for a single crop and US$119/ha/crop for double cropping. When farmer labour is charged to the budget, rice production was a loss making exercise with net incomes of minus US$103 and minus US$74 for single and double cropping respectively.

Other crop budget summaries are presented in Table 10 indicating the low level of rice farm income across the Lower Mekong Basin.

Table 8.10: Crop budgets for NE Thailand

Rice Rice Rice Corn Potatoes Cultivation type Rainfed Irrigated Irrigated Irrigated Irrigated

Season Wet Wet Dry Dry Dry

Variety Local HYV HYV

Production costs (US$/ha) 98.4 118.0 110.0 128.1 260.9

Cash gross income (US$/ha) 96.9 119.7 130.1 279.2 713.1

Net crop income (US$/ha) -44 -49 21 73 603

* Net crop income assumes labour cost (hired or family) of US$2.5 per day

Source: Euroconsult (1998) in Nesbitt (2005)

It is therefore common for farmers to supplement their farm incomes by seeking labouring jobs nearby or in the cities.

Despite the low profitability of agriculture, it employs more than 80% of the workforce (in terms of person-days) and accounts for around 70% of total household income. In Boribo district, income from rice cultivation is insufficient to

Unit WS rice DS Rice Corn Potatoes Beans Sugarcane Pineapple VegetablesIrrigated area ha 21,612.00 1,109.00 65.00 32.00 1.10 2.70 2.30 51.00Yield t/ha 1.30 2.15 2.00 2.00 2.00 16.40 10.00 2.00Price US$/kg 0.12 0.12 0.09 0.27 0.69 0.11 0.24 0.19Gross value US$/ha 156.00 258.00 185.06 546.01 1,378.67 1,818.18 2,355.89 372.16Production costs 139.09 87.38 138.80 409.50 1,034.00 1,363.64 1,766.92 279.12

Seed US$/ha 12.00 12.00Labour US$/ha 97.50 45.00Fertiliser US$/ha 17.81 17.81Pesticide US$/ha 0.00 0.79Water US$/ha 11.78 11.78Pumping costs US$/ha

Net crop income US$/ha 16.91 170.62 46.27 136.50 344.67 454.55 588.97 93.04Cultivated area per hou ha 2.13 0.11 0.01 0.00 0.00 0.00 0.00 0.01Ave h/hold income US$ 36.00 18.64 0.30 0.43 0.04 0.12 0.13 0.47

Assumptions:1/ Labour is valued at US$1.50 per day (both hired and family); wet season rice requires around 65 days of labour per ha2/ Seed costs US$0.12 per kg. To cultivate 1 ha of rice requires approx 100kg of seed3/ Fertiliser is applied at a rate of around 60kg/ha. One kg costs 1,232 riel4/ Pesticides are applied at a rate of around 0.4 bottles per ha. One bottle costs 8.166 riel5/ Yields for supplementary crops are based on MAFF (2004-5) statistics for Pursat6/ Producer prices for supplementary crops are based on FAOStat database for Cambodia (2003)7/ In the absence of detailed data, production costs for supplementary costs are assumed to be 75% of farmgate prices.

This is consistent with values obtained from individual farm budget studies


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support some households so these households sometimes borrow from other farmers. The loan is paid back the following year from revenue generated by rice sales.

Improving the irrigation system would allow more farmers to engage in dry season paddy production but is unlikely to have the desired effect on poverty unless irrigation improvements are accompanied by:

• investments in appropriate technologies (including higher yield varieties, more water efficient crops and cropping techniques, a shift to higher value crops)

• agricultural extension (including marketing and value-adding), access to markets (including storage, transport infrastructure and the terms of trade offered to farmers)

• some form of agricultural insurance for farmers who are prepared to diversify against the risks of external shocks and stresses such as drought and severe flooding

Livestock

As mentioned earlier, livestock is regarded as both a source of income and as a livelihood safety net. Animal sales are a major source of income for subsistence farmers who see them as ‘banks’ for accumulation of wealth. However, in most cases, livestock are only sold in times of need, for instance in response to shocks such as illness or expenses associated with marriage or death.

The value added by water to livestock is estimated as follows:

• Livestock health (and thus value) is assumed to be directly (but not linearly) related to the availability of sufficient volumes of water for drinking and cleaning. However, water is only one of a number of requirements for good animal health. Since the relationship between water consumption and animal value is not known, the net benefit values in Table X reflect the total value of livestock that water availability supports. They do not reflect the value-added by water alone.

• The gross value of livestock to individual households is equivalent to the market value of total stock holdings (and not simply cash sales) at any given time

• The net value of livestock includes the cost of purchase and raising

Information from the household surveys shows that on average, households earn around US$320 per year from the sale of livestock but the net value of total holdings (shown in Table 8.11) is up to 45 percent higher and provides an important safety net to these households in times of need.


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Table 8.11: Livestock value in the Boribo Sub-basin

It is important to understand that the water-related benefits presented above are believed to be overstated for the following reasons:

• They do not reflect the value-added by water alone, but rather the total net benefits of livestock, where water is just one of a number of inputs.

• The full economic costs of livestock husbandry have not been considered. In practice, there are real costs associated with the feeding and care of animals, including provision of shelter, medication, etc.

During times of drought and severe flood, livestock productivity is adversely affected. Farmers interviewed in Psar and Melum communes reported losses of between 20-40% of their livestock during the floods of 2000. Livestock reportedly suffer ill-health during times of drought, which are an annual occurrence in Boribo Sub-basin. Although the diseases may not be fatal, they require expensive treatment which lowers the total net benefits that households are able to obtain from their livestock holdings.

Domestic consumption

The value of water for household consumption is based on estimates of household willingness-to-pay (WTP).

Most households in the study area collect and store rainwater in large 225 litre jars during the wet season. Each household will have between 3 and 5 jars. The harvested rainwater is used for drinking and cooking only and will last until around Feb/March, where after households either purchase water from vendors (in urban areas) or fetch it from rivers in rural areas.

Those households who purchase water from vendors spend up to US$2 per m3 (information from household surveys). Those households who cannot afford to pay for water are able obtain it from the nearest pagoda or community well. Assuming

Number of head in Boribo basin

Sales value (US$/head)

Gross value to the basin (US$ millions)

Gross value to

each household

(US$)

Purchase costs

(US$/head)

Raising costs from

time of purchase to time of

sale (US$/head)

Net value to the basin

(US$ millions)

Net value to each

household (US$)

Cows 11,085 289 3 316 169 0 1.34 132Buffalo 18,050 289 5 514 169 0 2.17 214Pigs 14,993 108 2 160 24 36 0.72 71Poultry 131,023 3 0 37 0 0 0.38 37Total 175,151 10 1,028 5 454

Assumptions:1/ Market price of chicken is 8000 riel/kg. Each head of chicken produces 1.5kg of meat2/ Households purchase young cows and buffaloes (<3 years) at a cost of 600,000 - 800,000 riel.3/ Households are able to sell mature cows and buffaloes (>3 years) at a price of 1,200, 000 riel.4/ Costs of raising cows and buffalo are minimal (but not zero)5/ Each household spends 2,000 riel per day on pig feed (for 2-3 pigs) or 1,000 riel per day per pig6/ Replacement/purchase costs of poultry are zero. The poultry population regenerates itself.7/ Households sell cows and buffalo on average once every 3 years8/ Pigs are sold every 4-6 months


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that all households hold the same value for a reliable source of clean drinking water (regardless of ability to pay), the value of the benefits derived from drinking water can be set equivalent to the willingness-to-pay for water from vendors.

Water also has significant real costs of supply. Various kinds of costs are involved (Briscoe, 1996; Cotton et al, 1991; Winpenny, 1994; Herrington, 1987; Rogers, Bhatia and Huber, 1997; Webster, 1998):

• Supply costs (the capital and recurrent costs associated with the installation of the necessary infrastructure required to treat, transport and provide services, operation and maintenance costs of this infrastructure and the depreciation costs which accrue over the life of the project as parts need to be repaired or upgraded).

• Opportunity costs (the value of water in its next best alternative use). The size of the opportunity cost depends on the value of the water in its highest alternative current-use value.

• Environmental costs (both direct and indirect, relating to the abstraction, distribution and use of the resource).

Together, the opportunity and supply or use costs make up what is commonly referred to as the ‘economic cost’ of water.

Table 8.12 shows average tariffs and unit production costs for the Phnom Penh water supply authority. It is assumed that district authorities will face similar, if not higher unit production costs.

Table 8.12: Average tariff and unit production costs

Average tariff Unit production cost Phnom Penh 0.244 USD/m3 0.082 USD/m3

Source: ADB (2004) Water in Asian Cities

Table 8.13: Net benefits of domestic water supply

Based on this information, the annual net benefits of domestic water supplies are estimated to be in the region of US$81 per household (Table 8.13).

UnitWTP US$/m3 1.927711Cost of provision US$/m3 0.082Net benefit US$/m3 1.845711Net benefit per household US$ 80.57144

Assumptions:

1/

2/

Vendors sell water for 10,000 riel per truck load (1,250 litres)

The unit costs of production are based on data from Phnom Penh Water Supply Authority (ADB, 2004)


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Fisheries

Net fishery values can be estimated as the yield, times average farm-gate price less the cost of harvesting or production. A very simplistic analysis of the potential gross value of fish in the Boribo Sub-basin is shown in the table below.

Table 8.14: Gross value of the potential fish yield in Boribo Sub-basin

To estimate the net value (i.e. sales value less costs of raising and production), the production costs are estimated to be around 30% of gross (or sales) value (MRC, 2006). This works out to approximately US$21,000.

Standard functional forms for the evaluation of the relationship between water flows and the value of fish production (necessary to calculate the value added by water to the value of fisheries) are not readily available. However, productivity is known to be a function of multiple factors including:

• fishing practices

• total fishing effort

• river flows

• barriers to river migration

• access to and from floodplain habitats and habitat changes

Recent advances have, however, been made in modelling how fisheries productivity may be affected by changes in hydrological flow levels (MRC, 2005) using indicators relating to habitat availability and migration. However, the parameters required to calculate the productivity changes were not available for the project area at the time of this study.

Summary

The findings of the analysis above, suggest that – from a household perspective – livestock raising is the most valuable use of water. Even allowing for the fact that the estimate for the value-added by water to livestock productivity was significantly overstated, this value far exceeds the net benefits achieved by any of the other water uses. Irrigated agriculture provides the lowest net benefits to

Area of water (ha) 408Fish productivity (kg/ha) 150Fish yield (kg) 61,200Fish value (US$) 41,616Fish value per ha (US$) 102

Assumptions:

1/

2/

3/

Fish productivity is based on work by Van Zalinge et al (2001)Fish value is based on farmgate prices for capture fisheries (MRC, 2006)

Ave fish density is uniform across all water bodies in the Boribo sub-basin


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households, based on the data made available from the household surveys. This is unsurprising given the poor quality of soils in the sub-basin, low yields, limited dry-season water availability and high input costs.

From a household perspective, the value of the fishery can be simply estimated on the basis of the value of household consumption and sales. If each household in Boribo Sub-basin is assumed to consume around 100kg per year, then the value of fish to each household is around US$70 per annum. However, the data collected during household surveys suggests that present total demands (around 1,000 tonnes per year) significantly exceed available supplies (around 61 tonnes per year).

Figure 8.6: Value added by water to livelihoods in the Boribo Sub-basin

8.5 Water user groups This section provides background information for ToR Task 17: Inventory of water users committees

Information on Water User Groups (WUGs) was collected from the PDWRAMs.

The WUGs were established with support from the SEILA Program and PDWRAM.

There are two WUGs in Boribo Sub-basin: Thlea M’am Boeng Kantuot Water User Group and Thlea M’am Ou Sandan Water User Group.

They are located in Krakor district (Pursat Province) and use the water from Thlea M’am irrigation system. Both are already registered with PDWRAM Pursat.

Based on the field survey and interview, we found out that those WUGs do not work at all because:

- The irrigation scheme are not yet complete, it has only the main canal and the tributaries are not yet rehabilitated. So the supply of water for farmers are not efficient.

Value added by water to livelihoods in Boribo / Thlea Maam sub-basin

050

100150200250300350400450500

Irrigated agriculture Livestock Domesticconsumption

FisheriesNet

ben

efits

(US

$/ho

useh

old)


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- The water regulation does not work well

- The capacity of the Water User Group Committee is limited

- Lack of budget for O&M of the irrigation system because the community members are not willing to pay because of inefficient service of water supply.

Table 8.15: Water User Groups in Boribo Sub-basin

No Community Province District Commune Registered 1 Thlea Ma’arm Pursat Krakor Boeng Kanturt yes

2 Thlea Ma’arm Pursat Krakor O Sandan yes

Data: PDWRAM in Pursat Province


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References (References marked 'EL' are available in the Electronic Library)

CTI and DHI (Aug 03): Consolidation of hydro-meteorological data and multi-functional hydrological roles of Tonle Sap Lake and its vicinities, Phase II. Final reports. CTI Engineering International Co., Ltd. and DHI – Water & Environment. Client: Mekong River Commission (EL)

CTI (May 04): Consolidation of hydro-meteorological data and multi-functional hydrological roles of Tonle Sap Lake and its vicinities, Phase III. Final report. CTI Engineering International Co., Ltd. And DHI – Water & Environment. Client: Mekong River Commission (EL)

Halcrow (Dec 03): Ranking criteria report. Irrigation Rehabilitation Study in Cambodia, prepared for the Mekong Secretariat by Sir William Halcrow and Partners Ltd. in association with Mandala Agricultural Development Corporation. Contract CAM.IRS 238.93, UNDP Grant 3.3.37/92/UNP, B/L 21

Halcrow (Apr 04): Inventory & analysis of existing systems. Volume 1: Main report; and Volume 6: Pursat, Siem Reap, Svay Rieng, Takeo. Irrigation Rehabilitation Study in Cambodia, prepared for the Mekong Secretariat by Sir William Halcrow and Partners Ltd. in association with Mandala Agricultural Development Corporation. Contract CAM.IRS 238.93, UNDP Grant 3.3.37/92/UNP, B/L 21

Halcrow (Jun 04): Final report: Main report; Annex A: Hydrology; Annex B: Agronomy; Annex C: Lowland rice soils of Cambodia; Annex D: Socio-economics; and Annex F: Environmental assessment. Irrigation Rehabilitation Study in Cambodia, prepared for the Mekong Secretariat by Sir William Halcrow and Partners Ltd. in association with Mandala Agricultural Development Corporation. Contract CAM.IRS 238.93, UNDP Grant 3.3.37/92/UNP, B/L 21

JICA and MRD (May 02): The study on groundwater development in Central Cambodia. Final report prepared for Japan International Cooperation Agency and Ministry of Rural Development, Cambodia, by Kokusai Kogyo Co. Ltd.

MOWRAM (March 2002): Smallholder water and land management in Cambodia. Prepared for Ministry of Water Resources and Meteorology with the assistance of M. P. Mosley as Project Report 5 under the North West Irrigation Sector Project, Part A: Capacity-building in Ministry of Water Resources and Meteorology, Cambodia, funded by ADB (TA 3758-CAM)

MRC-BDP (Nov 05): National Sector Reviews. BDP Library Volume 13, October 2004, revised November 2005. Mekong River Commission

MRC-WUP-JICA (Mar 04a): The study on hydro-meteorological monitoring for water quantity rules in Mekong River Basin. Final report, Volume I (Main report), prepared by CTI and Nippon Koei (EL)

MRC-WUP-JICA (Mar 04b): The study on hydro-meteorological monitoring for water quantity rules in Mekong River Basin. Final report, Volume 2a (supporting documents 1: Improvement of hydrological stations; 2: Gap filling of rainfall data; 3: Hydrological monitoring; 4: Development of hydro-hydraulic model for the Cambodian floodplains; 5: Application of hydro-hydraulic model; and 6: Water use in the Lower Mekong Basin), prepared by CTI and Nippon Koei (EL)

MRC-WUP-JICA (Mar 04c): The study on hydro-meteorological monitoring for water quantity rules in Mekong River Basin. Final report, Volume 2b (supporting documents 7: Maintenance of flows on the Mekong mainstream; 8: institutional strengthening; and 9: Water use management), prepared by CTI and Nippon Koei (EL)

MRC-WUP-JICA (Mar 04d): The study on hydro-meteorological monitoring for water quantity rules in Mekong River Basin. Final report, Volume III (Summary), prepared by CTI and Nippon Koei (EL)

Le van Sanh (June 02): Mission Report, Analysis of Hydrological Data at Stations around the Great Lake and on Mekong, Bassac Rivers in 1960s and from 1998 to 2001. Phnom Penh

Nanni, Marcella (April 2001): End of assignment report, submitted to MOWRAM (Cambodia) by SMEC International Pty. Ltd. under the Agricultural Hydraulics Component of the Agricultural Productivity Improvement Project

Nhim Sophea (Mar 06): Water quality data assessment 2005, MRC water quality monitoring network. Water Quality Office, Department of Hydrology and River Works, MOWRAM

OADA (Mar 03): Study report on Kamping Puoy Irrigation Scheme Rehabilitation project in Battambang Province, the Kingdom of Cambodia. Overseas Agricultural Development Association

WUP-FIN (Aug 02b): Data report. MRC Water Utilization Program, WUP-FIN component - Modelling of the flow regime and water quality of the Tonle Sap Karri Eloheimo, Seppo Hellsten, Teemu Jantunen, Janos Jozsa, Mikko Kiirikki, Hannu Lauri, Jorma Koponen, Juha Sarkkula, Olli Varis, and Markku Virtanen (EL)


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Appendix 1: Thematic maps Note: This appendix is intended to provide an overview. The maps are submitted separately

Sub-basin map

Administrative units

Land use

Geology


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Elevations

Protected areas

Soils

Floods


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Gauges


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Appendix 2: Data files Note: The data files are submitted separately

Table A2.1: Time series data

File name Contents [email protected] Daily, monthly and annual rainfall at Battambang (8 years), Kg Chhnang (55 years),

Pursat (60 years), Krakor (36 years), Kravanh (10 years), Svay Donkeo (6 years), Talo (6 years), Bamnak (15 years) and Boeung Khnar (7 years)





[email protected] Daily water level at Kg Chhnang 1995-2004 (10 years)

[email protected] Daily water level at Prek Kdam 1995-2004 (10 years)

[email protected] Daily and monthly flow at Prek Kdam 1964-73 (10 years)

[email protected] Daily water level and calulated flow at Boribo (St. 590101) Jun 98 - Dec 05 (7.5 years)

[email protected] Daily water level and calulated flow at Maung Russey (St. Dauntry) (St. 5501101) Jun 01 - Dec 02 (1.5 years)

[email protected] Flow records from St. Boribo (91 months), St. Dauntri (19 months), and St. Pursat (72 and 58 months)

Table A2.2a: Data tables: Geography. livelihoods

File name Contents Area-population.xls Area and population (2002-04) within the study area; buffaloes, cows, horses, goats,

pigs, and poultry; families using fertilizer; by province, district and commune

Communes-catchments.xls Commune areas within each sub-catchment

Elevations.xls Distribution of land elevation within each sub-basin

Forestcover.xls Forest cover within each sub-basin (1993, 1997, 2002, 2005), and rate of change

Soils.xls Soil classification in each sub-basin

Geology.xls Geological classification of each sub-basin

Protectedareas.xls Protected areas in each sub-basin


B-farming-econ-03-05.xls Boribo sub-basin, PRD survey Jul-Aug 2006: Economy of farming households (2003-05)

Table A2.2b: Data tables: Water uses

File name Contents Domesticdemand.xls Present and projected domestic water demand in each sub-basin

Irrigation.xls Wet and dry season irrigated areas, actual and potential, in each sub-basin

Subprojects.xls Water availability for candidate sub-projects, and irrigable areas


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Table A2.2c: Data tables: Water balance

File name Contents Monitoringstations.xls Rainfall, water level and flow monitoring stations inside or near the study area

B-W-balance-4of5yrs.xls Boribo Sub-basin, calculated water balance, present conditions, with water uses and availability, in 4 out of 5 years, whole sub-basin and details


D-W-balance-4of5yrs.xls Dauntry Sub-basin, calculated water balance, present conditions, with water uses and availability, in 4 out of 5 years, whole sub-basin and details

D-W-balance-scenarios.xls Dauntry Sub-basin, calculated water balance, alternative scenarios: Damnak Ampil canal, candidate sub-projects, and impact of climate change

Wells.xls Inventory of groundwater wells and yield

Wells-KgChhnang.xls Inventory of groundwater wells in Kg Chhnang, with yield and geological layers


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Appendix 3: Water management structures

St. Boribo


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St. Bamnak


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St. Thlea Maam


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Appendix 4: Water balance tables Note: The water balance tables are also submitted as electronic data files

Base situationRainfall Evaporation Storage and Water Domestic Irrigation Livestock Outflow

losses availability uses uses uses from catchment[m3/s] [m3/s] [m3/s] [m3/s] [m3/s] [m3/s] [m3/s] [m3/s]

January 1.7 10.8 -11.8 2.7 0.014 0.611 0.013 2.1February 2.5 4.0 -2.8 1.3 0.014 0.611 0.013 0.7March 20.4 20.4 -0.8 0.8 0.014 0.523 0.013 0.2April 38.4 38.4 -0.7 0.7 0.014 0.523 0.013 0.1May 73.4 57.5 10.9 4.9 0.014 0.523 0.013 4.4June 65.0 53.8 0.7 10.6 0.014 0.523 0.013 10.1July 68.4 47.1 -2.6 23.8 0.014 1.746 0.013 22.1August 89.2 41.7 -0.6 48.1 0.014 1.746 0.013 46.4September 115.9 32.9 17.5 65.4 0.014 1.746 0.013 63.7October 111.3 36.3 24.6 50.5 0.014 1.746 0.013 48.7November 54.6 43.4 -6.4 17.7 0.014 1.746 0.013 15.9December 8.8 33.7 -31.1 6.2 0.014 0.611 0.013 5.6Yearly 54.1 35.0 -0.3 19.4 0.014 1.055 0.013 18.3

Table A4.1: Summary statistics for water balance of Boribo Sub-basin, base situation

Increase in domestic water useRainfall Evaporation Storage and Water Domestic Irrigation Livestock Outflow



Table A4.2: Summary statistics for water balance of Boribo Sub-basin, increase in domestic water use


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Climatic changeRainfall Evaporation Storage and Water Domestic Irrigation Livestock Outflow



Table A4.3: Summary statistics for water balance of Boribo Sub-basin, climatic change.

Candidate projects 50%-50% distributionRainfall Evaporation Storage and Water Domestic Irrigation Livestock Outflow



Table A4.4: Summary statistics for water balance of Boribo Sub-basin, candidate project 50%-50% distribution

Candidate projects 100%-0% distributionRainfall Evaporation Storage and Water Domestic Irrigation Livestock Outflow



Table A4.5: Summary statistics for water balance of Boribo Sub-basin, candidate project 100%-0% distribution


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Table A4.6a: Water balance on monthly basis for catchments 13, 14 and 11, base situation

Catchment 13 Base situationArea (km2): 129 Water useRunoff Rainfall Inflow from Domestic Irrigation Livestock Outflowm3/s m3/s upstream m3/s m3/s m3/s m3/s

jan 0.23 0.15 0.00 0.0003 0.0020 0.0002 0.23feb 0.11 0.20 0.00 0.0003 0.0020 0.0002 0.11mar 0.06 1.74 0.00 0.0003 0.0020 0.0002 0.05apr 0.04 3.28 0.00 0.0003 0.0020 0.0002 0.03may 0.42 6.32 0.00 0.0003 0.0020 0.0002 0.42jun 0.91 5.57 0.00 0.0003 0.0020 0.0002 0.91jul 2.04 5.87 0.00 0.0003 0.0620 0.0002 1.98aug 4.13 7.66 0.00 0.0003 0.0620 0.0002 4.06sep 5.61 9.95 0.00 0.0003 0.0620 0.0002 5.54oct 4.33 9.56 0.00 0.0003 0.0620 0.0002 4.26nov 1.51 4.68 0.00 0.0003 0.0620 0.0002 1.45dec 0.53 0.75 0.00 0.0003 0.0020 0.0002 0.53






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Table A4.6b: Water balance on monthly basis for catchments 15, 10 and 8, base situation








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Table A4.6c: Water balance on monthly basis for catchments 9, 7 and 6, base situation








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Table A4.6d: Water balance on monthly basis for catchments 5, 68 and 6, base situation








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Table A4.6e: Water balance on monthly basis for catchments 2, 16 and 17, base situation








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Table A4.6f: Water balance on monthly basis for catchments 18 and 19, base situation




jan 0.25 0.16 0.98 0.0023 0.5010 0.0025 0.72feb 0.12 0.22 0.48 0.0023 0.5010 0.0025 0.09mar 0.06 1.90 0.23 0.0023 0.4130 0.0025 -0.13apr 0.04 3.59 0.15 0.0023 0.4130 0.0025 -0.23may 0.46 6.91 1.80 0.0023 0.4130 0.0025 1.84jun 0.99 6.09 3.87 0.0023 0.4130 0.0025 4.44jul 2.24 6.42 8.30 0.0023 0.0120 0.0025 10.52aug 4.51 8.38 17.18 0.0023 0.0120 0.0025 21.68sep 6.14 10.88 23.50 0.0023 0.0120 0.0025 29.62oct 4.73 10.44 18.04 0.0023 0.0120 0.0025 22.75nov 1.66 5.11 6.04 0.0023 0.0120 0.0025 7.68dec 0.58 0.82 2.25 0.0023 0.5010 0.0025 2.33


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Table A4.7a: Water balance on monthly basis for catchments 13, 14 and 11, increase in domestic water use

Catchment 13 Increase of domestic water useArea (km2): 129 Water useRunoff Rainfall Inflow from Domestic Irrigation Livestock Outflowm3/s m3/s upstream m3/s m3/s m3/s m3/s







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Table A4.7b: Water balance on monthly basis for catchments 15, 10 and 8, increase in domestic water use








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Table A4.7c: Water balance on monthly basis for catchments 9, 7 and 6, increase in domestic water use








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Table A4.7d: Water balance on monthly basis for catchments 5, 68 and 67, increase in domestic water use








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Table A4.7e: Water balance on monthly basis for catchments 2, 16 and 17, increase in domestic water use








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Table A4.7f: Water balance on monthly basis for catchments 18 and 19, increase in domestic water use






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Table A4.8a: Water balance on monthly basis for catchments 13, 14 and 11, climatic change

Catchment 13 Climatic changeArea (km2): 129 Water useRunoff Rainfall Inflow from Domestic Irrigation Livestock Outflowm3/s m3/s upstream m3/s m3/s m3/s m3/s







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Table A4.8b: Water balance on monthly basis for catchments 15, 10 and 8, climatic change








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Table A4.8c: Water balance on monthly basis for catchments 9, 7 and 6, climatic change








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Table A4.8d: Water balance on monthly basis for catchments 5, 68 and 67, climatic change








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Table A4.8e: Water balance on monthly basis for catchments 2, 16 and 17, climatic change








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Table A4.8f: Water balance on monthly basis for catchments 18 and 19, climatic change






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Table A4.9a: Water balance on monthly basis for catchments 13, 14 and 11, candidate project 50%-50%

Catchment 13 Candidate project (50%-50% diversion)Area (km2): 129 Water useRunoff Rainfall Inflow from Domestic Irrigation Livestock Outflowm3/s m3/s upstream m3/s m3/s m3/s m3/s







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Table A4.9b: Water balance on monthly basis for catchments 15, 10 and 8, candidate project 50%-50%








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Table A4.9c: Water balance on monthly basis for catchments 9, 7 and 6, candidate project 50%-50%








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Table A4.9d: Water balance on monthly basis for catchments 5, 68 and 67, candidate project 50%-50%








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Table A4.9e: Water balance on monthly basis for catchments 2, 16 and 17, candidate project 50%-50%








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Table A4.9f: Water balance on monthly basis for catchments 18 and 19, candidate project 50%-50%






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Table A4.10a: Water balance on monthly basis for catchments 13, 14 and 11, candidate project 100%-0%








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Table A4.10b: Water balance on monthly basis for catchments 15, 10 and 8, candidate project 100%-0%








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Table A4.10c: Water balance on monthly basis for catchments 9, 7 and 6, candidate project 100%-0%








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Table A4.10d: Water balance on monthly basis for catchments 5, 68 and 67, candidate project 100%-0%








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Table A4.10e: Water balance on monthly basis for catchments 2, 16 and 17, candidate project 100%-0%








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Table A4.10f: Water balance on monthly basis for catchments 18 and 19, candidate project 100%-0%






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Appendix 5: Water quality simulations

A5.1 General MIKE Basin set-up

A MIKE Basin Water Quality model was setup for the Boribo study area based on the water balance. The water balance is based on down stream discharges calculated from the water level measurements and Q/h relations which are available for 1998 – 2005. The Q/h relation is primarily based on measured discharge data from 2001. Calculated discharges have been translated into area specific runoffs as input for the MIKE Basin model.


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A5.2 Present conditions Figure A5.1: Average concentration of BOD for 2000 and 2001

Figure A5.2: Maximum concentration of BOD for 2000 and 2001

Please note: Not same scale as the above figure


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Figure A5.3: Average concentrations of NH4 for 2000 and 2001

Figure A5.4: Maximum concentrations of NH4 for 2000 and 2001


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Figure A5.5: Average concentrations of NO3 for 2000 and 2001

Figure A5.6: Maximum concentrations of NO3 for 2000 and 2001


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A5.3 Implications of irrigation development Figure A5.7: Average concentration of BOD for the candidate sub-projects

Figure A5.8: Maximum concentration of BOD for the candidate sub-projects

Please note: Not same scale as the above figure


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Figure A5.9: Difference in BOD concentrations between the candidatesub- projects and the present situation

Figure A5.10: Average concentrations of NH4 for the candidate sub-projects


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Figure A5.11: Maximum concentrations of NH4 for the candidate sub-projects

Figure A5.12: Difference in NH4 concentrations between the candidate sub-projects and the present situation


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Figure A5.13: Average concentrations of NO3 for the candidate sub-projects

Figure A5.14: Maximum concentrations of NO3 for the candidate sub-projects


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Figure A5.15: Difference in NO3 concentrations between the candidate sub-projects and the present situation

Figure A5.16: Difference in total-phosphorus concentrations between the sub-candidate projects and the present situation

Project Working Team of River Basin Study-Package 2 Dr. Tue Kell Nielsen Team Leader Mr. Toch Sophon Co Team Leader Mr. Henrik Garsdal Hydrology Expert Mr. Jens Erik Lyngby Water Quality Expert Mr. Teang Sokhom GIS and Remote Sensing Specialist Mr. Prum Peurn Water Use and Water Balance Specialist Ms. Petrina Rowcroft Environmental Economic Expert Ms. Sorn Somoline Socio-Economic Specialist Mr. Nay Sophon Community Development Specialist

final report vol2-river basin study

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