final report vol3-river basin study

8/14/2019 Final Report Vol3-River Basin Study

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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 3: Dauntri Sub-basin

5 December 2006

Prepared for

MINISTRY OF WATER RESOURCES AND METEOROLOGY

by

PRD Water & Environment in association with DHI Water & Environment


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North West Irrigation Sector Project

River basin and water use studies, Package 2

Revisions

Version 1: New section 4.4: Water availability

Summary expanded

Table 8.3 changed

Version 1a: Section 4.4 expanded

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

Version 2: Section 3.5: Reference added to Appendix 3

Sections 4.3 and 4.4, new Table 4.14: Discussion of a further extension of the

Damnak Ampil Canal all the way to St. Dauntri (to serve the Prek Chik candidatesub-project), with exemplification of achievable benefits

New Section 4.5 (allocation of manageable flows), with explanation of manageableflows, 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 ProvincialDepartments, the district officers, and the many individual persons who have kindly taken time out toshare their knowledge for the purpose of the present study. MOWRAM, the PMO, the PIUs and theTA Consultant have provided valuable guidance and shared data and knowledge, including resultsfrom monitoring programmes and previous related studies. MRC has kindly made data and GIS layersavailable 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 Franaise de Dveloppement (AFD). Ithas the overall objective of supporting the effort of the Royal Government of Cambodia to reducepoverty in rural areas of northwest Cambodia through enhanced agricultural production. Theimmediate objectives are to improve the use of water resources and to take advantage of the potentialfor irrigated agriculture.

One activity of the NWISP is a series of river basin and water use studies, which have the over-allobjective 'to provide a framework leading eventually to institutional means for installing ascientifically 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 the Dauntri Sub-basin in Battambang and Pursat Provinces, and theBoribo Sub-basin in Pursat and Kg Chhnang Provinces (and with a small corner in Kg Speu Province).

The present 'Final Report, volume 3'describes the water balance and water uses in Dauntri 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 presentstudy. The analyses have been supported by numerical river basin modeling of water balance andwater quality.

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

Dauntri Sub-basin (St. Kambot, St. Svay Donkeo and St. Dauntri)Area: 3,542 km2 (21 percent of which is more than 100 m above mean sea level)Cultivated area (rice and other crops) (2005): 1,623 km2, of whichwet season irrigated: 17 km2 (actual), 447km2 (potential)dry season irrigated (2 crops per year): 5 km2 (actual), 3 km2 (potential)Population (2004): 233.509

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

Rainfall Evapo-ration Storage andlosses

Wateravailability

Domesticuses

Irrigationuses

Livestockuses

Outflow

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

119,9 81,0 0,1 38,8 0,1 6,5 0,4 31,8

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

33,3 22,5 - 10,8 - 1,8 0,1 8,8

'-' means 'less than 0.05'


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

Water availability at candidate sub-projects

Krouch Sauch Anlong Svay Anlong Svay and RoneamPrayol (to share)

Prek Chik

Low estimate High estimate Low estimate High estimate Low estimate High estimate

(a) (a) (a) (a) (a), (b) (a), (b) (c)

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

J 1,5 2,7 2,4 4,0 2,4 4,0 0,3

F 0,9 1,7 1,3 2,3 1,3 2,3 -0,1

M 0,9 1,7 1,3 2,3 1,3 2,3 -0,3

A 0,9 1,7 1,3 2,3 1,3 2,3 -0,3

M 1,5 2,7 2,2 3,8 2,2 3,8 -0,3

J 2,1 3,6 3,3 5,4 3,3 5,3 0,9

J 4,9 7,1 9,6 12,6 9,9 12,9 8,2

A 8,2 10,5 17,0 20,0 18,2 21,2 21,3

S 10,2 12,5 21,4 24,4 23,1 26,1 29,1

O 8,2 10,4 16,9 19,9 18.0 21,0 21,1

N 4,1 6,4 7,9 10,9 8,1 11,1 5,2

D 2,2 3,7 3,7 5,7 3,7 5,7 1,5

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 Krouch Sauch, Anlong Svay and Roneam Prayol is influenced by the operation of the DamnakAmpil Canal. The low and high estimates are based on assumptions about the future operation. Please refer to text fordetails

(b) The water availability at Roneam Prayolis influenced by the implementation of the Anlong Svay scheme

(c) Negative values means that water is inadequate for the assumed future domestic and livestock demand

No allocation has been made for in-stream demands


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River basin and water use studies, Package 2 i

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 ......................................................................................42.4 Irrigation.................................................................................................................6

3 Hydrology..........................................................................................................................10

3.1 Data ......................................................................................................................10

3.2 River network and catchment delineation............................................................10

3.3 Rainfall and evaporation ......................................................................................14

3.4 Streamflow ...........................................................................................................15

3.5 Regulation ............................................................................................................17

4 Water uses and water balance............................................................................................22

4.1 Water uses ............................................................................................................22

4.2 Water balance.......................................................................................................23

4.3 Candidate sub-projects .........................................................................................39

4.4 Water availability .................................................................................................41

4.5 Allocation of manageable flows...........................................................................45

5 Morphology, floods and drought.......................................................................................51

5.1 Data ......................................................................................................................51

5.2 Morphology..........................................................................................................51

5.3 Floods and drought...............................................................................................52

6 Aquatic environment .........................................................................................................55

6.1 Data ......................................................................................................................55

6.2 Pollution loads......................................................................................................55

6.3 Water quality........................................................................................................63

6.4 Implications of irrigation development ................................................................65

7 Fisheries.............................................................................................................................69

7.1 Dauntri River........................................................................................................69

7.2 Svay Don Keo River ............................................................................................69

7.3 St. Kambot............................................................................................................69

8 Socio-economics................................................................................................................71

8.1 Data ......................................................................................................................71


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River basin and water use studies, Package 2 ii

8.2 Socio-economic context .......................................................................................71

8.3 Water utilization...................................................................................................77

8.4 Economic analysis................................................................................................85

8.5 Water user groups ................................................................................................91

References..............................................................................................................................................92

Appendix 1: Thematic maps ..................................................................................................................93

Appendix 2: Data files ...........................................................................................................................98

Appendix 3: Water management structures .........................................................................................100

St. Dauntri (St. Moung) ...................................................................................................100

St. Svay Donkeo ..............................................................................................................101

St. Kambot (Preahmlu)....................................................................................................102

Appendix 4: Water balance tables........................................................................................................103Appendix 5: Water quality simulations................................................................................................133

A5.1 General ...............................................................................................................133

A5.2 Present conditions ..............................................................................................135

A5.3 Implications of irrigation development..............................................................139


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River basin and water use studies, Package 2 iii

Figures

2.1: Communes in Dauntri Sub-basin

2.2: Land elevations in Dauntri Sub-basin

2.3: Land elevation distribution in Dauntri Sub-basin

2.4: Land use in Dauntri Sub-basin

2.5: Irrigation schemes in Dauntri Sub-basin

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

3.2: Comparison between sub-basin boundaries

3.3: Ou Souphi Offtake

3.4: Monthly average flow, St. Dauntri

3.5: Structures along the Damnak-Ampil Canal

3.6: The Damnak Ampil Canal and regulator under construction (6 July 06)

3.7: The Damnak-Ampil Canal from Pursat River to Prek Chik

3.8: Photos from the Damnak-Ampil Canal

4.1: MIKE Basin model of the Dauntri Sub-basin

4.2: Schematic representation of sub-catchments

4.3: Rainfall-runoff simulation for the Dauntri catchment

4.4: Simulated and observed discharge in Stung Sangker at Battambang

4.5: Schematisation of the Damnak-Ampil irrigation canal

4.6: Water availability, present conditions, April, m3/s

4.7: Specific water availabilty, present conditions, April (l/s/km2)

4.8: Water availability, present conditions, September (m3/s)

4.9: Specific water availabilty, present conditions, September (l/s/km2)

4.10: Specific water availabilty, present conditions, annual (l/s/km2)

4.11: Ratio between groundwater flow and total runoff

4.12: Schematization of St. Kambot

4.13: Schematization of St. Svay Donkeo

4.14: Schematization of St. Dauntri

5.1: Erosion and accretion

6.1: Amount of annual BOD load by sub-catchment

6.2: Location of the sub-catchments

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

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

6.5: Time series results for the outlet of St. Dauntri, present conditions

6.6: Simulated discharge for reference scenario and the candidate sub-projects


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River basin and water use studies, Package 2 iv

6.7: Changes in water discharge from the present situation after irrigation development

6.8: Time series results for the outlet of St. Dauntri after irrigation deveopment

8.1: Household income structure

8.2: Main sources of drinking water in Pursat and Battambang Provinces

8.3: Irrigated cropping areas in Dauntri Sub-basin

8.4: Present and future composition of major extractive water demands

8.5: Value added by water to livelihoods in Dauntri Sub-basin

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 2001A5.5: Average concentrations of NO3 for 2000 and 2001

A5.6: Maximum concentrations of NO3 for 2000 and 2001

A5.7: Average concentrations of Total-phosphorus for 2000 and 2001

A5.8: Maximum concentrations of Total-phosphorus for 2000 and 2001

A5.3 Implications of irrigation development

A5.9: Average concentration of BOD for the candidate sub-projects

A5.10: Maximum concentration of BOD for the candidate sub-projects

A5.11: Difference in BOD concentrations between the candidate sub-projects and the presentsituation

A5.12: Average concentrations of NH4 for the candidate sub-projects

A5.13: Maximum concentrations of NH4 for the candidate sub-projects

A5.14: Difference in NH4 concentrations between the candidate sub-projects and the present situation

A5.15: Average concentrations of NO3 for the candidate sub-projects

A5.16: Maximum concentrations of NO3 for the candidate sub-projects

A5.17: Difference in NO3 concentrations between the candidate sub-projects and the present situation

A5.18: Average concentrations of total-phosphorus for the candidate sub-projects

A5.19: Maximum concentrations of total-phosphorus for the candidate sub-projects

A5.20: Difference in total-phosphorus concentrations between the candidate sub-projects and thepresent situation


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River basin and water use studies, Package 2 v

Tables

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

2.2: Land use

2.3: Forest cover

2.4: Irrigation schemes in Dauntri Sub-basin

3.1: Distribution of annual rainfall

3.2: Pan evaporation

3.3: Assumed flow from Pursat River into the Damnak-Ampil Canal

4.1: Estimate of future domestic demand, Dauntri Sub-basin

4.2: Summary water balance, base situation, 4 out of 5 years

4.3: Summary water balance with the Damnak Ampil Canal

4.4: Monthy simulated ratio between groundwater flow and total runoff

4.5: Summary water balance with Damnak Ampil Canal and candidate sub-projects

4.6: Summary water balance with Damnak Ampil Canal, candidate sub-projects, and climatechange

4.7: Estimated water availability at Krouch Saeuch

4.8: Estimated water availability at Anlong Svay

4.9: Estimated water availability at Roneam Prayol

4.10: Estimated water availability at Prek Chik4.11: Manageable flows downstream of candidate sub-projects

4.12: Rainfall deficit

4.13: Irrigable areas

4.14: Irrigable area at Prek Chik assuming a supply from the Damnak Ampil Canal

5.1: Cultivation areas affected by floods and drought

5.2: Occurrence of floods and drought

6.1: Distribution of areas for rice cultivation and estimated fertiliser application

6.2: Overall generated load of BOD, nitrogen and phosphorus

6.3: Estimated BOD load reaching the river in each subcatchment

6.4: Estimated nitrogen load reaching the river in each subcatchment

6.5: Estimated phosphorus load reaching the river in each subcatchment

8.1: Sources of cash income in each sub-basin

8.2: Summary socio-economic indicators

8.3: Cultivated areas in Dauntri Sub-basin

8.4: Irrigated crop areas


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River basin and water use studies, Package 2 vi

8.5: Future demands for irrigation in Dauntri Sub-basin

8.6: Present livestock water demands in Dauntri Sub-basin (2005)

8.7: Projected livestock water demands to 2030

8.8: Projected domestic consumption demands

8.9: Crop budget summary for Dauntri Sub-basin

8.10: Livestock value in Dauntri Sub-basin

8.11: Average tariff and unit production costs

8.12: Net benefits of domestic water supply

8.13: Value of the potential fish yield in Dauntri Sub-basin

8.14: Water User Groups in Dauntri Sub-basin

A2.1: Time series data

A2.2: Data tables

A4.1: Summary water balance, base situation

A4.2: Summary water balance, base situation with Damnak Ampil Canal

A4.3: Summary water balance with Damnak Ampil Canal and candidate sub-projects

A4.4: Summary water balance with Damnak Ampil Canal, candidate sub-projects and climatechange

A4.5: Water balance, base situation

A4.6: Water balance with Damnak Ampil Canal

A4.7: Water balance with Damnak Ampil Canal and candidate sub-projects

A4.8: Water balance with Damnak Ampil Canal, candidate sub-projects and climate change


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River basin and water use studies, Package 2 vii

Acronyms and abbreviations

ADB : Asian Development Bank

AFD : Agence Franaise de Dveloppement

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


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River basin and water use studies, Package 2 viii

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)


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River basin and water use studies, Package 2 ix

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 specificlocation (like a cross-section of a river or canal, or a lake or reservoir). A catchment isdelineated by a catchment boundary. It can be a river basin or a part of a river basin. Same asdrainage area

Catchment boundary: The boundary of a catchment (or a river basin or a sub-catchment). The surfaceflow of rain falling on each side of the boundary will proceed towards different locations. Areview 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 usedboth for the Mekong Basin and the Tonle Sap Basin. (In some other studies, the Tonle SapBasin is referred to as a sub-basin of the Mekong Basin)

Study area (Package 2): The Dauntri/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 withthe Dauntri/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, anirrigation scheme will receive water from a sub-catchment, and sub-catchments are used asunits 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 acatchment. Watershed management can cover different aspects of water-related managementwithin 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,Dauntri/Dauntry /Daun Try, etc.

St. Dauntri is also named St. Muong, and St. Kambot is also named St. Preahmlu.


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River basin and water use studies, Package 2 x

Location map

1 450 000

1 400 000

1 350 000

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


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River basin and water use studies, Package 2 1

1 Introduction

The Northwest Irrigation Sector Project (NWISP) is being implemented by

MOWRAM, with assistance from Asian Development Bank (ADB) and AgenceFranaise de Dveloppement (AFD). It has the overall objective of supporting theeffort of the Royal Government of Cambodia to reduce poverty in rural areas ofnorthwest Cambodia through enhanced agricultural production. The immediateobjectives are to improve the use of water resources and to take advantage of thepotential for irrigated agriculture. It is intended to establish ten to twelverehabilitated and sustainably operational small to medium-scale irrigation systemsand other water control infrastructure.

The NWISP is managed by a Project Management Office (PMO) withinMOWRAM, assisted by a TA Consultant (BCEOM/ACIL/SAWAC). Theassistance 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, Package2', covering Dauntri Sub-basin in Battambang and Pursat Provinces, and BoriboSub-basin in Pursat and Kg Chhnang Province. This work is being carried out byPRD Water & Environment in association with DHI Water & Environment.

The scope of the river basin and water use studies is specified in the Terms ofReference 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 masterplanning 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 hasbeen indexed and compiled on a CD.

A report about Dauntri Sub-basin was discussed at a workshop in Battambang on27 October 2006. The present revised report is based on guidance received at theworkshop as well as from the TA Consultant.


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2 Geography

2.1 DataThis 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 (showingtopographical 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. Thecommune is the basic unit for a substantial part of the geographic, agricultural andsocio-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; byprovince, district and commune

In Dauntri-Svay Don Keo Sub-basin, the population density was 56 persons/km2 in2004and the population growth was 1.5 percent/year from 2002 to 2004.

The Tonle Sap Basin in general witnesses the highest population growth within the

Lower Mekong Basin, with 4.8 % per year as compared with Cambodia's averagerate of 2.2/2.5 % per year (CNMC October 04, p. 30). The difference is partlyrelated to migration.

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 higherin urban areas than in rural areas.

District and commune boundaries, areas and population are shown in the followingfigure and table.


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Figure 2.1: Communes in Dauntri Sub-basin

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

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

Population withinsub-basin (2004)

Battambang Moung Ruessei Moung 50.9 38.9 12,672

Kear 96.2 96.2 15,941

Prey Svay 143.6 143.6 13,114

Ruessei Krang 163.1 163.1 14,251

Chrey 491.7 280.3 6,478

Ta Loas 135.9 73.9 4,288

Kakaoh 85.6 36.2 4,904

Robas Mongkol 128.8 104.3 9,228

Prek Chik 139.2 139.2 12,544

Prey Tralach 273.6 273.6 20,663

Koas Krala Doun Ba 199.2 39.8 620

Chhnal Moan 624.5 218.6 992

Pursat Bakan Boeng Bat Kandaol 194.9 25.3 1,276

Boeng Khnar 56.6 56.6 12,188

Khnar Totueng 53.7 53.7 7,734

Me Tuek 265.0 262.3 14,429

Ou Ta Paong 292.0 292.0 15,674

Rumlech 52.9 52.9 8,154

Snam Preah 228.9 13.7 984

Svay Doun Kaev 29.9 29.9 5,978

Ta Lou 305.0 305.0 15,354

Trapeang Chong 83.0 69.5 16,119

Phnum Kravanh Bak Chenhchien 40.7 14.7 2,543

Phteah Rung 156.1 143.6 14,396

Samraong 546.6 36.0 634

Sampov Meas Lolok Sa 42.7 7.7 1,700

Veal Veaeng Krapeu Pir 705.6 535.5 532

Pramaoy 865.9 35.7 118

Total 3,541.9 233,509

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


Landuse.xls Land use within each sub-basin (2005), and forest cover within eachsub-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

The land elevation in the sub-basin is illustrated below. The highest elevation inDauntri-Svay Don Keo Sub-basin is around 1,273 m (according to the 50 x 50 mresolution DEM).

Figure 2.2: Land elevations in Dauntri Sub-basin

Figure 2.3: Land elevation distribution in Dauntri Sub-basin

0-20 m (55.4 pct)

20-50 m (19.5 pct)

50-100 m (4.4 pct)

> 500 m (2.3 pct)

200-500 m (8.4 pct)

100-200 m (10.0 pct)


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Land use and soils

The present land use (2005) is shown in the following figure, which provides animportant 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 givenin Tables 2.2 and 2.3.

Figure 2.4: Land use in Dauntri Sub-basin

Data: Interpretation from Landsat ETM (2005)

Table 2.2: Land use (2005)

Land use Area (km2)

Evergreen forest 386

Semi-evergreen forest 182

Deciduous forest 543

Other forest 552

Grassland 181

Dry season rice 6

Rain fed rice 1,538

Other crop 85

Village 60

Water 10

Total 3,542


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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 224 224 395 386 0,0 4,8 4,6

Semi-evergreen forest 298 298 186 181 0,0 -3,2 -3,3

Deciduous forest 427 427 549 543 0,0 3,5 3,3

Other forest 996 973 516 552 -0,6 -13,5 -12,5

Non-forest 1.598 1.621 1.895 1.879 0,6 8,4 7,9

Total 3.542 3.542 3.542 3.542 0,0 0,0 0,0

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

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


Irrigation.xls Wet and dry season irrigated areas (actual and potential)

Many of the schemes were registered and evaluated under the so-called Halcrowstudy in 1994, conducted for the Mekong Committee (today's MRC). Some ofthem, including most candidate sub-projects, were re-visited and evaluated underNWISP 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 theirnames. The UTM coordinates provide the best identification.

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

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


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Figure 2.5: Irrigation schemes in Dauntri Sub-basin


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Table 2.4: Irrigation schemes in Dauntri Sub-basin

District Name Commune Existing Potential Status

Wet (ha) Dry (ha) Wet (ha) Dry (ha)

Moung R. Po Canal, Ream Kun Chrey, Ta Lass 400 0 2.500 0 2

Moung R. Don Try Chrey, Ta Lass 70 20 1.550 0 1

Moung R. Ta Nak Kear 8 0 65 0 2

Moung R. Our Beng Kear 20 0 20 0 2

Moung R. Our Veng Kear 0 0 50 0 1

Moung R. Ream Koun Kear, Chrey, Prey Svay 190 0 4.700 0 2

Moung R. Kbal Mus Moung 0 0 300 0 1

Moung R. Prek Ta Am Moung 400 0 1.000 0 3

Moung R. Anglong Koub Muong Reusei 0 450 1.350 0 2

Moung R. Basac Reservoir Prek Chik 0 0 3.500 0 1

Moung R. Or Rum Chek Prek Chik 0 0 0 30 1

Moung R. Tracheak Chett Prek Chik, Prek Talach 0 0 1.900 0 1

Moung R. Srer Sdao Prek Chik, RobasMongko

0 0 500 0 1

Moung R. Prek Chik Prek Chik, RuesseiKran

490 0 18.470 0 CS, 2

Moung R. Chhouk Prey Svay 0 0 240 0 1

Moung R. Tum Leng Prey Svay 0 0 100 0 1

Moung R. Rum Chek Prey Svay 0 0 90 0 1

Moung R. Chay Vay Prey Svay 0 0 90 0 1

Moung R. Taserk Prey Tralach 0 0 900 0 1

Moung R. Prey Tralach Prey Tralach 0 0 2.700 0 1

Moung R. Cheang Chaot Prey Tralach 0 0 40 0 1

Moung R. Pov Eang Prey Tralach 0 0 100 0 1Moung R. Mokh Rea Prey Tralach 0 0 100 0 1

Moung R. Prey Klot Prey Tralach 0 0 100 0 1

Moung R. Tramkong Reusei Krang 0 0 740 0 1

Moung R. Nikom Le Reusei Krang 0 0 330 0 1

Moung R. Dai Ta Chan, Kampang Reusei Krang 50 0 300 0 2

Moung R. Dam Nak Angkrong Rubos Mungkoul 40 0 550 0 2

Moung R. Beung Ktum Rubos Mungkoul 0 0 25 0 1

Moung R. Sdei Ta Lass 0 0 400 0 1

Moung R. Brour Lay Sdao Ta Lass 50 0 95 0 2

Bakan Kroch Seuch Boeng Bat Kandaol Unknown Unknown 132 0 CS

Bakan Vaot Chre Boeng Khnar Unknown 400 1Bakan Boeng Khnar Boeng Khnar Unknown Unknown 0 0

Bakan Koah Khsach Me Toek 0 0 100 30 3

Bakan Vaot Leab Me Toek 0 0 335 170 3

Bakan Boeng Kanthor Me Toek 0 0 382 73 3

Bakan Roneam Prayol O Ta Paong Unknown Unknown 300 0 CS

Bakan Anlong Svay Rom Leach Unknown Unknown 220 0 CS

Total (ha) 1.718++ 470++ 44.674 303

++: Figure may be higher, but data coverage is incomplete


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Speech by the PM visiting the Damnak Ampil irrigation system on 5 October 2006

Today I have a great pleasure to be with you all to inspect an irrigation system at Damnak Ampil thatis very important for the irrigation of three districts of Sampeo Meas, Ba Kaan and Phnom Kravanh ofPursat, covering a total area of about 27467 hectares of rainy season rice and another 1500hectares of dry season rice. ... I first came to this place 21 years ago and again in June, 2005. I

remember seeing a bad road condition and dilapidated irrigation system in those days ... As time hascome, ... the system has now been almost completed.

... Rice cultivation this year in this area as well as throughout the country seems to be better ingeneral. HE Chhay Saret reported just now that the area of cultivation this year is 7488 hectares or93.90% of the total cultivation land. This is great news. As far as the irrigation system is concerned,we are happy because of the fact that the system serves not only as water channel but also roadaccess. Take for instance we used to have a ferry boat to cross the river here and now we have abridge. Since the area is quite granted with natural availability, perhaps there would be room fordevelopment that might attract tourists to this area in the near future. This proves that we have putour country on a correct path of development ...

According to HE Chan Sarun, Minister for Agriculture, Forestry and Fisheries, last year we havecollected about six million tons of paddy rice or two million tons more than local consumptiondemand. This amounts to 1.3 million tons of milled rice in conversion. This was the result of ricecultivation on 1.8 million hectares of land. But this year we have increased the area of cultivation to2.13 million hectares or about 30,000 hectares more than last year. The state of the rice is in good

prospect. Therefore it is worth mentioning with confidence that the rice harvest this year would alsobe increasing.

I would take this opportunity to share with you that agriculture in the last few years has played a veryimportant role in the country's economic development. Land for cultivation has increased from 70,000hectares to 900,000 hectares. We should try to enlarge land for cultivation in area with irrigationcoverage and also deal with areas where irrigation is still a problem so that the total area ofagricultural production will play an increasingly important economic role.

Irrigation is important for agriculture and we have to do everything we can to get the i rrigation inplace.

I have come frequently to this place and once I said to the people from Satre commune about thepossibility of swapping their long-term rice cultivation to that of short-term rice cultivation. Accordingto statistics I wish to share with you that the area of cultivation under short-term rice species hasincreased, though we maintain to grow long-term rice in high-level of water fields. Area where level ofwater accessibility is low, the Royal Government has advised our people to opt for short-term ricecultivation. What remains to be our focus has been to guarantee food security level in the country

and we have made a great achievement in this endeavor because we were able to have a surpluseven in the worst year of 2000, 2002 or even in 2004.


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In connection with the present study, the catchment boundary has been revised asfollows:

1. Southern part of the Stung Dauntri Basin: The revision is based on the DTMmodel and check with contour lines. From the contour lines, the water at the

revised area is drained to Stung Pursat Basin and not to Stung Dauntri Basin.

2. Eastern part of the Stung Dauntri Basin: The revision is based on the DTMmodel and check with the satellite images, aerial photographs, river networkand field check. Some part of the basin boundary followed along the roadsand some other parts follows the levee of the rivers. The water at the revisedarea is drained to Stung Pursat Basin and not to Stung Dauntri Basin.

3. Western part of the Stung Dauntri Basin: The revision is based on the DTMmodel and check with the satellite images, aerial photographs, river networkand field check. Some part of the basin boundary follows the levee of therivers. The water at the revised area is drained to Stung Sangke Basin throughO Say river.

4. North-western part of the Stung Dauntri Basin: The revision is based on theDTM model and check with the satellite images and aerial photographs. Therevised basin boundary follows the levee of the rivers. The water at therevised area is drained to Stung Dauntri Basin.

The picture below illustrates the revised area. The red color boundary is the newboundary and the black color is the old one (taken from MRC). The differencebetween the areas is as follows:

Old Sub-basin boundary (MRC): 3,695.97 km2

New Sub-basin boundary (present study): 3,541.91 km2

Figure 3.2: Comparison between sub-basin boundaries


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The sub-basin receives water from the adjacent Pursat Sub-basin via the DamnakAmpil Canal (please refer to section 4.6, regulation), and also via a natural offtakelocated downstream of this canal. During high stages, this offtake diverts waterfrom St. Pursat across the catchment boundary and into Ou Souphi (in the DauntriSub-basin), and further to Ou Bakan and St. Kambot. This offtake is shown in thefigure below.

Figure 3.3: Ou Souphi Offtake

1 km

DamnakAmpil Canal

Ou Souphi

St. Pursat

Railway

National Road 5

Sub-basin boundary


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3.3 Rainfall and evaporation

This section relates to ToR, Task 9: Hydrological analysis


[email protected] Daily, monthly and annual rainfall at Battambang (8 years), KgChhnang (55 years), Pursat (60 years), Krakor (36 years), Kravanh(10 years), Svay Donkeo (6 years), Talo (6 years), Bamnak (15years) 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), withsummary 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 SiemReap 1996-2000

Rainfall

The long-term record from Pursat has been chosen as the basis for the waterbalance analysis presented in this study. The rainfall in Dauntri Sub-basin can beestimated as the rainfall in Pursat minus 6 percent.

Hereby, the analysis builds on (i) 53 years of'good'data (which is fullyacceptable); (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) aless 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, Dauntri Sub-basin (mm)

1986 4 of 5 yrs Average 1995

Year 819 1.055 1.241 1.956

Jan 0 3 3 0

Feb 0 4 5 23

Mar 5 33 39 33

Apr 18 62 73 67

May 77 120 141 224Jun 119 105 124 161

Jul 88 111 131 268

Aug 188 145 170 210

Sep 142 189 222 398

Oct 101 181 212 369

Nov 44 88 104 173

Dec 36 14 17 30

Data: Estimated as Pursat minus 6 percent


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Evaporation

Evaporation data are sparse. The following figure and related table are based on 9station-years of'accepted'data from two different stations - Battambang andPochentong, which are located on each side of the study area. There was no overlap

between the 'accepted'records, but the difference between the stations remainedwithin 5 percent on an over-all average basis. The average variation from one yearto 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 onthe so-called pan coefficient and also on the vegetation cover (that varies verymuch over the year in the study area). In view of the uncertainties, a conservativeestimate of 0.7 times the pan evaporation has been applied.

3.4 Streamflow



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

Rating curves from St. Pursat and St. Dauntri have been considered.

St. Pursat

There is no indication that BacTrakoun station is subject toback water effects. FurtherCarbonnel and Guiscafresuggest that the rating curve isof the type Q=f(H), where H isthe water level at Bac Trakoun.The correlation coefficient isvery good, 0.99. The formulareads (JICA 2004):

( )20856.05.25 = BakTrakounHQ

Rating curve Stung Pursat at Bak TrakounQ=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]

Gaugeheight[m]


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St. Dauntri

The rating curve at Maung issuggested to be of the typeQ=f(H) (Carbonnel and

Guiscafre). It means that thereare no back water effects at thestation. Despite very few datafrom year 2001, a rating curvehas been established (JICA2004). The rating curve has theformula:

At the gauging location, the flow in St. Dauntri appears to be highly variable, witha peak of 323 m3/s (on 27 Oct 02), as compared with an average flow of 7,87 m3/sand a median flow of 2,36 m3/s. The corresponding specific yield is 6,5 l/s/km2 or169 mm/year (average) and 1,9 l/s/km2 (median). The variation of the monthlyaverage flow is shown in the Figure below.

Figure 3.4: Monthly average flow, St. Dauntri

Data: Maung (St. 5501101), catchment area 1214 km2, June 01-Dec 02

Rainfall versus discharge

The runoff in a catchment is clearly a result of the amount of rainfall. However, interms of establishment of a relation between the rainfall and runoff, the outcomemay be more of less successful. The reasons are several: The selected rainfallstation(s) may not be representing the entire catchment, the infiltration rate may beunevenly distributed throughout the catchment, and there may be flow regulation

and storage occurring, just to mention a few.

( )22439.14.12 = MaungHQ

Rating curve Stung Dauntri at Maung, Q=f(H)

0.

0.5

1.

1.5

2.

2.5

3.

0 5 10 15 20

Q [m3/s]

Gaugeheight[m]

0

10

20

30

40

50

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


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

3.5 Regulation


The Damnak Ampil Canal

The Damnak Ampil Canal was built under Khmer Rouge between Maung and St.Pursat. Part of it has been restored, and a diversion weir is in an advanced stage ofcompletion across St. Pursat to feed the canal (where the flow went in the oppositedirection in the past). The structure will also provide water to irrigation systems onthe right bank of St. Pursat. The project is a government project implemented byMOWRAM.

So far, 7.7 km of the canal has been restored from Damnak Ampil and towardsSvay Don Keo. Later on, it will be restored further all the way to Svay Don Keo.The width of the canal is app. 10 m, and the slope is 0.0002 m/m.

Water is distributed by a network of new and old 2nd order gates and canals.

Figure 3.5: Structures along the Damnak-Ampil Canal


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Figure 3.6: The Damnak Ampil Canal and regulator under construction (6 July 06)

No data for the canal or its diversion structure on the Pursat river was available to

the consultant. However, upon physical inspection of the canal and intake site, aswell as with the available flow data from the Pursat river, it was possible to providean estimate of the flow in the irrigation canal. The subsequent diversion of thecanal flow into the catchment has been assumed.

The extent of the Damnak-Ampil canal (in its full extent during KR times) is seenin the figure below. The length the canal that has been restored as per 2006 is alsoindicated. It is seen that the canal is going to influence the water availability in theupstream catchments in the Kreuch Sauch and Anlong Svay areas.

The photos show the conditions of the canal during the field visit in June 2006.


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Along the restored reach, 3 pairs (one on each side of embankment) of secondarygates were observed. The purpose of these gates is to convey flows into the paddyfield areas on both sides of the canal. A typical layout of one of these gates is seenin the bottom-left photo. At some reaches flooding outside the laft embankmentcould be observed. The water level in this areas was significantly higher than in thecanal.

As mentioned, no data of flow capacity were available to the consultant. Hence thecanal capacity was estimated using Mannings formula and the observed crosssection geometry.

The canal is approximately 10 m wide. The water depth at the time of visit wasapp. 1.75 m. Information from the provincial department in Pursat reveals that theslope of the canal is 0.0002. Assuming a roughness coefficient of n=0.02, the canalflow capacity can be computed as follows :

Q = 1/n * A * R2/3 * S1/2

where n: is Mannings roughness coefficient

A: is cross section area

R: is hydraulic radius (~D*W/(2D+W), where D is depth and W is width )

S: is canal slope (m/m)

Using the Mannings formula with the above assumptions gives a flow of app. 15m3/s.

Figure 3.7: The Damnak-Ampil Canal from Pursat River to Prek Chik

Dark dots are candidate sub-projects


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Obviously the canal can not carry this flow at all times, as it will be dependent onthe flows in the Pursat river. An attempt to derive a monthly variation of theirrigation canal flow has been made. First, the discharge rating curve for Pursatriver at Pursat as derived by the WUP-JICA study was used to produce a dailyrated discharge for three years, 2001-2003. Then the daily discharge on monthlybasis was derived for each of these years, and finally the average daily dischargeon monthly basis was derived, see the table below. A sound judgement of apossible water intake into the canal for each month was hereafter applied.

Figure 3.8: Photos from the Damnak-Ampil Canal

Damnak-Ampil canal near Pursat River Gates on Damnak-Ampil Canal

Section of the restored canal Flooding outside of the embankment

Gates towards paddy fields Un-excavated part of the canal


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Table 3.3: Assumed flow from Pursat River into the Damnak-Ampil Canal

The geographical position of the pairs of secondary gates along the Damnak-Ampilcanal were recorded during the field trip in June 2006.

Please refer to Appendix 3 for an overview of regulation in each of the catchmentsof the sub-basin. Details are provided in the thematic 'Sub-basin map', submittedseparately.

Average daily flows, based on Average of Assumed abstractedrated discharge [m3/s] years 01-03 flow from Pursat river

Month Year [m3/s] [m3/s]

2001 2002 2003January 20.8 9.5 8.7 13.0 8February 9.6 6.2 16.0 10.6 5March 51.7 3.8 11.3 22.2 5April 13.2 8.2 16.5 12.6 5May 17.2 13.9 23.0 18.0 8June 37.6 13.0 12.9 21.2 10July 64.7 17.4 104.4 62.2 15August 75.6 54.4 86.6 72.2 15September 88.2 79.0 104.6 90.6 15October 279.1 99.4 424.9 267.8 15November 60.1 65.9 35.3 53.8 15December 16.4 23.3 18.3 19.3 10


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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


Area-population.xls Area and population (2002-04) within the study area; buffaloes,cows, horses, goats, pigs, and poultry; families using fertilizer; byprovince, district and commune

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

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

Domestic water usesAn attempt has been made to illustrate the possible development of domesticdemand. The following assumptions have been made:

The actual long-term population growth within the sub-basin, including theeffect 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 somewherebetween 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 besafely predicted when it will be reached.

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

Year Population Unit demand Total demand

Highestimate Lowestimate Highestimate Lowestimate Highestimate Lowestimate

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

2004 233.509 233.509 23 23 2,0 2,0

2009 257.813 233.509 33 28 3,1 2,4

2014 284.646 233.509 43 33 4,5 2,8

2019 314.272 233.509 53 38 6,1 3,2

2024 346.982 233.509 63 43 8,0 3,7

2029 383.096 233.509 73 48 10,2 4,1

2034 422.969 233.509 83 53 12,8 4,5

Data: The present unit demand of 23 l/d is from TSBMO (Mar 03); the present pupolation is from theCommune 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 animportant role in terms of social and economic value, including livelihoods.

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

Distribution of water uses

Spatial and monthly distributions of present and future domestic demand, livestockdemand 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


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

D-W-balance-scenarios.xls Dauntri Sub-basin, calculated water balance, alternative scenarios:Damnak Ampil Canal, candidate sub-projects, and impact of climatechange

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 presentstudy is shown in the following figure.


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

The MIKE Basin model is divided into 21 sub-catchments with associated rivernetwork as well as water uses. The sub-catchments follow largely internalcatchments divides, and are thus derived on basis of physical boundaries. In somecases the topographical information was insufficient for a sub-catchmentdelineation, instead the average distance to tributaries has been used.

During the field visits it was observed that the Damnak Ampil irrigation canal wasrestored for a distance of about 7 km from Pursat river and into the catchment. Thewater intake structure on the Pursat river was almost completed, and it isanticipated that this canal will be in operation in year sometime in 2007. TheDamnak Ampil Canal is going to have a major impact on the available water in the

catchment. Although not confirmed, this canal is likely to be extended further tothe Svay Don Keo river. Since the is almost in operation, its presence and functionas a water supply source appears in all simulations except the first, which isconsidered a base condition.

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


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Figure 4.2: Schematic representation of sub-catchments

Sub-catchments are given by a number (eg. C21) and an area in km2 (eg. 413).Grey: St. Kambot; yellow: Flow directly to the Great Lake; green: St. Svay Donkeo; red: St. Dauntri.

The Damnak Ampil irrigation canal and its entry points in the catchments are shown with red arrows

The calibration is made in two steps: First the NAM model is calibrated for theStung Sangker (the results from WUP-JICA is used). Then the calibratedparameters were applied for the Dauntri catchment, and a comparison madebetween the observed (only few measurements) and the simulated discharge, as itwas not possible to establish a rated discharge due to lack of water level data.

Rainfall-runoff model calibration

In the Dauntri Svay Don Keo catchment there is only one station in whichdischarges have been observed in recent times, namely at Prek Chik. This station islocated somewhat upstream in the catchment, and catches mainly flows from thehilly areas. Further the station represents only approximately 20% of th entireDauntri Svay Don Keo catchment. However, since this is the onle station withinthe catchment which has flow measurements, this information should be used tosupport the calibration of the model. The discharge measurements are few,altogether 11 measurements measured in year 2001. This is hardly enough to base amodel calibration upon. An attempt to match the observed discharge with the NAMmodel has been made, as illustrated in the figure below.

C26

155

C25

216

C24

6

C23

196

C8156

C2

367

C1184

C21

413

C2045

C1828

C17504

C15

24

C16

191

C10

95

C19122

C12

74

C14

27

C4

121

C6104

C22

186

C7331


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In order to get in the order of the observed discharge, a very low runoff coefficienthad to be used (= 0.05). This value is questionable in itself, and it is not physically

justifiable to bring this value further down. It is seen from the figure that the modelpredicts a discharge which is twice the recorded one. The explanation for thisambiguity is likely to be found in the data basis, both the rainfall, and possibly theobserved discharge as well.

There are no rainfall stations in the mountain areas which could possibly improvethe model prediction. Also there are no further of water levels at Prek Chik madeavailable to the consultant to derive a rated discharge which could improve the databasis for model calibration. Therefore, instead of attempting a further improvementof the calibration on the sparse data basis described above, it was decided to applythe calibrated NAM model parameters from the Stung Sangker catchment, whichwere derived through the WUP-JICA study. This catchment is neighbouring to thenorth of the Dauntri catchment. It was concluded in the WUP-JICA study that theNAM parameters from the Stung Sangker calibration could be transferred to the

Stung Dauntri catchment. For illustration of the NAM calibration of the StungSangker, please refer to Figure 5.6. The NAM parameters from the Stung Sangkercalibration are listed in Appendix 3.

The calibrated NAM parameters from Stung Sangker have been applied for theentire Dauntri Svay Don Keo catchment in the MIKE Basin model together withthe various water uses.


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Figure 4.3: Rainfall-runoff simulation for the Dauntri catchment

Figure 4.4: Simulated and observed discharge in Stung Sangker at Battambang

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

01-01-98 01-01-99 01-01-00 01-01-01 01-01-02

Discharge[m3/s]

SimulatedObserved

0.0

100.0

200.0

300.0

400.0

500.0

600.0

01-01-98 01-01-99 01-01-00 01-01-01 01-01-02

Discharge[m3/s]

Observed

Simulated


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Water uses

The water uses that have been accounted for in the model are domestic, irrigationand livestock water uses. The data from the commune data base have been used toderive the above 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 sub-catchment takes water from the same sub-catcment node, which is always located in the downstream end of the sub-catchment. Since the sub-catcments are based on physical boundaries and the wateruses are based on commune data, it has been necessary to calculate the fractionalcontribution of each commune to each of the sub-catchments. The commune data(eg. number of persons) are then assumed to be evenly distributed in thecommunes.

Domestic water uses: It is assumed that each person presently consumes 23 l/d in

the catchment. On basis of the results from the Boribo Thlea Maam catchmentmodelling, which showed that future increase in domestic water use has only minoreffect on the water balance, it was decided not to make a scenario simulation withinceased domestic water use.

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

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

Livestock water use: In the MIKE Basin model it is assumed that the major waterconsuming livestock are cows, buffalos, pigs and poultry.

The Damnak Ampil Canal

The Damnak-Ampil irrigation canal is likely to convey flows from the Pursat intothe Dauntri - Svay-Don Keo catchment some time in year 2007. It is thereforeconsidered important to include the function of this canal into the model analysis.

A short description of the canal is provided in Section 4.6.

The schematisation of the Damnak-Ampil irrigation canal is made by defining a

river branch which at the upstream end starts outside the Dauntri catchment, i.e. in


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the Pursat river. The river branch is then extended into the Dauntri catchment forapp. 7.5 km. The location of the 3 pairs of gates is used to determine which sub-catchments will receive water from the canal. There is no distinction between gateslocated on the left or right side of the canal. Hence, altogether three abstractionpoints have ben defined along the river branch representing the Damnak-AmpilCanal.

The flow abstracted from the Pursat river is assumed as indicated in Table 3.3(Section 3.5). However, it is based on an assessment of both the capacity of thechannel (using Mannings formula) and the water availability in the Pursat river.The latter is derived using the extended flow record at Pursat. An underlyingassumption is that the the amount of water available at Pursat is likewise availableat the Damnak Ampil water intake.

The time-series of assumed abstracted flow from the Pursat river is fed into thecanal at its upstream (sutheastern) end.

A total of three abstraction points along he Ampil canal has been assumed. Thishas been done in order to provide each of the three subcatchments which the canaltraverses with irrigation water. This corresponds approximately to the observationsmade in the field, where sets of gates were observed along the channel. Since theflow in the Ampil canal is assumed, it is subject to uncertainty. Therefore the flowat the three abstractions points has been assumed to be equal.

The schematisation is shown in the figure below.

The water diverted from the irrigation canal is used for irrigation of paddy fields ina reasonable vicinity of the canal. It is assumed that 30% of the abstracted flow is

returned to the local river systems. This additional water in the rivers will beavailable for water use, for example for the proposed candidate sub-projects. Ifreturn flows were neglected, the effect of the canal would be neutral in thesimulations.


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Figure 4.5: Schematisation of the Damnak-Ampil irrigation canal

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.

The following table shows the summary of the water balance for the Dauntri Svay Don Keo catchment under the existing conditions. The conditions imply thatall existing water uses have been included. However, the Damnak Ampil canal isnot included in this simulation.

It is seen from the table that the water uses in general constitute a small fraction ofthe available water, at least on a yearly basis and during the wet season. In the dryseason January to May, the water uses are of the same magnitude as the available

water. In March to May there are no outflows from the catchment. Both presently(in some years) and in the future there is therefore competition for water in thedriest months of the year, as not all demands can be met. Proper planning of thewater allocation is therefore inevitable, if the situation is to be improved.

Conversely, as seen in table, in the period of June to November, that is in the wetseason, as well as a part of the recession period (December), there is plenty ofavailable water for irrigation water use or other uses. Presently most water in thisperiod flows into the Tonle Sap Lake, were it naturally serves other purposes.

The numbers in the table are based on precipitation data that represent a 4 out of 5years situation, or 80 % reliability. This means that in 1 out of 5 years the wateravailability may be less.

Location ofabstractionpoints forirrigation


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Table 4.2: Summary water balance, base situation, 4 out of 5 years

Rainfall Evapo-ration

Storageand losses

Wateravailability

Domesticuses

Irrigationuses

Livestockuses

Outflow

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

January 3,9 19,6 -19,2 3,6 0,1 1,5 0,4 1,7February 4,9 7,1 -4,4 2,2 0,1 1,5 0,4 0,3

March 45,2 45,2 -3,4 3,4 0,1 2,9 0,4 0,0

April 84,6 84,6 -3,4 3,4 0,1 2,9 0,4 0,0

May 163,2 135,7 24,2 3,4 0,1 2,9 0,4 0,0

June 143,6 126,9 10,3 6,4 0,1 2,9 0,4 3,0

July 151,4 111,1 -7,7 48,0 0,1 12,5 0,4 35,1

August 197,7 98,3 -12,3 111,6 0,1 12,5 0,4 98,7

September 256,7 77,7 29,4 149,6 0,1 12,5 0,4 136,7

October 246,8 85,6 50,6 110,6 0,1 12,5 0,4 97,7

November 121,0 102,3 -15,3 34,0 0,1 12,5 0,4 21,0

December 19,7 78,3 -67,5 8,8 0,1 1,5 0,4 6,9Year 119,9 81,0 0,1 38,8 0,1 6,5 0,4 31,8

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 5,4 -5,3 1,0 0,0 0,4 0,1 0,5

February 1,4 2,0 -1,2 0,6 0,0 0,4 0,1 0,1

March 12,6 12,6 -0,9 0,9 0,0 0,8 0,1 0,0

April 23,5 23,5 -0,9 0,9 0,0 0,8 0,1 0,0

May 45,3 37,7 6,7 0,9 0,0 0,8 0,1 0,0

June 39,9 35,2 2,9 1,8 0,0 0,8 0,1 0,8

July 42,0 30,8 -2,1 13,3 0,0 3,5 0,1 9,7

August 54,9 27,3 -3,4 31,0 0,0 3,5 0,1 27,4

September 71,2 21,6 8,2 41,5 0,0 3,5 0,1 37,9

October 68,5 23,7 14,1 30,7 0,0 3,5 0,1 27,1

November 33,6 28,4 -4,2 9,4 0,0 3,5 0,1 5,8

December 5,5 21,7 -18,7 2,4 0,0 0,4 0,1 1,9

Year 33,3 22,5 0,0 10,8 0,0 1,8 0,1 8,8

mm mm mm mm mm mm mm mm

January 3 15 -14 3 0 1 0 1

February 3 5 -3 1 0 1 0 0

March 34 34 -2 2 0 2 0 0

April 61 61 -2 2 0 2 0 0

May 121 101 18 2 0 2 0 0

June 103 91 7 5 0 2 0 2

July 113 83 -6 36 0 9 0 26

August 147 73 -9 83 0 9 0 73

September 185 56 21 108 0 9 0 98

October 184 64 38 82 0 9 0 73

November 87 74 -11 24 0 9 0 15

December 15 58 -50 7 0 1 0 5

Year 1055 713 -14 356 1 58 3 294

The detailed water balance assessment for each individual sub-catchment is

presented in Appendix 4.


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Figure 4.6: Water availability, present conditions, April, m3/s


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Figure 4.7: Specific water availabilty, present conditions, April (l/s/km2)


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Figure 4.8: Water availability, present conditions, September (m3/s)


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Figure 4.9: Specific water availabilty, present conditions, September (l/s/km2)


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Figure 4.10: Specific water availabilty, present conditions, annual (l/s/km2)

Water balance, future conditions

Apart from the implications of irrigation development (which is described in aseparate section below), water balances have been calculated for three developmentscenarios:

Implementation of the Damnak Ampil Canal;

Implementation of the Damnak Ampil Canal and the canidate sub-projects;

and


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Implementation of the Damnak Ampil Canal and the canidate sub-projects inconnection with climate change - illustrated by tentative (and quite uncertain)assumptions as described in Section 4.8.

Base situation with Damnak-Ampil Canal included: In this scenario, the Damnak-Ampil irrigation canal has been incorporated in the model setup, to study theinfluence of abstracting water from the Pursat river. The assumptons and technicalspecifications for the canal are described in Section 4.6.

A summary of the water balance for this scenario is seen in the following table.Detailed water balances for each sub-catchment are presented in Appendix 4.

The general conclusion when comparing to the base situation is that the canalconveys sufficient water to the Dauntri Svay Don Keo catchment, that there willalways be an outflow from the catchment as a whole. The outflow from thecatchment is increased in all months of the year, including the dry months. This

means that all present water demands can be met.

Table 4.3: Summary water balance with the Damnak Ampil Canal


Storageand losses

Wateravailability

Domesticuses

Irrigationuses

Livestockuses

Outflow

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

January 3,9 19,6 -24,2 8,6 0,1 1,5 0,4 6,7

February 4,9 7,1 -8,6 6,4 0,1 1,5 0,4 4,5

March 45,2 45,2 -6,6 6,6 0,1 2,9 0,4 3,2

April 84,6 84,6 -7,5 7,5 0,1 2,9 0,4 4,2

May 163,2 135,7 17,3 10,2 0,1 2,9 0,4 6,9

June 143,6 126,9 -1,5 18,2 0,1 2,9 0,4 14,8

July 151,4 111,1 -22,7 63,0 0,1 12,5 0,4 50,1

August 197,7 98,3 -27,3 126,6 0,1 12,5 0,4 113,7

September 256,7 77,7 14,4 164,6 0,1 12,5 0,4 151,7

October 246,8 85,6 35,6 125,6 0,1 12,5 0,4 112,7

November 121,0 102,3 -25,9 44,6 0,1 12,5 0,4 31,7

December 19,7 78,3 -75,7 17,1 0,1 1,5 0,4 15,2

Year 119,9 81,0 -11,1 49,9 0,1 6,5 0,4 42,9

It is important to emphasize that while this holds true for the catchment as a whole,it does not apply to the Dauntri river itself, which does not receive additional waterfrom the Pursat river. This is clearly seen in the tables of each individual sub-catchment in Appendix 4.

Groundwater

No groundwater data has been available for the study wherefore a directassessment of this resource could not be made. Instead, the groundwater flow hasbeen determined indirectly through calibration of the NAM model. Practically thisis obtained by adjusting the various parameters until a reasonable fit exist betweenobserved total runoff and simulated total runoff. Through the various exchangefunctions in the model (threshold values for overland flow, interflow andgroundwater flow) the groundwater flow (or base flow) comes implicitly as a

result.


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The figure below shows the simulated relative contribution of the groundwaterflow to the total runoff for Dauntri Sub-basin. The base case is shown. The tablebelow contains average monthly values of the ration between the groundwater flowand the total runoff.

Figure 4.11: Ratio between groundwater flow and total runoff

Table 4.4: Monthy simulated ratio between groundwater flow and total runoff

Month Groundwater flow : total runoff

JF

MAMJJASO

ND

11

111

0.370.010.110.280.390.520.90


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4.3 Candidate sub-projects

This section relates to ToR, Task 23: Assessment of impacts of each sub-projects on downstream wateruses; and Task 24: NWISP candidate sub-projects


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

D-W-balance-scenarios.xls Dauntri Sub-basin, calculated water balance, alternative scenarios:Damnak-Ampil Canal, candidate sub-projects, and and impact ofclimate change

There are four proposed candidate sub-projects in the catchment, namely KreuchSauch, Anlong Svay, Roneam Prayol and Prek Chik.

Two sets of water balances have been calculated: One without an ssumed climate

change, and one including the (uncertain) effects of a climate change. Both setsinclude the Damnak Ampil Canal.

Damnak-Ampil Canal and candidate sub-projects included: This scenarioincorporates the Damnak Ampil Canal as well as the proposed candidate sub-projects in the model. The candidate sub-projects are simply treated as the presentirrigation systems, namely with a demand of 2 l/s/ha and no return flows. Returnflows may occur in the future, but disregarding them is on the conservative sidewith regards to water availability. The following table gives a summary of thewater balance for this scenario. For details, please refer to Appendix 4.

Table 4.5: Summary water balance with Damnak Ampil Canal and candidate sub-projects


Storageand losses

Wateravailability

Domesticuses

Irrigationuses

Livestockuses

Outflow

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

January 3,9 19,6 -24,2 8,6 0,1 1,9 0,4 6,3

February 4,9 7,1 -8,8 6,6 0,1 1,9 0,4 4,3

March 45,2 45,2 -7,0 7,0 0,1 3,3 0,4 3,2

April 84,6 84,6 -7,9 7,9 0,1 3,3 0,4 4,2

May 163,2 135,7 16,9 10,6 0,1 3,3 0,4 6,9

June 143,6 126,9 -1,5 18,2 0,1 3,3 0,4 14,4

July 151,4 111,1 -22,7 63,0 0,1 23,7 0,4 38,9

August 197,7 98,3 -27,3 126,6 0,1 23,7 0,4 102,5

September 256,7 77,7 14,4 164,6 0,1 23,7 0,4 140,5

October 246,8 85,6 35,6 125,6 0,1 23,7 0,4 101,5

November 121,0 102,3 -26,4 45,1 0,1 23,7 0,4 20,9

December 19,7 78,3 -75,7 17,1 0,1 1,9 0,4 14,8

Year 119,9 81,0 -11,2 50,1 0,1 11,4 0,4 38,2

The main conclusion for the catchment as a whole, in comparison with the previoussimulation described, is that the catchment outflows are reduced in the wet season,whereas it is unchanged in the dry season. The reason for this is that there are nodry season irrigation in the proposed candidate sub-projects, except at Prek Chik.


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However, looking at the detailed results for Stung Dauntri river, it can beconcluded that the Prek Chik candidate sub-projects will not be able to receive allof its water demand. The insufficient amounts of water held back for the Prek Chikcandidate sub-project, has further as a consequence that downstream flows arefurther reduced, extending the period with zero or near zero aoutflows from thecatchment.

The remaining candidate sub-projects Krouch Saeuch, Anlong Svay and RoneamMneash have sufficient water when combined with the Damnak-Ampil irrigationCanal. Without the canal, the Anlong Svay candidate sub-projects will be short ofwater in periods, whereas the demands from Krouch Saeuch and Roneam Mneashare just fulfilled. However, the fulfilment for the latter two are on the expense offlows downstream from these projects.

A detailed analysis can therefore be carried out in which the optimal allocation ofwater at the three abstraction points along the Damnak-Ampil Canal is determined.

Damnak-Ampil Canal, candidate sub-projects, and climate change: The assumedchanges are a decrease of 2 % in the rainfall and and an increase in evaporation of2%. These changes have been imposed on the rainfall and evaporation series thatwere used for the base situation simulation. No other changes have been consideredas compared with the previous scenario.

Results are shown in the table below. Detailed water balances for each sub-catchment are presented in Appendix 2.

The climate change mainly involves a change in the catchment outflow during thewet season, and to a lesser degree dur

final report vol3-river basin study

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