Final Report Vol1-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 1: Methodology and general findings

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

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Revisions Version 1: Summary expanded

Version 2: Summary expanded with 'Management issues and scope for development' (drawn from Chapters 8 and 9)

Section 6.3 (floods) expanded with new estimates of flood flows

New Section A2.6, briefly introducing the 'Pocket calculator', with locations of candidate sub-projcets added

Chapter 9: Title changed, chapter re-structured; new Section 9.2 (storage capacity) with comments and suggestions about storage capacity; Section 9.4 (monitoring of water resources) expanded, with suggestions on future monitoring of rainfall and streamflow; Section 9.8 (fish yield and fish migration) expanded, with observations on fish passages

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 General 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 with 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 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.

Findings are presented in three reports:

Volume 1: Methodology and general findings

Volume 2: Boribo Sub-basin

Volume 3: Dauntri Sub-basin

Water balance and water availability Summary water balances for the sub-basins are as follows:

Boribo - Thlea Maam Sub-basin 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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Dauntri Sub-basin 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 which wet 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 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

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'

The study area has 6 schemes that have been identified as candidate sub-projects under the NWISP. The estimated manageable water availability at each scheme is summarized below.

Water availability at candidate sub-projects

Boribo Dauntri Bamnak Tram Mneash Krouch Sauch Anlong Svay Roneam Prayol Prek Chik (alone) (to share

with Bamnak)

(to share with Anlong Svay)

Low estimate

High estimate

Low estimate

High estimate

Low estimate

High estimate

Low estimate

High estimate

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

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

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

F 0,3 0,3 0,6 0,9 1,7 1,3 2,3 1,3 2,3 -0,1

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

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

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

J 2,7 2,7 5,5 2,1 3,6 3,3 5,4 3,3 5,3 0,9

J 5,8 5,6 11,3 4,9 7,1 9,6 12,6 9,9 12,9 8,2

A 12,1 12,0 24,1 8,2 10,5 17,0 20,0 18,2 21,2 21,3

S 16,6 16,5 33,1 10,2 12,5 21,4 24,4 23,1 26,1 29,1

O 12,7 12,6 25,3 8,2 10,4 16,9 19,9 18,0 21,0 21,1

N 4,1 4,0 8,1 4,1 6,4 7,9 10,9 8,1 11,1 5,2

D 1,6 1,6 3,2 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 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 (b) The water availability at Krouch Sauch, Anlong Svay and Roneam Prayol is influenced by the operation of the Damnak

Ampil Canal. The low and high estimates are based on assumptions about the future operation (c) The water availability at Roneam Prayol is influenced by the implementation of the Anlong Svay scheme (d) 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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Management issues and scope for development Water availability

An increased water availability in the dry season would be a clear benefit, if it can be achieved in a practical way. The following options are available: (i) Increased storage capacity; and/or (ii) groundwater utilization.

Increased storage capacity can be achieved by (i) Traditional storage reservoirs, as they exist in many places in Cambodia (the most famous example being the West Baray, built around 1050 and still serving its original purpose); (ii) upstream storage reservoirs located in the mountains; (iii) in-stream storage; (iv) optimization of retention irrigation; and (v) pumping water from the Great Lake. Implications, advantages and disavantages are discussed in Section 9.2.

A fruitful synergy can be achieved between added storage capacity and improved operation. Apart from a moderate additional in-stream storage, provision of storage capacity is expensive. In comparison, improved operation (of existing and new) storage facilities can be achieved at a small cost. This would call for improved information exchange (including weather statistics, real-time meteorological data, and flood and rainfall forecasts), some contemporary decision-support and management tools, related education of the involved agencies, and close dialogue with the farmers about the time and space distribution of the available water.

Groundwater is often overlooked in connection with national water resources management, partly because good data are either limited or not easily accessible. For several reasons (that include the economic feasibility and a finite groundwater yield), groundwater cannot replace surface water as the raw water source for irrigation. Still, there is an attractive potential for using groundwater for small-scale supplementary irrigation that can in some cases highly improve the livelihoods of the farmers. This has been clearly demonstrated elsewhere in Cambodia.

A first glance at the geology - an alluvial flood plain surrounded by mountains - indicates a high potential for groundwater utilization in the Tonle Sap Basin. Knowledge about the groundwater resources exists, but is incomplete and is located with different agencies and operators. Expectations among practitioners though, indicate that groundwater yield is low in the study area.

Monitoring

Resources are finite for monitoring of water resources: Time; money; facilities; and knowledge. Today, the monitoring is visibly affected by technical and financial constraints.

Long-term rainfall records are available from Kg Chhnang, Pursat, and Battambang, and . These stations are particularly important, because they already have a good data coverage, so that they can serve as references for analyses of shorter records from other stations. This is irrespective of the difficulties experienced under the prsent study with inter-station correlations. Large parts of the study area are elevated. Rainfall data would be useful from the elevated areas, where the rainfall is higher than at the exisiting monitoring stations (but where access is difficult).

Regarding streamflow monitoring, it could be worthwhile to consider trading a substantial number of the stations for more complete records at the remaining ones.

Evapotranspiration represents by far the most significant uncertainty in the water balance analyses, and hereby in our knowledge about water availability. Also, assumptions about the evapotranspiration is an important part of the basis for determination of crop requirements. Therefore, local data would be highly useful in connection with agricultural development efforts.


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Any information about groundwater utilization, availability and quality would highly assist possible assist future efforts to develop this resource.

Morphological changes can cause severe damage to buildings and infrastructure, and can add to the flood risk. Monitoring of morphological developments can allow for timely intervention and control of potential consequences.

Water quality and aquatic habitats

Regarding surface water, the situation in the study area today is that habitat degradation is a more imminent threat than pollution, and much more difficult to control. A potential threat is contamination from agricultural runoff containing fertilizer residues and pesticides, which can eventually contaminate edible fish and hereby the public health.

Another aspect to keep in mind is pollution incidents, such as spills, that can cause short-term or long-term damage to aquatic ecosystems.

The potential pollution from irrigation tailwater is best managed by promotion of good practices, which in many cases represent 'win-win' solutions to the farmers and the environment.

Another potential pollution source is fish farms.

For the purpose of the present study, information has been sought about evidence of observed extraordinary flow-related impacts in the project area. The information is inconclusive, however, since there seem to have been no such incidents. The riverine ecosystems are adapted to low or no flow occuring annually in the dry season.

Findings under the present study indicate that in the past and today, a typical (and possibly critical) cause-effect relationship in relation to fish habitats in the study area is as follows: (1) Structural intervention (gates, regulators) with inadequate sediment conveyance capacity, causing (2) upstream siltation (and downstream erosion and consequential downstream accretion); causing (3) blocking of fish migration routes, causing changed species composition and, possibly, reduced yield.

Capacity-building

In the context of the present study, examples of relevant capacity-building topics are (i) socio-economic, hydraulic, and environmental implications of water uses in general, and of irrigation development in particular; and (ii) monitoring routines (water utilization, groundwater, water quality, morphology), including cost-effectiveness and participatory techniques.

Capacity-building in support of hydraulic operation of irrigation schemes is of a particualar importance.

Strengthening of Water User Groups can provide a decisive (and cost-effective) contribution towards the desired socio-eceonomic benefits of irrigation rehabilitation.

Amplification of benefits

The benefits of irrigation schemes can be amplified, or are in some cases directly dependent on supplementary measures, such as:

• Technical support to de-central management, operation and maintenance of the irrigation systems (by Water User Groups);

• access to proven new crops and cultivation systems, including inputs (seeds, fertilizers, etc.) and technology;


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• access to markets and support to marketing, eventually at the national scale;

• support to development of agro-processing industries;

• smooth information flows (basic meteorology, flood warnings, and market conditions);

• support to conflict resolution among land owners and water users; and

• support to response to risks and social shocks (like illness in the family, which can cause loss of land).

Several of these issues are outside the responsibility (and control) of MOWRAM. Inter-agency networking and collaboration is required to reach the full benefits of irrigation development.

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 General geography...............................................................................................................2

2.1 Data ........................................................................................................................2 2.2 Population, administrative boundaries ...................................................................2 2.3 Elevations, land use, soils ......................................................................................3

3 Livelihoods and economics .................................................................................................5 3.1 Data ........................................................................................................................5 3.2 General ...................................................................................................................5 3.3 Cultivation..............................................................................................................6 3.4 Livestock ................................................................................................................9 3.5 Fisheries ...............................................................................................................10 3.6 Industries ..............................................................................................................10 3.7 Other livelihoods..................................................................................................11

4 Hydrology..........................................................................................................................13 4.1 Data ......................................................................................................................13 4.2 Water level in Tonle Sap......................................................................................15 4.3 Rainfall and evaporation ......................................................................................16 4.4 Streamflow ...........................................................................................................24 4.5 Groundwater.........................................................................................................27 4.6 Climate change.....................................................................................................37

5 Water uses and water balance............................................................................................38 5.1 General .................................................................................................................38 5.2 Water uses ............................................................................................................38 5.3 Water balance.......................................................................................................44 5.4 Development scenarios ........................................................................................47

6 Morphology, floods and drought .......................................................................................49 6.1 Data ......................................................................................................................49 6.2 Morphology..........................................................................................................49 6.3 Floods...................................................................................................................49 6.4 Drought ................................................................................................................57

7 Aquatic environment .........................................................................................................59 7.1 Data ......................................................................................................................59 7.2 Fish, fish habitats .................................................................................................59

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7.3 Water quality criteria............................................................................................60 7.4 Pollution loads......................................................................................................64 7.5 Water quality........................................................................................................74

8 Socio-economics................................................................................................................76 8.1 Data ......................................................................................................................76 8.2 Background and approach....................................................................................76 8.3 Water dependencies .............................................................................................78 8.4 Trends...................................................................................................................79 8.5 Implications of irrigation development ................................................................82 8.6 Main findings of economic analysis.....................................................................87 8.7 Water user groups ................................................................................................87

9 Management issues and scope for development................................................................89 9.1 Hydraulic feasibility of irrigation development ...................................................89 9.2 Storage capacity ...................................................................................................91 9.3 Groundwater development ...................................................................................93 9.4 Monitoring of water resources .............................................................................94 9.5 Morphology..........................................................................................................99 9.6 Water quality......................................................................................................100 9.7 Ecological demand of streamflow (environmental flows) .................................101 9.8 Fish yield and fish migration..............................................................................103 9.9 Capacity-building...............................................................................................107

References............................................................................................................................................110

Appendix 1: Data files .........................................................................................................................113 Appendix 2: MIKE Basin set-up..........................................................................................................115

A2.1 The MIKE Basin model .....................................................................................115 A2.2 Rainfall-runoff applications ...............................................................................116 A2.3 Water balance applications.................................................................................125 A2.4 Pollutant load applications .................................................................................126 A2.5 Water quality applications..................................................................................127 A2.6 River basin 'pocket calculator'............................................................................130

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Figures 2.1: District boundaries 2.2: Land elevations around the Tonle Sap Basin 2.3: Soil suitability for paddy cultivation 3.1: Cultivation systems 3.2: Cultivation cycles, summary 3.3: Cultivation cycles, details 3.4: Flood height and fish yield in Tonle Sap 3.5: Chrak La Eang waterfall on St. Bamnak 4.1: Rainfall stations 4.2: Seasonal water level variation in Tonle Sap 4.3: Normal rainfall in Cambodia 4.4: Distribution of monthly rainfall, Pursat 4.5: Distribution of annual rainfall, Pursat 4.6: Average rainfall in percent of the average rainfall at Pursat 4.7: Monthly average rainfall at Kravanh and Svay Donkeo 4.8: Distribution of rainfall over days with most rain 4.9: Pan evaporation 4.10: Average monthly rainfallversus runoff, Maung Russey 4.11: Average monthly rainfall versus runoff, Kg.Tralach 4.12: Rated discharge at Bac Trakoun versus that of Peam 4.13: Discharge relation between Bac Trakoun and Peam 4.14: Geological layers from Well SS1 4.15: Geological layers from Well PS1 4.16: Geo-resistivity profile, Kg Chhnang Town 5.1: Rationale of water use and water balance analysis 5.2: Water balance for the Great Lake 6.1: Annual water level range in the Great Lake 6.2: Time series of flow in St. Pursat, St. Boribo and St. Dauntri 6.3: Regression line for annual maximum flows 6.4: Ranking of annual maximum rainfall, Pursat 6.5: Inundation August and September 2006 7.1: Population density per commune for the 2 sub-basins 7.2: Livestock densities (cows) 7.3: Livestock densities (buffalos) 7.4: Livestock densities (pigs)

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7.5: Livestock densities (poultry) 7.6: Land area in each commune used for rice cultivation. 8.1: Network of rural livelihood dependencies 9.1: Distribution of accumulated rainfall in May-August 9.2: Average accumulated rainfall in May-August 9.3: Pursat monitoring station 9.4: Rainfall monitoring stations (past and present) 9.5: Rainfall monitoring stations (present and proposed future) 9.6: Flow monitoring stations (past and present) 9.7: Flow monitoring stations (present and proposed future) 9.8: Bamnak monitoring station 9.9: Example of a structure threatened by scour 9.10: Risk matrix for morphological developments 9.11: Cause-effect relationships affecting fish habitats 9.12: Vatlieb Gate, built in 1977, blocking sediments and fish migration 9.13: Khohkhsach Gate, built in 1977, blocking sediments and fish migration 9.14: Kruchsaerch Gate, built in 1994, with sediment and fish passage 9.15: Prek Am Gate, built in 2002, with sediment and fish passage A2.1: Rainfall-runoff model of MIKE Basin A2.2: Structure of the NAM model A2.3: Generation of overland flow A2.4: Schematic view of the structure of MIKE Basin A2.5: Nitrogen components and processes in MIKE Basin WQ A2.6: Input table, set-up (Boribo Sub-basin) A2.7: Input table, set-up (Dauntri Sub-basin) A2.8: Input table, water availability A2.9: Input table, water uses A2.10: Output table, entire sub-basin A2.11: Output table, each sub-catchment A2.12: Summary of manageable water availability at candidate sub-projects A2.13: Manageable water availability at each candidate sub-project A2.14: Rainfall deficit for a given irrigation demand A2.15: Summary of irrigable areas at candidate sub-projects

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Tables 3.1: Livestock in the study area 3.2: Present change in livestock population, Cambodia 4.1: Rainfall stations 4.2: Distribution of monthly rainfall, Pursat 4.3: Distribution of annual rainfall, Pursat 4.4: Days with rain in Pursat 4.5: Rainfall at Pursat, Battambang and Kg Chhnang 4.6: Pan evaporation 4.7: Estimated effective evaporation 4.8: Stations with extended stream flow record 4.9: Groundwater potential in Kg Chhnang and Kg Cham Provinces 4.10: Log of Well SS1 in Battambang Provincial Town 4.11: Log of Well PS1 in Pursat Provincial Town 4.12: Wells in Khet Kampong Chhnang 4.13: Geo-resistivity transects in Kampong Chhnang 4.14: Wells in Boribo and Dauntri Sub-basins 5.1: Current water uses in Cambodia 5.2: Estimated population growth, Cambodia 5.3: Typical unit demands for irrigation, traditional paddy cultivation 5.4: Specific crop water requirements 5.5: Unit demands for livestock 5.6: Estimated water demand for industries and institutions 5.7: Water level, surface area and volume of the Great Lake 5.8: Water balance for the Great Lake 5.9: Scenarios for water demand and utilization 6.1: Extreme flows 6.2: Estimated return periods for extreme flows 6.3: Extreme rainfall 6.4: Dry periods of 10 days or more in May-August 7.1: Water quality criteria to protect human health 7.2: Selection of protected public water standards including rivers 7.3: Ecological quality classes for rivers 7.4: Areas for rice cultivation and estimated fertiliser application 7.5: Runoff coefficients for pollutants 7.6: 1.order distance specific decay factors for pollutants 7.7: Overall generated load of BOD, nitrogen and phosphorus

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8.1: Drivers of change 8.2: Costs and benefits of irrigation development 9.1: Rainfall in May-August 9.2: Rainfall deviation from average in May-August 9.3: Types of morphological effects and management options 9.4: Capacity-building topics A1.1: Time series data A1.2: Data tables A2.1: Rainfall runoff parameters A2.2: BOD statistics A2.3: Total phosphorus statistics

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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

GDP : gross domestic product

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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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 (same)

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 Vol1 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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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 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 with the 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, 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, Dauntri/Dauntry/Daun Try, 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. Dauntri is also named St. Muong, and St. Kambot is also named St. Preahmlu.

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Location map

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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 the 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.


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2 General 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

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 average rate of 2.2/2.5 % per year (CNMC October 04, p. 30). The difference is partly related 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 higher in urban areas than in rural areas.


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Figure 2.1: District boundaries

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 Tonle Sap Basin forms a rather flat flood plain surrounded by mountains, as illustrated in the following figure.


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Figure 2.2: Land elevations around the Tonle Sap Basin

The soil suitability in relation to paddy cultivation has been evaluated by MRC. As seen in the following figure, the quality in most of the study area is marginally or not suitable, with a small part only rated as moderately suitable. In this connection, it is noted that paddy cultivation in general has lower requirements to the soils than most other crops.

Figure 2.3: Soil suitability for paddy cultivation

From CNMC (Oct 04), p. 17

m above sea level

> 500

200 - 500

100 - 200

50 - 100

30 - 50

20 - 30

10 - 20

0 - 10

Moderately suitable

Marginally suitable

Not suitable


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3 Livelihoods and economics


Information has been achieved from

• the commune database;

• previous studies, as conducted by for example ADB, MRC and WUP-FIN; and

• interviews and surveys conducted under the present study with province and district authorities and individual farmers.

3.2 General 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

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

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

Household income is a major development concern in the Tonle Sap Basin. 38% of people living in the 5 provinces surrounding the Tonle Sap are below the official poverty line (Chaudry and Juntopas Jan 05).

In a widely quoted text, ADB (Aug 03) observes that

'the Tonle Sap Basin is home to nearly 3 million people, most of whom derive their livelihoods directly from its natural resources. Around half of those people depend on the lake and its associated wetlands, which is also the predominant source of protein for the whole of Cambodia.

Competition for scarce resources is intense. An increasing proportion of the population of the Tonle Sap Basin is landless. This particularly applies to female-headed households, which are more vulnerable to shocks and resort to selling land to meet short-term health and other crises, and to the ethnic minorities who can make less claim to land rights. Access to common property is important to the livelihoods of large numbers of people, not just the landless, who depend on fishing and foraging for a living. These common property resources are, however, inadequately managed and may be hugely overexploited or become the preserve of a favored few. The dismantling of the fishing lot system in the Tonle Sap in 2000 was supposed to reduce commercial exploitation and increase the fishing area available to local


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communities. However, commercial enterprises still account for a high proportion of the total fish catch. In the catchment, commercial logging, mostly illegal, has eroded the evergreen forest.

Notwithstanding, the Tonle Sap Basin offers significant opportunities for supporting productivity by providing the irrigation water needed to expand irrigated rice areas and raise yields to levels nearer to those of Cambodia’s neighbours. It has potential for provision of energy from hydropower, which could reduce some of the pressures on the forested areas. And its natural resource base ought also to favor the emergence of small and medium enterprises.'

3.3 Cultivation This section relates to ToR, Task 1: Collection of general data and information; and Task 16: Field surveys of water uses





Cultivation systems

Characteristic cultivation systems and cultivation cycles are shown in the figures below, which have been compiled with guidance by provincial and district authorities.

Typically, at one given location, only one crop will be cultivated per year - either in the wet or in the dry season. The land of one farmer can be divided in small plots, so that many farmers cultivate both in the dry and the wet season, but at different plots of land.

Supplementary irrigation in the wet season (for seed beds and during dry spells) is practiced where water is available for the purpose, which is generally in the close vicinity of irrigation canals - often within a distance of 100 m only.

In a few places, where irrigation water is reliably available, farmers can grow 2 short-term dry season crops between mid December and mid July.

The traditional floating rice is still grown in some places, but has in recent years been largely replaced by recession irrigated paddy or by lotus.

Other crops (including corn, potato, beans, sugar cane, pineapple and vegetables) occupy a small part of the cultivated area but contribute significantly to the economy.


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Figure 3.1: Cultivation systems

Figure 3.2: Cultivation cycles, summary

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

Average rainfall

Average Great Lake waterlevel

Wet season rice

Dry season rice (recession irrigation)

Dry season rice (irrigated)

Brown paddy (floating rice)

Data: NWISP-2 survey 2006

Upland area, sparsely cultivated

Wet season paddy cultivation, one crop per year, supplementary irrigation (if available)

Dry season paddy cultivation, supported by recession irrigation, 1 short-term crop per year

Brown paddy (floating rice), 1 long-term crop per year, in recent years largely abandoned

Littoral zone, not cultivated

National Road 5

Great Lake annual low water level, small variation from year to year

Great Lake annual high water level, varying from year to year


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Figure 3.3: Cultivation cycles, details

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

Average rainfall

Average Great Lake waterlevel

Wet season rice Land preparation (3-5 days) Transplanting (2-4 days) Growing (5 months) Harvesting (2-3 days)

Recession irrigated Land preparation (3-5 days) Direct seeding (1 day) Growing (around 75 days) Harvesting (2 days)

Dry season irrigated Land preparation (3-5 days) Transplanting (2-4 days) Growing (70-80 days) Harvesting (2-3 days)

The bars show the over-all indicative duration for the study area as a whole. The duration in a specific year depends on the water availability

The farmers do not carry out the tasks at the same time; on the contrary, they help each other (and/or draw on a shared pool of labour for labour-intensive operations like transplanting and harvesting)

Durations in brackets are typical values for each individual farmer

Data: NWISP-2 survey 2006

In general, the cultivation is highly rain-dependent. Year by year, the national GDP is visibly influenced by a timely and adequate rainfall.

Rainfall and GDP In separate reports released Tuesday [14 Nov 06], The World Bank and the Economic Institute of Cambodia predicted a high level of GDP growth in Cambodia for 2006: 8.9 percent in the case of The World Bank and 8.5 percent according to EIC. With the new methods, Cambodia ... will have the second highest growth rate in East Asia in 2006, trailing only China.

This year's rainfall was strong and should produce a similar crop to last year, said World Bank senior country economist Robert Taliercio. But to increase crops significantly year after year, Cambodia needs to invest more heavily in canals and dams to free agriculture from boom-and-bust cycles that depend on the monsoon.

'To predict GDP, you have to be a bit of a weatherman in Cambodia', Talierco said ... 'Irrigation is vital for sustained growth in agriculture and to reduce volatility'.


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Bumper rice crop Thanks to increased irrigation and advice to farmers on fertilizer and seeds, the government expects a million tons of surplus rice to be available for export from a harvest of 2.2 million hectares.

Phnom Penh Post Dec 1-14 2006

3.4 Livestock This section relates to ToR, Task 1: Collection of general data and information; and Task 16: Field surveys of water uses




Livestock comprises cows and buffaloes, pigs, and poultry (ducks and chicken). The numbers of heads are estimated in the following table, which has been compiled from the Commune database (listing the number of families with different kinds of livestock) and surveys under the present study (providing information about the typical number of heads per family).

Table 3.1: Livestock in the study area

Sub-basin Area (km2) Cows Buffaloes Pigs Poultry Boribo 1.499 11.085 18.050 14.993 131.023

Dauntri 3.680 64.297 20.057 40.333 386.026

Values are estimates for 2005, based on a combination of the Commune Database and project surveys

The following table shows recent over-all changes in livestock population for Cambodia as a whole. More detailed (but short-term) data are available from the Commune Database. In the recent past, the number of buffaloes has been decreasing, while other animals have been increasing. These trends, however, provide only an uncertain indication of the long-term development, which will partly be market-driven and which can take place s an irregular and unpredictable process as much as a gradual and predictable one.

In Cambodia in general, there is a development from small-scale operation towards large-scale operation within breeding of poultry, pigs, and milking cows.

Table 3.2: Present change in livestock population, Cambodia

Livestock (no. of heads) Change 1991-2001 Cattle (heads) 2.2 percent per year

Pig (heads) 1.7 percent per year

Buffalo (heads) -2.4 percent per year

Chicken (heads) 5.5 percent per year

Duck (heads) 3 percent per year

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


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3.5 Fisheries This section relates to ToR, Task 1: Collection of general data and information; and Task 16: Field surveys of water uses

The Tonle Sap Basin is famous for its large fish yield and for its intense fisheries.

Capture fisheries take place in the Great Lake itself, in its tributaries, in lakes and reservoirs, and in the paddy fields. There is also some aquaculture in the project area, and aquaculture is expected to increase in the course of time.

The estimated fish yield of the Great Lake and the Tonle Sap river itself is estimated as high as 139-190 kg/ha/year (by Van Zalinge et al 2001). Different, but consistently very high estimates have been reported of the proportion of the population that depend wholly or partly on fisheries for their livelihoods, not to speak of their protein intake.

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

Figure 3.4: Flood height and fish yield in Tonle Sap

The figure shows the relationship between maximum flood level of the season and catch of the dai (bag-net) fishery in Tonle Sap. It origins from Nicolaas van Zalinge, Deap Loeung, Ngor Pengbun, Juha Sarkkula and Jorma Koponen: Mekong flood levels and Tonle Sap fish catches. Second International Symposium on the Management of Large Rivers for Fisheries, Phnom Penh, February 2003

3.6 Industries This section relates to ToR, Task 16: Field surveys of water uses

Today, there are no significant industries in the study area.


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3.7 Other livelihoods This section relates to ToR, Task 16: Field surveys of water uses

Tourism

It is a safe guess that tourism will emerge as a high-growth sector with significant livelihood implications, also in the present study area.

Water-related tourism comprises scenic areas, cultural heritage sites, trekking routes, kayaking, fishing areas and bird-watching areas. It is said that 'where there is water there is fish', but it may also be claimed that 'where there is water there is tourism'.

Today, the tourism development in the study area is low, in terms of livelihoods and value generated. This is largely due to a defunct road network that makes access to large parts of the area next to impossible in the wet season, except by ox cart.

Figure 3.5: Chrak La Eang waterfall on St. Bamnak


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The planned upgrading of the railway in the years to come may well generate a flow of tourists to the area, or through the area.

The tourism sector in the study area has an attractive potential for development, supported by the location not far from Phnom Penh.

One example of a scenic spot is the Chrak La Eang site, a series of 3 waterfalls over a reach of 1 km. There is a picnic area, toilet facilities, and a 2 kW micro-hydropower facility. The waterfall is maintained by DOE.

Sand extraction

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.

Figure 3.6: Sand extraction in St. Boribo (5 July 06)

This operation extracted 5 m3/day at a value of 2 USD/m3)


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4 Hydrology

4.1 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 2001-03 (3 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. Dauntri)

(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)

Data from altogether 33 rainfall stations, 7 evaporation stations, 22 water level and 17 discharge stations have been collected and screened for the present study. Following the screening, sub-sets of the data were selected with a suitable relevance and quality.

General

The two sub-basins covered by the present study have only few hydrological data. Data for rainfall and evaporation are available to some extent within the sub-basins and in neighbouring sub-basins. However the network density is low, and the quality of the data varies. Further there are gaps in the data series. Likewise water level and discharge measurements are sparse. Though attempts have been made, the discharge records are hardly sufficient to produce rating curves with great validity.

Rainfall data

Rainfall data were received partly from Ministry of Water Resources and Meteorology (MOWRAM), the Mekong River Commission, and Department of Meteorology. The most recent data (year 2000 to 2005) were obtained from Department of Meteorology.

In general the network density is low. Most of the rainfall stations are located close to the provincial and district centers, and very few in remote areas. Especially the


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mountain areas lack rainfall stations. Many of the rainfall stations have been installed only recently (between 1997 and 2001).

The following figure and table show the rainfall stations that were selected for analysis. Several other stations were skipped, in most cases because they were too far from the study area.

Figure 4.1: Rainfall stations

Table 4.1: Rainfall stations

Station Code E N Avg Max Min Coverage Battambang 130315 304855 1448889 1140 1428 731 1939-40, 96, 01-04 (8 years)

Kompong Chhnang

120401 463747 1354221 1613 2853 1020 1920, 22-25, 27, 29, 31-35, 37-39, 52-53, 62-69, 71-73, 82-85, 87-92, 94-05 (50 years)

Ponley 110407 442035 1374530 1460 1706 1139 1930, 94, 96-98, 01-04 (9 years)

Pong Ro 120418 454687 1356076 1282 1616 1076 2001-04 (4 years)

Pursat 120302 380497 1387622 1302 2081 289 1913-28, 30, 35, 39-42, 52, 56-63, 73, 81-05 (54 years)

Krakor 120403 411269 1383824 1499 2015 1142 1930, 39, 41-43, 46-53, 61-72, 94, 96, 99-04 (34 years)

Kravanh 120312 353040 1401189 1473 2042 810 1994-96, 98-04 (10 years)

Svay Donkeo 581102 353399 1400653 1011 1207 847 1999-04 (6 years)

Talo 120309 353314 1384061 1013 1390 829 1999-04 (6 years)

Bamnak 120406 409388 1361711 1272 2069 705 1939-42, 61-64, 93, 99-04 (15 years)

Boeung Khnar 120426 364242 1396912 1232 1705 930 1994-96, 01-04 (7 years)


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Evaporation data

Evaporation data from two stations were obtained from Department of Meteorology, Pochentong and Siem Reap. A data record for the former of 5 years from 2000 to 2005 has been provided, whereas data from the latter cover the 5 years from the period 1996 to 2000.

Water level and discharge data

Most of the water level data are available up to year 2005, however some data are still being collected. The water levels which are directly applicable in the study area are from the 6 stations : Maung Russey, Boribo, Bac Trakoun, Peam, Prey Khlong downstream and Kompong Loung. The discharge measurements are in general few, mainly due to financial constraints within the Department of Hydrology and River Works.

Catchment boundaries

The catchment boundary delineation has been done by ArcView GIS software based on:

• Topographical map 1:50,000 and 100,000;

• Digital Terrain Model (DTM);

• river networks; and

• road and railway networks

In addition, several field checks have been made in case of doubt.

4.2 Water level in Tonle Sap This section relates to ToR, Task 9: Hydrological analysis

Related data (submitted electronically) [email protected] Daily water level at Kg Chhnang 2001-03 (3 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)

The lower parts of the study area are affected by annual flooding from Tonle Sap. The flooding supplies water for retention irrigation and floating rice cultivation.

The water level is shown in the following figure. The annual minimum varies within a small interval from year to year - between 0.6 and 1.0 m - while the annual maximum varies considerably, between 6.7 m and 10.3 m in the 10-years period considered.


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Figure 4.2: Seasonal water level variation in Tonle Sap

Data: Prek Kdam1995-2004 (10 years), MOWRAM and MRC. Zero level = 0,08 m above mean sea level

4.3 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 normal rainfall in Cambodia is shown in the following figure. The figure is indicative, because it was prepared in the late 90-ies on the basis of limited data. It is seen that the rainfall in the Tonle Sap Basin is less than in most other parts of the country.

12 m

10 m

8 m

6 m

4 m

2 m

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

Prek Kdam


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Figure 4.3: Normal rainfall in Cambodia (mm/year)

Analysis by MOWRAM based on data from1984-98

Rainfall data are treated as daily, monthly or annual. Because of local variation in meteorological conditions (wind, evaporation, humidity etc.) the instantaneous rainfall can vary substantially between neighbouring stations.

Pursat is well located in the middle of the present study area. Data are available since 1912, but with several long gaps in the record. A series of 53 years between 1913 and 2005 has been selected for analysis, skipping years with indications of malfunctioning or erroneous registration.

A summary of findings is presented below. Figure 4.7 and Table 4.2 show the distribution of monthly values (month by month). Figure 4.8 and Table 4.3 show the observed variation interval of annual values. The two sets of values are different because - for example - a low rainfall in May does not necessarily coincide with a low rainfall in June or July.

1986 was the year with the lowest annual rainfall in the data series (66 percent of average), while 1995 was the year with the highest annual rainfall (158 percent of average). The '4 out of 5 years' distribution has been estimated by scaling (as 85 percent of the average distribution).


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Figure 4.4: Distribution of monthly rainfall, Pursat (mm/month)

Data: 1913-23, 26, 28, 30, 35, 39-42, 56-63, 73, 81-05 (53 years)

Table 4.2: Distribution of monthly rainfall, Pursat (mm/month)

Lowest 4 of 5 yrs Average Highest Jan 0 0 4 37

Feb 0 0 5 35

Mar 0 2 42 247

Apr 0 29 78 214

May 0 82 150 351

Jun 0 76 132 304

Jul 0 83 139 290

Aug 30 111 181 373

Sep 29 172 236 468

Oct 0 127 226 571

Nov 0 40 110 311

Dec 0 0 18 110

Data: 1913-23, 26, 28, 30, 35, 39-42, 56-63, 73, 81-05 (53 years)


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Figure 4.5: Distribution of annual rainfall, Pursat (mm/month)

Data: 1913-23, 26, 28, 30, 35, 39-42, 56-63, 73, 81-05 (53 years)

Table 4.3: Distribution of annual rainfall, Pursat (mm/year or mm/month)

1986 4 of 5 yrs Average 1995 Year 871 1.121 1.321 2.081

Jan 0 3 4 0

Feb 0 4 5 25

Mar 5 35 42 35

Apr 19 66 78 72

May 82 127 150 238

Jun 126 112 132 171

Jul 94 118 139 286

Aug 200 154 181 224

Sep 151 200 236 423

Oct 108 192 226 392

Nov 47 94 110 184

Dec 39 15 18 31

Data: 1913-23, 26, 28, 30, 35, 39-42, 56-63, 73, 81-05 (53 years)


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Table 4.4: Days with rain in Pursat

Min 4 of 5 yrs Avg Max Risk of no rain in month

Jan 0 0,0 0,5 3 0,68 pct

Feb 0 0,0 0,9 6 0,57 pct

Mar 0 1,0 3,5 14 0,13 pct

Apr 0 3,0 6,0 17 0,02 pct

May 0 8,0 11,3 26 0,02 pct

Jun 0 8,4 11,0 19 0,06 pct

Jul 0 8,0 12,8 24 0,04 pct

Aug 0 10,0 14,7 28 0,00 pct

Sep 7 14,0 16,8 25 0,00 pct

Oct 0 9,4 13,1 22 0,02 pct

Nov 0 4,0 7,8 18 0,04 pct

Dec 0 0,0 2,1 14 0,38 pct

Year 35 76,8 100,2 157

Data: 1913-23, 26, 28, 30, 35, 39-42, 56-63, 73, 81-05 (53 years)

With a study area that spans some 100 km from north to south, some 180 km from west to east, and more than 1,700 m vertically, a visible rainfall variation within the area is expected beforehand. Unfortunately, however, the data do not allow for a safe conclusion regarding the spatial variation:

In order to examine the spatial variation, 13 stations with simultaneous registrations were selected for analysis. The figure below shows the average rainfall at each station in percent of the rainfall in Pursat.

Figure 4.6: Average rainfall in percent of the average rainfall at Pursat

Data: 2001-04 (4 years)

Kravanh and Svay Donkeo stations


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It is seen that the analysis is clearly inconclusive. The figures confirm a general, slight decrease in rainfall along the Great Lake, in the direction from Kg Chhnang towards Battambang. On the other hand, the pattern is far from clear, and in general, the rainfall decreases from low-lying stations towards more elevated stations, which is opposite of what would have been expected. This is due to the short period (of 4 years only), but also - and more significant - an rather low correlation between the stations.

As an example of the occasional low correlation between adjacent stations, the following figure shows the monthly average rainfall at the Kravanh and Svay Donkeo stations, which are located only 650 m apart on a flat flood plain, without any mountains in between.

Figure 4.7: Monthly average rainfall at Kravanh and Svay Donkeo (mm/month)

Data: 2001-04 (4 years). The distance between the stations is 650 m

The low correlation is partly due to the rainfall being highly influenced by 'events' (like thundershowers) that are confined in time and space. It is a surprise, however, that a pattern does not seem to exist on a monthly (or even annual) basis, where one would expect that some apparent relationship would emerge even between distant, monsoon-affected rainfall stations in Southeast Asia.

The uneven distribution of rainfall over time is illustrated in the following figure, where the percentage contribution to the annual rainfall is shown for the most rainy day, the 2 most rainy days, the 3 most rainy days, and so forth. On the average (over the 53 years considered), the most rainy day will provide 7.4 percent of the annual rainfall, while the 16 most rainy days in a year provide more than half of the annual rainfall.


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Figure 4.8: Distribution of rainfall over days with most rain

Data: Pursat 1913-2005 (53 years)

A comparison was made between Pursat, Battambang and Kg Chhnang, where data are available from all three stations in 7 years. Results are shown in the table below. The analysis has been made for monthly and annual values, with only the latter shown in the table. Values are clearly uncorrelated, even on an annual basis. Interestingly, this analysis supports the 'normal' rainfall shown in Figure 4.6, while being based on different years. It makes good sense that the rainfall in Pursat is higher than in Battambang but lower than in Kg Cham. With a distance of 185 km between the Battambang and Kg Chhnang rainfall stations, this dataset indicates a gradient of the annual rainfall along the Great Lake of 1.3 mm/year per km in the direction from Battambang past Pursat towards Kg Chhnang.

Table 4.5: Rainfall at Pursat, Battambang and Kg Chhnang (mm/year)

Pursat Battambang Kg Chnang 1939 1419 1101 2389

1996 1834 1396 1602

2001 1129 1428 1311

2002 1405 1174 1160

2003 1485 1058 1114

2004 1056 994 1262

2005 1248 1237 1272

Average 1.368 1.198 1.444

Pct of Pursat 100 pct 88 pct 106 pct

Data: 1939, 96, 2001-05 (7 years)

Example: The 20 most rainy days provide 57 percent of the annual rainfall


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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.

Figure 4.9: Pan evaporation (mm/month)

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

Table 4.6: Pan evaporation (mm)

J F M A M J J A S O N D Year 1996 132 110 114 137 131 153 165 154 153 133 117 118 1,617

1997 116 121 140 144 195 146 152 154 149 147 112 183 1,757

1998 156 119 182 182 200 155 145 120 97 106 83 93 1,637

1999 112 146 190 150 137 123 116 121 119 114 108 108 1,543

2000 118 129 167 154 134 133 164 171 129 113 147 143 1,702

2001 136 184 177 187 120 115 134 121 106 123 126 145 1,673

2002 133 116 156 161 147 138 153 83 102 105 149 115 1,555

2003 112 131 157 151 125 158 167 167 155 129 136 147 1,736

2004 151 162 217 203 195 167 159 165 138 145 150 148 2,000

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. An alternative, but less accurate estimate would be that the ratio between the actual evaporation and the pan evaporation varies between 0.7 in the wet season and half of that value in the driest month, when soils are dry and the vegetation is defoliated (without leaves), so that little evaporation can take place. The distribution between these values can for example reflect the monthly annual rainfall. Hereby, the average ratio between


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pan evaporation and effective evaporation becomes 0.51. This estimate is presented in the table below It has been included because it may possibly reflect reality better than the more traceable estimate. It should be applied with caution, though.

Table 4.7: Estimated effective evaporation (mm)

J F M A M J J A S O N D Year Factor 0.35 0.35 0.41 0.46 0.57 0.54 0.55 0.62 0.70 0.68 0.51 0.37 0.51

Highest 53 57 89 94 111 91 88 102 97 100 77 55 1,011

Average 45 47 68 75 88 78 83 86 89 85 64 49 858

Lowest 39 51 78 69 78 67 64 75 83 78 55 40 777

Data: Free estimates based on Battambang and Pochentong, corrected with a pan coefficient varying between 0.7 and 0.35

4.4 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 -


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

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.

In the course of the study possible relations between rainfall and runoff will be explored. However, at this stage it is envisaged that the outcome may be less successful. It is thought that the rainfall-runoff modelling with MIKE Basin will give a more consistent picture of the relations and processes.

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.


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Figure 4.10: Average monthly rainfall Figure 4.11: Average monthly rainfall versus runoff, Maung Russey versus runoff, Kg.Tralach

Extension of stream flow records

Available discharge data in the Tonle Sap Basin tributaries are very few. Nevertheless, an attempt was made in the WUP-JICA study to derive discharge rating curves for the main tributaries. There has been no additional discharge measurements carried out since the data reported in JICA (2004).

In this study, the rating curves were used to generate rated discharge for the periods in which daily water levels exist at the stations. Discharge was generated upto year 2001, provided that water level data existed at the stations. In the present study the same rating curves are applied to generate discharge upto year 2005.

The table below shows the periods for the relevant stations for which discharge data is generated on basis of available water level data.

Table 4.8: Stations with extended stream flow record

River Station 94 95 96 97 98 99 00 01 02 03 04 05 St. Boribo Boribo Q Q Q Q

St. Pursat Bac Trakoun Q Q Q

St. Dan Try Maung Russey Q

Years in which measurements are made are shown with ‘Q’

Years with available daily water levels for discharge generation are shown with shading

The extension of stream flow records is extremely useful, even though the data basis for their derivation is limited. The reason is that the records provide a basis

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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for model calibration (see next section), and comprise (together with the actual observations) the only information on runoff from the catchments under study.

If two stations within the same catchment are selected then a correlation can be expected. In Figure 4.12 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 4.13 the square root of the product of the two discharges are plotted against the discharge at Peam. The correlation is acceptable.

Figure 4.12: Rated discharge at Bac Trakoun Figure 4.13: Discharge relation between versus that of Peam, year 2001 Bac Trakoun and Peam, year 2001

The extension of the stream flow record at Boribo has been made in order to obtain a longer period for which the NAM model could be calibrated. At the outset of the model calibration all years 1998-2005 were used. However the general fit between simulation results and rated discharge was not satisfactory when all years were applied. The reason is likely found in the somewhat different runoff pattern (as predicted by the rated discharge) for the years 2002-2005, see figure 4.12 in Tech.Rep. No.1. The dry season flows in this period show unusual fluctuations, and the total volume during floods are less than previous years. This could of course be attributed to a change in hydrology, but it is suggested that a change in the flow distribution at Bamnak in recent years (confirmed by interview of local people at Bamnak) plays a stronger role. Therefore the original period 1998-2001 as used in the WUP-JICA study was used in the present study for model calibration.

The rating curve at Stung Dauntri was less useful, as there were no additional water levels available to derive a rated discharge.

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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The extension of the stream flow record at Pursat was useful in the sense that rated discharges from relatively recent years (2001-2003) could be used to derive the flows available for the Damnak Ampil channel.

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

4.5 Groundwater This section relates to ToR, Task 9: Hydrological analysis

Related data (submitted electronically) Wells.xls Inventory of groundwater wells in Boribo and Dauntri Sub-basins.

PRD survey 2006 Wells-KgChhnang.xls Logs of 22 wells in Kg Chhnang Province, reported by W.C.

Rasmussen and G.M. Bradford

Groundwater exploration has been conducted in the past by projects such as PRASAC and SEILA, by provincial water supply authorities (under Ministry of Industries, Mine and Energy), and by the provinicial departments of Ministry of Rural Development.

Regional groundwater development studies were undertaken in central and south eastern Cambodia in 2000-02 by JICA and Ministry of Rural Development (JICA and MRD May 02). Unfortunately, this comprehensive study does not cover the present study area. However, its findings (summarized in the table below) provide useful indications of the groundwater availability in the study area.

The town of Siem Reab is supplied by groundwater at a withdrawal rate of 1500-1600 m3/day (CNMC Oct 04, p. 45). Some private enterprises (like the large hotels in Siem Reab, and some water-consuming industries) use groundwater from deep aquifers. Deep wells with hand pumps are in general use for village supply. Small-scale exploitation of shallow aquifers is common for dry season household supplies, and in some cases for supplementary irrigation undertaken by entrepreneurial farmers.

Groundwater-related water quality issues have been reported in relation to cloride, iron, manganese, arsenic, fluoride and nitrate (JICA and MRD May 02). In some places, there is some reluctance among the farmers to use groundwater due to a concern that a high bicarbonate contents can adversely affect the soil structure. (It is believed that the risk is small as long as the groundwater supply is small as compared with the direct rainfall). Some people in Cambodia believe that a high bicarbonate content in drinking water represents a health risk.


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Arsenic in groundwater • Wells with high arsenic concentrations are generally found in the immediate vicinity of the

Mekong, Bassac and Tonle Sap and some smaller rivers • The contaminated wells were located within the alluvial floodplain sediments of the modern or

Holocene geological era. However, not all wells within these geological units are contaminated.

• The older (Pleistocene era) “platform and terrace deposits” that flank the modern floodplain sediments are not associated with high arsenic concentrations (>50? g/L) but often have groundwater with arsenic levels in the 10-50 μg/L range.

• The broad flood plains (flooded forest) surrounding the Tonle Sap lake are generally low in arsenic.

• None of the wells developed in basement rocks or basalts have been found to have elevated arsenic levels.

The arsenic testing program in Cambodia confirmed that arsenic contamination is generally associated with tube-wells rather than open wells. Testing has also confirmed that, in general, very shallow wells (< 15m) are not significantly contaminated with arsenic. The flood plain surrounding the Great Lake are classified as 'Zone 2 - Low Risk'. The risk of arsenic exceeding 50 ? g/L in this zone is only 0.2% but about 5% of the tube-wells in this zone have moderately elevated arsenic levels (10-50 ? g/L). Some exposure to arsenic may occur through consumption of vegetables, rice and meat but in general arsenic intake via these routes is not high and the arsenic is primarily in organic forms which are considerable less toxic, however, it should be noted that the importance of food as a source of dietary arsenic in Cambodia is not well characterised at present. It is emphasized that more knowledge about the subject is desirable. (Fredericks, Jan 04)


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Table 4.9: Groundwater potential in Kg Chhnang and Kg Cham Provinces

Province District Hydrogeology Main aquifer Specific capacity Warer quality Potential

Kg Chhnang

Kg Leng Chul Kiri Baribo Kg Chhnang Rolea Phier Kg Tralach

Located along the Tonle Sap. Covered by thin alluvial sediments forming a shallow aquifer of poor quantity and quality. Fissure and weathered basement rocks become an aquifer

Tuk Pros Samaki

Meanchey

Covered by thin pleistocene sandy and clayey sediments. Basement rock is located at shallow depth

Fissure and weathered basement rocks (sandstone, rhyolite)

Basement rocks: 0.2 - 200 m2/day, depending on the fracture zone

Shallow alluvial aquifers locally affected by iron and arsenic. Basement rock aquifers locally affected by fluoride

(1) Alluvial shallow aquifer (10-20 m depth): Low potential (2) Basement rock (> 10 m depth): Generally impermeable, but fissured and weathered parts become excellent aquifers with high potential. Test pumping 3.7 -63.4 m3/day

Kg Cham Bateay Cheng Prey Kang Meas Kroch Chma Srei Santhor Kok Sotin

Located along the Tonle Sap and the Mekong. Alluvial and plio-pleistocene formation consists of thich clayey sediments. Shallow thin sandy layers form aquifer of saline or iron rich groundwater

Alluvial and plio-pleistocene sediments

Alluvial aquifer: 15.6 m2/day at the test well in Cheng Prey

Generally high iron, locally accompanied by high arsenic. High cloride (386 mg/l) and TDS (1507 mg/l) at the test well

Potential low in terms of quality. High iron and arsenic contents in shallow aquifer (20 m depth). Locally, high chloride. Test pumping: 68.9 m3/day

Stung Trang Chamkar Leu Prey Chhor Kg Siem Kg Cham

Plio-pleistocene sandy layers and basalt form good aquifers. One pleistocene sandy aquifer is locally artesian

Plio-pleistocene basalt and sediments

Basalt: 49.9 m2/day at the test well in Chamkar Leu

Generally good quality. Slightly elevated iron contents in the pleistocene aquifer

High potential. Well depth 50-80 m. Test pumping: 180 m3/day. Artesian yield: 30-40 l/min

Tbong Khmum

O Reang Ov Dambe Ponhea Krek

Plio-pleistocene sand or gravel layers and basalt form good aquifers. One plio-pleistocene aquifer is locally artesian

Quaternary basalt and plio-pleistocene sediments

Plio-pleistocene: 115-670 m2/day Basalt aquifer: 5.5-27.9 m2/day

(same as above)

Excellent potential. Well depth 40-100 m. Test pumping 60-90 m3/day (basalt), 185-230 m/day (plio-pleistocene). Artesian yield: 60 l/min

Memot Located on the gently undulated hill composed of basalt and plio-pleistocene sediments forming good aquifers. Basement rock locally found at 15 m depth

Basalt, plio-pleistocene sediments, basement rocks (sandstone)

Sandstone: 6.7-114.6 m2/day Basalt: 2.9-52 m2/day Plio-pleistocene: 20.7 m2/day

Good quality. No iron nor arsenic. No fluoride in the basement rock aquifer

High potential: Well depth 25-50 m. Test pumping: 14.4-192 m3/day

JICA and MRD (May 02), p. 4-264


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Geological setting

The base level of the study area is at the surface of the Great Lake, about 9 m above sea level. From there the plain rises gradually to20m above sea level at Battambang. On the south the plain merges rather abruptly with the Chuar Phnum Kravanh. The predominant formation, occupying the vast central plain, is the Young Alluvium. In the Chuar Phnum Kravanh mountain massif to the south is a complex at consolidated sedimentary rocks associated with intrusive and extrusive igneous rocks. No Old Alluvium is mapped in the south at the base at the Chuor Phnum Kravanh. Apparently there has been subsidence, so. that active erosion at the mountains has buried any Old Alluvium beneath a mantle at Young Alluvium.

The Chua Phnom Kravanh is composed at resistant Mesozaic and Paleozoic sedimentary rocks which lie around a care at crystalline rocks. The core is made up at gabbros. intrusive into. crystalline schist. Sandstone, conglomerate, breccias, and sandy shale at the lndosinios Formation, partly covered and partly intruded by basalt, andesine, decide, and hyalite, add to. the complexity at the massif. Permian limestone's and Devonian limestone, marl, siltstone, sandstone, and shale crop out an the fringes at the mountain massif and also in isolated hills.

The Groundwater Resources of Cambodia, Geological Survey Water Supply Paper 1608P: The report and survey done by W.C. Rasmussen and G.M. Bradford, discussed the geology and hydrology by Cambodian provinces. Numerous well records were also tabulated. Among those wells records, there is only one well, SS1, which has been drilled and recorded on an April 4th, 1961 in Battambang Provincial Town. The well is about 60 m north of the electric plant and it was abandoned at 30 m in alluvium.

Table 4.10: Log of Well SS1 Figure 4.14: Geological in Battambang Provincial Town layers from Well SS1

From To Lithology m m

0 7 Gray clay

7 12 Yellow clay

12 15 Black and white gravel

15 30 White clay with fine sand


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From this source, only one well record is available in Pursat and it was of an unproductive well. The well, PS1, was located in Subdivision of the Public Works Pursat (in those time). The log is shown in the table and the figure below.

Table 4.11: Log of Well PS1 Figure 4.15: Geological layers in Pursat Provincial Town from Well PS1

From To Lithology m m

0 7 Fine sand

7 4 Fine sand and gravel

4 14 Gravel and white clay

14 16 Coarse, white sand

16 5 Sand, white and brown earth

5 28 Brown earth with stones

28 32 Sand and white stone

32 35 Earth, sand, and stone

35 56 Muddy sand and hard rock

56 59 Hard rock

59 76 Clay and rock

76 86 Pure clay

86 97 Hard, white to black rock

From the same source, there are 22 wells drilled and record in Khet Kampong Chhnang. The wells are distributed in three of the five sroks. Around the capital, Kampong Chhnang, 7 of 11 wells were productive. In Srok Kampong TraIach, only two wells were drilled for water, and both were productive. Seven holes were drilled as foundati,on tests to an average depth of 11.6 m. Two successful wells were drilled at Phumi Romeas in Srok Toek Phos. The water wells range in depth from 18 to 80 m and are 36.7 m deep on the average. The wells range in yield from 49 to 200 l/min and yield 114 l/min on the average.

The table below contains all the logs of 22 well s in Kampong Chhnang Province. For details, please refer to the electronic data table Wells-KgChhnang.xls.


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Table 4.12: Wells in Khet Kampong Chhnang

Well no. Town or village Completed Depth Water table depth Yield m m litres/min

Srok Kampong Tralach

KTr 1 Phumi Svay Pok (Khum Svay)

04-06-1962 28 7 200

KTr 2 Long Vek 4-25-62 25 6 150

KTr 3 Khum Tbeng Khpos 5-14-62 12

KTr 4 do 5-18-62 13

KTr 5 do 5-22-62 12

KTr 6 do 5-23-62 13

KTr 7 do 5-26-62 10

KTr 8 do 06-08-1962 12

KTr 9 Khum Tbeng Khpos 06-09-1962 8

Srok Rolea Pier

RP 1 Kg Chhang 1-22-61 22 190

RP 2 do 2-19-61 48 114

RP 3 do NP

RP 4 do 3-13-61 30 114

RP 5 Prey khmer (khum Rolea Peir)

5-30-61 28 49

RP 6 Khum Kampong Chhnang 6-13-61 31 114

RP 7 do 07-11-1961 48 114

RP 8 Prey Khmer 41.7 95

RP 9 Phum Chey Bak 01-08-1963 18 NP

RP 10 do 1-31-63 80 NP

RP 11 Phum Chrey Bak 2-18-63 38 NP

Srok Toek Phos

TP 1 Khlong Popok (Khum Khlong popok – Barang )

04-06-1961 30 20 57

TP 2 do 5-20-61 46 57

In addition to the survey mentioned above, 5 geo-resistivity transects have been mapped in Kampong Chhnang Provincial Town by PRD in connecgtion with a study of groundwater potential under the 'Urban and peri-urban water supply project'. The location of those survey lines are listed below.

Table 4.13: Geo-resistivity transects in Kampong Chhnang Provincial Town

Line-ID Start line Centre End line Direction E N E N E N KCHH-1 463283 1353727 463612 1353966 463929 1354188 SW to NE

KCHH-2 462494 1354444 462409 1354829 462347 1355222 SE to NW

KCHH-3 462774 1356285 462687 1355903 462626 1355518 N to S

KCHH-4 463920 1356981 463563 1356808 463198 1356646 NE to SW

KCHH-5 465134 1352909 465085 1353303 465079 1353697 S to N


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The geo resistivity survey shows a low resistivity formation from the surface to 20-35m, and a high resistivity formation from 35 m to the bottom of these inversions. The low resistivity formation was interpreted as unconsolidated sediment present as recent alluvial. The high resistivity formation was interpreted as basement rock.

The yields are estimated per well and general upper and lower estimated bounds based on resistivity value are used. As general experience in Cambodia, the interpreted type of weather rock and alluvial fine sand with resistivity range from 35 to 60 Ωm have an estimate yield of 50 to 250 m3/day.

The figures below show the geo-resistivity profiles.

Figure 4.16a: Geo-resistivity profile, Kg Chhnang Town (1)

SW NE


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Figure 4.16b: Geo-resistivity profile, Kg Chhnang Town (2)

Figure 4.16c: Geo-resistivity profile, Kg Chhnang Town (3)

SE NW

N S


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Figure 4.16d: Geo-resistivity profile, Kg Chhnang Town (4)

Figure 4.16e: Geo-resistivity profile, Kg Chhnang Town (5)

During the present study, information was collected about 21 wells in Boribo and Dauntri Sub-basins, as indicated in the following table. Reference is made to the electronic data table for additional information.

NE SW

S N


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Table 4.14: Wells in Boribo and Dauntri Sub-basins (examples)

District Commune Village Well depth

Pump dept

Yield Households served

m3/h

Krokor Tnoatchum Thmei 40m 18m 0,7

Krokor Tnoatchum Tboengchum 30m 0,7 12

Krokor Tnoatchum Tboengchum 30m 12m

Krokor Tnoatchum Senpen 40m 29m 0,7 30 to 40

Krokor Kampongroa Chekchao 25m 1,5 23 to 40

Moung Prekchik Chhkoekhambres 25m 12m 3,5

Moung Prekchik Chhkoekhambres 33m 2 6 to 7

Krokor Boengkantuot Krang

Boribo Anchangroung Preashkoal 30m 22m 1,5

Boribo Anchangroung Preashkoal 28m 1,2

Boribo Phsa Phsa 25m 1 5 to 6

Boribo Anchangroung Preashkoal 32m 24m 1 10

Boribo Mealum Tuolthlork 6m

Boribo Mealum Mealum 20m 3

Krokor Tnoatchum Choeteal

Krokor Tnoatchum Boengveal

Bakan Romlech Takok 8m 5 to 6

Bakan Romlech Kampongkdey 5m

Bakan Romlech Kampongkdey 8m 5 to 6

Krokor Chhoetom Charmthmei 22m 2 25

Krokor Chhoetom Charmthmei 24m 1,8

Data: PRD 2006

The sandstone mountains in the study area probably absorb considerable infiltration from rainfall and deliver it as base flow to the main rivers. The alluvium especially old alluvium on the plain may ultimately provide some yields to water wells. The young alluvium in the trough bordering the TonIe Sap will yield small quantities of water.

Also, the hard rock of mountains are expected to yield little water to the wells. The most productive area for ground water is probably the terrace plain of the old alluvium.

There are two types of aquifer in the study area: Shallow aquifer and aquifer in basement rock. The shallow aquifer is draws groundwater from unconsolidated alluvium or recent alluvium from the surface to 30-40m depth. This formation is dominanted by clay and silty clay so yield is not high, about 0.5 to 6m3/h. The aquifer in basement rock is the aquifer that take the water from hard rock. Most of these wells are from 30-100m in depth. These aquifers have a high risk of being non-productive. Typical yields are 2 to 8m3/h.


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4.6 Climate change This section relates to ToR, Task 9: Hydrological analysis; and Task 22: Assessment of trends in water availability and demand

A speculative outlook for the possible over-all effects of climate change is offered by MRC (Nov 05) (p. 22):

'The study results [published by Arora and Boer (2001)], using a general global climate circulation model] predicted that over land, precipitation would decrease by 2 per cent and evaporation would increase by 2 per cent. These two effects would combine to reduce freshwater supply to the oceans by 14 per cent. ... According to the model, runoff and river discharge decrease in a warmer world.

Results for the Mekong predict lower mean annual flows and floods but the seasonal distribution of water remains the same. Flood season volumes would decrease by 15 per cent'.

One possible element is an increased frequency of occurrence of various anomalities, such as the timing, duration and intensity of flood and drought events.


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5 Water uses and water balance

5.1 General This section relates to ToR, Task 6: Approach to hydrological analysis

A distinction will be made between (i) the water availability; (ii) the water demand; and (iii) the actual water use. These key characteristics are linked as far as production systems and livelihoods have, in the course of centuries, adapted to the water availability. For the purpose of analysis and decision-support, however, they can be regarded as independent.

This clear distinction is not a matter of course in water resources analyses, but it is believed that it will provide a robust and useful analysis - much in the same line of thought as when an economic analysis distinguishes between revenue and costs.

Figure 5.1: Rationale of water use and water balance analysis

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




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

Overview

The current water utilization in Cambodia is summarized in the table below. The following characteristics apply:

Availability Demand Actual use

Scope for infrastructural development

Livelihoods and d evelopment affected by water ava ilability


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• Irrigated cultivation is the predominant use. The demand is much higher than the actual use, which is limited by the irrigation infrastructure

• Domestic uses are 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

Table 5.1: Current water uses in Cambodia

Consumption Mm3/year Irrigated cultivation (1) 455

Domestic (2) 136

Livestock 100

Industry, commerce and institutions (3) 30

Other 79

Total 800

(1) MOWRAM & CNMC (2003a) (2) 28 litres per one person (average for rural and urban areas) (3) MOWRAM & CNMC (2003b) Source: MOE (Apr 05)

Domestic water uses

Domestic water uses are small in terms of volume but represent the highest Total Economic Value of water utilisation.

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. Most villagers (and some urban households) must either carry the water to their homes or have it delivered by vendors in part of the year.

Therefore, in Cambodia today, people in urban areas use much more water (65,1 l/p/d) than the rural population (20,7 l/p/d) (2001, according to MRC Jun 03)1.

It is expected that the present consumption is not a safe guideline in relation to the future demand, which, in the course of time, inevitably will be affected by new lifestyles and consumer patterns. (These will not only influence the volumes of water used, but also the volumes of wastewater generated).

Therefore, an assessment of the future domestic water uses must draw on experience from elsewhere in Cambodia and elsewhere in the Lower Mekong Basin.

1 Other sources present somewhat different values


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Because of the small volumes, conflicts of interest between domestic and other water uses are not expected to be significant. Still, when managing the water allocation, priority must be given to domestic uses.

The future demand will be determined by a combination of 3 inter-related developments, each of which is certain to take place:

• Over-all population growth

• Urbanisation (migration from rural to urban areas)

• Increased per capita demand, reflecting 'new lifestyles' and improved access to water - notably an expanded coverage of piped supply directly to each household.

Fot the present study area, the over-all population growth will inevitably be affected by migration, and the effect of urbanisation may be negative, since there are no urban centres (such as provincial towns) in the study area. National gross values, as listed below, may be misleading. In fact, the possibilty exists that the 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.

Another effect to be considered is that the statistics register the people's home address, but not where they actually live (and consume water). An increasing part of the rural population have their livelihood (and their actual, although perhaps temporary address) in urban centres. This effect will be more pronounced in the years to come because of the increase in the (presently quite low) average age. 2

Table 5.2: Estimated population growth, Cambodia

Population 2000 2020 Growth Urban 2,1 mio. 5,3 mio. 6.2 pct/year

Rural 11,0 mio. 15,2 mio. 1.2 pct/year

Total 13,1 mio. 20,5 mio. 2.3 pct/year

Source: MRC (Jun 03), quoting World Resources Institute (2002)

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.

2 43 percent of the population was below 15 years in 2002 (World Resources Institute)


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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.

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.

Table 5.3: Typical unit demands for irrigation, traditional paddy cultivation

Water use Demand Crop demand and infiltration 1 l/s/ha or 10 mm/day,

minus direct rainfall

Conveyance losses 1 l/s/ha or 10 mm/day, highly depending on system layout, maintenance, and operation

Return flows From 50-100 mm/crop and up to 1 l/s/ha or 10 mm/day, depending on water availablity

Source: T. K. Nielsen (Dec 04)

The agricultural water use is highly influenced by the actual crops and cropping cycles, and by the applied technology. Apart from infrastructural upgrading of water storage and distribution, the development will include new technologies and, expectedly, higher water efficiencies and much higher economic efficiencies of water utilisation. As it is the case with the domestic water uses, the present use can provide little more than an indication of the future demand, and experience from elsewhere must be included in the assessment.

As illustrated by the following table, the future irrigaction demand depends not only on the planned rehabilitations and expansions of irrigation systems, but also very much on the crops and the cultivation routines. Apart from different rice varieties having different demands of water, crops other than rice will generally have a lower (or even much lower) demand as compared with rice. In broad general, such crops can at the same time represent a higher market value (but have different needs in terms of distribution, and may impose various risks to the farmers).


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Table 5.4: Specific crop water requirements

Crop Water requirement Banana 970 m3/ton

Groundnut 1880 m3/ton

Maize 780 m3/ton

Soybean 3050 m3/ton

Sugarcane 200 m3/ton

Watermelon 270 m3/ton

Onion (dry) 490 m3/ton

Rice 4050 m3/ton

Note: Various irrigation losses and post-harvest loses are not included Source: Hoekstra and Hung (2002), Appendix III, pp. 3, 6, 9, 12 (Example, Thailand 1999) (a similar pattern has been reported from Viet Nam and elsewhere)

Table 5.5: Unit demands for livestock

Water use Present demand Future demand Source Buffaloes 100 l/d 100 l/d MRC-BDP (Nov 05)

Cows 100 l/d 120 l/d Present: Estimate Future: MRC-BDP (Nov 05)

Pigs 50 l/d 50 l/d MRC-BDP (Nov 05)

Poultry 20 l/d 20 l/d MRC-BDP (Nov 05)

Businesses and industries

Businesses and industries represent (in most cases) water uses that are small in terms of volume, but which generate an added value that is much higher than agriculture.


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Table 5.6: Estimated water demand for industries and institutions

Description Consumption allowance Basic factory requirement for cleaning and sanitation 0.05 m3/day/worker

Average consumption in light industrial estates 0.25-50 m3/day/worker

Average consumption in light industrial estates that include a proportion of factories engaged in food-processing, soft drink manufacture, ice making

0.90-1.10 m3/day/worker

Requirements for specific industries: dyeing fabric and leather production paper production plastics chemicals soft drinks and breweries meat production/slaughtering concrete products terrazzo tiles

70-85 m3/t 150 m3/t 30-80 m3/t 10-20 m3/t 7 m3/t 5 m3/t livestock 1 m3/t 1 m3/10-20 m2 of tiles

Small shops and traders, offices 25 l/head/day

Large offices 65 l/head/day

Hospitals and hotels 350-500 l/bed/day

Schools 25-75 l/persons/day

Source: MOWRAM estimates presented in MRC-BDP (Nov 05), p. 73

One exception is mining, which can require large volumes of water for ore processing and can generate water pollution by sediments and by residues of processing chemicals. There is no mining in the present study area, however (except small-scale sand extraction form the rivers).

In the course of time, businesses and industries are expected to become more important in the project area terms of livelihoods and economy, in accordance with clear trends elsewhere in Cambodia. The significance of an adequate water allocation will increase accordingly.

Hydropower: The demand of electricity is high, and increasing, and the economic viability of largescale and small-scale hydropower production increases accordingly.

If combined with storage facilities, hydropower production will influence the downstream water availability - sometimes positively, if water is stored in periods with abundance and released in periods with a shortage. The value depends on the regularity of the operation, with a high regularity providing benefits (as the increased flow can be regarded as 'reliable') (farmers have less benefit from irregular or unexpected supplies).

Hydropower development is not expected in the study area in the foreseeable future.

In-stream water uses

In-stream water uses are related to fisheries; navigation; and preservation of habitats and water-related assets. They can have a high, but not very visible Total Economic Value, and can have a high social importance by providing a basis for various present and future rural livelihoods.


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In-stream water uses must be duly kept in mind in connection with over-all water resources allocations. They are closely related to the ecological demand (or the 'environmental flows'), as well as to the tourism and recreation sector with its attractive development potential.

Distribution of water uses

Spatial and monthly distributions of present and future domestic demand, livestock demand and irrigation demand are shown in Appendix 4.

5.3 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

Water balance for the Great Lake

The relation between water level, surface area and volume of the Great Lake is shown in the following table, which was produced under the MRC WUP-JICA Programme.

Table 5.7: Water level, surface area and volume of the Great Lake

Elevation Area (km2) Volume (MCM) 0.5 0 0 0.6 21 1 0.8 666 70 1.0 1,379 274 1.2 1,874 600 1.4 2,125 999 1.6 2,325 1,444 2.0 3,611 2,631 3.0 4,671 6,772 4.0 5,828 12,022 5.0 7,218 18,545 6.0 8,518 26,413 7.0 9,690 35,517 8.0 10,935 45,830 9.0 12,198 57,397

10.0 13,352 70,172 11.0 14,330 84,013 12.0 15,243 98,800

The Great Lake has been delineated at Kg Chhnang Datum: Hatien MSL (2001) (at Prek Kdam, the Hatien MSL is located 7 cm below the MSL applied in the Mekong Hydrological Yearbooks and the MRC data tables) Ref: MRC-WUP-JICA (Mar 04b)


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A water balance for the Great Lake has been established by various sources, see e.g. (MRC-WUP-JICA, Mar 04b) and (Carbonnel and Guiscafre). The water balance (based on volume) has the following components, by order of significance:

1 Exchange with the Mekong via the Tonle Sap

2 Runoff from the lake's own catchment area

3 Exchange with the Mekong by overland flow

4 Direct rainfall on the lake

5 Evaporation from the surface of the lake

The catchment area of the Great Lake (if delineated at Kg Chhnang) is some 61,365 km2 minus the varying area of the lake itself (of between some 2,500-3,000 km2 and up to around 10-14,000 km2).

It is noteworthy that the largest monthly contribution of runoff from the Lake's own catchment always occurs in October. October is also the month where the flow is reversed in Tonle Sap river and water flows out of the lake. Therefore the net volume contribution becomes negative.

The implication of this is that the maximum water levels in the lake does not coincide with the maximum runoff from the Tonle Sap Basin itself. This aspect is worthwhile remembering in the present study, where we are concerned about flooding both from the catchment and from the lake.

Year 2000 is characterized by a particularly large inflow and outflow, and by a substantial part of the outflow to the Mekong taking place by overland flow. In normal years, part of the inflow will take place by overland flow, while the outflow largely will take place via Tonle Sap. Over the period shown in the table, there has been a net outflow of 11,6 km3/year (or 368 m3/s).

Table 5.8: Water balance for the Great Lake (example, 2000)

Month Direct Evaporation From catchment From Mekong From Mekong Total rainfall via Tonle Sap by overland flow km3 km3 km3 km3 km3 km3 A 0,3 -0,3 0,4 -2,6 0,0 -2,2 M 0,3 -0,3 0,3 1,5 0,0 1,9 J 0,4 -0,4 0,8 9,3 0,0 10,1 J 1,6 -0,6 2,6 20,1 3,1 26,8 A 1,7 -0,7 2,4 10,0 3,8 17,1 S 2,3 -0,6 4,0 5,4 8,4 19,4 O 3,9 -0,7 6,8 -20,6 -1,2 -11,8 N 0,1 -0,7 3,9 -23,6 -1,7 -21,9 D 0,1 -0,7 1,3 -20,0 0,0 -19,3 J 0,2 -0,7 0,4 -15,3 0,0 -15,3 F 0,1 -0,7 0,1 -9,6 0,0 -10,0 M 0,3 -0,6 0,5 -6,7 0,0 -6,4 Total 11,3 -7,0 23,5 -52,1 12,4 -11,6

Source: MRC-WUP-JICA (Mar 04b)


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Figure 5.2: Water balance for the Great Lake (example, 2000)

Source: MRC-WUP-JICA (Mar 04b)


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MIKE Basin set-up

Water balances have been calculated using the MIKE Basin modeling system. Please refer to Appendix 2 for a general description.

River basin modeling system: Software used to develop the specific river basin models useful for the present studies. As hydraulic and hydrologic laws are quite universal, it can be used for river basins everywhere in the world. It is not a specific development for Cambodia context. River basin model: The specific representation of a river basin (hydrological process, water uses, hydraulics structures) using a river basin modeling system or developing a specific code.

The water balance for each individual subcatchment within both the Boribo and the Dauntri catchments are derived on the following relation:

Inflow = outflow + storage, where

Inflow = Rainfall + river inflow + diversions from other catchments

Outlow + storage = Catchment outflow + infiltration + evaporation + diversions to other catchments + other consumptive uses + storage

Through the MIKE Basin results it is possible to extract the above to assess the water balance. In the various tables of water balance in the report, infiltration is included in ‘Storages and losses’.

5.4 Development scenarios This section relates to ToR, Task 22: Assessment of trends in water availability and demand

It can be taken as a matter of fact that the future water demand and the future water utilization will be different from today's. Possibly, the present conditions, as described in the preceding sections, provide only a vague indication of the future conditions.

Some scenarios for water use development are listed in the following table.

The scenarios are indicative and conceptual, with an uncertain time frame. For example, while present production systems are socially unsustainable (because people will remain in poverty as long as they prevail), it is difficult to predict which production systems will eventually replace them: High-yield and high-intensity, or perhaps low-yield organic niche production with a high added value. In general, the implications for the water demand can be positive as well as negative.

Still, the scenarios illustrate the importance of a continued water resources management.


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Table 5.9: Scenarios for water demand and utilization

Sector Potential development Domestic supplies New lifestyles. Water supply services improved in terms of

network coverage and supply capacity. Much higher per capita consumption (100 l/p/day ??) Increased use of groundwater for urban supplies Increased volumes of sewage and solid waste

Irrigated agriculture Full development of potential irrigation areas; water utilization limited by the water availability (all available water used) Increased water efficiency and land use efficiency Partial shift towards crops that are less water-consuming and more valuable than rice More use of fertilizers and pesticides, potentially affecting the water quality Introduction of private, large-scale irrigation schemes

Livestock More (and bigger) cows, less buffaloes; emergence of large production units for pigs and poultry (potentially affecting the water quality) Higher water demand and increased waste production

Fisheries Continued intense fisheries in the Great Lake; higher production efficiencies; declining fisheries in tributaries and paddy fields

Tourism Increased tourism: Many more arrivals, longer stays, much higher spending per day; increased water demand for consumption by tourists, and continued in-stream demand for environmental and recreational purposes

Hydropower Possibly, no major developments within the study area ?

Industry Moderate industrial development based on agriculture, forestry and fisheries; increased water demand, increasingly served by groundwater

Rural livelihoods Improved rural livelihoods due to private investment, and public investment in improved infrastructure, extension services, education and micro-credit. The idea has been raised of a 'one-village-one-product' scheme, with inspiration from Thailand

Transport Improved network of secondary roads; railway upgraded and connected to Thailand and Viet Nam


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6 Morphology, floods and drought

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

Related data (submitted electronically) R@Pursat-12-05 Daily and monthly rainfall data from Pursat 1912-2005 (53 years),

with summary statistics [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 -


(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)

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

6.2 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.

6.3 Floods This section relates to ToR, Task 11: Flood characteristics

The severity of floods depends on the time and the duration of the inundation. In rural parts of the Cambodian flood plains, people speak of a ‘beautiful flood’ if the time and level is such that water and nutrients is abundantly available for cultivation, while damages are negligible. A 'beautiful flood' is one slightly higher than normal, like the one in 2003. The cultivation will suffer both if the peak of the flood is significantly lower and significantly higher than this.

The fish yield and the fisheries will benefit in proportion to the flood height. In consequence, an extreme flood is traditionally regarded as 'bad for rice - good for fish'.

There are three categories of floods in the project area:

• Floods caused by the annual water level variation in the Great Lake;

• floods caused by flows from upstream catchments, and


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• floods caused by direct rainfall.

These have different significance, depending on the context, as briefly described below.

Floods related to the Great Lake

Floods related to the Great Lake are highly important to the aquatic ecosystem and hereby the highly valuable fisheries in the Tonle Sap Basin. They also form the basis for floating rice cultivation and recession irrigation. They are determined by the over-all water balance of the entire Mekong Basin, which in the wet season largely depends on the monsoon rainfall, and to some extent on snow melt in the Himalaya, and to a small extent on storage and withdrawals. In the dry season, the sea level sets a lower limit for the water level.

In the study area, these floods occur in the lowermost parts only. They are quite regular, even if small deviations from 'normal' can cause severe inconveniences - because cultivation systems and infrastructure have adapted to the high regularity. Also the aquatic ecosystem has adapted to the regularity; benefits of floods occur in case of regular, rather that irregular floods.

The annual minimum water level is fairly similar from one year to another, varying between around 0.6 and around 1.2 m above sea level, while the annual maximum water level varies around 6.7 m and around 10.3 m above sea level, within an annual range of between around 6.1 m and around 9.3 m (Prek Kdam 1995-2004), as illustrated below.

Figure 6.1: Annual water level range in the Great Lake

Data: Prek Kdam 1995-2004

Floods caused by flows from upstream

Floods caused by flows from upstream are of interest for flood impact analyses and for design of structures such as gates and culverts. With the relatively small catchments in the study area, the critical events will be related to thunderstorms or local depressions drifting in the downstream direction along the upstream reaches of the river.


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Many flood-related damages are seen to present structures in the area. In their comprehensive 1994 inventory, Halcrow notes that '.. there is often insufficient provision to pass flood flows safely, resulting in damage to reservoir embankments and structures... The 1991 flood caused significant damage, although its return period has been estimated at not more than 15 years.' 3

The extent of such floods depends on the rainfall intensity, the land use in the catchment, and the flow resistance in the river: Reduced flow resistance upstream and increased flow resistance downstream (for example due to morphological developments) will add to the flood risk at a given location, while increased flow resistance upstream and reduced flow resistance downstream can reduce the flood risk, within limits.

Unfortunately, there is no firm information available from within the study area. Also, the the information from adjacent rivers - St. Pursat and (further away) St. Sangker - is somewhat inconclusive. The table above origins from a previous study. It shows that for St. Pursat, the average annual peak flow is estimated at 0.20 m3/s/km2, while for example the estimated 50-years peak flow is estimated at 0.48 m3/s/km2. Some other rivers are listed for comparison. The estimate for St. Sangker is around twice as high, while other Tonlse Sap tributaries (further away, and with much higher catchment areas) are much lower. (The value will generally decrease with the area of the catchment, because an extreme rainfall is likely to cover a confined part of the catchment only).

Table 6.1: Extreme flows

River Station Catchment area

Average annual flood

Return period

10 years 20 years 50 years 100 years km2 m3/s m3/s m3/s m3/s m3/s

St. Sangker Treng 2,135 922 1,560 1,804 2,120 2,357 St. Pursat Taing Luoch 2,080 422 725 840 990 1,102 St. Sen Kg Thom 14,000 846 1,017 1,082 1,167 1,230 St. Sen Kg Putrea 9,080 1,003 1,632 1,872 2,183 2,417 Prek Thnot Anlong Touk 3,650 384 568 638 729 797

km2 m3/s/km2 m3/s/km2 m3/s/km2 m3/s/km2 m3/s/km2 St. Sangker Treng 2,135 0,43 0,73 0,84 0,99 1,10 St. Pursat Taing Luoch 2,080 0,20 0,35 0,40 0,48 0,53 St. Sen Kg Thom 14,000 0,06 0,07 0,08 0,08 0,09 St. Sen Kg Putrea 9,080 0,11 0,18 0,21 0,24 0,27 Prek Thnot Anlong Touk 3,650 0,11 0,16 0,17 0,20 0,22

km2 Percent of average annual peak flow St. Sangker Treng 2,135 100 169 196 230 256 St. Pursat Taing Luoch 2,080 100 172 199 235 261 St. Sen Kg Thom 14,000 100 120 128 138 145 St. Sen Kg Putrea 9,080 100 163 187 218 241 Prek Thnot Anlong Touk 3,650 100 148 166 190 208

Source: CTI and DHI (Aug 03), Appendix 2.2, Table 2.11

3 Halcrow (Apr 94) Vol. 1 p. 12-13


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A more detailed analysis has been made of the rather short time series from St. Pursat and St. Boribo, and a very short (19 months) series from St. Dauntri.

The following figure shows time series plots of flow from each station, in order to illustrate the general pattern of seasonal varability.

In the record from St. Pursat, flows higher than 500 m3/s occur from August to early December, whie flows higher that 88 m3/s occur in September and October.

A visible difference is seen between the records from St. Pursat and St. Boribo. This is because the St. Boribo record includes the years 1999 and 2000, which were strongly atypical with respect to rainfall distribution, with a very rainy pre-monsoon (or an early onset of the monsson). This anomaly was observed all over the country. The St. Pursat record does not include these two years.


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Figure 6.2: Time series of flow in St. Pursat, St. Boribo and St. Dauntri


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The records have been analysed for extreme flows. Different approaches were tried, and the following was selected because it was more robust (and conservative): The highest flow in each year was selected, trading a bit of the data coverage for an assurance that the events were in fact entirely independent. These annual maximum flows were ranked and fitted to a logarithmic, linear regression line from which the return periods were read. The applied fits are shown in the figure below, and results are presented in the following table.

Figure 6.3a: Regression line for annual maximum flows, St. Pursat

Figure 6.3b: Regression line for annual maximum flows, St. Boribo

Figure 6.3c: Regression line for annual maximum flows, St. Dauntri

10,000 m3/s

100 m3/s

1,000 m3/s

y = -0,0335x + 3,0874

0 2 4 6 8 10

y = -0,0339x + 2,3295

0 2 4 6 8

400 m3/s

100 m3/s

200 m3/s

100 m3/s

200 m3/s

y = -0,3645x + 2,6919

0 1 2


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Table 6.2: Estimated return periods for extreme flows

Return period St. Pursat at Bac Trakoun

St. Boribo at Boribo

St. Dauntri at Mong Russey

St. 580103 St. 590101 St. 551101

C. area: 4245 km2 803 km2 1214 km2

Data: 72 months 91 months 19 months

m3/s l/s/km2 m3/s l/s/km2 m3/s l/s/km2

2 years 864 204 156 195 (213) (175)

5 years 1.064 251 188 235 (352) (290)

10 years 1.141 269 201 250 (416) (343)

20 years 1.181 278 207 258 (452) (373)

Catchment areas are from MOWRAM (Aug 06b Numbers in brackets ( ) are less reliable due to poor data coverage

Although the data coverage is less than ideal (and outright inadequate in the case of St. Dauntri), it is seen that the extreme specific flows resemble each other quite well. This indicates the possibility that a fair estimate can be made of flows that occur with return periods like the ones listed in the table.

Direct rainfall

The direct rainfall is of interest for design of distribution canals and drainage systems.

Information about extreme daily rainfall is available from the 53 years record from Pursat. In this series, there were 3 incidents of clearly independent extreme rainfall events, that deviated from the general pattern, as shown in the following figure:

210 mm/day on 25 October 1996

178 mm/day on 18 October 1958

164 mm/day on 18 September 1919

These rainfalls were probably caused by extreme, stagnant thunderstorms lingering immediately above the monitoring stations.


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Figure 6.4: Ranking of annual maximum rainfall, Pursat

The figure shows 53 annual maximum values sorted by rank. Data: Pursat 1913-2005 (53 years)

The following estimate of extreme rainfalls is based on these 3 events, plus an assumption that the extreme rainfall in Pursat is valid for the study area as well (without applying the 3 percent correction that has been estimated for normal rainfall).

In 6 out of 10 years, the highest annual rainfall will occur in August, September or October. In the 53 years record, the highest annual rainfall never occurred in December, January nor February.

Table 6.3: Extreme rainfall

Frequency Rainfall Once in 10 years 138 mm/day

Once in 20 years 168 mm/day

Once in 50 years 207 mm/day


A recent ilustration of inland floods is shown in the figure below. The inundation is caused by a combination of direct rainfall, flow from upstream, and deliberate retention (on paddy fields).


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Figure 6.5: Inundation August and September 2006

Radarsat-1 imagery, 28 Aug and 21 Sep 06. MRC Black: Perennial water bodies Dark blue: Flooded on 28 Aug and 21 Sep 06 (including reverse flow into Tonle Sap) Light blue: Flooded on 28 Aug 06 (including rainfed paddy fields) Reddish: Flooded on 21 Sep 06 (including rainfed paddy fields)

6.4 Drought hThis section relates to ToR, Task 9: Hydrological analysis

Droughts can be related both to the stage (of the Mekong mainstream) and to the direct rainfall. A distinction may be made between different kinds of drought:


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• Wet season droughts related to a low flood pulse or an irregular or late onset of the annual flood. A severe flood-related wet season drought occurred in 1998

• Wet season droughts related to irregular rainfall during the onset of the monsoon, or - worse - to less than normal rainfall in the 'small dry season' in July and August

• A low annual minimum flow in the Mekong (on a monthly or seasonal time scale). Droughts of this type occurred in 2005 and 2006. This type of drought has less severe impacts in Cambodia, because few cultivation systems depend on the mainstream flow at this time of the year, but the impacts in the Delta can be significant. The damage is related to intrusion of saline water from the sea, affecting both urban and domestic water supplies and cultivation

Wet season drought The wet season is the traditional and the main cultivation season, where a water shortage is serious, for example if it occurs after transplanting the rice. From a technical point of view, the problems are caused by inconsistencies between the cultivation cycle and the water availability. A wet season drought has particular socio-economic impacts in Cambodia in general and in the study area in particular. The area that is recorded as affected by drought is generally much larger in the wet season than in the dry season (because a much larger area is cultivated in the wet season). The social significance of a wet season drought is enhanced because it affects the many households that raise one crop per year only - and with small land holdings that prevent risk diversification.

Table 6.3: Dry periods of 10 days or more in May-August

Year Period 1986 1987 1989 1998 2001 2003 2005

10 days in July/August 10 days in June 16 days in June/july 12 days in May 10 days in August 11 days in June/July and 10 days in August 12 days in June



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7 Aquatic environment

7.1 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.

The work has included:

• compilation and processing of input data for pollution load estimation;

• compilation and processing of input data for MIKE Basin Water Quality model; and

• post-processing of simulation results.

No monitoring data on water quality has been available for the study areas. Thus, the results presented in the chapter do not reflect calibrated concentration level. Instead pollution loads and water quality parameters have been adjusted to reach expected concentrations levels based on measurements available from rivers in the coastal area of Cambodia.

7.2 Fish, fish habitats This section relates to ToR, Task 12: Fish, fish habitats and fish migration. The analysis is preliminary

It is well known that fisheries have a high social and economic significance in the Tonle Sap Basin. The particular social value is related to the following circumstances: Fisheries provides an alternative subsistence during agricultural failures; Fisheries can generate an income with little capital investment; and Fisheries is largely independent on land ownership.

It is noted that the value is extremely high in the Tonle Sap itself and its Great Lake, but somewhat less in areas that are not affected by the regular annual floods.

The fish stock and the fisheries varies from one place to another within the project area. The impacts of physical interventions, and the viability of potential mitigation measures are correspondingly site-specific.

The main ecologically fish related compartments of all the studied river basin areas are the river, the rice fields, the flooded forest and the Tonle Sap Lake. In the wet season the lake water extends far into the downstream part of the basin. The floodplain and the flooded forest form spawning and nursery grounds for a large


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number of fish, both in terms of species and quantity. The passageways between these ecological compartments have sustained the fishery resources of these lowland rice fields of Cambodia.

The downstream areas of the studied river basins form and extensive floodplain with numerous creeks, waterways and permanent water bodies such as oxbows and marshes. These areas are where the fisheries, especially family scale fisheries are importantly practiced.

Black and white fish

The fish found in the seasonally inundated areas belong to two categories. Some species depend on the upstream/adjacent perennial pools/lakes and swamps, or even local perennial water for their dry season habitat, from where the adult fish migrate downstream or just laterally. They spawn in the seasonal waterbodies: Floodplains, ricefields, seasonal swamps and lakes. These species belong to a category normally referred to as 'black fish'. They are tolerant to the water quality conditions, which are typical for small waterbodies (irrigation canals, swamps, small perennial lakes, etc). Many species are especially adapted to low oxygen concentrations and can survive for extended periods of time by using atmospheric oxygen. These fish normally follow the water level and stop their migration when the physical conditions are acceptable. This means that they follow the increased water levels at the onset of the rainy season and colonise all available wetland, including the flooded rice fields. The 'black fish' have adapted food requirements so that they in general are carnivorous or omnivorous. The other ecotype is called the 'white fish'. Fish belonging to this type are generally more migratory than the 'black fish'. The often undertake long seasonal migrations; both up-and downstream in mainstreams and laterally into floodplains and ricefields. Many of the 'white fish' species have an opportunistic life cycle: They are often short-lived and are highly reproductive. They often congregate in schools that can be of impressive size. In perennial rivers fish belonging to both ecotypes can be expected to occur all year. The number of migratory species and the overall biomass of migratory species will increase during the periods of up- and downstream migration. These periods are closely associated with the increase in water levels. Fish that survive in pools ponds and lakes in the upstream reaches will normally start to migrate or spread laterally and downstream when the seasonal rains take effect on the water levels. Some of the 'white fish' spend the dry season far up-stream in the Mekong River or its larger tributaries and start their downstream migration towards the Chaktomuk area, enter the Tonle Sap and its adjacent floodplains, rivers, and canals, when the water levels allow. After spawning and living in the rivers, floodplains, ricefields, canals and swamps the fish follow the receding water. During the upstream migration but particularly during the downstream migration, these fish are subject to a large fishing pressure from all categories of the Cambodian inland fisheries: Family-, semiindustrial and industrial fisheries. They constitute the backbone at least in terms of volume of these fisheries and provide a very important source for animal protein of all sorts - direct human consumption as fresh, smoked, dried, fish sauce, fermented ('prahok') or indirect as feed for farm animals especially chicken or feed for fish kept and transported live in large cages (snakeheads and Pangasius Spp.)

7.3 Water quality criteria This section relates to ToR, Task 25: Exisiting WQ data and classification

Presently work is undergoing under the MRC for producing Water Quality Objectives (WQOs) and for providing Water Quality Criteria (indicators and target values) to support the WQO for the Mekong Basin, see MRC-WUP (Jun 05): Integrated Water Quality Management Rep. 1 (draft).

The stated Water Quality Objective is:


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“To maintain the water quality in all reaches of the Mekong River so the risk to human health from domestic or other human contact uses will not increase”

This objective was derived to support two beneficial uses:

1. Domestic use of water (drinking - in rural areas with minimal treatment) and

2. Human contact activities such as swimming, food collection and bathing

Water Quality Criteria (i.e. Indicators and Target Values) which can be used to assess performance against the WQO have been proposed for potentially hazardous constituents in river water. In general, the order of priority for managing water for the protection of public health is to:

• Ensure an adequate supply of microbiologically safe water

• Manage chemical contaminants known to cause adverse health effects, and

• Address other chemical contaminants

In the water quality criteria proposed no indicators or target values have been proposed for the last category of contaminants.

Table 7.1: Water quality criteria to protect human health

Beneficial use WQ objective Water quality criteria Indicator Target value

(Phase 1) Target value (Phase 2)

Domestic No increase in human health risk (all reaches)

E. coli or thermotolerant coliforms

<1000 org/100 ml (P80)

Natural levels (P80)

Toxicants No values recommended

Middle course (12-15 indicators and values)

Human Contact No increase in human health risk (all reaches)

E. coli or thermotolerant coliforms

<1000 org/100 ml (P80)

Natural levels (P80)

Chlorophyll-a (for toxic blue green algae)

10 ug/l and 50 ug/l

10 ug/l and 50 ug/l

Toxic blue green algae cell concentration

20,000 cell/ml 100,000 cell/ml scums

20,000 cell/ml 100,000 cell/ml scums

Toxicants No values recommended

Middle course (12-15 indicators and values)

Source: MRC-WUP (Jun 05)

E.coli has not been measured in Cambodia as a routine parameter, where only sporadic measurements of total coliforms have been made, and this parameter can not be directly related potential human health hazards. Similarly the additional parameters given for Human Contact have not been carried out in Cambodia before.

In Cambodia the legislation identifies two types of ambient water bodies:


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• protected public water areas which are used by the public, such as rivers; and

• unprotected public water areas which may include sewers

Cambodian legislation also includes a National Standard for source water that is used for domestic purposes namely “Water Quality Standard in public water areas for public health protection”. This standard is based on the WHO Drinking Water Quality Guidelines (MIME 2004)

In the table below, some of the values provided in the Cambodian National Surface Water Quality Standards have been summarised for the most relevant parameters.

Table 7.2: Selection of protected public water standards including rivers

Indicator Value

BOD5 1-10 mg/l

Dissolved oxygen 2-7.5 mg/l

Total Coliform 5000 MPN/100 ml

Total Nitrogen 0.1 – 0.6 mg/l

Total Phosphorus 0.005-0.05 mg/l

The implementation of the Water Framework Directive (WFD) in the European Union Member States have required better knowledge about all sources having an impact on the water quality and the ecological status of European surface and ground waters. The directive has adopted the principle of looking at water in a holistic way, where the resources are linked to the uses, the terrestrial environment, the aquatic environment and finally to development and human health. The Directive also clearly integrates economics into future water policies. Fifteen years after the date of entry into force of the Water Framework Directive, all surface waters have to be able to fulfil the criteria for "Good ecological status". The Directive was implemented in 2000, so a good ecological status for surface waters shall be obtained by the member states in the end of year 2015.

For fulfilling the requirements stated by the Directive a set of operational quality standards and quality objectives have been proposed for the surface, ground and coastal waters. An environmental quality standard is defined as the concentration of a substance, which must not be exceeded by some statistical measure if a specified quality objective of the aquatic environment is to be obtained. It is therefore necessary to implement a classification system based on representative monitoring parameters. Followed by a system of quality objectives based on those standards to ensure that good status of surface and coastal water is achieved throughout the Community and that deterioration in status is prevented.

Identification of significant anthropogenic pressure on the surface water and analysis of potential impacts of these pressures is required according to the Water Framework Directive. Hence, parameter selection should be based on which measures that significantly reflects human induced pressure on the aquatic ecosystem and at the same time these monitoring variables should be robust, operational, descriptive and cost effective.


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One of the most common environmental problems that are observed for the aquatic environment is eutrophication. Eutrophication is caused by excessive enrichment with nutrients from diffuse sources and point sources, which lead to increased levels in phytoplankton, and as a result deterioration in light conditions. These conditions will affect the depth distribution of macrophytes attached to the bottom and the zoobenthos community.

Chemical, physical and partly biological parameters have been measured systematic and regularly in European waters since the mid 1970-ies.

An important aspect in relation to the Water Framework Directive is the establishment of ecological quality objectives for aquatic ecosystems, as ecological objectives have been given higher importance than chemically derived objectives. In most countries the freshwater monitoring have mainly focused on the chemical parameters.

Five parameters (dissolved oxygen, BOD, ammonium, total nitrogen and total-phosphorus) are used to describe the main river pollution problems in some EU states. The chemical classification divides the quality of rivers waters into five classes.

The annual average has often been used for estimation of water quality, but the mean value is not enough to describe the water quality. The most frequently used value is the standard deviation, and a certain percentile is a more suitable value for general characterisation of data. Percentiles can be taken as weighted mean values and compared with mean value and standard deviation.

To provide some guidance for the quality in the studied catchments a system have been established based an index derived system, where high quality is given the value 100 and then the other quality classes is expressed in relation to this.

In the following table, the proposed criteria ranges for classifying river water in the studied catchments have been provided.

Table 7.3: Ecological quality classes for rivers

Parameter High quality Good quality Fair quality Poor quality Bad quality

Physical/ chemical

Tot N 100 101 – 144 145- 260 261 – 480 > 480

Tot P 100 101 – 184 185 – 421 422 – 1310 > 1310

Ecological variables

Chlorophyll-a 100 101 -320 321 – 800 801 –2000 > 2000

The above classes are based on the systematic of the WFD and using a statistical approach. High quality is given as 100 and then the remaining classes is shown in ranges of this value

In the following assessment of water quality it will be assumed that the quality in the upper reaches will obtain a High Quality as very little loadings affect these areas. The lower reaches will then be assessed relative to this for the different parameters


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




The Load Calculator, which is an add-on tool for MIKE Basin Water Quality is a calculator for determining pollution loads for river basins. The tool calculates the average mass fluxes of pollutants for individual sub-catchments (e.g. kg/catchment/year). The tool can provide the pollution load input data for the MIKE Basin Water Quality model.

Pollution loads may include both point and non-point sources. All loads are initially calculated as constant mass fluxes for each sub-catchment, e.g. kg/year, however when applying the Load Calculator together with e.g. the MIKE Basin WQ model there are several ways to translate the constant mass fluxes into mass flux time series depending on e.g. runoff time series or any other known temporal variations.

Distance specific decay or retention of pollutants can be included taking into account the distance between the location of the pollution sources and the presumed outlet in the river network in MIKE Basin.

All input data for the Load calculator include GIS layers describing the geographical distribution of populations, agricultural sources (e.g. livestock and/or fertilizer application), land uses and/or point sources representing wastewater from industries or population centres.

Pollution load estimation – input data Pollution load estimations for the study areas are based on statistical data of population numbers, livestock numbers and land use available at commune level. Data are compiled from different sources as described in the following sections.

Population data is available for 2002 – 2004 from the commune database. Data for 2004 has been applied in calculation of domestic loads.


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Figure 7.1: Population density (pers/km2) per commune for the 2 sub-catchments

The figure above shows the population density in the model area. The map is produced on the basis of 2004 population density statistics for each commune. The total population for each commune is one of the necessary themes for the LOAD model. A uniform area distribution of the inhabitants in each commune is assumed in these calculations. In Boribo catchment the highest densities in seen in Krakor (Boeung Kantout commune) and Baribour districts (Khon Rang commune).

For the Dauntri catchment the highest densities are recorded in Moung Ruessei and Bakan districts. The highest density of 326 ind/km2 was found in Moung commune in Moung Russei district and the commune with the highest density in Bakan district of 215 ind/km2 was Boeng Khnar commune.

Livestock Livestock data has been available for 2005 at commune level for the following four districts:

• Moung Reussey District, Battambang Province

• Bakan District, Pursat Province

• Phnum Kravanh District, Pursat Province

• Boribour, Kampong Chhnang Province

These four districts include the majority of the study areas in the lowlands. Available data include number of buffalo, cows, pigs, horses, goats, chicken and ducks.

Additional 6 districts are considered in the 2 study areas:

• Kroas Krata District

• Veal Veaeng District


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• Phnum Kravanh District

• Sampov Meas District

• Kandieng District

• Tuek Phos District

For these districts livestock numbers for each commune have been estimated. The estimation is based on data on numbers of families owning cows and pigs - data available for 2004 from the Commune database.

For these families it has been assumed that all families having pigs and/or cows would also have poultry, and it is assumed that only families having cows also have buffalos.

Based on a more detailed analysis of the data collected from the Bakan district and compared with data from the commune data base in can be calculated that each family would then have an average of:

2.0 cows per family

1.2 buffalos per family

1.9 pigs per family

15 poultry (chicken and ducks) per family

Below the livestock densities and total livestock numbers are shown within the Dauntri and Boribo sub-catchments.

It can clearly be seen from the figures that the livestock density in the upland parts of the catchments are very low. The density of cows and pigs in the upland areas are between 0-5 and 0-2 no./km2, whereas in the middle part of the catchments the density of cows and pigs are between 35-50 and 10-50 no./km2, respectively.

The details are presented in the following table, which shows the total numbers of cows, buffalos, pigs and poultry for each commune.


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Figure 7.2: Livestock densities (cows/km2) per commune

Figure 7.3: Livestock densities (buffalos/km2) per commune


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Figure 7.4: Livestock densities (pigs/km2) per commune

Figure 7.5: Livestock densities (poultry/km2) per commune


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Fertilizer application No data is available regarding the total amount of fertiliser applied on cultivated land for the 2 study areas. Instead indirect measures such as the total area under cultivation in each commune and the average annual fertiliser applied to each ha has been used to estimate the presumed fertiliser application at commune level.

Cultivated areas in the 2 study areas consist almost entirely of rice cultivation. Different types of cultivation include e.g. irrigated dry paddy, purely rain fed wet paddy and partially irrigated wet paddy. Data on the distribution of the three types of cultivation have been provided for four districts:

• Moung Reussey , Battambang Province

• Bakan, Pursat Province

• Phnum Kravanh, Pursat Province

• Boribo, Kampong Chhnang Province

The types of cultivation include wet paddy, dry paddy and other types of crop. These data imply that wet paddy in average constitutes more than 90 % of the total cultivated areas in both study areas.

For the remaining districts data on total area used for rice cultivation at commune level is available from the commune database (2004).

• Kroas Krata

• Veal Veaeng

• Phnum Kravanh

• Sampov Meas

• Kandieng

• Tuek Phos

The data on the total area for cultivation for districts and communes are summarised in the figure and table below.

It can be seen that in the Boribo catchment rice cultivation at present is relatively limited and amounts in the majority of the communes to approx. 5-10 percent of the commune area, with some higher percentage in the lower reaches.

In the Dauntri sub-basin, a greater percentage of the commune areas are used for rice production with areas being from 10 to more than 50%.


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Figure 7.6: Land area in each commune used for rice cultivation.

Numbers are percent of total commune area

To estimate the amount of fertilizer applied area specific application rates were used. For wet paddy the typical application rate of fertilizer for each crop cycle is approximately:

NPK – fertiliser: 150 kg/ha (15% N, 15% P)

UREA: 50 kg/ha (84% N, 0% P)

(Reference: survey questionnaires, PRD agronomists)

These correspond to:

64.5 kg-N/ha

22.5 kg-P/ha

The available information for this project states that on average 1 crop is cultivated per year.

Despite that the application rates may differ between the different types of rice cultivation and other crops, the above numbers have been applied in the pollution load estimation for all cultivated area.


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Table 7.4: Distribution of areas for rice cultivation and estimated fertiliser application, per commune

PROVINCE DISTRICT COMMUNE Area Cult. Cult. Fertiliser P Fertiliser N

km2 ha pct kg/year kg/year

Kg Chhnang Baribour Anhchanh Rung

27 1595 60 40719 116727

Khon Rang 0 20 72 449 1288 Kampong

Preah Kokir 13 121 9 3036 8703

Melum 26 951 37 58538 167809 Phsar 21 1347 64 38618 110704 Pech

Changvar 14 459 33 9310 26687

Tuek Phos Chieb 84 481 6 10821 31020 Krang Skear 229 1357 6 30538 87543

Pursat Kandieng Kanhchor 10 359 36 8080 23161

Krakor Ansa Chambak

3 31 10 817 2343

Boeng Kantuot

24 422 18 12292 35237

Chheu Tom 172 1398 8 71093 203800 Kampong Pou 45 700 16 19900 57047 Ou Sandan 59 710 12 19169 54950 Sna Ansa 14 81 6 4160 11926 Svay Sa 189 1509 8 26095 74805 Tnaot Chum 145 1319 9 31789 91130

Phnum Kravanh

Prongil 406 542 1 12196 34961

Sampov Meas Roleab 0 1 8 19 56

Kg Speu Aural Trapeang Chour

18 101 0 2273 6515

Battambang Moung Ruessei

Moung 39 6964 179 43811 125592

Data on rice cultivation are (i) from the commune database and (ii) collected from local agricultural authorities. Statistics refer to the proportion of each commune that lies within the study area. Numbers for Moung and Svay Don Kaeo commune were not correct since total cultivated area exceeded total commune area. Instead a cultivation percentage of 50 % pct have been assumed for both communes

Pollution sources For pollution estimation based on population and livestock data, the unit loads applied for livestock were based on a similar study in China (Shanghai region), while per capita loads applied were based on values typically used for rural populations in third world countries.

When referring to Total N this means to Total INORGANIC nitrogen. Organic nitrogen is a fraction of the BOD which will be released as NH4 during BOD decay. Below is provided how nitrogen is expected to be distributed in the different pollution sources.


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Applied factors for NH4 vs TN and NO3 vs TN are as follows:

Population: NH4/TN = 0.8 NO3/TN = 0.2

Livestock: 4 NH4/TN = 0.5 NO3/TN = 0.5

Fertilizer: NH4/TN = 0 NO3/TN = 1

Background: NH4/TN = 0.1 NO3/TN = 0.9

Runoff coefficients are applied to reflect the amount of pollutants which leaches from the top soil after application of fertilizer or manure, or the amount pollutants which are not subject to treatment of domestic sewerage. These coefficients are empirical based reduction factors and may represent various types of retention processes within the catchment.

Table 7.5: Runoff coefficients for pollutants

BOD TN TP Ecoli

Domestic 0.1 0.1 0.1 0.1

Livestock 0.1 0.1 0.1 0.1

Fertilizer 0.1 0.1 0.1 0.1

Background 1 1 1 1

For domestic sources the higher runoff coefficients is based on the assumption that most people live close to minor or major streams and rivers where as agricultural and background sources are assumed to be evenly distributed within each commune.

Distance decay is another empirical factor applied to reflect the increasing retention of pollutants with increasing distance from pollutant source to the river. The factor has the unit km-1 and distance decay is calculated as a first order distance specific decay.

Table 7.6: 1.order distance specific decay factors for pollutants

BOD TN TP E. coli

Domestic 0.1 0.1 0.3 0.3

Livestock 0.2 0.2 0.5 0.5

Fertilizer 0.2 0.2 0.5 0.5

Back ground 0.2 0.2 0.5 0.5

4 At the time of application of fertilizer the value would be between 0.8 and 1 – however due to nitrification of ammonia to nitrate, and relative higher mobility of nitrate in soils, nitrate will constitute a more significant fraction of the total nitrogen eventually entering the river


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For TP and E. coli the relative higher distance decay rate is based on the assumption that phosphorous in general has a low mobility in soils, and E. coli is highly degradable (or has a high death rate) in soil matrices.

Pollutant loads The pollution load calculated and load reaching the water bodies in the different subcatchments are discussed in more detail in the following section.

To establish a priority programme of potential actions it is important to know the main sources of pollution and the pollution load from these. It is especially important to know the role and amount of the different sources of pollution for determining priorities. Based on the estimations above and use of the Load Module of the Mike Basin model the overall load of BOD, Total-nitrogen and Total-phosphorus in the two sub-catchments have been estimated for the major pollution sources. Furthermore, it has been used to calculate the amount of the separate pollutants that ends up in the rivers and also for quantification of the pressure of human activities for each of the sub-catchments. For each of the catchments also a calculation has been made on the distribution of the calculated load between point and non-point sources.

Table 7.7: Overall generated load of BOD, nitrogen and phosphorus (t/year)

Source BOD Total-nitrogen Total-phosphorus t/year t/year t/year

Point sources NS NS NS

Non-sewered population 630 115 40

Livestock (generated) 14000 1910 615

Fertiliser (used) - 1150 400

Background load incl. precipitation 750 750 75

A short discussion of the different potential sources and their significance is given below considering the categories: point sources, non-sewered population, background load including precipitation, livestock and fertiliser use.

Point sources

The present load from point sources is very low or non-existent for the moment but potential point sources in the future could be wastewater treatment plants, industries, and hotels giving rise to significant load to certain stretches of the rivers.

Non-sewered population

The population today is not connected to a wastewater system and the pollution load from this source will also end up in the river system after different forms of reduction and decay which is considered as described above. The generated load from this source of BOD, nitrogen and phosphorus can be estimated to 630, 78 115 and 40 tons/year, respectively for the Boribo Sub-basin.


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Background load

As the nutrients are naturally occurring in the nature, the natural processes and cycling of elements will contribute to the overall load of the catchments. These estimations are based on findings from other areas.

Livestock

The livestock on the farms in the catchment areas contributes significantly to the overall generated load of the river system. Based on the statistics described above on livestock numbers in the households it can be estimated that approximately 14000, 1910 and 615 tons/year of BOD, nitrogen and phosphorus, respectively, are produced in the Boribo Sub-basin.

Mineral fertiliser

Based on the received information regarding fertiliser use the amount applied make up a significant proportion of the estimated generated load in each of the catchment areas. Based on the area of agricultural land and the use of unit figures of nitrogen and phosphorus application a total amount of 1150 and 400 tons/year are used in the Boribo Sub-basin.

Using the Load Module of Mike Basin the load of BOD, nitrogen and phosphorus for the different sub-catchments in the two catchments have been calculated. The figures also indicate in which sub-catchments the pressure from human activities are most significant.

7.5 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.

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.

Water quality settings For water quality simulations the following input is needed (apart from catchment associated pollutant sources described earlier):

• Pollutant residence time in river reaches calculated using Mannings equation

• Water quality rate constants

• Temperature in river water

• Concentration of pollutants in base-flow


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• Pollutant residence time

• Pollutant residence time in river reaches is calculated as a function of river discharge using Mannings equation:

• River width: 10 m - applied for all branches

• River Slope: calculated average from digital elevation model

• Manning number: 25

• River discharge: from MIKE Basin water balance calculation

Water quality rate constants

The following standard decay process rates were applied:

BOD decay 0.1 day-1

Denitrification 0.2 day-1

Nitrification 0.2 day-1

P retention 0.1 day-1

N/BOD 0.1

A constant water temperature of 27 degrees Celsius was applied to correct for temperature dependent processes.

Base-flow concentrations

Base-flow concentrations are most often significanty lower than concentration of pollutants in surface or drainage runoff due to much longer residence time in the groundwater and a significant retention of pollutants. The base-flow concentrations applied were:

BOD: 0.1 mg/l

NO3: 0.5 mg/l

NH4 0.05 mg/l

TP: 0.01 mg/l

Ecoli: 0

Calibration

The following targets (= average concentration levels) have ben applied for simulated concentrations of water quality components:

BOD 1 mg/l

NO3 0.5 – 1 mg/l

NH4 0.1 – 0.5 mg/l

TP 0.01-0.05

Ecoli (no target available)


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8 Socio-economics






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 Background and approach The purpose of the economic analysis is to describe the socio-economic situation and to present the findings of an economic analysis of present and future water uses for each of two sub-basins in the NWISP-2 study area. This includes

• Livelihoods and water resource dependencies in each sub-basin

• Principal water uses in the sub-basins and their economic values, including possible trade-offs between competing uses

• Long-term development opportunities in the basin, with respect to water availability and use

Economic considerations should play a key part in any system of integrated water resource management. They complement the hydrological studies and modelling. In particular, the economic analysis of water uses is used to construct the general economic profile of the river basin and its key water uses and significant pressures in terms of:

• Economic analysis of water uses, e.g. collating information for significant water uses on income, number of beneficiaries, agricultural and industrial area or employment, etc;

• Stressing the importance of water for economic and regional development and the evidence of this importance provided in existing economic strategies and plans


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Survey coverage and methodology A total of 119 households were surveyed across the Boribo and Dauntri basins. The coverage is as follows: Households Surveys Boribo 11,353 48 Dauntri 47,255 71 Total 58,608 119 Communes Surveys Boribo 10 7 Dauntri 25 16 Total 35 23 Not all communes were surveyed, largely because of problems with accessing some villages by road in the rainy season.

Household selection Through the observation, we can identify that the condition of their living are very homogeneous so we selected 2-3 household in each village to interview. Each household was chosen by systematical-random (e.g. one household at the beginning, one at the middle and one at the end of the village). The households interviewed are believed to be representative of the sub-basin populations as living conditions were noted to be very homogeneous across villages.

Survey method Before the survey questionnaire, a test was conducted among 13 households in Boribo (Thnot Chum Commune) and Moung Reiseiy ( Prek Chik commune). The survey structure was changed slightly after the test. 80% of the interviews were conducted with individuals and 20% were conducted with groups in the rice field (The interviews were in the harvesting season) Each interview took around one hour, on average. A few households were unavailable for interview because the heads of the household were busy at the farm and some household off-farm. Both women and men were interviewed. The choice of who to interview was limited to whoever was available. All respondents were willing to participate but some (around 20%) had some difficulty understanding some of the survey questions. Most of them got stuck with the question of the payment on the external labour for planting, harvesting.

Ultimately, this information should support thinking around:

• which combination of measures are the most cost-effective means of alleviating poverty through rural development;

• the relative contribution of different economic sectors to the pressure on the water environment and how these contributions may change over time; and

• how the candidate sub-projects within each sub-basin may contribute towards or exacerbate existing or potential water availability issues.

The approach used here draws on guidance set out under the EU Water Framework Directive, adapted to suit both the scale and context of the present project. In particular, the analysis is undertaken from the perspective of the household, rather than the national economy, reflecting both the subsistence nature of agriculture in these river basins and the overall project objectives (i.e. poverty reduction).

The analysis is not intended to be a detailed cost-benefit analysis, but rather to offer a more general overview of the socio-economic context of the study areas


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and, more importantly, to provide a quantitative analysis of competing water uses in the basin from an economics perspective.

Ultimately, its purpose is to support decisions around the most appropriate locations for investment in irrigation development and to inform the design of financial and economic feasibility studies. It is believed that this is best done through the development of an economic assessment framework that can guide decision-makers towards optimal investment choices. The results of this analysis thus provide the background needed to help identify, and prioritise the collection of the more detailed economic data that will be necessary in some cases to design the appropriate water distribution structures.

Results are reported in NWISP2 Working Paper 4: Economics of water use (Nov 06), and in volumes 2 and 3 of the present final report.

A synthesis of general findings is given in the following sections.

8.3 Water dependencies This section provides background information for ToR, Task 19: Economic analysis of water utilization

Context

Most livelihoods in the study area are water-dependent or water-related.

ADBs' Tonle Sap Basin strategy (ADB Apr 05) contains an analysis of the cause-effect relationships that affect the poverty in the area. An extract is provided in the text box below.

Poverty in the Tonle Sap Basin • Poorly developed human resources: High illiteracy, weak health care system, undeveloped

vocational education and training systems, ..... • Rapid population growth • Scarce employment opportunities: High-risk investment climate, shortage of skilled labour • High vulnerability to external shocks: • Lack of basic infrastructure: Transport, communication, energy supply, market systems • Diminishing natural resources: Weak institutional and legal framework, weak enforcement, forest

clearance, overfishing, habitat degradation • Low agricultural productivity: Inefficient water management, exposure to floods, drought and

pests, insecure land tenure and resource utilization rights, weak extension system, lack of affordable capital, and lack of access to markets

After ADB (Apr 05), Appendix 4 Other factors affecting agriculture: • Small land holdings by each household • Poor soil quality • Lack of access to contemporary cultivation technology

In its Strategic Plan (Aug 04), MOWRAM notes that

'Water plays a key role in achieving the Royal Government’s over-arching goals in poverty alleviation, economic development, food security, and


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environmental conservation. Water is a basic resource in many sectors, including agriculture, energy, industry, domestic use, navigation, tourism, fisheries, and ecosystem maintenance. Water distribution need to balance the requirements of all these sectors, so that water is used to the greatest total national benefit.

Every year, farmers face shortages of water, drought, and floods, and these have a major impact on agricultural production. At present, irrigation infrastructure is still limited and is not able to provide enough water for agricultural production.

Most farmers in the provinces around the Tonle Sap-Great Lake, along the Mekong River, and in other areas of Cambodia do not achieve high crop yields. This is partly because of inefficient management and a lack of sustainability of irrigation systems. Farmers do not participate sufficiently in management of irrigation schemes but rely on the Government, because they believe that irrigation systems belong to the Government. '

Livelihood development depends highly on the availability of water and water-related services, as addressed by MOWRAM. A number of other factors and services must be available at the same time, such as for example cultivation-related services and infrastructural facilities. A critical lack of one can reduce or even eliminate the benefits of other development and support initiatives.

8.4 Trends This section identifies and assesses possible trends and pressures relating to water availability and consumption based on economic and physical drivers of water demand and proposed water-related measures across the basins. It was decided to present the trends together, as they are very similar in each of the two sub-basins.

The table below summarises the major likely ‘drivers’ of water use in the sub-basins and their individual implications for water demand and availability.

Table 8.1: Drivers of change

Driver Trend Pressure Demography Population growth

Changing lifestyles Rural-urban migration

Simple aggregate demand for all uses of water will increase proportionately or more. This will be manifest in numerous ways, e.g., • Increasing demand for

domestic water supplies. • Increasing demand for

more and higher value food products

• Fish catches will need to be both maintained in scale and expanded in productivity in order to meet consumption demands

Climate change Possible long-term climate change could result in prolonged and more frequent droughts; less predictable flood events

• Limited water availability during the dry season.

• Conflicts between water-using sectors


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Driver Trend Pressure Sector policies and regional initiatives

Agricultural intensification coupled with improved water-use efficiency Improved living standards and hygiene education programmes Infrastructure development (particularly the road and rail network) could support growth in tourism and agricultural development Emergence of small-scale industry/home enterprises. Tourism promotion and development

• Net impact is likely to be an increase in demand unless farmers switch to less water-intensive crops (i.e. away from rice). The proximity of the sub-basin to Phnom Penh and Thai border area provides potential markets for agricultural output; but likely to remain subsistence agriculture for foreseeable future.

• Increased per capita demand for safe supplies of drinking water and sanitation

• Increased water demands by tourists; farmers are provided with an incentive to boost agricultural productivity through improved access to markets

• Small-scale industrial development may stimulate the demand for water but the scale of such development is likely to be severely limited by low levels of education and literacy among basin residents

GDP / purchasing power per capita

Rising off-farm incomes • Increased demands for water for agriculture production

• Increasing energy demands

Factors affecting economic growth, agricultural productivity and possible water resource issues

Relating to the above, some of the possible factors affecting economic growth and associated water resource issues include:

Infrastructure and technology (road improvements, possible railway development; commercial leasing of land to private agricultural development companies)

The most direct impact on water demand resulting from infrastructure improvements would be a change in farming practices. However, farmers wishing to change farming systems to improve their income need to take into consideration a number of factors. These include land and soil suitability for the new system, climate variations, access to markets, marketability of commodity, commodity price, storage, potential yields, pests and diseases, capital costs, labour availability, recurrent costs plus a range of other issues concerning knowledge, technical support and finance. Most importantly, the farmer must be able to make allowances for the risk of these parameters changing before, during or after implementing new systems (Nesbitt, 2005).

Farmers in the LMB remain poor due to the low prices received for the major agricultural commodities and the relatively high input costs. Rationalisation


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of the industry to achieve greater economies of scale is unlikely to occur in the foreseeable future because of the basic subsistence nature of the farms in the study area. Already, farmers receive cash supplements from off farm activities to support their incomes. Farmers are therefore unlikely to pay for irrigation water. On-farm overuse or miss use of water may however, be reduced through the promotion of water saving techniques and the introduction of crops with higher water use efficiencies. This needs to be accompanied by a reduction in the risk farmers face in the adoption of new crops and practices.

Soil quality

Economically viable sites for more intensive farming have been difficult to find in the past because of the flat nature of Cambodia and the poor soils. For the country as a whole, over 10 million ha of gentle sloping and flat land (Class 4 and 5) are unutilised for agriculture, almost eight million ha of which is classified as irrigable (Class 5). Most (59%) of the area is on poor acrisol soils diminishing the economic viability of developing this land for irrigated agriculture (Nesbitt, 2005). This situation is relevant to the areas under study, particularly the Boribo Sub-basin where only a small area of land is classified as marginally suitable for irrigated agriculture.

Global market forces

Improved infrastructure may expose farmers to greater competition form efficient producers in Thailand, China and elsewhere, further reducing the potential for farmers to profit from cash crops.

Likely features of future agricultural and economic growth

Some of the likely features of agricultural growth and economic development are summarised below.

Subsistence/maintain food security

Given poor soil quality, small landholdings, high input costs and poor access to markets, farming in the sub-basins is likely to remain at a subsistence scale for the foreseeable future. The low returns to paddy farming, provide little incentive for farmers to produce any more than that required to meet household demands. With improved off-farm networks and better access to urban areas, it is possible that a greater share of household income and employment will come from off-farm activities.

Some crop diversification if extension facilities to reduce farmer risk

Non-rice crops fetch higher prices, use less water and should provide an attraction option for farmers who want to expand beyond subsistence production. However, given the risks involved, low levels of capital and poor access to markets, many farmers are unwilling to diversify. Improvements in agricultural productivity (yields per unit effort) need to be accompanied by extension services that reduce the level of risk faced by farmers and which enhance their share in the value chain. If this support is provided, it is expected that there will be some moves towards crop diversification (and hence growth in household income levels) particularly in the Dauntri Sub-basin.


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Migration to urban centres

The urbanisation rate in Cambodia is around 18% (NIS, 2004) but it is estimated that in the next 25 years, one third of all Cambodians will be living in urban areas (Skeldon, 1998; World Bank, 2001). Some of the highest negative net-migration rates occur in the provinces around Tonle Sap – Siem Reap, Battambang, Pursat, Kampong Chhnang and Kampong Thom (Census, 1998). These provinces experienced population losses of 1-2% due to migration in the five years between 1993 and 1998 (NIS, 2000).

The primary motive for migration is economic, with over 20% of all migrants citing economic reasons and poor employment opportunities as push factors.

8.5 Implications of irrigation development This section relates to ToR, Task 20: Economic analysis of long-term development opportunities.

Some of the likely implications of irrigation development in the sub-basin areas are summarised below.

Net benefits likely to be relatively low - Because the main crop in the region is unprofitable at a net economic value level simply growing more rice will not substantially improve the economic well being of the population.

Sustainability – how are these systems going to be different to those that were available in the past and which have fallen into disrepair? The project will need to consider how these projects can be self-sustaining so as to avoid problems with the projects in the past and which have fallen into disrepair.

Cost recovery - Given low household income levels in the sub-basins, the potential for cost-recovery from irrigation beneficiaries is low. This has significant implications for the sustainability of the system.

Feasibility – the marginal gains from investment in irrigation run the risk of being considerably lower than the investment costs. Rehabilitating irrigation infrastructure in the Boribo Sub-basin is not a sufficient condition for poverty alleviation through improved agricultural productivity. While irrigation may help improve yields and the quality of production, the investment costs may not be justified by the marginal gains in productivity. Water is a limiting factor to production but it is not the only one. Poor soils, high input costs and poor terms of trade (including access to markets) severely constrain the benefits that may otherwise be achieved by irrigation.

Costs and benefits - When considering the feasibility of irrigation systems, the full range of costs and benefits need to be identified and quantified as far as possible. Some of the costs and benefits that may be associated with such schemes are shown in the table below.


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Table 8.2: Costs and benefits of irrigation development

Costs Benefits Construction, operation and maintenance Improved crop yields which could improve

household incomes where supported by appropriate investment in extension activities

Possible decline in fisheries productivity as a result of impediments to migration

Reduced vulnerability of farmers, food self-sufficiency

Conflicting water uses / social tensions Emergence of co-operative management systems/water user groups

Ecosystem integrity could be jeopardized Opportunities for crop diversification (and hence higher income from crop sales) where farmer risk is perceived to be lower

Improved yields could support the development of small-scale agro-industry in the area

Reduced water losses (e.g. through leakage) therefore freeing up some of the resource for use elsewhere

Improved flood control Greater resilience to impacts of drought Employment (?)

Decisions ought to be made within the context of overall development needs in the basin. Economic efficiency requires that resources are directed to those activities yielding the highest net benefits to society as a whole. Furthermore, sustainability requires that project investment is demand-driven such that intended project beneficiaries are willing and able to contribute to the ongoing operation and maintenance of the system long after the period of project funding has come to an end.

Impacts

An integral part of the cost-benefit analysis, is an understanding of the likely direct and indirect impacts (both intended and unintended) of the irrigation development.

Poverty impact

Given that irrigated agriculture is the main economic activity benefiting from the project, and that the current agricultural systems are broadly unprofitable, the impact of the project on poverty will be limited unless agricultural systems are substantially transformed.

Environmental impacts

The environmental impacts resulting from the development of irrigation systems are as follows:

• effects of changes in water flow patterns and quantities resulting from the construction of reservoirs and dams;

• effects of changes in water quality due to over excessive pesticide and fertilizer use;

• changes in habitat resulting from the draining of wetlands or creation of reservoirs; and


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• salinity problems because of excessive irrigation in the dry season (CNMC, 2003).

These have potential economic impacts that need to be assessed as part of the feasibility of the project.

Fisheries

Built structures such as dams, weirs, and flood control works bring social and economic benefits. But they can also alter water quantity, quality, and timing; modify flooding patterns; induce loss of habitat; affect fishery resources by blocking fish migration and access to spawning areas; and ultimately impact communities that depend on natural, especially aquatic, resources (ADB, 2005).

Consideration will have to be given to the first-order impacts, namely (i) changes in resource access by different social groups; (ii) diet (including seasonal variation); and (iii) income, and, if feasible, second-order impacts such as conflict over fishery resources.

Overview of benefits

Three important benefits can be achieved by irrigation development:

• Increased household income, due to a higher crop intensity, a higher yield, and the possible partial introduction of crops other than rice. This can in turn support the national goal of poverty alleviation;

• reduced risks to cultivation and household income, related mainly to the frequent, relatively minor drought events; and

• rural livelihood consolidation and development, a goal in its own right, with the attractive strategic side benefit of reducing the rate of (unavoidable, and possibly beneficial) urban migration to a level where the urban infrastructure, services, accomodation and employment can realistically serve the demand

Development of irrigation infrastructure is an important step in this direction. It is noted, however, that whether or not water is amply available, traditional cultivation of low-yield, long-term rice on small plots of land with poor soils will hardly elevate the farmers above the poverty line.

Overview of risks

Risks and impediments can be general (and difficult to control by the participants); or site-specific (within the influence of the participants). Some risks are related to the design and structural features of the irrigation scheme, while others are related to the institutional context (including the water suers) and the management modality. Some of the risks relate mainly to the construction phase and the initial operation of a new irrigation scheme.

The following long list of risks has been compiled from JICA (2004), Nanni (Apr 2001), MOWRAM (Mar 2002) and Öjendal (2000):

• Actual lack of technical performance of the irrigation system (for many reasons); the reasons can comprise faulty design (over-all layout and/or detailed design), construction faults, and water shortage (foreseeable or unforeseeable);


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• perceived lack of technical performance (or perceived lack of value added) of the irrigation system - often related to lack of knowledge and/or communication, typically during the initial years of operation;

• traditional orientation towards (and economic networking within) the village community and village authority rather than towards the community within an irrigation system;

• lack of (actual or perceived) ownership of the irrigation system;

• lack of transparency in the financial management of operation and maintenance, possibly due to inadequate information flow;

• inadequate income of farmers (for example due to low yield, lack of good seeds and other inputs, disasters, market access, or market failure) (occurring in connection with traditional, uneconomical paddy cultivation, or - at the other extreme - in connection with new risky cash crops);

• unsupportive or overly complicated Water User Group statutes;

• lack of managerial capacity (and of support to the management) of Water User Groups; members and managers misunderstanding their own and each other's roles and responsibilities; lack of planning;

• general lack of willingness or ability to collaborate, possibly due to an absence of tradition for collaborating and agreeing on operational water management;

• general lack of willingness to pay water fees, even among the wealthier water users;

• conflicts of interest among the farmers, for example related to different interests in access to water, or different benefits of the irrigation scheme, its actual operation, different cropping cycles, and the imposed extent and timing of maintenance requirements. This can in turn be related to the size of land, the location of land, ownership, preferred crops and cultivation technology, and traditional upstream/downstream conflicts of interest;

• conflicts of interest can emerge already in the construction stage about land allocation for reservoirs and canals, and the location of distribution canals;

• conflicts of interest between core water users (within the command area) and surrounding marginal water users, who receive a less reliable supply and who are not Water User Group members;

• political interference in operation;

• lack of coordination between maintenance of distribution canals (by the water users) and maintenance of the headworks (by the authorities); without one, the other one is pointless;

• lack of access to technical and managerial assistance and extension services; and

• the possibility of adverse social impacts, if landless and other underprivileged people are harmed by construction and operation of an irrigation scheme.

A different type of risk is land value escalation that puts land ownership under pressure, potentially undermining a supportive land ownership structure - as it would be the case if irrigated land is bought for investment and left uncultivated.


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This risk can be met by various measures, such as ownership restrictions and taxation of idle agricultural land.

Amplification of benefits

The benefits of irrigation schemes can be amplified, or are in some cases directly dependent on supplementary measures. Examples are:

• Technical support to de-central management, operation and maintenance of the irrigation systems (by Water User Groups);

• access to proven new crops and cultivation systems, including inputs (seeds, fertilizers, etc.) and technology;

• access to markets and support to marketing, eventually at the national scale;

• support to development of agro-processing industries;

• smooth information flows (basic meteorology, flood warnings, and market conditions);

• support to conflict resolution among land owners and water users; and

• support to response to risks and social shocks (like illness in the family, which can cause loss of land).

Several of these are outside the responsibility (and control) of MOWRAM. Inter-agency networking and collaboration is required to reach the full benefits of irrigation development.

Figure 8.1: Network of rural livelihood dependencies


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8.6 Main findings of economic analysis The main findings of the economic analysis of water uses in the two sub-basins are as follows:

• The present levels of socio-economic development and projected trends in economic growth and development described in the sections above, support the conclusion that there are unlikely to be major conflicts between different water-using sectors on average in the foreseeable future although seasonal competition between water users can be expected.

• Household food security is tenuous in the Boribo basin; strategies are required to support farmers in attaining and maintaining self-sufficiency. Irrigation is a necessary but not sufficient condition for rural poverty reduction. The net benefits to irrigation development are relatively low as long as rice remains the principal crop. Where farmers can be encouraged to diversify into higher value crops, and where this is supported by appropriate and affordable extension services, the returns to agriculture may improve with associated increases in household income.

• The impacts on fisheries, which are fundamental to household nutrition, need to be carefully considered.

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

WUGs and FWUCs

WUG (water user group): A more or less formal group of water users (farmers sharing the same irrigation system), formed for the sake of representation and participation in operation and maintenance (and possibly some extent of ownership)

FWUC (farmers' water user community): A water user group that has been legally formalised by MOWRAM's endorsement of its bylaws

MOWRAM is promoting WUGs/FWUCs in connection with its ongoing development of irrigation systems. Often, the formation of a WUG/FWUC is made a condition for a rehabilitation, imposed by MOWRAM and/or by a funding agency.

Six WUGs have been established in the study area, and none of the function well. As elsewhere in Cambodia, there is a scope for strengthening the farmers' participation in the water management. This is for several good reasons, one being that the irrigation systems are quite complex and not at all easy to operate, by any standard.

In this connection, ADB 5 observes that 'institutional arrangements for managing irrigation and drainage works (which account for most water use) are reasonably well-defined, with some lack of clarity regarding relative responsibilities ...

5 in its April 2003 'Road Map'


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However, water management systems cannot be sustained because of limited government resources. MOWRAM therefore is implementing a policy of irrigation management transfer and participatory irrigation management and development. These are being applied to new and rehabilitated schemes and progressively introduced to existing systems, with establishment of Farmer Water User Communities. ... farmers are not always keen (or capable) to accept responsibility. ... At present, functional irrigation systems and infrastructure are few, and generally supply water on a supplementary, gravity-fed basis using simple (and often decrepit) structures ... institutional arrangements for assuring beneficiary participation and scheme sustainability must be established ... '

Appropriate scheme operation can be supported by information, including real-time data and forecasts, that exist, but which are today not readily available to those who need it: 6

• Conceptual information about scheme capacities (for storage and flow) and related capacity margins

• Historical information about normal and 'reliable' rainfall and runoff. For example, the 'small dry season' is critical to the traditional cultivation cycle and hereby to the livelihoods and household economy of the farmers. Any knowledge about its characteristics can support an appropriate scheme operation (as well as decisions on when and how to cultivate)

• Real-time information about rainfall and water level

• Short-term forecasts of rainfall and water level (all year) as well as flood forecasts (in the wet season)

It is noted that typically, the persons who are responsible for scheme operation have no information even of the normal monthly rainfall.

(The same is probably the case for those who conceived and designed some of the schemes, including many of those that were constructed during the Pol Pot regime).

Access to information about actual storage capacities and (unserved) demands would indicate what is technically possible under the circumstances, and hereby facilitate appropriate decisions on cultivation in general and irrigation scheme operation in particular.

The same is the case with information about rainfall, drought and floods.

The lack of knowledge is unfortunate, because it would require a minor effort only to provide it.

Apart from support to operation, the knowledge would be of high value in connection with minor scheme rehabilitations and expansions that might be carried out without comprehensive design studies, for example at household or village level. In the long term, improved decision-support would assist in the development away from risk minimization towards value maximization that is a necessity for rural poverty alleviation.

6 The remainder of this section quoted from Yem Dararath and T. K. Nielsen (Sept 06)


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9 Management issues and scope for development

9.1 Hydraulic feasibility of irrigation development This section relates to ToR, Task 13: Support to electing candidate NWISP sub-projects.

Also, please refer to 'Guideline: Hydraulic assessment of irrigation schemes' (submitted separately)

Most irrigation development in the study area aims at supplementary wet season irrigation. A particular concern in this connection is a higher reliability of the water availability in the early part of the wet season.

This is illustrated in the following figure. In an average year there are no problems, but already in every 5th year there are extended periods with little or no rain, occurring at a critical stage of the cultivation cycle. Every 10th year, traditional wet season cultivation is entirely dependent on irrigation supplies in several months from mid May(early June and onwards.

Figure 9.1: Distribution of accumulated rainfall in May-August


1935 is the year with the lowest recorded rainfall (0 mm) in Pursat in June-July. In Kg Chhnang, where data is available from the same year, the rainfall was 656 mm, which is well above the average of 405 mm.


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The corresponding average accumulated rainfall is shown below. This can be regarded as an indicative reference curve for the traditional rainfed wet season rice. Depending on the cultivation system (and to some extent the soil type), a major rainfall deficiency will impede the cultivation. The average rainfall in the period of 4.9 mm/day is well below what is generally regarded as ideal for paddy cultivation. In reality, however, it appears that the farmers can cultivate their land by direct rainfall even in years where the rainfall is somewhat below average, although with a low yield.

Figure 9.2: Average accumulated rainfall in May-August


If the average rainfall is taken as a guideline (for traditional cultivation systems), a deficit of around 115 mm in May-August will occur every 5 years, and a deficit of around 194 mm in the same period will occur every 10 years, as illustrated by the following tables.

Table 9.1: Rainfall in May-August

Time Accumulated since 1 May Average since 1 May end of May end of June end of July end of August

149 mm 280 mm 418 mm 598 mm

4.8 mm/day 4.6 mm/day 4.5 mm/day 4.9 mm/day


Table 9.2: Rainfall deviation from average in May-August

Frequency Rainfall deviation from average Once in 10 years Once in 5 years

598 - 404 mm = 194 mm in May-August 598 - 483 mm = 115 mm in May-August



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The demand will be quite different for potential alternative crops and cultivation systems. As sucessfully demonstrated elsewhere in Cambodia, the benefits (and feasibility) of new irrigation developments can be enhanced in two ways: (i) by a partial crop diversification (not least in the dry season, where water is sparse); and (2) by improved efficiency for traditional paddy cultivation systems, achieved by better seeds and increased use of fertiliser.

An increased water availability in the dry season would be a clear benefit, if it can be achieved in a practical way. Beforehand, the following options are available:

• Increased storage capacity; and/or

• groundwater utilization.

These options are briefly discussed in the following sections.

9.2 Storage capacity General

The time variation of rainfall and water availability makes the question about storage capacity highly relevant.

In the so-called Halcrow Study (1993-95), it is observed that 'economically justifiable irrigation projects are likely to involve major storage reservoirs and crop diversification ...' Halcrow (Dec 03, p. 1).

There is some natural storage capacity in the study area, by groundwater exchange and surface storage in ponds, lakes, at the streams themselves. The hydrological analysis indicates a storage release of somewhere around 40 mm/month in February and March both in Boribo and in Dauntri Sub-basin. In many places, however, the natural storage is inadequate for maintaining any streamflow, not to speak of making water available for cultivation.

Apart from groundwater utilization (which is discussed in the following section), there are several ways to increase the storage capacity:

• Traditional storage reservoirs, as they exist in many places in Cambodia (the most famous example being the West Baray, built around 1050 and still serving its original purpose);

• upstream storage reservoirs located in the mountains;

• in-stream storage;

• optimization of retention irrigation; and

• pumping water from the Great Lake.

Advantages and disadvantages

Traditional storage reservoirs can provide a good control of the supply of irigation water. Often, they have vaulable side advantages such as fisheries, tourism development, and provision of water for livestock and domestic uses. Their main disadvantage (which is significant) is that such facilities take up a lot of land (and often agricultural land), if built in flat areas. Allowing for losses, the ratio between command area and reservoir area becomes small, which gives an equally small


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ratio between costs and benefits. Furthermore, it is difficult to identify locations that are attractive both in terms of hydraulic operation and land availability. Re-settlement, if required, can be a significant issue.

Storage reservoirs located in the mountains may be feasible, as far as they - depending on the site characteristics - can provide a reasonable ratio between volume and surface area. In some cases, they can be built as multi-purpose reservoirs, providing hydropower (and perhaps flood protection) in addition to the water storage for irrigation. Successful examples of such facilities are found in Thailand and Vietnam. They require large investments and are often disputed if they are located in forests or protected areas, or if they require re-settlement.

In-stream storage can be achieved by exiting and new control structures in combination with careful operation - the idea being to retain water everywhere it is practical, within the streams and ponds and adjacent wetlands, to be released in the beginning of the dry season. In principle, this can be done with small investments and requires little land. The volumes provided may not be large, but each dry season m3 counts in the study area, and even small amounts of water could allow for some supplementary crops that are selected in accordance with the water availability. Good operation would require careful real-time monitoring, development of a suitable decision-support system for the hydraulic management, and close collaboration with the intended beneficiaries regarding timing and location of a reliable water availability - otherwise the system could do more harm than good. In-stream storage can have environmental implications that can basically be negative (due to impeded fish passage in a part of the year) as well as positive (due to larger water volumes and inundated areas in a part of the year).

Optimization of retention irrigation (in relevant parts of the study area) can be achieved by structural and/or non-structural measures. Elsewhere in the Tonle Sap Basin, in Battambang and Kg Thom Provinces, there have been recent developments of large-scale retention irrigation systems, at private initiative and with private funding, which indicates that there is a scope for upgrading of the retention irrigation7. It is possible that improved decision-support for operation can be achieved at a small cost and can give benefits that justify the efforts. Activating the full benefits may require an adaptation of the cultivation systems.

The Great Lake represents a large natural reservoir, from where water could be drawn for irrigation relatively easiliy. This would require investments in pipes and pumping stations, and operation costs for energy, that would only be justified if the value of the agricultural production is much higher than today. This, in turn, would require well educated farmers, good capacity for operation, and a reasonable soil quality. Quite possibly, such schemes could be feasible some years from now at some locations within the Tonle Sap Basin. Consider, in comparison, Thailand's so-called water grid scheme, which includes procurement of land in neighbouring countries for construction of reservoirs from where the water can be pumped to Thailand. This scheme is claimed to be feasible (but has not yet been implemented).

7 According to info from WUP-FIN. These private irrigation schems are of little value to the farmers, who are expected to lend their land on long-term leases for around 50 USD per ha per year


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Structural and non-structural measures

A fruitful synergy can be achieved between added storage capacity and improved operation. Apart from a moderate additional in-stream storage, provision of storage capacity is expensive. In comparison, improved operation (of existing and new) storage facilities can be achieved at a small cost. This would call for improved information exchange (including weather statistics, real-time meteorological data, and flood and rainfall forecasts), some contemporary decision-support and management tools, related education of the involved agencies, and close dialogue with the farmers about the time and space distribution of the available water.

9.3 Groundwater development This section relates to ToR, Task 33: Response to data shortcomings

Groundwater is often overlooked in connection with national water resources management, partly because good data are either limited or not easily accessible. For several reasons (that include the economic feasibility and a finite groundwater yield), groundwater cannot replace surface water as the raw water source for irrigation. Still, there is an attractive potential for using groundwater for small-scale supplementary irrigation that can in some cases highly improve the livelihoods of the farmers. This has been clearly demonstrated elsewhere in Cambodia.

A first glance at the geology - an alluvial flood plain surrounded by mountains - indicates a high potential for groundwater utilization in the Tonle Sap Basin. Knowledge about the groundwater resources exists, but is incomplete and is located with different agencies and operators.

The comprehensive hydrological investigations conducted in the Tonle Sap Basin since 2002 by MRC under the WUP-JICA and WUP-FIN programmes do not provide much information about groundwater hydrology, due to lack of basic data. WUP-FIN (Aug 02b) states that 'there exist no detailed investigation of groundwater resources in Cambodia. Aquifers do not have, however, sufficient potential for large scale irrigation'. MRC's 'Overview of the hydrology of the Mekong Basin' (Nov 05) mentions the word 'grundwater' one time only, in connection with the potential future appliclation of a hydrological model.

A recent review observes that 'the alluvial deposits of the Tonle Sap River and Mekong River floodplain are believed to be very good shallow aquifers, with high recharge rates (5-20 m3/h) and a groundwater table generally within 4-6m of the surface. Groundwater quality is generally satisfactory. ... ' (ADB and CNMC, Mar 04, Tonle Sap Basin profile)

CNMC (Sep 03) quotes from a 1999 study that 'extensive and good shallow aquifers, which span an estimated 4.8 million ha, underlie most of the arable areas of Cambodia', while observing that 'more recent experience – unfortunately anecdotal and not supported by formal surveys – indicates that the scope for groundwater-based irrigation might be more limited, and that farmers tend to prefer to develop surface water sources, particularly ponds'.


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Advantages and disadvantages of tubewell irrigation as compared with canal irrigation Advantages (1) Isolated pieces of land which cannot be served by canals can easily be irrigated by tubewells,

and close collaboration between the farmers is not required. (2) Canal irrigation projects need large outlays which locked up for a considerable period before

the project is productive whereas tubewells may be constructed in a short time. (3) Sale of water is on a volumetric basis which results in optimum utilization of water at the

correct time. (4) There are no losses from reservoirs and only small losses from canals (because they are

shorter) (5) No risk of water logging. (6) The capital investment is less for a tubewell. Small tube wells are within the capacity of

individual households. (7) Return is quick. In tubewell irrigation 100% irrigation is possible in first year itself. On the

contrary canal irrigation takes number of years to build up. (8) The water from tubewells may be utilized for rural water supply. (9) The land required for a tubewell is much less. Reservoirs are not required, and water can be

pumped through pipes buried in the ground. (10) When used for small-scale irrigation, the water efficiency (output per m3 water) can be high,

because the water is used 'at the right time and right place'. Disadvantages: (1) Tubewell water is much costlier than canal water due to high operating cost. (2) The life of a tubewell is limited. (3) Maintaining mechanical equipment in isolated places is difficult resulting in frequent

breakdowns and consequent stoppage of water supply. (4) Theft of diesel engine and pump is quite common. After Keo Pheakdey (Aug 05)

9.4 Monitoring of water resources This section relates to ToR, Task 8: Review of river monitoring network; and Task 33: Response to data shortcomings. The analysis is preliminary

General

Hydrological monitoring is undertaken by MOWRAM, Department of Meteorology (rainfall, evaporation and more) and Department of Hydrology and River Works (water level, flow, and inland water quality). Data are stored in databases within these departments and at MRC.

Monitoring has two important aims:

• Timely & appropriate response to threats; and

• improved knowledge about states, processes, causes, effects, and risks

Monitoring principles can cover aspecs such as

• Goal-orientation

• Cost-efficiency

• Interaction, participation

• Decentralisation

• Transparency


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Resources are finite: Time; money; facilities; and knowledge. Today, the monitoring is visibly affected by technical and financial constraints:

• Inadequate budget for equipment maintenance and operation

• Inadequate budget for payment to gauge readers (some of which continue the registrations, hoping that someone will pay them when the data is needed)

• Sparse capacity for data communication, processing and dissemination

Figure 9.3: Pursat monitoring station (photo July 06)

Rainfall

Rainfall gauges are in operation in the provincial towns of Kg Chhnang, Pursat, and Battambang, and long-term records are available. These stations are particularly important, because they already have a good data coverage, so that they can serve as references for analyses of shorter records from other stations. This is irrespective of the difficulties experienced under the prsent study with inter-station correlations.

Large parts of the study area are elevated. Rainfall data would be useful from the elevated areas, where the rainfall is higher than at the exisiting monitoring stations (but where access is difficult).

Existing rainfall stations are shown below. Some of these are operational while others are not.

Also, a map has been compiled of 'recommended' stations for future monitoring, with a particular view to decision-support to irrigation operation.

The stations at the provincial towns are most important. Second comes a few stations inside the sub-basins, preferably including at least one in the upper part of each sub-basin.

Fot the sake of irrigation management it is highly recommended to operate the stations all year, and not only in the wet season. Wet season data serve important purposes, such as hydraulic design and flood management, but so do dry season data, which are necessary for feasibility assessment of irrigation schemes, and for streamlining of their operation once they have been built.


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Regarding technology and procedures, MOWRAM's Department of Meteorology holds a comprehensive expertise and experience, confirmed by the fact that there were not many indications of erroneous data during the present study (the problems being fragmented records and a pronounced space variation).

Figure 9.4: Rainfall monitoring stations (past and present)

Figure 9.5: Rainfall monitoring stations (present and proposed future)


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Flow (runoff)

Existing flow monitoring stations are shown below. Hereby, the word 'existing' is misleading, as far as water level is read at some of them only (and fewer year by year), while flow measurements are seldom carried out.

Figure 9.6: Flow monitoring stations (past and present)

Figure 9.7: Flow monitoring stations (present and proposed future)


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It would be worthwhile to consider trading a substantial number of the stations for more complete records at the remaining ones.

As exemplified by the present study, flow records are highly valuable, and will become even more valuable when irigation schemes have been upgraded and their operation becomes an issue.

A suitable location for runoff monitoring is just upstream of the Bamnak Diversion. This is the lowermost location in the sub-basin that is not significantly affected by irrigation withdrawals and regulation. Notably, the Bamnak Diversion itself can highly change the downstream flow distribution between St. Thlea Maam and St. Boribo. The location can be reached by railway.

Figure 9.8: Bamnak monitoring station

Location: E 410,336; N 1,359,333; elevation:Around 57 m above sea level; catchment area: 392 km2

Also, a raingauge exists at this location. Being surrounded by elevated land, the data may be valid for the near vicinity only, but are still useful in connection with the planned Bamnak candidate sub-project.

Regarding technology and procedures, MOWRAM's Department of Hydrology and River Works holds a comprehensive expertise and experience, confirmed by the fact that there were not many indications of erroneous data during the present study (the problems being fragmented records and a pronounced space variation).

Regarding the exact location of future stations, and possible adjustments of present ones, a flight reconnassiance is recommended - possibly a helicopter reconnaissance. This is in order to assess the complex river networks upstream of some of the stations

Evaporation and evapotranspiration

There are no measurements of evaporation within nor near the sub-basin. Data would be highly useful, particularly long-term time series.

Evapotranspiration represents by far the most significant uncertainty in the water balance analyses, and hereby in our knowledge about water availability. Also, assumptions about the evapotranspiration is an important part of the basis for determination of crop requirements. Therefore, local data would be highly useful in connection with agricultural development efforts.


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Groundwater

Groundwater is not widely used in the study area, and the experience is somewhat inconclusive. Still, groundwater is an important raw water source for rural households, and may also be useful to small-scale rural industries.

Any information about groundwater utilization, availability and quality would highly assist possible assist future efforts to develop this resource.

In this connection, a rough distinction can be made between shallow and deep wells, and (where information is available) between the different types and depths of viable aquifers.

Water quality

A distinction can be made between

• surface water quality,

• drinking water quality (groundwater, bottled water, and other vended water), and

• groundwater quality.

The issues are different for these categories.

Monitoring of water quality is allocated under MOWRAM, MoE, MIME and MRD.

9.5 Morphology This section relates to ToR, Task 33: Response to data shortcomings

Morphological changes can cause severe damage to buildings and infrastructure, and can add to the flood risk. Monitoring of morphological developments can allow for timely intervention and control of potential consequences.

Figure 9.9: Example of a structure threatened by scour

Photo from Kg Lor, Aug 06


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The following morphological effects occur in the study area: Bank erosion; bank accretion; and flow obstruction caused by sedimentation, landslides, fallen trees, or even broken gates and weirs. The example shown above is typical.

Table 9.3: Types of morphological effects and management options

Process Effects Management options Bank erosion Damage to cultivated land,

buildings, and infrastructure (including irrigation infrastructure)

Flow channel restoration Bank protection Management plan for an entire river or reach Control of sand extraction (if relevant)

Bank accretion Bank erosion elsewhere Flow channel restoration

Flow obstruction (sedimentation, landslides, fallen trees, broken structures)

Increased flood risk upstream Remove obstacles

As a basis for making priorities of required (and sometimes costly) intervention, a useful distinction can be made between slow and fast development rates, and between severe, medium and small effects, as illustrated in a risk matrix like the one below.

Figure 9.10: Risk matrix for morphological developments

Severe effects Medium effects Small effects

Fast rate

Slow rate

Immediate intervention

Urgent intervention

Less urgent intervention

A fairly reliable classification can be made on the basis of information from the district and commune authorities. Photo documentation can provide an inexpensive support to the monitoring.

9.6 Water quality This section relates to ToR, Task 33: Response to data shortcomings

Regarding surface water, the situation in the study area today is that habitat degradation is a more imminent threat than pollution, and much more difficult to control. A potential threat is contamination from agricultural runoff containing


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fertilizer residues and pesticides, which can eventually contaminate edible fish and hereby the public health.

Another aspect to keep in mind is pollution incidents, such as spills, that can cause short-term or long-term damage to aquatic ecosystems.

The potential pollution from irrigation tailwater is best managed by promotion of good practices, which in many cases represent 'win-win' solutions to the farmers and the environment.

Another potential pollution source is fish farms.

9.7 Ecological demand of streamflow (environmental flows) This section relates to ToR, Task 28: Environmental flows in representative reaches, and assessment of enforcement

Environmental flows represent the streamflow that is required to maintain a desired aquatic environment, which may for example involve preservation of fisheries and biodiversity, and, in turn, prevention of irreversible habitat degradation. In the over-all water balance, the environmental flows appear as a demand (rather than a supply), and they are sometimes referred to as the 'ecological demand of water'.

For wetlands and floodplain habitats, the water level is the determining factor, rather than the flow rate (although the former is basically determined by the latter). Notably, for the Great Lake of Tonle Sap, the fish yield is directly related to the annual 'flood pulse' (the height and duration of the annual peak flow).

Also in other cases, the environmental consequences are related to the annual flood flows as much as the dry season minimum flows. This is because many ecosystems are well adapted to the naturally occurring seasonal flow fluctuations. There can be a healthy fish stock even in streams with an annual minimum flow of nil.

One important exception in the Lower Mekong Basin is the maintenance of the salinity regime in the Mekong Delta, which is a determined by a delicate, dynamic balance that depends on the flow from upstream. (If, hypothetically, the flow in the Mekong was discontinued, the sea would penetrate to upstream of Phnom Penh and into Tonle Sap). The production systems in the Delta are highly sensitive to the salinity, which will increase in case of any reduction of the present annual minimum flow in the Mekong mainstream. It is roughly estimated that maintaining the present salinity regime requires a flow that equals around 2 l/s/km2 on the average for the entire Mekong Basin. Furthermore, there are indications that maintenance of this flow would largely prevent over-all degradation that is related to the dry season water availability. In general, however, the dependencies and consequences are highly site-specific, and there will be localities where a lower flow is acceptable, or where a higher flow is required.

For the purpose of the present study, information has been sought about evidence of observed extraordinary flow-related impacts in the project area. The information is inconclusive, however, since there seem to have been no such incidents. The riverine ecosystems are adapted to low or no flow occuring annually in the dry season.


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Important knowledge about environmental flows has been (or is presently being) produced by IUCN, and under the Integrated Basin Flow Management Project of Mekong River Commission.

Minimum flow maintenance

Maintenance of minimum flows is a challenge in many river basins.

The area covered by the present study is small as compared with the 795,000 km2 catchment area of the entire Mekong Basin, and the rainfall, storage capacity and water demand are known to differ widely within the basin. Therefore, while strictly observing the regional perspective, it makes some sense to give priority to local rather than regional implications of maintaining the required minimum flow. The two considerations may be fully compatible, however.

There are both scientific, technical and political aspects to consider in connection with maintenance of minimum flows. One example is the many small portable diesel engine pumps that are used in many countries, and which are increasingly popular in Cambodia, for direct withdrawal of water from the river for cultivation purposes. Elsewhere in the World, the cumulative effects of many small withdrawals, each of which is entirely insignificant, have caused severe downstream consequences and have resulted in an over-all water resources allocation that is far from optimal.

This is a major challenge to the national water resources management, and a challenge to which there are no simple and safe solutions.

Management options include (but are not limited to):

• Public awareness-building and dialogue: Public awareness about the need of a suitable water allocation and water-sharing must be maintained both within water user groups and individual water users, farmers as well as industries. Awareness should be built regarding water conservation, a fair water sharing, and the value of gradually increased water efficiencies.

• Appropriate feasibility criteria: Today, in Cambodia, only a small part of the cultivated area is irrigated, and there is a large demand of expanded irrigation coverage. On the other hand, an important lesson can be learned from the fact that a significant number of structures or entire systems, particularly from the Khmer Rouge regime (1975-79) are of little value, or are positively harmful to water management, due to poor or no design and/or inadequate construction methods (as pointed out in the 1994 Halcrow study and by many subsequent authors). An appropriate hydraulic feasibility can reduce misallocations (and failed investments as well), while supporting the maintenance of minimum flows.

• Appropriate design: In some cases, structures such as weirs and regulators can be designed in a way that prevents diversion of residual flows, and in most cases, such structures can be designed in a way that allows for operation aimed at preserving the minimum flows.

• Appropriate operation: This is an attractive management option, because the operation will in many cases be under the control of MOWRAM. The operation can be guided by transparent so-called safeguards (= overruling


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decision criteria), such as assuring raw water for domestic supplies. In order to prevent conflicts, however, the measure can suitably be supported by other management measures.

• Long-term promotion of improved water efficiencies and economic efficiencies of water utilization: This is a viable and safe management option, but less efficient in the short term, and efficient in the long term particularly if supported by other management options.

• Holistic, integrated water resources management, directed towards balance between stakeholder interests: This strategic measure is safe in terms of adverse side effects, but once again, it should be combined with other supportive measures.

• Gradual implementation of conditional water withdrawal permits and associated raw water fees: This management option has successfully been implemented in many other countries and may well be a viable measure also in Cambodia. Preparations are in place in the draft water law and in the related MOWRAM policies and guidelines.

Between them, the potential management options provide a framework for supporting (if not fully assuring) the maintenance of minimum flows, particularly if implemented gradually and consolidated in the course of time.

The national (draft) water law Article 8 Everyone has the right to use water resources without a licence for drinking, washing, bathing and other domestic purposes, the watering of domestic animals and buffaloes, fishing and the irrigation of gardens and orchards, in an amount not exceeding that necessary to satisfy the individual and family needs of the user, and for the purpose of extinguishing fires, testing fire-extinguishing equipment and training people in the use of such equipment. Article 9 The diversion, abstraction and use of water resources for purposes other than those mentioned in Article 8, and the construction of the waterworks relating thereto, are subject to a licence.

9.8 Fish yield and fish migration This section relates to ToR, Task 12: Fish, fish habitats and fish migration

Over-all management options comprise for example

- Maintenance of the over-all the hydraulic regime (including the seasonal flooding that is decisive to the fish yield);

- maintenance of the floodplain habitats;

- maintenance of connectivities and migration passages;

- control of the fishing activities;

- development of aquaculture; and

- improved resource valuation and monitoring of exploitation.


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Impacts of intervention can be positive and negative. They may roughly be categorized into

- habitat degradation, for example by intersection, drainage or reclamation of floodplains and wetlands;

- blocking of migration routes by weirs, dams and regulators;

- changed floodplain inundation, due to intersection or flow regulation;

- increased minimum flows, due to storage and subsequent releases;

- increased water volumes and water surface areas (in reservoirs); and

- contamination by polluted tailwater.

It is important to evaluate the impacts of planned irrigation structures jointly with other natural processes and human activities that affect the fisheries, such as morphological developments, road construction, flood protection and drainage, and the resource exploitation intensity.

As the character and the significance of impacts will vary from one place to another within the project area, it will in some cases be required to carry out a more detailed EIA in support of the initial evaluation.

Relevant management and mitigation options comprise for example:

• Appropriate design of gates and other structures that block the flow channels. In some cases, a passage for migrating fish can be a viable mitigation measure;

• appropriate design of the canal network, with due regard to the system connectivity (where practical);

• appropriate operation of gates, regulators and reservoirs, with consideration given to seasonal fish migration and fish breeding;

• appropriate regulation of fisheries around the structures and passages;

• ... and more.

Findings under the present study indicate that in the past and today, a typical (and possibly critical) cause-effect relationship in relation to fish habitats in the study area is as illustrated below.

Figure 9.11: Cause-effect relationships affecting fish habitats

This is illustrated by the following eaxmples.

Structural intervention (gates, regulators) with inadequate sediment conveyance capacity

Upstream siltation (and downstream erosion and consequential downstream accretion)


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Figure 9.12: Vatlieb Gate, built in 1977, blocking sediments and fish migration

Figure 9.13: Khohkhsach Gate, built in 1977, blocking sediments and fish migration


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Figure 9.14: Kruchsaerch Gate, built in 1994, with sediment and fish passage

Figure 9.15: Prek Am Gate, built in 2002, with sediment and fish passage


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9.9 Capacity-building This section relates to ToR, Task 38: Knowledge-sharing with designated counterpart staff

Institutional capacity building can comprise a variety of aspects. The following table lists some general skill requirements in relation to river basin management and IWRM in Cambodia.

Table 9.4: Capacity-building topics

Organisation Topic General • Implications of delivery of water and water-related

services for domestic, industrial, and agricultural uses

• Disaster preparedness and response: Drought, floods, pests

• Implications of new crops and cultivation systems • Project formulation and project management • Data management • Conflict resolution • Basic computer skills and Internet skills

Provincial departments of MOWRAM

• Contemporary IWRM, including sustainable water resources allocation

• Water resources implications of new crops and cultivation systems

• Morphological management: Classification, monitoring and intervention

• Water quality management: Classification, monitoring and intervention

• Groundwater monitoring

Other provincial departments • Preservation of aquatic habitats and ecosystems, including headwater areas and active floodplains

• Quality of drinking water • Urban and rural water supply

Water user groups • Soil improvement • Good practices for use of fertilizer and pesticides • Financial management • Operation and management of irrigation systems,

including basic meteorology

In the context of the present study, the relevant issue is transfer of the acquired insight, as acquired during the work, together with certain related suggestions and thoughts to share:

• Socio-economic, hydraulic, and environmental implications of water uses in general, and of irrigation development in particular; and

• monitoring routines (water utilization, groundwater, water quality, morphology), including cost-effectiveness and participatory techniques

Capacity-building in support of hydraulic operation of irrigation schemes is of a particualar importance.

Strengthening of Water User Groups can provide a decisive (and cost-effective) contribution towards the desired socio-eceonomic benefits of irrigation rehabilitation. Suggestions in this respect are given in NCDP (Feb 05), where thoughts are shared as shown below.


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Recommendations on FWUC strengthening (1) MOWRAM (Aug 2003): Farmer Water User Communities – report on workshop held on 28-29 August 2003, Phnom Penh, under the Flood Emergency Rehabilitation Project (FERP), Rehabilitation of Flood Control and Irrigation Systems Component (IDA credit 3472-KH). Prepared by Mott MacDonald Ltd. in association with BCEOM and SAWAC for Ministry of Water Resources and Meteorology, Cambodia

1 Public awareness building 1.1 Awareness raising on ownership, responsibility and spiritual and materialistic contribution for

FWUCs should be conducted 1.2 Extension and distribution of documents should be made in every village 1.3 Materials should include posters, documents, leaflets, video shows, etc. 2 Fully rehabilitate existing systems and expand small facilities 2.1 Rehabilitate the existing irrigation systems and furter expand new systems (main canals, sub-

canals) 2.2 Rehabilitate the construction of a system that has not been entirely completed 2.3 A system has been completed, but not yet used, and goes broken 2.4 Immediately repair the structures that have already been completed, but cannot be used

(water gates cannot be closed and opened, water gates are not tightly fastened, and water flows out)

2.5 Construction quality is not 100 percent satisfactory 2.6 Construction companies must guarantee both quality and quantity of their construction works,

and warrant their works for 1 year 3 Training 3.1 Human resources training for officials from the ministry, provinces, communities and farmers 3.2 Provide trainees with adequate teaching materials (handouts) 3.3 Teach about water distribution and system maintenance 3.4 Train and encourage women to understand and participate in social work 3.5 Organize a national workshop at least once a year 3.6 Encourage the communities to participate in the workshop and study tours 4 Strengthen the implementation of laws and statute 4.1 Government Circular no. 1 and Prakas no. 306 of Ministry of Water Resources and

Meteorology should be effectively enforced (ministry, provincial department, communities and NGOs need to support to ensure successful implementation)

4.2 The statute of the FWUCs should be prepared based on Government Circular no. 1 and Prakas no. 306 of Ministry of Water Resources and Meteorology

4.3 The statute of the communities should be formulated appropriate to living conditions of the farmers

4.4 The statute should be properly enforced and implemented 4.5 Local authorities and relevant institutions of all levels should take part in supporting and

developing the water resources sector , and in effective implementation of the statute of the FWUC

5 Encouragement 5.1 Encourage the community committee with incentives, including cash, training, study tours and

other materials 5.2 Encourage women to contribute their ideas, join the dialogues and become leaders in the

FWUCs 5.3 Encourage local authorities to contribute various materials to the activities of the FWUCs 6 Relationships 6.1 Create relationships with relevant ministries and departments in order to precisely make the

land title deeds for the farmers 6.2 Create relationships with the departments related to the production of agricultural products

(rice seeds, fertilizers, roads) 6.3 Create relationships with the Ministry of Water Resources and Meteorology in order to lobby

for the water law to be passed and adopted in a quick way 6.4 Create relationships with different politicians in order to get support for the activities of the

FWUCs


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Recommendations on FWUC strengthening (2) NCDP (December 2004): Completion report from training workshop: Water & livelihoods, Phnom Pros Hotel, Kampong Cham, 20-22 December 2004

General • Identification of weaknesses and strengths within the communities • Encouragement to grow any value crops other than rice in case of water shortage • Site visits to other places in order to gain valuable insight into their professional practices FWUC-government relations • Clarification of roles and responsibilities • Facilitate sharing of information and experience among farmers in the region • Train/educate farmers in the community on benefit of participating in the community • Make farmers participate in the community • Strengthen water by-laws and disseminate them to the farmers • Strengthen the implementation of by-law • Systematic monitoring and evaluation • Train community staff • Base decisions on what has been suggested by the members of the community • Realistic water fees • Improved inter-agency coordination • Conflicts, if any, should be immediately solved Scheme management • Inter-farmer collaboration (within the scheme) on water management and water sharing • Strengthened management capacity of community staff • Transparent and proper financial management in the community • Reports on financial management should be distributed to farmers and other organizations

involved • Water should be sufficiently and equitably distributed Technology and skills • Proper design and construction of irrigation systems • Dissemination of modern technology to the farmers • Additional knowledge about crop cultivation • Seed selection suited for the specific soil types in the cultivated areas


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

ADB (2005) Technical Assistance to the Kingdom of Cambodia for the Study of the Influence of Built Structures on the Fisheries of the Tonle Sap (Financed by the Government of Finland). ADB: Manila

ADB (2006) ADTA 4645-CAM: Restructuring of the Railway in Cambodia. [http://www.adb.org/Documents/PIDs/37534012.asp]

ADB (Apr 05): The Tonle Sap Basin strategy (EL) ADB (Aug 03): Fighting poverty in Cambodia. The Tonle Sap Basin Strategy. Prepared by O. Serrat, D. Moffatt, and T.

Gallego-Lizon (EL) ADB (Jan 05): Country strategy and program 2005-09, Kingdom of Cambodia (EL) Asian Development Bank (2006) Asian Development Outlook 2006. (Available on the Internet) BCEOM (May 06): Hydrologist/river basin specialist, 2nd mission report, April-May 2006. Consulting services for

Northwest Irrigation Sector Project, prepared for Ministry of Water resources by BCEOM in association with ACIL and SAWAC

Beecham, R. and Cross, H. (2005) Modelled Impacts of Scoping Development Scenarios in the Lower Mekong Basin. Report prepared for the MRC-BDP

Bell, R.W. and Seng, V. (2004) Rainfed lowland rice-growing soils of Cambodia, Laos and Northeast Thailand. ACIAR Proceedings No. 116e, pp161-173

Carbonnel, J.P and J. Guiscafre: Grand Lac du Cambodge. Sedimentologie et Hydrologie, 1962-63. Ministiere des Affaires Etrangeres, Gouvernement Royal du Cambodge

Chaudhry, Peter and Muanpong Juntopas (Jan 05): Water, poverty and livelihoods in the Lower Mekong Basin. Prepared for the Basin Development Plan of Mekong River Commission (EL)

CNMC (Oct 04): Basin Development Plan Programme, sub-area analysis. The Tonle Sap Sub-area (9C) (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)

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)

FAO (2002) Investment in land and water in Cambodia. Proceedings of the Regional Consultation. RAP 2002/09. Bangkok French Ministry of Ecology and Sustainable Development (2003): Procedure for the preparation of the inventory:

characterization of the river basin district and the register of protected areas. Water Department 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

Halcrow (Apr 04): Inventory & analysis of existing systems. Volume 1: Main report; Volume 2: Banteay Meanchey, Battambang, Kampot, Kandal; 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 (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

Hoekstra, A. Y. and P. Q. Hung (Sept 02): Virtual water trade - a quantification of virtual water flows between nations in relation to international crop trade. Value of Water Research Report Series no. 11, IHE, Delft, The Netherlands (EL)

JICA (March 2004): Rural livelihood in Komping Puoy area (Cambodia), a baseline survey. Jointly prepared by Provincial Department of Agriculture, Forestry and Fishery (PDAFF) and Japan International Collaboration Agency (JICA) under the Battambang Agricultural Productivity Enhancement Project

JICA and MOWRAM (Dec 01): The Study on the Rehabilitation and Reconstruction of Agricultural Production System in the Slakou River Basin, progress report 3. Prepared by Nippon Koei Co. Ltd, Docon Co., Ltd. and Pasco International Inc. for Japan International Cooperation Agency and MOWRAM

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.


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Keo Pheakdey (Aug 05): Design of tube wells for small scale groundwater irrigation in Kampong Cham Province. National Capacity Development Project (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

MAFF (May 05): Agricultural statistics 2004-05. Statistics Office, Department of Planning, Statistics and International Cooperation

McKenney, B. and Tola, P. (2002) Natural resources and rural livelihoods in Cambodia: A baseline assessment. Working Paper 23. Cambodia Development Resource Institute: Phnom Penh.

MoE (Apr 05): State of the Environment Report 2004. Ministry of Environment, Royal Government of Cambodia MOWRAM (Aug 06a): Rainfall monitoring stations, Tonle Sap Basin. Dept. of Meteorology, with assistance from Tonle Sap

Lowland Stabilisation Project MOWRAM (Aug 06b): River flow monitoring stations, Tonle Sap Basin. Dept. of Hydrology and River Works, Office of

Research and Flood Forecasting, with assistance from Tonle Sap Lowland Stabilisation Project MOWRAM (Aug 04a): Strategic plan on water resources management and development (EL) MOWRAM (Aug 04b): Rectangular strategy on water resources and meteorology (EL) MOWRAM (Jan 04): National water resources policy for the Kingdom of Cambodia, as approved by the Council of

Ministers on 16 January 2004 (EL) MOWRAM (2003) Irrigated Agriculture – National Sector Review. Report prepared by MOWRAM in association with

Cambodia National Mekong Committee: Phnom Penh. 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 (2003) Social Atlas of the Lower Mekong Basin. Mekong River Commission Secretariat: Phnom Penh. MRC (2003) State of the Basin Report 2003. Mekong River Commission: Phnom Penh. MRC-BDP (Nov 05): National Sector Reviews. BDP Library Volume 13, October 2004, revised November 2005. Mekong

River Commission MRC-DMPF (Jun 04): Final report on DMPF data collection in Cambodia. Program to Demonstrate the Multi-functionality

of the Paddy Fields over the Mekong Basin. Edited by Mao hak, Chhea Bunrith, Sao Vannsereyvuth and Oum Kosal MRC-WUP (Jun 05): Integrated water quality management report no. 1 (draft). Mekong River Commission, Water

Utilization Programme 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)

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

NCDP (Feb 05): Strengthening of Farmer Water User Communities (FWUCs). Draft note prepared under the National Capacity Development Project (EL)

Nesbitt, H. (2003) Lower Mekong Basin: Future Trends in Agricultural Production. Draft BDP Discussion Paper. Mekong River Commission: Phnom Penh

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


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OADA (Mar 05): Study report on irrigation development projects of Mongkol Borey River in the Kingdom of Cambodia. Overseas Agricultural Development Association

PRD (July 2006): Inception Workshop, Pursat. River basin and water use studies, Package 2: Dauntri and Boribo Sub-basins. Report prepared under the North West Irrigation Sector Project for Ministry of Water Resources and Meteorology by PRD Water & Environment in association with DHI Water & Environment (EL)

PRD (Oct 2006): Technical Workshop no. 2, Battambang. River basin and water use studies, Package 2: Dauntri and Boribo Sub-basins. Report prepared under the North West Irrigation Sector Project for Ministry of Water Resources and Meteorology by PRD Water & Environment in association with DHI Water & Environment (EL)

PRD (Sep 2006): Technical Workshop no. 1, Pursat. River basin and water use studies, Package 2: Dauntri and Boribo Sub-basins. Report prepared under the North West Irrigation Sector Project for Ministry of Water Resources and Meteorology by PRD Water & Environment in association with DHI Water & Environment (EL)

van Zalinge, N. P., T. Nao and N. Sam (2001): Status of the Cambodian inland capture fisheries sector with special reference to the Tonle Sap Great Lake. pp.10-17 in van Zalinge, N.P., R. Ounsted and S. Lieng (eds). Cambodia Fisheries Technical Paper Series 3. Mekong River Commission and Department of Fisheries, Phnom Penh, Cambodia

WMO (1980): Operational Hydrology, Report No. 13: Manual on Stream Gauging, Volume II, Computation of Discharge. World Meteorological Organization

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)

Yem Dararath a and T. K. Nielsen (Sep 06): Decision-support for operation of irrigation systems in Tonle Sap, Cambodia. 2nd International Symposium on Sustainable Development in the Mekong River Basin, Phnom Penh (EL)

Öjendal, Joakim (March 2000): Sharing the good - modes of managing water resources in the Lower Mekong Basin. Department of Peace and Development Research, Göteborg University, Sweden


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Appendix 1: Data files Note: The data files are submitted separately

Table A1.1: 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. Dauntri) (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 A1.2a: 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 A1.2b: 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 A1.2c: 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

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

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-basin and details

D-W-balance-scenarios.xls Dauntri 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 2: MIKE Basin set-up Note: The model with input files and a user guide are submitted separately

A2.1 The MIKE Basin model The model system applied in the present study is MIKE Basin, developed by DHI-Water & Environment, Denmark. The model is basically a water allocation model for river basins that allows optimization calculations of water uses, e.g. irrigation, hydropower reservoirs, domestic water consumption, environmental flows etc. It is thus useful for basins in which the various pressures on the water resource need to be optimized for maximum benefit. The model system can calculate pollutant load and water quality processes.

The MIKE Basin model is integrated with the ArcGIS software system (the successor to ArcView), supplied by ESRI.

MIKE Basin MIKE Basin is a GIS-linked river network modelling system, used for decision support within water resource management at catchment level. MIKE Basin describes the water balance of the major water bodies, including the river network itself, storage reservoirs, and groundwater aquifers. Rainfall run-off can either be calculated (by different models) or can be specified based on results from field data and/or separate analyses. A distinction is made between surface runoff and groundwater flow. The modelling system allows for a detailed description of water allocations for various purposes, such as water supplies, irrigation, and hydropower. MIKE Basin includes a water quality module that describes the transport, transformation and retention of the most important pollutants in rivers, groundwater aquifers and reservoirs. Pollution sources are specified as point sources (for example sewage discharges) and non-point sources (for example fertilizers from agriculture).

In the present study, MIKE Basin has been used for

• support to the the hydrological analysis;

• basic water balance calculations;

• analyses of future water availability in connection with various development scenarios;

• analysis of pollutant loadings; and

• analysis of surface water quality.


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A2.2 Rainfall-runoff applications Overview

The rainfall-runoff module of MIKE Basin generates catchment runoff (or stream flow records) for natural as well as for catchments influenced by human activities. The following figure shows some of the different hydrological processes, which are described in the rainfall-runoff module of MIKE Basin. In addition, the model describes water storage on surface, root-zone and groundwater, as well as capillary rise.

A mathematical hydrological model like NAM is a set of linked mathematical statements describing, in a simplified quantitative form, the behaviour of the land phase of the hydrological cycle. NAM represents various components of the rainfall-runoff process by continuously accounting for the water content in four different and mutually interrelated storages. Each storage represents different physical elements of the catchment. NAM can be used either for continuous hydrological modelling over a range of flows or for simulating single events.

Figure A2.1: Rainfall-runoff model of MIKE Basin, examples of processes

The NAM model is a well-proven engineering tool that has been applied to a number of catchments around the world, representing many different hydrological regimes and climatic conditions.

One relevant previous application was a study for JICA (2004), in which runoff records were generated for all sub-catchments surrounding the Tonle Sap Lake. In that study, the rainfall-runoff model was set up for for 12 subcatchments surrounding the Great Lake. Each catchment was considered as one unit with a single or a distributed outlet to the Great Lake.

It shall be mentioned that the general lack of long data records of good quality poses a general problem in the hydrological analysis and modelling of the Tonle Sap tributaries. Essentially the accuracy of the model outputs is not better than the

Rainfall

Evaporation

Overland flow

Interflow

Baseflow

Recharge


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quality of the underlying data. However, the model is useful in the sense that it interpolates in time and space, and additional information can therefore be achieved.

The model is able to provide runoff from ungauged catchments by using calibration parameters from a neighboring gauged catchment, provided that the two areas reemble each other with respect to terrain, geology, soil properties, vegetation cover and type. Obviously, the results will be subject to some uncertainty.

NAM structure

A conceptual model like NAM is based on physical structures and equations used together with semi-empirical ones. Being a lumped model, NAM treats each catchment as a single unit. The parameters and variables represent, therefore, average values for the entire catchment. As a result some of the model parameters can be evaluated from physical catchment data, but the final parameter estimation must be performed by calibration against time series of hydrological observations.

The model structure is shown below.

Figure A2.2: Structure of the NAM model


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The structure reflects the land phase of the hydrological cycle. NAM simulates the rainfall-runoff process by continuously accounting for the water content in four different and mutually interrelated storages that represent different physical elements of the catchment. These storages are:

• Snow storage

• Surface storage

• Lower or root zone storage

• Groundwater storage

In addition NAM allows treatment of man-made interventions in the hydrological cycle such as irrigation and groundwater pumping.

Based on the meteorological input data NAM produces catchment runoff as well as information about other elements of the land phase of the hydrological cycle, such as the temporal variation of the evapotranspiration, soil moisture content, groundwater recharge, and groundwater levels. The resulting catchment runoff is split conceptually into overland flow, inter-flow and baseflow components.

NAM components

Surface storage

Moisture intercepted on the vegetation as well as water trapped in depressions and in the uppermost, cultivated part of the ground is represented as surface storage. Umax denotes the upper limit of the amount of water in the surface storage.

The amount of water, U, in the surface storage is continuously diminished by evaporative consumption as well as by horizontal leakage (interflow). When there is maximum surface storage, some of the excess water, PN, will enter the streams as overland flow, whereas the remainder is diverted as infiltration into the lower zone and groundwater storage.

Lower zone or root zone storage

The soil moisture in the root zone, a soil layer below the surface from which the vegetation can draw water for transpiration, is represented as lower zone storage. Lmax denotes the upper limit of the amount of water in this storage.

Moisture in the lower zone storage is subject to consumptive loss from transpiration. The moisture content controls the amount of water that enters the groundwater storage as recharge and the interflow and overland flow components.

Evapotranspiration

Evapotranspiration demands are first met at the potential rate from the surface storage. If the moisture content U in the surface storage is less than these requirements (U < Ep), the remaining fraction is assumed to be withdrawn by root activity from the lower zone storage at an actual rate Ea. Ea is proportional to the potential evapotranspiration and varies linearly with the relative soil moisture content, L/Lmax, of the lower zone storage

Ea = (Ep – U) x L/Lmax


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Overland flow

When the surface storage spills, i.e. when U > Umax, the excess water PN gives rise to overland flow as well as to infiltration. QOF denotes the part of PN that contributes to overland flow. It is assumed to be proportional to PN and to vary linearly with the relative soil moisture content, /Lmax, of the lower zone storage

where CQOF is the overland flow runoff coefficient (0<= CQOF <=1) TOF is the threshold value for overland flow (0<=TOF<=1)

The proportion of the excess water PN that does not run off as overland flow infiltrates into the lower zone storage. A portion, ΔL, of the water available for infiltration, (PN -QOF), is assumed to increase the moisture content L in the lower zone storage. The remaining amount of infiltrating moisture, G, is assumed to percolate deeper and recharge the groundwater storage.

Interflow

The interflow contribution, QIF, is assumed to be proportional to U and to vary linearly with the relative moisture content of the lower zone storage.

where CKIF is the time constant for interflow, and TIF is the root zone threshold value for interflow (0 <= TIF <= 1).

Interflow and overland flow routing

The interflow is routed through two linear reservoirs in series with the same time constant CK12. The overland flow routing is also based on the linear reservoir concept but with a variable time constant

where OF is the overland flow (mm/hour), OFmin is the upper limit for linear routing (= 0.4 mm/hour), and ß = 0.4.

⎪⎩

⎪⎨⎧

≤

>−

−⋅

=TOFLforL

TOFLLforPTOF

TOFLLCQOFQOF N

max/0

max/1max/

⎪⎩

⎪⎨⎧

≤

>−

−⋅

=TIFLforL

TIFLLforPTIF

TIFLLCKIFQIF N

max/0

max/1max/

⎪⎩

⎪⎨

⎧

≥⎟⎟⎠

⎞⎜⎜⎝

⎛

<

= −

minmin

12

min12

OFforOFOFOFCK

OFOFforCK

QK β


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The constant ß = 0.4 corresponds to using the Manning formula for modelling the overland flow. The equation above ensures in practice that the routing of real surface flow is kinematic, while subsurface flow being interpreted by NAM as overland flow (in catchments with no real surface flow component) is routed as a linear reservoir.

Groundwater recharge

The amount of infiltrating water G recharging the groundwater storage depends on the soil moisture content in the root zone

where TG is the root zone threshold value for groundwater recharge (0 <= TG <= 1)

Soil moisture content

The lower zone storage represents the water content within the root zone. After apportioning the net rainfall between overland flow and infiltration to groundwater, the remainder of the net rainfall increases the moisture content L within the lower zone storage by the amount

ΔL = PN – QOF – G

Baseflow

The baseflow BF from the groundwater storage is calculated as the outflow from a linear reservoir with time constant CKBF.

NAM calibration parameters

This section provides a short description of the model parameters, their physical interpretation and importance along with suggestions for parameter adjustments in the calibration.

Maximum water content in surface storage, Umax

Umax [mm] defines the maximum water content in the surface storage. This storage is interpreted as including the water content in the interception storage (on vegetation), in surface depression storages, and in the uppermost few cm's of the ground. Typical values of Umax are in the range 10-20 mm.

One important characteristic of the model is that the surface storage must be at its maximum capacity, i.e. U = Umax before any excess water, PN, occurs. In dry periods, the amount of net rainfall that must occur before any overland flow occurs can be used to estimate Umax.

⎪⎩

⎪⎨⎧

≤

>−

−⋅−

=TGLforL

TGLLforTG

TGLLQOFPG N

max/0

max/1max/)(


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Maximum water content in root zone storage, Lmax

Lmax [mm] defines the maximum water content in the lower or root zone storage. Lmax can be interpreted as the maximum soil moisture content in the root zone available for the vegetative transpiration. Ideally, Lmax can then be estimated by multiplying the difference between field capacity and wilting point of the actual soil with the effective root depth. The difference between field capacity and wilting point is referred to as the available water holding capacity (AWHC).

It should be noted that Lmax represents the average value for an entire catchment, i.e. an average value for the various soil types and root depths of the individual vegetation types. Hence, Lmax cannot in practice be estimated from field data, but an expected interval can be defined.

Since the actual evapotranspiration is highly dependent on the water content of the surface and root zone storages, Umax and Lmax are the primary parameters to be changed in order to adjust the water balance in the simulations. In the preliminary stages of the model calibration, it is recommended to fix the relation between Umax and Lmax, leaving only one storage parameter to be estimated. As a rule, Umax = 0.1Lmax can be used unless special catchment characteristics or hydrograph behaviour indicate otherwise.

Overland flow runoff coefficient CQOF

CQOF is a very important parameter, determining the extent to which excess rainfall runs off as overland flow and the magnitude of infiltration. CQOF is dimensionless with values between 0 and 1. Physically, in a lumped manner, it reflects the infiltration and also to some extent the recharge conditions.

Small values of CQOF are expected for a flat catchment having coarse, sandy soils and a large unsaturated zone, whereas large CQOF-values are expected for catchments having low, permeable soils such as clay or bare rocks. CQOF-values in the range 0.01-0.90 have been experienced.

It should be noted that during periods where the groundwater table is at the ground surface the model excludes the infiltration component, and hence CQOF becomes redundant.

Time constant for interflow CKIF

CKIF [hours] determines together with Umax the amount of interflow ((CKIF)-1 is the quantity of the surface water content U that is drained to interflow every hour). It is the dominant routing parameter of the interflow because CKIF >> CK12.

Physical interpretation of the interflow is difficult. Since interflow is seldom the dominant streamflow component, CKIF is not, in general, a very important parameter. Usually, CKIF-values are in the range 500-1000 hours.

Time constant for routing interflow and overland flow CK12

The time constant for routing interflow and overland flow CK12 [hours] determines the shape of hydrograph peaks. The value of CK12 depends on the size of the catchment and how fast it responds to rainfall. Typical values are in the range 3-48 hours.


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The time constant can be inferred from calibration on peak events. If the simulated peak discharges are too low or arriving too late, decreasing CK12 may correct this, and vice versa.

Root zone threshold value for overland flow TOF

TOF is a threshold value for overland flow in the sense that no overland flow is generated if the relative moisture content of the lower zone storage, L/Lmax, is less than TOF. The behaviour of the threshold value is illustrated in the figure below. Similarly, the root zone threshold value for interflow TIF and recharge TG act as threshold values for generation of interflow and recharge, respectively.

Figure A2.3: Generation of overland flow

Physically, the three threshold values should reflect the degree of spatial variability in the catchment characteristics, so that a small homogeneous catchment is expected to have larger threshold values than a large heterogeneous catchment.

For catchments with alternating dry and wet periods, the threshold values determine the onset of the flow components in the periods where the root zone is being filled up. This can be used in model calibration. It should be noted that the threshold values have no importance in wet periods. The significance of the threshold value varies from catchment to catchment and is usually larger in semi-arid regions.

In areas with alternating dry and wet seasons, TOF can be estimated on the basis of situations where even very heavy rainfall does not give rise to the quick response of the overland flow component. The parameter has an impact only during the first, few weeks of the wet season. Values of TOF in the range 0-0.7 have been experienced.

Root zone threshold value for interflow TIF

The root zone threshold value for interflow has the same function for interflow as TOF has for the overland flow. It is usually not a very important parameter, and it can in most cases be given a value equal to zero.

Baseflow time constant CKBF

The time constant for baseflow, CKBF [hours], determines the shape of the simulated hydrograph in dry periods. According to the linear reservoir description the discharge in such periods is given by an exponential decay. CKBF can be estimated from hydrograph recession analysis. CKBF-values in the range 500-5000 hours have been experienced.


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If the recession analysis indicates that the shape of the hydrograph changes to a slower recession after a certain time, an additional (lower) groundwater storage can be added to improve the description of the baseflow.

Root zone threshold value for groundwater recharge TG

The root zone threshold value for recharge has the same effect on recharge as TOF has on the overland flow. It is an important parameter for simulating the rise of the groundwater table in the beginning of a wet season.

NAM calibration

In the NAM model the parameters and variables represent average values for the entire catchment.

While in some cases a range of likely parameter values can be estimated, it is not possible, in general, to determine the values of the NAM parameters on the basis of the physiographic, climatic and soil physical characteristics of the catchment, since most of the parameters are of an empirical and conceptual nature. Thus, the final parameter estimation must be performed by calibration against time series of hydrological observations.

Calibration criteria

The following objectives are usually considered in the model calibration

1 A good agreement between the average simulated and observed catchment runoff (i.e. a good water balance)

2 A good overall agreement of the shape of the hydrograph

3 A good agreement of the peak flows with respect to timing, rate and volume

4 A good agreement for low flows

In this respect it is important to note that, in general, trade-offs exist between the different objectives. For instance, one may find a set of parameters that provide a very good simulation of peak flows but a poor simulation of low flows, and vice versa.

In the calibration process, the different calibration objectives 1-4 should be taken into account. If the objectives are of equal importance, one should seek to balance all the objectives, whereas in the case of priority to a certain objective this objective should be favoured.

For a general evaluation of the calibrated model, the simulated runoff is compared with discharge measurements. For individual calibration of the groundwater parameters, the simulated average groundwater level can be compared with groundwater level measurements in the catchments.

Both graphical and numerical performance measures should be applied in the calibration process. The graphical evaluation includes comparison of the simulated and observed hydrograph, and comparison of the simulated and observed accumulated runoff. The numerical performance measures include the overall water balance error (i.e. the difference between the average simulated and observed runoff), and a measure of the overall shape of the hydrograph based on the


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coefficient of determination or Nash-Sutcliffe coefficient R2. A perfect match corresponds to R2 = 1.

An exact agreement between simulations and observations must, however, not be expected. The goodness-of-fit of the calibrated model is affected by different error sources, including

1 Errors in meteorological input data

2 Errors in recorded observations

3 Errors and simplifications inherent in the model structure

4 Errors due to the use of non-optimal parameter values

In model calibration only error source (4) should be minimised. In this respect it is important to distinguish between the different error sources since calibration of model parameters may compensate for errors in data and model structure. For catchments with a low quantity or quality of data, less accurate calibration results may have to be accepted.

Satisfactory calibrations over a full range of flows usually require continuous observations of runoff for a period of 3-5 years. Runoff series of a shorter duration, however, will also be useful for calibration, although they do not ensure an efficient calibration of the model. For a proper evaluation of the reliability and hydrological soundness of the calibrated model it is recommended to validate the model on data not used for model calibration (split-sample test).

Manual calibration

The process of model calibration is normally done either manually or by using computer-based automatic procedures. In this section a manual calibration strategy for the NAM model is outlined.

In manual calibration, a trial-and-error parameter adjustment is made until satisfactory results are obtained. It is recommended, especially for the less experienced users, to change only one parameter between each trial, so that the effect of the change can be easily discerned. The manual calibration strategy outlined below is based on the different rainfall-runoff process descriptions for calibration of the relevant model parameters, i.e. the parameters that mostly affect the considered process description.

A calibration usually commences by adjusting the water balance in the system. The total evapotranspiration over a certain period should correspond to the accumulated net precipitation minus runoff. The evapotranspiration will increase when increasing the maximum water contents in the surface storage Umax and the root zone storage Lmax, and vice versa.

The peak runoff events are caused by large quantities of overland flow. The peak volume can be adjusted by changing the overland flow runoff coefficient (CQOF), whereas the shape of the peak depends on the time constant used in the runoff routing (CK12).

The amount of base flow is affected by the other runoff components; a decrease in overland flow or interflow will result in a higher baseflow, and vice versa. The shape of the baseflow recession is a function of the base-flow time constant


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(CKBF). If the baseflow recession changes to a slower recession after a certain time, a lower groundwater reservoir should be added, including calibration of CQlow and CKlow.

Initially, the root zone threshold values TOF, TIF and TG can be set to zero. After a first round of calibration of the parameters Umax, Lmax, CQOF, CK12 and CKBF, the threshold parameters can be adjusted for further refinement of the simulation results.

For individual calibration of the groundwater parameters GWLBF0 and SY, the simulated groundwater level is compared to observed groundwater levels. Inclusion of the shallow groundwater reservoir description is important in lowland areas, as found e.g. in swamps or river delta areas, where the groundwater table may reach the ground surface during the wet season.

The calibration of the NAM model for the Boribo and Dauntri catchments has been made through an trial and error process carried out manually. The general guidelines as described above is applied with variation of one parameter at a time.

The calibration parameters for the two catchments are shown in the table below.

Table A2.1: Rainfall runoff parameters

Parameter Boribo Dauntri Maximum water content in root zone storage (Lmax) 50 50

Maximum water content in surface storage (Umax) 15 18

Overland flow runoff coefficient (CQOF) 0.6 0.4

Ratio of ground water catchment to topographical (surface water) catchment area (Carea)

1 0.8

Root zone threshold value for ground water recharge (TG) 0.7 0.7

Root zone threshold value for interflow (TIF) 0.5 0.5

Root zone threshold value for overland flow (TOF) 0.1 0.1

Time constant for interflow (CKIF) 500 400

Time constant for routing baseflow (CKBF) 1000 800

Time constant for routing interflow and overland flow (CK12) 20 50

A2.3 Water balance applications For a given river basin, MIKE Basin provides a complete and consistent water balance with a desired time increment and spatial resolution, including all significant determinants and processes:

• Rainfall, evapotranspiration, infiltration, seepage;

• surface flows and groundwater flows ('interflows' and 'baseflows');

• regulation: Diversions and storages, with given operation rules;

• required minimum flows for navigation, ecological demand, transboundary commitments, or other priority allocations; and


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• abstractions and discharges (or return flows) from urban and industrial water uses, irrigation schemes, and reservoirs.

The model connects all water uses and sources in the catchment in a nodal point system, as illustrated in the following figure.

Figure A2.4: Schematic view of the structure of MIKE Basin

River branches represent rivers and nodes represent calculation points within the river network. The river catchment is divided into a number of sub-catchments each assigned to a given river section. Water users such as water supply and irrigation can be specified at any of the calculation points in the model

Results can be presented as maps and tables of flow rates and water availability, directly available for GIS analysis.

A2.4 Pollutant load applications The Load Calculator, which is an add-on tool for MIKE Basin Water Quality is a calculator for determining pollution loads for river basins. The tool calculates the average mass fluxes of pollutants for individual sub-catchments (e.g. kg/catchment/year). The tool can provide the pollution load input data for the MIKE Basin Water Quality model.

Pollution loads may include both point and non-point sources:

- Annual fertilizer consumption per district (nitrogen and phosphorus);

- runoff coefficients per district for each fertilizer pollutant;

- load per year pr head (kg/animal/year) for each pollutant;

- annual livestock including buffaloes, cows, pigs, and poultry;

- runoff coefficients for livestock loads of each pollutant;


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- population size, including numbers connected to sewer systems and treatment plants (none in the present study area);

- Sewage treatment removal efficiencies per district for each pollutant (none in the present study area); and

- rainfall and runoff; and

- industrial load for each pollutant (none in the present study area).

All loads are initially calculated as constant mass fluxes for each sub-catchment, e.g. kg/year, however when applying the Load Calculator together with e.g. the MIKE Basin WQ model there are several ways to translate the constant mass fluxes into mass flux time series depending on e.g. runoff time series or any other known temporal variations.

Distance specific decay or retention of pollutants can be included taking into account the distance between the location of the pollution sources and the presumed outlet in the river network in MIKE Basin.

All input data for the Load calculator include GIS layers describing the geographical distribution of populations, agricultural sources (e.g. livestock and/or fertilizer application), land uses and/or point sources representing wastewater from industries or population centres.

A2.5 Water quality applications Overview

MIKE Basin includes a water quality module that describes the transport and transformation/retention of the most important pollutants in rivers, ground water aquifers and reservoirs. Nitrogen is modelled as 2 components – ammonia-N and nitrate-N. In addition, an organic fraction can be included modelled implicitly as a fraction of organic matter (BOD). Pollution sources are specified as point sources (in relation to water supplies) and as non-point sources(in relation to each of the sub-catchments). Transformation processes include ammonification, nitrification and denitrification. Each process is described by a differential equation. Other pollutants include total phosphorous, BOD, COD, dissolved oxygen and coliform bacteria.

MIKE Basin WQ can simulate reactive steady-state transport of the most important substances affecting river water quality such as:

- organic matter (~BOD)

- ammonia-nitrogen (NH4)

- nitrate-nitrogen (NO3)

- total phosphorous (TP)

- coliform bacteria (E-Coli)

- other user defined substances


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Figure A2.5: Nitrogen components and processes described in MIKE Basin WQ

The degradation process for all substances is described including reactive transformations (e.g., ammonia / nitrate, DO / BOD). In general, first-order rate laws are assumed. The water quality simulation can, in an approximate way as MIKE Basin is not a hydrodynamic model, include dissolved oxygen (DO). Re-aeration from weirs is accounted for.

The steady-state approach is consistent with MIKE Basin's solution to the water allocation problem. Thus, advection can not be modeled properly with MIKE Basin. In other words, pulses of solute entering the stream do not travel downstream as simulation time advances. Therefore the time step applied for water quality simulations in MIKE Basin must exceed the total residence of the system studied, typically >= 1 week depending on the size of the river basin. Thus this way the simulated concentrations will represent an average concentration for a given time interval, or time step, rather than an instantaneous concentration.

In reaches where you specify routing (linear, Muskingum, wave translation), the water quality simulation can (if you so choose) properly reflect the residence time and the effects of mixing between reach storage and inflows. The same holds (always) for reservoirs and groundwater, the two other storages of water in MIKE Basin.

Calibration

No water quality data has been available from the studied sub-basins which could be used for model calibration.

However, in the Environmental Management of the Coastal Zone project (Danida and Ministry of Environment 1997-2007) water quality monitoring has been conducted through a two year period and with sampling in monthly intervals. As the population density and livestock densities are somewhat comparable to the studied sub-basins the data from these rivers have been used to provide guidance for the levels to expect in the sub-basins. The tables below summarises the data for BOD and total-phosphorus from 12 coastal rivers over a two-year period.


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Table A2.2: BOD statistics

May 05 - Apr 06 Wet and dry Wet Dry mg/l mg/l mg/l

10th Percentile 0.4 0.4 0.4


Median 0.7 0.8 0.7

Maximum 1.5 1.5 1.2

Minimum 0.3 0.3 0.4

Average 0.8 0.8 0.7

Standard Deviation 0.4 0.5 0.3




Median 0.7 1.0 0.6

Maximum 3.5 3.4 1.5

Minimum 0.2 0.3 0.2

Average 1.1 1.4 0.7


BOD = biological oxygen demand

Data: 12 rivers in the coastal area of Cambodia

Table A2.3: Total phosphorus statistics


10th Percentile 0.002 0.002 0.002

90th Percentile 0.021 0.026 0.016

Median 0.007 0.008 0.006

Maximum 0.036 0.035 0.020

Minimum 0.001 0.002 0.002

Average 0.010 0.012 0.008



10th Percentile 0.003 0.009 0.003

90th Percentile 0.030 0.033 0.028

Median 0.013 0.017 0.008

Maximum 0.053 0.041 0.037

Minimum 0.002 0.007 0.002

Average 0.017 0.020 0.013


Data: 12 rivers in the coastal area of Cambodia


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A limited number of measurements have been available for Tonle Sap which indicates average levels of 0.01 – 0.07 mg/l for total-phosphorus, with the highest levels in April-May. Similarly, the level of NH4 range from 0.02 – 0.12 mg/l (Water Quality Data Assessment 2005, Department of Hydrology and River Works, March 2006).

Based on the above approach the following targets (= average concentration levels) for simulated concentrations of water quality components have been used for calibration purposes:

BOD 1 mg/l

NO3 0.5 – 1 mg/l

NH4 0.1 – 0.5 mg/l

TP 0.01-0.05

Ecoli (no target available)

A2.6 River basin 'pocket calculator' A small 'river basin pocket calculator' has been prepared for the purpose of the present study.

It consist of 3 Excel workbooks, each with a number of linked spreadsheets:

B-w-balance.xls Water balance, water uses and water availability for Boribo Sub-basin on a monthly basis

D-w-balance.xls Water balance, water uses and water availability for Dauntri Sub-basin on a monthly basis

Subprojects.xls Water availability and irrigable areas for candidate sub-projects on a monthly basis

The 'pocket calculator' is easy to use by anyone with just introductory level skills in Excel software.

The water balance workbooks describe the sub-basins as divided into sub-catchments in the same way as in the MIKE Basin set-up:

• Boribo Sub-basin has been divided into 17 sub-catchments, and the Bamnak diversion is explicitly included;

• Dauntri Sub-basin has been divided into 21 sub-catchments, and the Damnak Ampil Canal is explicitly included.

There is no rainfall-runoff module, and basically only one storage volume in each sub-basin (although it can be sub-divided into 2 if need be and data are available).

Calibration is made (for a given net rainfall) by adjusting the monthly storage exchange values in a way that gives a desired (monthly) outflow from any sub-catchment where flow data are available.

Examples of input and output tables are shown below.


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Figure A2.6: Input table, set-up (Boribo Sub-basin)

Figure A2.7: Input table, set-up (Dauntri Sub-basin)


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Figure A2.8: Input table, water availability (Dauntri Sub-basin)

Figure A2.9: Input table, water uses (Dauntri Sub-basin)


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Figure A2.10: Output table, entire sub-basin (Dauntri Sub-basin)

Figure A2.11: Output table, each sub-catchment (Dauntri Sub-basin)


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Figure A2.12: Summary of manageable water availability at candidate sub-projects

Figure A2.13: Manageable water availability at each candidate sub-project


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Figure A2.14: Rainfall deficit for a given irrigation demand

Figure A2.15: Summary of irrigable areas at candidate sub-projects

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

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