flood damage emergency reconstruction project additional...

, KINGDOM OF CAMBODIA

Nation Religion King

Ministry of Water Resources

and Meteorology Asian Development Bank

Flood Damage Emergency Reconstruction Project – Additional Financing ADB Loan Number : 3125-CAM(SF)

GoA (DFAT) Grant Number: 0285-CAM(EF)

DESIGN REPORT

TUMNUB LUOK IRRIGATION SYSTEM Version 1

January 2017

In association with

KEY CONSULTANTS (CAMBODIA)

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Document quality information

General information

Author(s) Leighton Williams

Project name Flood Damage Emergency Reconstruction Project – Additional Financing

Document name Design Report: Tumnub Luok Irrigation System

Date 31 January 2017

Reference -

Addressee(s)

Sent to:

Name Organisation Sent on (date):

Huy Vantha PIU 31 January 2017

Copy to:

Name Organisation Sent on (date):

History of modifications

Version Date Written by Approved & signed by:

1 R0 31 January 2017 Leighton Williams TL/IE Leighton Williams TL/IE

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Contents

1. Introduction .......................................................................................................... 1

1.1. Purpose of Report ......................................................................................... 1 1.2. FDERP-AF ...................................................................................................... 1

1.2.1 Scope of FDERP-AF.............................................................................................1 1.2.2 Scope for Irrigation Subprojects ...........................................................................1

1.3. Project Stages ................................................................................................ 1 1.4. Tumnub Luok Irrigation System Subproject ................................................ 2

1.4.1 Location ................................................................................................................2 1.4.2 Project History ......................................................................................................2 1.4.3 Irrigation System in 2013 ......................................................................................4 1.4.4 FDERP-AF Works .................................................................................................4

1.5. Structure of Report ........................................................................................ 5 1.5.1 Main Report ..........................................................................................................5 1.5.2 Accompanying Documents ...................................................................................5

2. Studies and Investigations .................................................................................. 6

2.1. Subproject Design ......................................................................................... 6 2.2. Subproject Profile .......................................................................................... 6 2.3. Topographic Survey and Design .................................................................. 6 2.4. Socio-economic and Agricultural ................................................................. 7 2.5. Safeguards Screening for Resettlement ...................................................... 8 2.6. Safeguards Screening for Environment ....................................................... 8 2.7. Hydrological Setting ...................................................................................... 8 2.8. Rainfall ........................................................................................................... 8 2.9. Flood Discharge .......................................................................................... 12

2.9.1 Climate Change ................................................................................................. 12 2.9.2 Theoretical Estimates of Discharge ................................................................... 12 2.9.3 Recommended Design Discharge ..................................................................... 12

2.10. Spillway and Stilling Basin ......................................................................... 13 2.10.1 Background ........................................................................................................ 13 2.10.2 Adopted Solution ............................................................................................... 13

2.11. Water Resources Estimate .......................................................................... 14 2.12. Reservoir ...................................................................................................... 16 2.13. Flood Routing .............................................................................................. 17 2.14. Water Balance .............................................................................................. 18

2.14.1 Components of Water Balance .......................................................................... 18 2.14.2 Irrigated Area ..................................................................................................... 19 2.14.3 Cropping Calendar............................................................................................. 19 2.14.4 Water Resource ................................................................................................. 19 2.14.5 Water Balance Calculation ................................................................................ 19 2.14.6 Water Passing Spillway ..................................................................................... 19 2.14.7 Example Water Balances .................................................................................. 20

2.15. Flood Management ...................................................................................... 20

3. Design and Operation ........................................................................................ 24

3.1. Scope of Design .......................................................................................... 24 3.1.1 Stage 2 Civil Works ........................................................................................... 24 3.1.2 Stage 3 Civil Works ........................................................................................... 24

3.2. Objectives of the Design ............................................................................. 24 3.3. Description of the System ........................................................................... 24

3.3.1 System arrangement ......................................................................................... 24

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3.3.2 Supply Area ....................................................................................................... 27 3.4. Embankment Dam ....................................................................................... 27

3.4.1 Condition prior to FDERP-AF Repairs ............................................................... 27 3.4.2 Damage from 2013 Flood .................................................................................. 28 3.4.3 FDERP-AF Repairs ........................................................................................... 28 3.4.4 Flood damage in 2015 ....................................................................................... 28

3.5. Replacement Spillway and Stilling Basin .................................................. 30 3.6. Head regulators ........................................................................................... 30 3.7. FDERP-AF Canals ........................................................................................ 31

3.7.1 Canals rehabilitated ........................................................................................... 31 3.7.2 Earthen Canals .................................................................................................. 31 3.7.3 Main Canal MC1 ................................................................................................ 32 3.7.4 Main Canal MC3 ................................................................................................ 33

3.8. Water Distribution........................................................................................ 34 3.8.1 Water Distribution Principles ............................................................................. 34 3.8.2 Head Regulators ................................................................................................ 34 3.8.3 Cross Regulator MC2 ........................................................................................ 37

4. As-Built Drawing List ......................................................................................... 39

4.1. Stage 2 As-Built Drawing List ..................................................................... 39 4.2. Stage 3 As-Built Drawing List ..................................................................... 41

References ............................................................................................................... 72

List of appendices

Appendix 1: Hydrological Methods ....................................................................................... 44

Appendix 2: Hydrological Calculations .................................................................................. 51

Appendix 3: Hydraulic Calculations ...................................................................................... 59

List of figures

Figure 1: Location of Tumnub Luok Irrigation System ............................................................. 3

Figure 2: Existing Cropping Pattern Tumnub Luok Subproject................................................ 7

Figure 3: Tumnub Luok Catchment ........................................................................................ 9

Figure 4: Summary of monthly rainfall at Samroang ............................................................. 10

Figure 5 – Summary of monthly rainfall at Bankurat, Thailand .............................................. 11

Figure 6 – Rainfall-intensity-duration curves for Bankraut, Thailand ..................................... 11

Figure 7: Stage-discharge curve for spillway ........................................................................ 14

Figure 8: Stage-storage curve for Tumnub Luok Reservoir .................................................. 17

Figure 9: Flood routing effect of reservoir upon outflow downstream from the spillway ......... 18

Figure 10: Average year water balance ................................................................................ 21

Figure 11: Dry year water balance ........................................................................................ 22

Figure 12: Arrangement of Tumnub Luok Irrigation System .................................................. 25

Figure 13: Schematic layout of Tumnub Luok Irrigation System ........................................... 26

Figure 14: Morphology of Tumnub Louk Reservoir ............................................................... 29

Figure 15: Operating curves for head regulator at 0+588 (direct to fields) ............................ 35

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Figure 16: Operating curves for head regulator at 1+413 (MC1) ........................................... 36

Figure 17: Operating curves for head regulator at 2+380 (MC3) ........................................... 37

Figure 18: Operating curves for cross regulators on main canal MC1 ................................... 38

Figure 19: Slope Class S ...................................................................................................... 48

List of tables

Table 1: Daily rain gauge records for locations closest to Tumnub Louk .............................. 10

Table 2: Summary of various estimates of peak discharge at Tumnub Luok ........................ 12

Table 3: Water availability (MCM) entering Tumnub Luok .................................................... 15

Table 4: Water availability (m3/s) entering Tumnub Luok ...................................................... 16

Table 5: Cropping Calendar ................................................................................................. 19

Table 6: Procedure for Flood Management of Reservoir ...................................................... 23

Table 7: Details of head regulators ....................................................................................... 31

Table 8: Hydraulic design parameters for Main Canal MC1 .................................................. 32

Table 9: Structures along Main Canal MC1 .......................................................................... 32

Table 10: Hydraulic design parameters for Main Canal MC2 ................................................ 33

Table 11: Structures along Main Canal MC3 ........................................................................ 34

Table 12: Gate openings for peak irrigation demand ............................................................ 35

Table 13: Silt factor f for Lacey Equations ............................................................................ 45

Table 14: Soil Class I ........................................................................................................... 47

Table 15: Land use factor CL ................................................................................................ 48

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Acronyms and Abbreviations

$ United States Dollar

ADB Asian Development Bank

AH Affected Households

AWS Automatic Weather Station

EMP Environmental Management Plan

FSL Full Supply Level

FWUC Farmer Water User Community

FWUG Farmer Water User Group

FDERP-AF Flood Damage Emergency Reconstruction Project – Additional Financing

GoA (DFAT) Government of Australia (Department of Foreign Affairs and Trade)

GTFM Generalised Tropical Flood Model

ha Hectare

IEE Initial Environmental Examination

IFAD International Fund for Agricultural Development

IRS Irrigation Rehabilitation Study

ITCZ Inter Tropical Climatic Zone

l Litre

m Metre

mm Millimetre

m2 Square metre

m3 Cubic metre

MAF Mean Annual Flood

MC Main canal

MD Main drain

M&E Monitoring and Evaluation

MC Main canal

MCM Million cubic metre

MOWRAM Ministry of Water Resources and Meteorology

MRD Ministry of Rural Development

NA Not applicable

O&M Operation and Maintenance

PDWRAM Provincial Department of Water Resources and Meteorology

/ Per

s Second

SDR Special Drawing Right

Sta. Station

WRMSDP Water Resources Management Sector Development Program

ZOA South East Asia (in Dutch language)

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Flood Damage Emergency Reconstruction Project – Additional Financing Page 1

1. Introduction

1.1. Purpose of Report

The purpose of the Design Report is to summarise the studies and design and present for record

purposes the calculations and drawings prepared for implementation of the Tumnub Luok Irrigation

System Subproject.

1.2. FDERP-AF

1.2.1 Scope of FDERP-AF

The Flood Damage Emergency Reconstruction Project – Additional Financing (FDERP-AF) is for

urgent reconstruction following damage caused by the 2013 flood. Tumnub Luok Irrigation System is

one of nine subprojects under Output 3: Irrigation rehabilitation and flood management which includes

flood damaged irrigation infrastructure subprojects.

1.2.2 Scope for Irrigation Subprojects

For irrigation, the objective of FDERP-AF is to restore the operation of existing irrigation systems.

Although the catalyst was damage from the 2013 floods, the nine subprojects had mostly suffered

earlier flood damage, both on an annual basis and from other major floods in 2011 and 2009

(Ketsana). The systems were also to varying degrees degraded due to incorrect operation, insufficient

maintenance and failure to carry out essential annual repairs of systems constructed within the last

decade, or of canals and embankments first constructed under the Khmer Rouge Regime between

1975 and 1979, and in some cases, even earlier during the French colonial period.

Therefore, the overall scope includes both emergency reconstruction of flood damage and partial

rehabilitation of irrigation systems to the extent that was possible within the limited funds available.

FDERP-AF is also a “fast-track” project to be substantially completed within three years. It is therefore

important to understand that for these reasons the outcome of the FDERP-AF intervention is not a

fully studied and functioning irrigation system which will deliver the full potential benefits of

the system. To deliver the full benefits, systems will need to be fully developed and/or extended, and,

for community systems, have a fully functioning Farmer Water User Community (FWUC).

1.3. Project Stages

Because of the urgent requirement to reconstruct flood damaged infrastructure, implementation has

been divided into three stages as follows:

1. Stage 1: Immediate repairs to restore vital function of the infrastructure on a temporary basis.

This was done by the Royal Government of Cambodia in late 2013, using its own resources.

For MOWRAM this mostly included temporary earthworks at breached dams and

embankments.


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2. Stage 2: Fast-track repairs necessary to restore functionality of infrastructure as soon as

possible before the 2014 or 2015 wet seasons. This required advance action by the line

ministries, which is MOWRAM for irrigation; and Direct Contracting to expedite the Stage 2

works which all began in 2014. Nevertheless, the Stage 2 works were of necessity limited by

the resources and funds which could be mobilised within the short available time window.

Therefore, the works proceeded without much consideration of the design options or solutions.

3. Stage 3: Improvement of selected subproject infrastructure, but also works to restore

functionality which could not be completed under Stage 2, for implementation during the 2015

and 2016 dry seasons. In preparation, Subproject Profile reports were compiled to: confirm

the subproject selection, examine the design proposals and hydrology, and address

safeguards issues including collecting some baseline information for monitoring and

evaluation (M&E). The Subproject Profiles were not feasibility or detailed studies, although

the topics addressed were of equivalent scope. The aim was to “build back better” with

improved sustainability including resilience to climate change impacts of drought and flood.

The works contracts were procured by competitive bidding.

In the case of Tumnub Luok Irrigation System works were carried out under Stages 1, 2 and 3.

1.4. Tumnub Luok Irrigation System Subproject

1.4.1 Location

The Tumnub Luok irrigation subproject is in Thnal Bath village, Sangkat Korn Kriel, Krong Samroang,

Udor Meanchey Province. It is reached by travelling 12 km north east on National Road No.68 from

the centre of Samroang toward the O Smach border crossing. The community road leading to

Tumnub Luok is to the right between kilometre posts 83 and 84 (Figure 1).

1.4.2 Project History

The first construction of Tumnub Luok was in 1954 when the chief monk at the Pagoda, named Plorm

Pleang initiated and led a community project to build a dam across a river (Trapeang Khtom) to store

water and create a fish pond for aquiculture. The first dam was a 150 m long earth embankment,

2.5 m high and with a crest width of 3 m.

Later the pond was incorporated into the Tumnub Luok irrigation system constructed during the

Sangkum Reasniyum, the King Preah Sihanouk regime, once again with the community participation.

Then the system fell into decline during the civil war between 1970 and 1975.

Between 1976 and 1979 under the Khmer Rouge regime the irrigation system was rehabilitated and

expanded using forced labour from the villages of Samroang District. The system comprised a longer

dam, three concrete and wooden water gates, and canals. There was forced resettlement to make

way for the works but the people had no alternative but to accept this and do as they were told.



Figure 1: Location of Tumnub Luok Irrigation System

Between 2003 and 2006 the Commune Council used the Commune/Sangkat Fund under the Seila

Program* to rehabilitate parts of the dam, main canal and facilities including a new 15 m wide spillway.

About the same time PDWRAM repaired two of the Khmer Rouge water gates.

Later, from 2009 to 2013, PDWRAM organised the operation and maintenance with the community

participation. They organised farmers into work parties to repair the dam. PDWRAM provided empty

sacks to be filled with soil to repair earthworks, and the Commune Council provided drinks and

snacks. The work activities which followed were liked and included: removal of weeds, moss and

water plants; repairing earth slips along the dam, grass planting to protect areas susceptible to

erosion, filling pot holes along the crest of the dam and resurfacing with Laterite, removal of debris and

blockage. However, nothing was done to recover the irrigation system which had largely been left to

deteriorate for more than a decade.

* The Seila program started in 1996 was a national program with multilateral donor support aiming to

achieve poverty reduction through local development and improved local governance; it facilitated

small infrastructure works supported by the RGC Commune/Sangkat Fund

Tumnub Luok



1.4.3 Irrigation System in 2013

Tumnub Luok irrigation system is shown by Figure 12. It comprises a 2.275 km long earth

embankment dam which “snakes” across the river valley capturing several rivers and streams which

rise on the Dangrek Escarpment to the north. The main river channel flowing downstream is on the

right side of the valley where, until the FDERP-AF interventions, at Station 0+060 m along the dam,

there was a small and inadequate 15 m long spillway.

Similarly, nearby at Station 0+131 m there was a triple water gate originally built by the Khmer Rouge

but which was fitted with three rising spindle steel gates by PDRWAM between 2003 and 2006. There

was a 0.5 km long canal downstream of this gate (main canal MC2). This gate was used to discharge

flood flow because the 15 m spillway had insufficient capacity.

There was a second smaller twin 1.0 m diameter pipe head regulator at Station 0+588 m but there is

no canal associated with this gate.

The main canal MC1 which is 5.0 km long starts at Station 1+413 m along the dam. As of 2014 there

was no head regulator to control flow into the canal until added in 2015 as Stage 2 works.

There was a double pipe culvert head regulator at Station 2+380 m along the dam. There was a canal

MC3 associated with this gate but due to scour and siltation it was not functioning.

It has been estimated by MOWRAM that the command area is 800 ha. However, the participatory

field investigations for preparation of the subproject profile1 indicated a larger command area 1,150 ha.

The reservoir is divided into upper and lower areas with a cascading flow until the reservoir fills

sufficiently to became a single lake. Earthworks placed by PDWRAM prior to 2013 have caused

further separation of the two areas. These unusual circumstances have been a factor for the frequent

flood damages to the dam which is discussed at Section 3.4.4.

Tumnub Luok is also being developed for community water supply. During late 2014 the existing

system comprised a filter chamber, pump, water tower and metered distribution system, and there

were plans to expand this system.

1.4.4 FDERP-AF Works

The works were done under Stages 1, 2 and 3 are as follows:

Stage 1: comprised:

urgent repairs to the dam following the 2013 were limited to closing the breaches with fill

so that light traffic could pass but this was done quickly and was not permanent repair of

the embankment dam.

Stage 2: comprised:

repairs and raising the crest level of the embankment dam over a length 2,275 m including

Laterite pavement but excluding grass sodding;

temporary repairs to the existing spillway;

earthworks for rehabilitation of 5,007 m long main canal MC1 but grass sodding, Laterite

after the first 500 m, and structures were not done until Stage 3; and

new head regulator for main canal MC1.

Stage 3: comprised:

demolition of large Khmer Rouge water gate.

provision of a 150 m long spillway at the location of the existing spillway;

raising 1,075 m section of embankment dam at upper reservoir area by 1.0 m and paving

with Laterite;



rehabilitation of 1,025 m long main canal MC3 including a new head regulator;

cross-regulators, off-takes and ox-cart bridges at locations along main canals MC1 and

MC3.

grass sodding of embankment dam and canals; and

construction of a FWUC Building.

1.5. Structure of Report

1.5.1 Main Report

This volume constitutes the main report of the Design Report. It is supported by the accompanying

volumes listed at Section 1.5.2. The Design Report is arranged as follows:

Chapter 2: Design and Field Investigations describes: topographical survey; socio-economic

and agricultural studies; screening for resettlement, social and environmental impacts;

hydrology including: hydrological setting, rainfall, flood discharges, spillway design, water

resources estimates, reservoirs, flood routing, water balance and flood management.

Chapter 3: Design and Operation describes: the scope and objectives of the FDERP-AF

designs, a description of the FDERP-AF systems, details for operational water distribution and

flood management, and explanation of the design calculations.

Chapter 4: As-Built Drawings lists the drawings which record what has been constructed

under FDERP-AF.

Appendices: with descriptions of hydrological methods, presentation of calculations made for

hydrology and hydraulic design.

1.5.2 Accompanying Documents

The following supporting documents should be read in conjunction with this Design Report:

Subproject Profile1.

Initial Environmental Evaluation (IEE)2.

As Built and Design Drawings.



2. Studies and Investigations

2.1. Subproject Design

The basic design of the subproject was fixed by it being an existing irrigation system in need of repair

rather than a completely new project. Additional to this was that FDERP-AF is a “fast track”

Emergency Repair project. Therefore, the works were chosen to restore irrigation systems within the

shortest possible time with no time available for detailed studies.

The FDERP-AF irrigation subprojects were proposed by MOWRAM justified by national and provincial

priorities. In most cases MOWRAM already had outline or detailed designs prepared for the works,

generally based on not very detailed study. On the other hand, studies were not necessary to justify

repair of obvious flood damage such as breached dams, such works could proceed under Stage 2

without much study or investigation. However, for Stage 3 to achieve the objectives to “build back

better” and to improve sustainability and provide resilience to climate change did justify more

considered studies and investigations to ensure cost effective solutions which will meet the objectives.

2.2. Subproject Profile

The study and investigation tool used was the Subproject Profile. These were prepared for all nine

FDERP-AF subprojects between October 2014 and January 2015. The objectives of the Subproject

Profiles were to provide information required to confirm and complete the detailed design, and to

screen the subprojects for compliance with the minimum required economic rate of return (EIRR) and

safeguard criteria stated in the Project Administration Manual (PAM). The Subproject Profile for

Tumnub Luok Irrigation System1 addressed the following:

location;

existing situation including description of facilities and state of repair;

socio-economic and agriculture assessment including baseline data and estimated EIRR;

details of existing FWUC, whether formally or informally established;

present arrangements for operation and maintenance (O&M);

scope of works under Stage 2 and Stage 3 including recommendations to vary or add additional

works;

cost estimate (provisional);

photographs;

general and irrigation specific screening including EIRR, resettlement and environment.

2.3. Topographic Survey and Design

The topographic survey and outline design were done by MOWRAM.

The survey established a local datum and is not tied into the national datum. The local datum is about

36 m lower than the national datum.

In broad terms the MOWRAM design was followed but was consolidated and improved in detail.

During the construction modifications were made and additional structures were added. Furthermore,



WS Medium Duration Rice

WS Late Duration Rice

Dry Season Rice

WS Short Duration Rice

a flood in October 2015 which led PDWRAM to make breaches in the embankment dam which had

only earlier in that year been repaired under Stage 2 highlighted risks at the upper reservoir area

which resulted in works under a Variation Order to raise the eastern end of the dam by 1.0 m (see

Section 3.4.4).

2.4. Socio-economic and Agricultural

The socio-economic and agricultural baseline of the subproject was addressed by the Subproject

Profile with information collected Q4 2014. This baseline information was updated in Q1 2016 during

implementation of the Stage 3 works. The sources and methods of data collection were the village

and commune chiefs, the local authorities and group discussion. The details are at Chapter 2-3 of the

Subproject Profile.

Currently the main crop grown at Tumnub Luok is wet season rice, some dry season rice is also

grown. The rice crop is broadcast and rainfed with supplementary irrigation if it is available during the

wet season. The cropping pattern is shown at Figure 2. Farmers use chemical fertilizer about

75 kg/ha on average during the wet season and 100 kg/ha on average during the dry season.

Figure 2: Existing Cropping Pattern Tumnub Luok Subproject

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

Source: Group discussion

Some 50% of the wet season rice is short duration rice, especially fragrant seeds of Phkar Romduol,

Phkar Malis and Lum Orng Khsach; 40% is medium duration rice like Phkar Doung and Phkar Sar;

and 10% is late duration rice like Srov Rath, Lolok Chit and Car 3 and 4. During the dry season the

seeds used are Sen Pidor and Sen Kro Oub. It is noted that on average 100 to 120 kg/ha of wet

season rice seed used is kept from the previous year’s crop or bought from neighbouring farmers.

Traditionally, farmers have grown late duration rice before short and medium duration rice in the

flooded area in the early wet season to avoid rotten rice with too much water. In general, wet season

rice starts at the same time each year from May to June with land preparation and harvesting in

November (short duration rice) and December or January (medium and late duration rice). Dry



season rice starts after the wet season crop is harvested in December or January with land

preparation and harvesting at the end of March or April.

In the future if reliable irrigation infrastructure is provided there is potential to increase rice production.

This can be achieved by promoting and applying the system of rice intensification, making

improvements to soil fertility, and better water management. Based on data from group discussion

and the field survey, the potential average wet season rice yield could be increased from the current

1.3-1.5 T/ha to 2.3 T/ha and dry season rice from the current 2.5 T/ha to 3.5 T/ha. Therefore, with the

total areas of irrigated rice, the current total rice production of about 1,710 T could be increased up to

2,996 T in the future. This would be an increase of 1,286 T over production prior to the FDERP-AF

interventions.

2.5. Safeguards Screening for Resettlement

The subproject was screened for resettlement in Q4 2014 during preparation of the Subproject Profile.

Screening used a resettlement impact check-list. At that stage this indicated that the subproject

interventions were within Category C for resettlement as per the Safeguards Policy Statement (ADB

SPS 20093). No resettlement issues arose during construction, no involuntary resettlement was

required and no resettlement categorisation report was prepared.

2.6. Safeguards Screening for Environment

The subproject was screened for potential social and environmental impacts in Q4 2014 during

preparation of the Subproject Profile. This determined that the subproject was not environmentally

critical and it was assessed as Category B under the ADB classification system. Category B means

that the potential adverse environmental impacts are site-specific, few if any of them are irreversible,

and in most cases mitigation measures can be readily designed. An IEE is required. This was

prepared in February 20152. The IEE included an environmental management plan (EMP).

The IEE and EMP were included in the bidding contract documents for the Stage 3 works (a generic

IEE and EMP had been included for Stage 2). The Contractor was required to comply with the EMP.

The Contractor’s social and environmental performance and compliance with the EMP was monitored.

Compliance with the project Gender Action Plan was monitored monthly during construction.

2.7. Hydrological Setting

Tumnub Luok is a shallow online reservoir used for flood spreading to rice fields downstream. The

catchment area is 291 km2 and is well defined. Steams flowing into the reservoir rise on the Dangrek

escarpment along the border with Thailand Figure 3.

2.8. Rainfall

At the time the design was prepared there were no available rainfall records from within the catchment

but there were some daily records for rain gauges surrounding the catchment, both in Cambodia and

Thailand Table 1.



Figure 3: Tumnub Luok Catchment

Catchment area: 291 km2

Stream length: 29,000 m

H85: 100 m elevation

H10: 50 m elevation

Tumnub Luok



Table 1: Daily rain gauge records for locations closest to Tumnub Louk

Rain gauge Year available

Number of years Annual average

Code Station No mm

Cambodia

140401 Samroang 10-13 4 1360

- Along Veng 10-12 3 1563

Thailand

140307 Bankruat 82-00 18 1278

140306 Prasat 80-98 18 1330

140402 Khukhan 82-89, 91-00 18 (9 incomplete) 1273

Although the Cambodian records are short the average annual totals are very similar to the stations in

Thailand. The consistency with the long records means that it is acceptable to use the Samroang

record for water balance and cropping schedules (Figure 4). However, the Thai rain gauge data is

better used for estimation of flood discharge and spillway design. The highest daily rainfalls have

been recorded at Bankraut and therefore this record was used. The summary record is shown in

Figure 5 and the derived rainfall-intensity-duration curves by Figure 6.

Figure 4: Summary of monthly rainfall at Samroang SUMMARY OF MONTHLY RAINFALL: SAMROANG

2010-2013

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

450.0

500.0

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

Rain

fall in

mm

Minimum monthly rainfall in mm for period of recordAverage monthly rainfall in mm for period of recordMaximum monthly rainfall in mm for period of record



Figure 5 – Summary of monthly rainfall at Bankurat, Thailand SUMMARY OF MONTHLY RAINFALL: 140307 BANKRUAT, THAILAND

0.0

100.0

200.0

300.0

400.0

500.0

600.0

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

Ra

infa

ll i

n m

m

Minimum monthly rainfall in mm for period of recordAverage monthly rainfall in mm for period of recordMaxima monthly rainfall in mm for period of record

Note: The high maximum for February is for a single storm in 1991 and appears anomalous although there are several other

instances on the record of high rainfalls in February.

Figure 6 – Rainfall-intensity-duration curves for Bankraut, Thailand

140307 BANKRAUT, THAILAND

Synthesised Rainfall-Intensity-Duration Curves

1

10

100

1000

0.0 0.1 1.0 10.0 100.0

Duration in hours

Rain

fall

In

ten

sit

y i

n m

m/h

2.33 yr return period

5 yr return period

10 yr return period

25 yr return period

50 yr return period

100 yr return period



2.9. Flood Discharge

2.9.1 Climate Change

There is limited specific guidance for climate resilience for Cambodia which can be applied for

engineering design. However, the recent NDF/ADB Climate Change Adaptation Project4 has used

hydrological modelling to predict the potential increase in flooding until the end of the century. This

indicates that flood flows may on average increase by 10% to 20% and that corresponding flood

depths might increase by 0.3 m to 0.5 m. These estimates must be treated with caution, because

local infrastructure developments and changes in land use have the potential for greater and more

immediate change in flood regimes. But nevertheless, the figures do provide a quantifiable basis for

considering climate adaptation.

For high risk infrastructure, such as dams and spillways it is prudent to err on the side of caution.

Therefore, the design standard adopted for spillway design was the 1 in 100-year peak discharge

increased by 20% being the upper bound average increase predicted by the Climate Change

Adaptation Project.

2.9.2 Theoretical Estimates of Discharge

Without any actual record of discharge at Tumnub Luok it is necessary to consider several methods to

estimate the discharge to decide whether these correspond with the physical evidence and anecdotal

evidence of flood flows at the site. The methods are described in Appendix 1 and the calculations are

presented in Appendix 2. The methods reported are:

Modified Irrigation Rehabilitation Study (IRS) Method;

Regime Theory;

Flood Transposition; and

Generalised Tropical Flood Model.

Table 2 lists the estimates from the four different methods. The estimates are of similar magnitude.

Only the Regime Theory is based on physical dimensions of the river channel and for this reason is

probably most representative of the impact of flood spreading and attenuation of flood flow through

rice paddies upstream. It is also the lowest estimate. For the design case the GTFM is 11% higher,

the Modified IRS Method 34% higher and the Flood Transposition Method 71% higher.

Table 2: Summary of various estimates of peak discharge at Tumnub Luok

Method of estimation

Peak discharge in m3/s

MAF Q50 Q100 Design†

Modified IRS 66 131 145 173

Regime Theory 49 98 107 129

Transposition 84 168 184 221

GTFM 55 109 120 144

† Q100 plus 20%

2.9.3 Recommended Design Discharge

Based on the theoretical estimates and the physical conditions controlling discharge it was decided

that the dam on Tumnub Luok would be designed based upon the Modified IRS Method and checked

for the Flood Transposition estimate that the flow will pass without significant reduction of freeboard.



2.10. Spillway and Stilling Basin

2.10.1 Background

The existing spillway had a crest level of 18.7 m elevation discharging towards the natural river

channel downstream. Although grossly undersized minor repairs were made to the spillway under

Stage 2 at the same time the dam was repaired. The repaired dam has a crest level 20.5 m elevation

and provided a freeboard of 1.8 m. Provision of increased spillway capacity was planned for Stage 3.

Just at the time Stage 3 construction was about to commence PDWRAM requested that the full supply

level of the reservoir be raised to 19.2 m. Increasing the full supply level reduced the freeboard to

1.3 m which meant that there would be reduced and insufficient freeboard when reservoir levels rise

during a flood. To keep acceptable freeboard would have meant a larger labyrinth weir and vehicle

bridge than have been proposed and there were insufficient funds for this. Therefore, the spillway was

changed to a broad crested weir with low level vehicle crossing which could be constructed within the

allocated budget.

2.10.2 Adopted Solution

The chosen solution is a 150 m long reinforced concrete broad crested weir and glacis† with a USBR

Type 1 stilling basin constructed of gabions. The spillway crest is at 19.2 m elevation. The crest also

provides a low-level vehicle crossing and this was made 6.0 m wide because of concerns for the

safety of vehicles, people and animals crossing when the spillway was flowing, which is normally for

than three months every year. The stage-discharge curve for the spillway is shown in Figure 7. The

hydraulic calculations are shown at Appendix 3.

A 150 m long weir will pass the design discharge of 173 m3/s with the reservoir level at 20.06 m

elevation. With this reservoir level the freeboard would be 0.44 m which is still less than the

recommended 0.9 m freeboard‡. However, as explained at Section 2.13 the routing effect of the

reservoir reduces the peak reservoir outflow of the design flood by about 9% compared to the peak

inflow. MOWRAM deemed the sub-standard freeboard to be an acceptable risk given the limitation on

available funds. Also, given the nature of the reservoir catchment which produces flash floods and

hydrographs with a sharp peak of short duration, the times when freeboard is less than 0.9 m are

expected to be of short duration and infrequent.

The stilling basin serves to dissipate the kinetic energy of the high velocity critical flow down the glacis

of the spillway and thereby prevent erosion which could undermine the structure or cause damage

downstream. A USBR Type 1 stilling basin is used to force a hydraulic jump to form and the flow to

change from shallow-fast-supercritical to deep-slow-subcritical. The excess energy is dissipated by

the turbulence and heat in the hydraulic jump. The stilling basin has been sized using the sequent

depth formula and for a length six-times the height of the hydraulic jump at the design flow 173 m3/s,

but the length was rounded-up to 10.0 m. Because of the width of the stilling basin, and there being a

much narrower river channel downstream to provide the water depth for a hydraulic jump to form, the

stilling basin floor had to be set at 14.8 m elevation, 0.8 m lower than the lowest places for the

previously existing downstream land which was about 15.6 m elevation. The step or sill is formed of

gabion boxes, as is the floor of the stilling basin. At low flows the hydraulic jump occurs on the glacis

† Glacis is the sloping slab downstream of weir crest.

‡ The minimum freeboard recommended for small dams by the US Bureau of Reclamation is 0.9 m.



but will move downstream into the stilling basin as the flow increases. As further protection against

erosion and scour undermining the stilling basin and structure from downstream a gabion mattress is

laid extending 6.0 m from the sill, this is designed to fold down into any scour hole and thereby prevent

erosion from progressing back upstream.

Figure 7: Stage-discharge curve for spillway

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

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0 25 50 75 100 125 150 175 200 225 250 275 300 325

Heig

ht

of

reserv

oir

ab

ove w

eir

cre

st

(m)

Discharge over spillway (m3/s)

2.11. Water Resources Estimate

There are currently no useable water resource observations for Tumnub Luok. The AWS at

Samroang only came into use in 2014, and the installation at Banteay Ampil only came into use from

July 2015, and 2015 was a drought year at Tumnub Luok. The best available long term river flow

records are for the Stung Sreng at Kralanh. The catchment at Kralanh is significantly larger than that

at Tumnub Louk and is characterised by blocked river channels, flow diversion and abstractions which

taken together mean that the records are of dubious quality for water resource planning.

The data for the Stung Sreng was most recently published by the Water Resources Management

Sector Development Program (WRMSDP), although the data is the same as published earlier in the

Tonle Sap Lowland Stabilization Project, Report on Water Availability5. The WRMSDP study was a

program component to address national water resources management and irrigation policy issues in

Cambodia, and an investment component to assist MOWRAM to rehabilitate small- and medium-scale

irrigation systems and deliver irrigation services within the Tonle Sap Basin. A detailed assessment of

water resources data was completed by WRMSDP in April 2014 and reported in the Cambodian Water

Resources Profile6.

At Annex 4 of the Report there are tabulations of the monthly flow volume of every gauged river in

Cambodia. Table 3 and Table 4 for flow entering Tumnub Luok are derived from the data for the



Stung Sreng at Kralanh using the same formula as flood transposition (Appendix 1). The limitations of

the estimates in the table are acknowledged but they are nevertheless currently the best data based

upon observation that is available for estimation of water availability from Tumnub Luok.

Table 3: Water availability (MCM) entering Tumnub Luok

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

1997 0.8 0.1 0.0 0.1 0.1 0.1 6.6 46.4 34.8 58.9 2.4 0.6 151.0

1998 0.1 0.0 0.0 0.0 0.0 0.0 2.0 9.1 11.3 34.3 12.1 1.1 70.1

1999 0.1 0.0 0.0 0.2 19.1 49.7 45.4 19.9 13.6 50.1 36.7 3.4 238.1

2000 0.4 0.0 0.0 0.6 4.7 34.4 90.0 65.1 61.0 60.3 28.6 2.3 360.8

2001 0.3 0.1 0.1 0.1 0.1 0.1 4.8 28.4 49.0 59.9 61.1 2.3 206.2

2002 0.2 0.0 0.1 0.0 0.1 1.0 9.6 7.5 63.8 56.7 19.2 4.5 162.9

2003 0.3 0.0 0.1 0.1 0.1 0.1 0.3 0.2 14.0 59.7 12.1 0.7 87.7

2004 0.1 0.0 0.0 0.0 0.0 9.7 4.2 62.2 58.7 26.8 1.9 0.8 164.5

2005 0.2 0.1 0.0 0.0 0.0 0.3 6.7 9.8 32.0 41.8 20.6 0.2 111.7

2006 0.0 0.0 0.1 0.0 0.1 0.1 3.5 63.8 62.9 83.2 34.8 2.2 250.7

2007 0.1 0.0 0.1 0.0 5.8 0.1 0.4 17.0 38.8 53.3 18.4 0.1 134.2

2008 0.1 0.0 0.0 0.0 0.1 0.3 6.4 24.2 65.1 76.2 70.6 13.5 256.6

2009 0.0 0.0 0.1 0.1 0.1 0.2 4.9 18.4 41.0 84.4 18.4 0.7 168.2

2010 0.3 0.3 0.3 0.3 0.3 1.3 1.8 64.3 77.0 99.9 37.8 0.2 283.9

Maximum 0.83 0.28 0.30 0.61 19.1 49.7 90.0 65.1 77.0 99.9 70.6 13.5 360.8

Average 0.21 0.06 0.07 0.12 2.2 7.0 13.3 31.2 44.5 60.4 26.8 2.33 189.0

Minimum 0.02 0.03 0.03 0.03 0.03 0.03 0.28 0.22 11.3 26.8 1.86 0.17 70.1

20% Exceedence 0.33 0.06 0.06 0.13 2.04 4.63 7.85 62.8 63.2 79.0 37.1 2.77 253.0

50% Exceedence 0.14 0.05 0.05 0.05 0.09 0.23 4.81 22.0 45.0 59.3 19.9 0.94 166.3

80% Exceedence 0.05 0.04 0.04 0.04 0.05 0.11 1.94 9.53 24.8 46.7 12.1 0.46 125.2

Source: Reference 5



Table 4: Water availability (m3/s) entering Tumnub Luok

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

1997 0.31 0.03 0.02 0.03 0.02 0.05 2.48 17.33 13.43 21.98 0.92 0.24 4.79

1998 0.02 0.01 0.01 0.01 0.01 0.01 0.76 3.40 4.35 12.80 4.68 0.40 2.22

1999 0.03 0.02 0.01 0.07 7.13 19.16 16.95 7.43 5.25 18.69 14.16 1.28 7.55

2000 0.14 0.02 0.01 0.23 1.74 13.3 33.6 24.3 23.5 22.5 11.0 0.87 11.4

2001 0.12 0.02 0.02 0.02 0.04 0.03 1.77 10.6 18.9 22.4 23.6 0.87 6.54

2002 0.08 0.02 0.02 0.02 0.04 0.40 3.57 2.80 24.6 21.2 7.4 1.69 5.16

2003 0.13 0.02 0.02 0.03 0.03 0.04 0.11 0.08 5.4 22.3 4.7 0.27 2.78

2004 0.02 0.01 0.01 0.01 0.02 3.73 1.55 23.23 22.7 10.0 0.7 0.30 5.20

2005 0.08 0.03 0.02 0.01 0.01 0.10 2.51 3.66 12.4 15.6 7.9 0.06 3.54

2006 0.02 0.02 0.02 0.02 0.02 0.05 1.31 23.82 24.3 31.0 13.4 0.81 7.95

2007 0.02 0.02 0.02 0.02 2.18 0.04 0.15 6.33 15.0 19.9 7.1 0.02 4.25

2008 0.02 0.02 0.02 0.02 0.06 0.10 2.39 9.02 25.1 28.5 27.2 5.03 8.11

2009 0.01 0.02 0.02 0.02 0.03 0.08 1.81 6.88 15.8 31.5 7.1 0.25 5.33

2010 0.12 0.11 0.11 0.11 0.11 0.49 0.68 24.02 29.7 37.3 14.6 0.07 9.00

Maximum 0.31 0.11 0.11 0.23 7.1 19.2 33.6 24.3 29.7 37.3 27.2 5.03 11.4

Average 0.08 0.03 0.02 0.05 0.82 2.68 4.97 11.6 17.2 22.5 10.3 0.87 5.99

Minimum 0.01 0.01 0.01 0.01 0.01 0.01 0.11 0.08 4.35 10.0 0.72 0.06 2.22

20% Exceedence 0.12 0.03 0.02 0.05 0.76 1.79 2.93 23.46 24.40 29.49 14.33 1.04 8.02

50% Exceedence 0.05 0.02 0.02 0.02 0.03 0.09 1.79 8.22 17.36 22.13 7.67 0.35 5.27

80% Exceedence 0.02 0.02 0.01 0.02 0.02 0.04 0.73 3.56 9.58 17.45 4.68 0.17 3.97

Source: Reference 6

2.12. Reservoir

The reservoir storage capacity and full supply water level (FSWL) are key factors to the reservoir

water balance§ because:

the volume of water that can be stored determines how much will be available for irrigation and

other purposes later in the year; and

determines how much water will flow over the spillway and therefore be lost to the irrigation

system.

Another factor is the reservoir water area at any given stage (level). The greater the area the greater

becomes direct evaporation water losses from the surface and infiltration losses through the reservoir

floor. It also means a larger area of land is flooded which will impact the ways the land around the

reservoir shore is farmed.

The reservoir area at Tumnub Luok has not been surveyed. The only survey was for the embankment

dam. However, the dam has numerous twists and turns in plan. Therefore, it was possible to use the

cross sections surveyed along the dam in combination with contours on topographical maps and

§ In hydrology, water balance describes the flow of water in and out of a system, in this case in and out

of the reservoir.



Google Earth imagery to estimate ground levels within the reservoir on 100 m grid. This was used to

derive stage-storage and stage area curves for the reservoir (Figure 8) which has been used for flood

routing (Section 2.13) and water balance calculations (Section 2.14).

Figure 8: Stage-storage curve for Tumnub Luok Reservoir

15.0

15.5

16.0

16.5

17.0

17.5

18.0

18.5

19.0

19.5

20.0

20.5

21.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

Re

se

rvo

ir s

tag

e (m

elv

)

Storage (MCM)

Reservoir stage-storage relationship FSWL Dam crest

2.13. Flood Routing**

Luok reservoir does have a flood routing effect. Although the reservoir capacity at full supply level is

only 2.18 MCM there is an additional 2.51 MCM of temporary storage between full supply level and

dam crest level which will attenuate the flood flow downstream. Another factor is that the catchment

area is modest at 291 km2 and the stream length is short at 29 km. This limits the total flood volume

resulting from single heavy rainfall events over the catchment and the peak of the inflow hydrograph

may arrive at the dam quickly in about nine hours. These are the characteristics of a flash flood, i.e. a

flood that comes quickly and of a duration lasting hours not day.

The flood routing was tested by applying a unit hydrograph to synthesise reservoir inflow for the peak

design flood of 173 m3/s. It was assumed that the peak inflow would be nine hours after the start of

the flood and that the flood inflow would last 45 hours. It is likely that the design flood would occur

during the main flood season either September or October and the spillway would already be flowing

due to baseflow in the river. The baseflow was allowed for by adding 18 m3/s to the inflow hydrograph

for the duration of the flood. The 18 m3/s is the estimated average flow for October and is equivalent

to an initial depth of flow at the spillway of 0.2 m. Figure 9 shows that for these assumptions the

routing effect for a peak inflow of 191 m3/s (173 m3/s + 18 m3/s) is to reduce peak outflow at the

spillway to downstream to 174 m3/s, that is by about 9%.

** Flood Routing is used to determine the attenuation of the outflow hydrograph when a fraction of the

inflow hydrograph enters temporary storage above the crest level of the reservoir spillway.



Figure 9: Flood routing effect of reservoir upon outflow downstream from the spillway

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

200.0

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45

Flo

w (

m3 /

s)

Time (h)

Inflow/Outflow Hydrographs

Inflow Outflow

2.14. Water Balance

The sufficiency of water resource for irrigation is determined by water balance calculations for the

reservoir. The water demand is set by the cropping plan and the calculation is made for 10-day time

steps. When river flow and rainfall exceed the irrigation water requirement the reservoir fills; when

they don’t it empties. The water balance was studied to confirm the irrigation potential for average and

dry years.

2.14.1 Components of Water Balance

Water balance describes the flow of water in and out of a system allowing for losses and water uses

such as irrigation:

Flow in: includes rainfall and river flow.

Losses: includes evaporation, water seeping into the ground and water wasted

because of operational inefficiency.

Uses: includes irrigation and village water supply.

Flow out: includes drainage and flood flows.

Flood irrigation of rice is a very inefficient use of water. Only a small part of the water is directly used

by the crop, most is wasted as drainage, to infiltration and to evaporation. Allowance for low efficiency

is made in water balance calculations.



2.14.2 Irrigated Area

The irrigated area is the area of land to which water is delivered. Based on information from the

Tumnub Luok community, the area which can be irrigated by the canals and water gates constructed

under FDERP-AF is about 1,150 ha.

2.14.3 Cropping Calendar

The demand for irrigation depends on the cropping calendar which means the types of crop and when

they are planted. Based on the findings of the Subproject Profile and discussion at community level

on crops which may be grown with supplementary irrigation, it was determined that the principal crops

will be short, medium and long duration rice plus dry season rice. The different growth stages and

durations for these crops assumed for the water balance calculations are shown in Table 5.

Table 5: Cropping Calendar

Crop growth stage Short duration

rice (days)

Medium

duration rice

(days)

Late duration

rice (days)

Dry season rice

(days)

Land soaking 10 10 10 10

Land preparation and seedbed 20 20 20 20

Transplanting 30 40 50 30

Vegetative stage 30 40 50 30

Reproductive and ripening stage 30 40 60 30

Drainage before harvesting 40 40 50 20

Total 160 190 240 240

2.14.4 Water Resource

For planning purposes, the available water resource for the water balance calculations has been

based on the monthly totals and flows in Table 3 and Table 4, and rainfall records for Samroang.

2.14.5 Water Balance Calculation

Water balance has been considered for an average year and for a 1 in 5 year dry year.

The water balance calculations are based upon limited historical data with no possibility to consider

climate change. The river flows are estimated based on observed flows in the Stung Krasang at

Kralanh adjusted using the flood transposition method for the Luok catchment, and are very

approximate. Over the next few years it is hoped better information will be available from river flow

measurement stations such as Svay Chrum and the AWS at Samroang plus the expanding network of

measurement stations. Therefore, the water balance should be reassessed as and when better

information is made available by MOWRAM.

2.14.6 Water Passing Spillway

It is important to understand that the storage provided by the reservoir is very small compared to the

flow into the reservoir. When the reservoir is full the extra flow will pass over the spillway for use by

other farmers and irrigation systems downstream.



In an Average Year the reservoir storage is about 0.8% of the flow passing over the spillway;

and

in a Dry Year the reservoir storage is about 1.0% of the flow passing over the spillway.

2.14.7 Example Water Balances

Example water balances are shown at Figure 10 and Figure 11. The water balance calculation is

made for 10-days periods; therefore, each month is divided into three periods. The water quantity is in

millions of cubic metres (MCM). Figure 10 is for an average year rainfall and river flow, Figure 11 is

for a 1 in 5 year dry year rainfall and river flow. These water balances are for the cropping patterns

stated in Section 2.14.5.

The water balance depends on the mix of short, medium and late duration rice. The cropping areas

and varieties considered for the average year water balance example calculations are those informed

during group discussions for preparation of the Subproject Profile1. This is for a total wet season

cropping area of 1,150 ha. In an Average Year the reservoir can be expected to store water well

beyond the end of the wet season which should allow an increase in dry season cropping from the

previous 40 ha to about 200 ha.

In a dry year there may be no water until late July or early August and medium and late duration crops

could not be grown. Instead, farmers may start a short duration crop when there is sufficient water,

maybe from late July. There may also be sufficient water in the reservoir at the end of the wet season

for some dry season cropping, but in a Dry Year they will not be storing water until July or August.

These example water balance calculations indicate the following crop areas are possible.

Average Year: 575 ha short duration + 460 ha medium duration + 115 ha late duration +

200 ha dry season.

1 in 5 Dry Year: 1,150 ha short duration + 40 ha dry season.

The water balance calculations have not considered recession cropping within the reservoir which has

potential to further increase the cropping area.

2.15. Flood Management

An important component of the scope for FDERP-AF was to make recommendations for flood

management.

For Tumnub Luok the recommendations are set down in Table 6. The severity of flooding is assigned

a Signal Number from 1 through 5, the higher the number the greater the severity. The Signal Number

is determined by the reservoir status; basically, the water level in the reservoir. The prevailing

situation is also considered, e.g. heavy rain, flood warning issued or large flow in the river. The action

is defined for each signal level. If the action does not bring the flood under control and the situation

progresses to the next Signal Number, then the defined sequence of actions is followed.

1. Reservoir status: basically, the water level in the reservoir.

2. Prevailing situation: Heavy rainfall, flood warning in place or large flow in river.

3. Action to be taken: the action to control the flood, if the action fails to control the flood go to the

next higher Signal Number.

4. Follow-on actions when the flood emergency has ended.



Fig

ure

10:

Ave

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e ye

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bal

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Apr

Ma

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Jul

Aug

Sep

Oct

No

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Jan

Feb

Ma

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0.0

10

0.0

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0.6

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0.6

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0.9

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0.3

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0.5

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0.3

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-5.0

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Avera

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Fig

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11:

Dry

yea

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bal

ance

Apr

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Jul

Aug

Sep

Oct

No

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Jan

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0-0

.04

-0.0

6-0

.05

-0.0

6-0

.06

-0.0

30

.00

0.0

00

.00

0.0

00

.00

0.0

00

.00

0.0

00

.00

0.0

0

Inflow

fro

m C

atc

hm

ent

0.0

10

.02

0.0

30

.02

0.0

20

.04

0.0

50

.06

0.0

71

.03

0.8

81

.03

9.4

01

1.2

81

6.9

12

2.6

42

3.3

52

4.7

73

6.5

63

1.9

92

2.8

51

8.3

55

.51

3.6

70

.35

0.2

10

.14

0.0

40

.02

0.0

20

.02

0.0

20

.02

0.0

20

.02

0.0

2

Irrig

atio

n0

.047

0.0

45

0.0

00

0.0

00

0.0

00

0.0

00

0.0

00

0.0

00

0.0

00

0.0

00

0.0

00

0.0

00

1.4

54

3.2

01

0.9

75

0.8

38

0.4

25

1.9

05

1.2

11

1.4

84

0.9

79

1.5

78

1.4

28

1.3

30

1.4

25

1.3

29

1.2

23

0.0

61

0.0

64

0.0

72

0.0

71

0.1

03

0.0

88

0.0

69

0.0

71

0.0

76

-5.0

00

0.0

00

5.0

00

10.0

00

15.0

00

20.0

00

25.0

00

30.0

00

35.0

00

40.0

00

Volumes (MCM)

Dry

Year

Reserv

oir

Wate

r B

ala

nce



KEY PRINCIPLES FOR FLOOD MANAGEMENT

There are two key principles which must be followed for flood management: 1. All flood flows must be released at the spillway, the only intervention which may be required is

to remove debris for the crest of the spillway, if it is safe to do so. 2. The canal head regulators must never be used to release flood flow, and all canal head

regulator gates must be closed and locked during a large flood. This is to prevent serious damage to canals and fields from scour and erosion, the canals are not sized to convey flood flows nor is bank protection provided against flow flows.

Table 6: Procedure for Flood Management of Reservoir

Reservoir No.1 status Prevailing situation Action Follow-on action

SIGNAL NUMBER 1

Reservoir water level rising quickly to crest of spillway

Heavy rain FWUC on standby, record reservoir water level every hour or other interval as appropriate

Stand down when reservoir begins to fall

Reports of flood from communities upstream

Flood warning from PDWRAM

Spillway flowing but depth of water less than 0.1 m.

Large river flow into Reservoir

Check head regulators are at correct opening for the irrigation requirements

Normal irrigation releases

Check head regulators not being used for irrigation are closed and locked

SIGNAL NUMBER 2

Flow depth on spillway greater than 0.1 m


Continue to record reservoir water level

Go to Signal 1 when reservoir begins to fall

Clear debris from spillway crest but only if safe to do so


recheck and adjust head regulators are at correct opening for the irrigation requirements

Check head regulators not being used for irrigation are closed and locked

SIGNAL NUMBER 3

Flow depth on spillway is greater than 0.5 m





Close and lock all head regulator gate to protect against damage to canals and fields directly supplied.

SIGNAL NUMBER 4

Flow depth on spillway still rising greater than 0.75 m



Go to Signal 3 when reservoir begins to fall Irrigation releases all

stopped

Request support from PDWRAM

Mobilise FWUC emergency response work parties

SIGNAL NUMBER 5

Flow over spillway greater than 1.0 m

Dam will be overtopping Emergency response work parties work to minimise damage to dam.




3. Design and Operation

3.1. Scope of Design

The location and types of works designed and constructed under FDERP-AF are described here.

3.1.1 Stage 2 Civil Works

Stage 2 works were constructed under contract FDERP-AF-MOWRAM-CW04. The works were

completed by 26 May 2015. The works included:

repairs and raising the crest level of the embankment dam over a length 2,275 m including

Laterite pavement but excluding grass sodding;

temporary repairs to the existing spillway;

earthworks for rehabilitation of 5,007 m long main canal MC1 but grass sodding, Laterite of only

the first 500 m, and structures were not done until Stage 3; and

new head regulator for the main canal MC1.

3.1.2 Stage 3 Civil Works

Stage 3 works were constructed under contract FDERP-AF-MOWRAM-CW09. The works were

completed by 31 December 2016. The works included:

demolition of large Khmer Rouge water gate.

provision of a 150 m long spillway at the location of the existing spillway;

raising 1,075 m section of embankment dam at upper reservoir area by 1.0 m and paving with

Laterite;

rehabilitation of 1,025 m long main canal MC3 including a new head regulator;

cross-regulators, off-takes and oxcart bridges at locations along main canals MC1 and MC2.

grass sodding of embankment dam and canals; and

construction of a FWUC Building.

3.2. Objectives of the Design

The objectives of the design were to:

repair, widen and raise the crest level of Tumnub Luok Dam damaged during the 2013;

construct a new spillway to increase spillway capacity;

rehabilitate irrigation infrastructure to part of the command area; and

provide a FWUC Building.

3.3. Description of the System

3.3.1 System arrangement

The general arrangement of Tumnub Luok is show by Figure 12, and the system is illustrated

schematically by Figure 13.



Figure 12: Arrangement of Tumnub Luok Irrigation System



Figure 13: Schematic layout of Tumnub Luok Irrigation System

Luok Reservoir

(lower part)

54 108

49 98

3989

81 163

66 167

70 140

22 44

36 72

0+190

0+600

1+640

2+665

1+685

0+080

0+510

0+085

0+

000

MC1

MC1

MC3

Luok Reservoir

(upper part)

31 62

44 88

57 114

33 66

0+980

1+350 42 84

1+000

1+875 22 124

2+270 42 84

34 68

35 70

3+870

1+900

2+700

3+080

3+900

4+385

4+610

5+007

1+025

0+

120

0+

588

1+

413

2+

380

2+

775

PDWRAM Dam

5+

010

0+070 42 84

4 8

4+375

12 24

4+395



Legend

Dam FDERP-AF Canal

Off-take

12 ha irrigated 24 l/s peak demand

Head/cross regulator/drop/ terminal structure

Spillway

0+620 Station (Sta.) Oxcart bridge

Reservoir

FWUC Building

3.3.2 Supply Area

The irrigation system constructed under FDERP-AF comprises two main canals and one direct supply

head regulator designed to the supply the following areas and peak irrigation requirements:

Main canal MC1 718 ha with peak irrigation requirement of 1,436 l/s

Main canal MC3†† 58 ha with peak irrigation requirement of 116 l/s

Head regulator at station 0+588 m 31 ha with peak irrigation requirement of 62 l/s

Total 807 ha with peak irrigation requirement of 1,614 l/s

The community have informed that the total area of irrigated land is 1,150 ha which will include land

irrigated from watercourses and within and around the reservoir.

Main canal MC1 supplies land downstream of dam on the left bank of the river which is the major

portion of the supply area. Main canal MC3 supplies a much smaller area further from the river which

would otherwise be difficult to irrigate.

The head regulator at station 0+588 m discharges to the natural river channel downstream and can be

used to release water for environmental flow and to other irrigation systems downstream, about

3.0 m3/s when Tumnub Louk reservoir is at FSWL.

3.4. Embankment Dam

3.4.1 Condition prior to FDERP-AF Repairs

The embankment dam is approximately 2,775 m long. The dam has a crest width of 4.0 m and had

been used for vehicle access to the irrigation system and surrounding land but not as a road

connecting settlements. The level at the centreline varied between about 18.8 m and 19.9 m elevation

†† Main canal MC2 was downstream of the Khmer Rouge head regulator at station 0+131 m. This

head regulator was removed and the supply to MC2 cut but construction of the 150 m spillway. The

canal was vulnerable to flood damage and not viable.

12 24



(project datum) but was breached in eight places such that the dam could not impound water. The

existing spillway was a low-level vehicle crossing with a 15.0 m long crest section at 18.7 m elevation

which discharged toward the natural river channel downstream which was nearby.

3.4.2 Damage from 2013 Flood

After the 2013 flood, the eight main breach locations along the dam were about stations 0+200 m,

0+825 m, 1+050 m, 1+350 m, 1+580 m, 1+825 m, 2+150 m and 2+750 m. The largest breach was

about station 0+200 m and was around 200 m wide and 2 m deep. The other breaches were between

20 m and 100 m width and up to 1.5 m deep. It is also noted that the breaches about stations

0+200 m, 1+050 m and 2+150 m were places where the natural river channels flowed before the dam

was constructed.

3.4.3 FDERP-AF Repairs

The work done under FDERP-AF Stage 1 was limited to placing loose fill at some breaches to provide

access for motorbikes and light vehicles, no permanent repairs were made.

The dam was repaired under FDERP-AF Stage 2 as urgent works. As such, no geotechnical

investigation or design was done. The site was surveyed and plan, profile and cross sections

prepared. The embankment was repaired with suitable fill material selected and placed in compliance

with a MOWRAM Specification. The crest of the dam was raised to 20.5 m elevation keeping the

original crest width of 4.0 m. The crest was paved with 150 mm thickness of Laterite for vehicle

access. The slopes were reconstructed at 1V:2H on the upstream and downstream sides. Slope

protection by grass sodding was not done until Stage 3 because of the limited Stage 2 budget. Under

Stage 2 limited work was done on the existing spillway comprising repairs to cracked concrete and to

badly eroded earthworks.

3.4.4 Flood damage in 2015

The replacement spillway was not constructed until 2016 which meant that flood protection for the

Stage 2 repairs to the dam completed by May 2015 for flood protection had to rely on the existing

inadequate spillway, the existing Khmer Rouge water gate, and the exiting 1.0 m diameter twin pipe

head regulator at station 0+588 m.

Flood during September 2015

On 16 September 2015 there was a large flash flood caused by heavy rainfall in the catchment. The

reservoir water level rose rapidly until it came close to overtopping the dam. The existing spillway and

water gates were insufficient to pass the flood flow downstream. To protect the dam PDRWAM made

breaches at three places: one besides the existing spillway at about station 0+080 m, and two more at

stations 1+050 m and 2+150 m, basically locations where the dam had blocked natural river channels.

The Consultant went to the site to assess the damage and the circumstances of the incident. Apart

from the obvious conclusion that the problems had occurred because the dam had been repaired

before an adequate spillway was constructed there was seen to be a more fundamental problem

which had not been fully addressed by the design.

The problem is a consequence of the piecemeal extension of the 1954 dam which was never intended

to capture flow from the main river, refer to Figure 1. In 1954 the 150 m long dam held water within a

natural swampy area of river flood plain. The extension during the Sangkum Reasniyum period

probably captured water flowing down the stream from the north. The Khmer Rouge extension

captured water flowing from the main river which rises at O Smach on the Dangrek Escarpment. But



this means that the dam runs up the river valley instead of across it. It also means that the east end of

the dam is several metres lower with respect to the surrounding land than the west end of the dam and

a level dam crest cannot provide freeboard for floodwaters flowing into the reservoir almost 2.0 km

further east.

Figure 1 also shows that the spillway location is far from the locations where the dam blocks the two

rivers. The dam must therefore divert flood flows through the reservoir to the spillway location. As has

been mentioned, the locations where the rivers are dammed are two of the locations where the dam

was deliberately breached by PDWRAM during the 16 September 2015 flood.

Figure 14: Morphology of Tumnub Louk Reservoir

Source of base image: Google Earth

PDWRAM Dam

Very significant is what shall be referred to as the PDWRAM dam constructed with community

participation in 2012. The purpose of the PDWRAM dam is to block the main river channel within the

reservoir to hold back water on the rice fields in the upper reservoir area. But this has the undesirable

consequence of raising water level against the eastern section of dam which already had little

freeboard. On 22 September 2015, it was observed that there was about 1.5 m difference in water

level upstream and downstream of the PDWRAM dam. Therefore, when the reservoir is filling and

during the early stages of a flood there are two discrete zones in the reservoir: the upper area

upstream of the PDWRAM dam, and the lower area between the PDWRAM dam and the spillway.

The upper area needs to fill sufficiently first before water flows to the lower area. As more water flows

into the reservoir the two areas merge and will become a single body of water with a level pond.

Flood Discharge

The flood discharges have been estimated as discussed at Section 2.9. The mean annual flood is

estimated to be about 66 m3/s and the design flood about 173 m3/s. The replacement spillway is

designed for peak flood discharge within this range.



Options for Solutions

For a main dam crest level of 20.5 m elevation the PDWRAM dam would have caused flood damage

during even small floods as occurred September 2015, almost certainly on an annual basis. The

construction of the permanent reservoir spillway would not have removed this risk. On the other hand,

the PDWRAM dam is effective in creating an upper rice terrace about 100 ha in area within the

reservoir. The requirements of the farmers meant that it was untenable to remove the PDWRAM dam.

It was not possible to move or add additional spillways where the main dam crosses the natural river

channels because these would release uncontrolled flow across the developed irrigated area and

most certainly wash away main canal MC1 reconstructed under FDERP-AF Stage 2. It is also still

necessary to pass the MAF and design flood.

The PDWRAM dam effectively blocks 200 m of a 400 m wide water path which about the width of the

river valley up to the 50 m contour (national datum) on the north side. It is necessary to allow flood

flows past this obstruction into the main reservoir. Various solutions were considered but first a

topographical survey was made of the PDWRAM dam and across the valley extending to higher

ground to the north. It was found that there were natural drainage channels and flow paths around the

northern flank of the PDWRAM dam which would flow when water rose behind it. In fact, this was

seen to be the case during a flood observed on 14 July 2016.

The chosen solution was to raise the crest of the eastern most 1,075 m of the dam by 1 m. The

objective is to contain the flood water in the upper reservoir area with a greater freeboard. In time for

the 2016 flood season, the new spillway and the raising of the main dam were nearing completion and

the works survived three significant floods which has provided some confidence in the chosen

solution. One of these floods caused damage to the PDWRAM. It was repaired during late 2016 but

because of its construction and location it remains vulnerable and can be expected to suffer more

damage in the future. Dealing with this issue was outside the scope and not covered by FDERP-AF

funding.

3.5. Replacement Spillway and Stilling Basin

As is described at Section 2.10.2, the replacement spillway has a crest level of 19.2 m which is 0.5 m

higher than the original which was at 18.7 m elevation. The crest length is 150 m, and has a width of

6 m to provide a low-level vehicle crossing. As already explained a crest length of 150 m was chosen

to maximise freeboard during a flood. A Type 1 USBR stilling basin constructed of gabions has been

provided to protect the structure from undermining by scour from downstream.

3.6. Head regulators

As mentioned at Section 1.4.4, the existing Khmer Rouge head regulator for main canal MC2 at

station 0+131 m along the dam, although originally to remain, had to be removed to accommodate the

new 150 m spillway.

The other existing head regulator at station 0+588 m along the dam has been retained. It comprises

twin 1.0 m diameter pipe culverts and each fitter with a vertical lift gate. There is no canal associated

with this head regulator but it supplies the land next to the dam and north of the natural river channel,

the latter which isolates this land from supply from main canal MC1. It also discharges to the natural

river channel downstream and can be used to release water for environmental flow and to other

irrigation systems downstream.



New head regulators were constructed for main canals MC1 and MC3. The head regulator for main

canal MC1 is at station 1+413 m along the dam. It comprises two 0.75 m clear opening vertical lift

gates. The gates are installed on an open channel and therefore will allow water into the canal by weir

flow if the reservoir water level is higher than the tops of the gates, even if the gates are closed.

The head regulator for main canal MC3 is at station 2+380 m along the dam. It comprises a single

1.50 m x 1.50 m clear opening vertical lift gates. The gate discharges to a box culvert and therefore

will not allow water into the canal when the gate is closed.

The details of these head regulators are summarised in Table 7. The hydraulic properties and

performance are discussed at Section 3.8.2.

Table 7: Details of head regulators

Gate Supply

area Demand

Number of gates

Diameter /height

Width FSL Invert Supplying Down-stream invert

ha l/s m m m elv m elv

0+588 31 62 1 1.0 - 19.200 17.350 Directly to fields

16.100

1+413 718 1,436 2 2.0 0.75 19.200 17.000 MC1 17.000

2+380 58 116 1 1.5 1.5 19.200 18.260 MC2 17.000

It should be noted from Table 7 that for the head regulator at station 1+413 m the top of the gate is

0.2 m lower than the reservoir FSWL. This is because the gates were install during Stage 2 and

designed for a reservoir FSWL 18.7 m elevation but shortly after award of the Stage 3 construction

contract the FSWL was changed to 19.2 m elevation (Section 2.10.1). The gates were not modified

for this design change. Therefore, when water is at 19.2 m elevation in the reservoir it will flow into

main canal MC1 by weir flow over the closed gates at the rate 0.24 m3/s for the two gates combined.

3.7. FDERP-AF Canals

3.7.1 Canals rehabilitated

Main canal MC1 and MC3 rehabilitated under FDERP-AF are both former Khmer Rouge canals. This

meant that both canals had established rights of way. There were no issues with land ownership and

resettlement. No voluntary resettlement was required.

3.7.2 Earthen Canals

Main canals MC1 and MC3 are unlined earthen canals constructed with a trapezoidal cross-section.

Earthen canals will not keep a trapezoidal cross-section, over time the transport of sediment by the

flowing water and the effect of erosion of the bed and banks will tend to change the canals to an

elliptical cross section9. This is the normal physical process and is not an indication of mistakes in

design or construction. Earthen canals work best for a constant steady flow. Erosion and damage

occurs more quickly if the flow is varied or the canals are not flowing or dry for periods of the year, as

will be the case at Tumnub Luok Irrigation System. Maintenance does not require canals to be kept

trapezoidal but bank failures should be repaired and sediment removed if this is reducing the flow

capacity. The alternative would be concrete lined canals which would have smaller cross-section, but

these are much more expensive to construct and therefore could not be provided from the limited

FDERP-AF funding.



3.7.3 Main Canal MC1

Main canal MC1 is a trapezoidal cross-section unlined earthen channel 5,007 m in length. The

hydraulic design is summarised in Table 9 and hydraulic calculations are at Appendix 3. The first

sections of canal have a compound section with 3.0 m wide berms on both sides up to about station

0+800 m, then a 3.0 m wide berm on the right bank only until about station 1+200 m, and then a single

trapezoidal section until the end of the canal. The final 612 m of the canal has no irrigation off-takes

and is basically a drainage channel alongside the right bank access road within a village, under Stage

2 only minimal excavation was done for this section of canal. The bed width is 2.0 m throughout. The

operational water depth for design is 1.50 m which gives a freeboard of 0.44 m. The maximum

capacity of the canal without berms at the point the banks will overtop is 5.7 m3/s, therefore the flow

released by the head regulator must not exceed 5.70 m3/s (the maximum discharge capacity of the

cross regulators with both gates open and the canal flowing full is only 6.90 m3/s, also see Table 12).

Table 8: Hydraulic design parameters for Main Canal MC1

Station Design flow

Design Velocity

Bed width

Depth of flow

Gradient Side

slopes Freeboard

From To

(m) (m) (m3/s) (m/s) (m) (m) % V:H m

0+000 5+007 1.40 0.43 1.50 1.50 0.033 1:1.5 0.44

There are embankments down both sides of the canal. There is an access road down the right side

with an embankment width of 4.00 m which is paved with 150 mm thickness of Laterite with a 3%

camber from the crown. The left embankment has 2.00 m crest width; it is not paved and the

earthworks are finished with a with a 3% camber from the crown. There is no left embankment over

the final 612 m final 650 m of within the village area.

Main canal MC1 is supplied the new double gate head regulator at station 1+413 m along the dam.

There are numerous structures, details of the structures along the canal are given in Table 9. There is

no tail structure at the end of the canal because it flows into an existing drain.

Table 9: Structures along Main Canal MC1

Station Type of

structure Supplying

Number of gates/spans

Diameter/ height

Width Invert

(m) (m) (m) (m) (m elv)

0+190 Off-take Left bank 1 0.80 16.974

0+190 Off-take Right bank 1 1.00 16.974

0+600 Off-take Right bank 1 1.00 - 16.821

0+980 Off-take Left bank 1 0.80 - 16.696


1+000 Check Canal 2 1.50 0.75 16.690




1+685 Bridge Type A Canal 1 1.80 1.50 16.464


1+900 Check Canal 2 1.50 0.75 16.392



Station Type of

structure Supplying


Diameter/ height

Width Invert

(m) (m) (m) (m) (m elv)




2+700 Check Canal 2 1.50 0.75 15.980

3+080 Bridge Type A Canal 1 1.80 1.50 15.857



3+900 Check Canal 2 1.50 0.75 15.584


4+385 Bridge Type B Canal 1 1.80 1.50 14.812


4+610 Bridge Type B Canal 1 1.80 1.50 14.621

5+010 Bridge Type B Outfall canal 1 1.80 1.50 14.552

3.7.4 Main Canal MC3

Main canal MC3 is a trapezoidal cross-section unlined earthen channel 1,025 m in length. The

hydraulic design is summarised in Table 10 and hydraulic calculations are at Appendix 3. The

maximum operation depth of flow is 1.00 m which gives a freeboard of 0.40 m. The maximum

capacity of the canal at the point the banks will overtop is 2.40 m3/s but the maximum discharge

capacity of the drop structure at station 0+510 is 1.30 m3/s, therefore the flow released by the head

regulator must not exceed 1.30 m3/s (see Table 12).

Table 10: Hydraulic design parameters for Main Canal MC2

Station Design flow

Design Velocity

Bed width

Depth of flow

Gradient Side

slopes Freeboard

From To

(m) (m) (m3/s) (m/s) (m) (m) % V:H m

0+000 1+025 0.12 0.212 1.50 1.00 0.03 1:1.5 0.40

There are embankments down both sides of the canal. There is an access road down the right side

with an embankment width of 4.00 m which is paved with 150 mm thickness of Laterite with a 3%

camber from the crown. The left embankment has 3.00 m crest width; and is paved with Laterite for

the first 85 m.

Main canal MC1 is supplied by new single gate head regulator at station 2+380 m along the dam.

There are several structures, details of the structures along the canal are given in Table 11.



Table 11: Structures along Main Canal MC3

Station Type of

structure Supplying


Diameter/ height

Width Invert

(m) (m) (m) (m) (m elv)



0+085 Drop structure Canal 1 1.40 1.50 16.975/16.675


0+980 Terminal Canal 2 (Stoplogs) 1.0 0.60 16.390

3.8. Water Distribution

3.8.1 Water Distribution Principles

The head regulators and canals can be operated independently whenever there is sufficient water

stored to flow to the canals and fields by gravity or to farmer pumps for distribution to fields.

Tumnub Luok is for flood spreading for supplementary irrigation. The system which has been built is

not suitable for division into blocks and a rigid schedule of rotation of water to each block.

The operational rules are therefore designed:

so that farmers can distribute water to their fields when they have a need for supplementary

irrigation;

to keep the reservoir at full supply level for as long a period as possible and for as long into

the dry season as possible; and

therefore, to stop water distribution by closing head regulator gates when there is no

requirement for irrigation downstream.

Given the large percentage of the river flow passing through the reservoir over the spillway, the

reservoir is expected to remain full through the main wet season but early and late wet season the

gates should be closed promptly to keep the maximum stored water.

3.8.2 Head Regulators

The head regulators are opened to let water flow into the main canals, or, in the case of no canal,

directly to the fields when farmers need water. The FWUC will learn the best gate openings to meet

the farmer requirements by operating the system. However, it is important the gates are opened with

caution and not in a way that will cause erosion of canal beds and banks.

The flow at each head regulator will:

increase the more the gate is open; and

decrease as water level falls in the reservoir.

The flows have been calculated and for convenience are shown for each head regulator by Figure 15

to Figure 17. However, reading off the flows from these figures requires basic mathematical

knowledge. Therefore, Table 12 has been prepared to show how much each head regulator must be

opened to: (1) supply the peak irrigation demand (2 l/s/ha); and (2) the maximum the gate may be



opened without risking damage to the canal and land downstream (e.g. during a flood). Table 12 is for

the reservoirs full, the gate opening can be increased if the reservoir is less than full.

Table 12: Gate openings for peak irrigation demand

Head regulator

Peak irrigation demand Maximum gate opening

Peak demand Gate opening

l/s m m Remarks

0+588 62 0.10 1.00 For d/s requirements

1+413 1,436 0.51 (one gate) 0.70 Using two gates

2+380 116 0.02 0.32 MC3

Figure 15: Operating curves for head regulator at 0+588 (direct to fields)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

Gate

op

en

ing

metr

es

Flow litres per second

Head Regulator MC3 at Station 2+380

Reservoir at crest of dam

Reservoir at full supply level

Reservoir level with top of culvert

Reservoir 0.2m above invert of culvert



Figure 16: Operating curves for head regulator at 1+413 (MC1)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Gate

op

en

ing

(m

)

Discharge (m3/s)

Head Regulator MC1 using one gate only

Upstream water depth 3.50m




0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Gate

op

en

ing

(m

)

Discharge (m3/s)

Head Regulator MC1 using two gates







Figure 17: Operating curves for head regulator at 2+380 (MC3)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

Gate

op

en

ing

metr

es







3.8.3 Cross Regulator MC2

The four cross regulators on main canal MC1 are used to pond of water to flow to the turnouts. The

hydraulic performance is the same for all four cross regulators and flows have been calculated and for

convenience are shown by Figure 18.



Figure 18: Operating curves for cross regulators on main canal MC1

0.00

0.25

0.50

0.75

1.00

1.25

1.50

Gate

op

en

ing

(m

)

Discharge (m3/s)

Cross Regulators MC1 using one gate only





0.00

0.25

0.50

0.75

1.00

1.25

1.50

Gate

op

en

ing

(m

)

Discharge (m3/s)

Cross Regulators MC1 using two gates







4. As-Built Drawing List

4.1. Stage 2 As-Built Drawing List

Drawing List. Stage 2: Contract package FDERP-AF-MOWRAM-CW04 Part A

Drawing Title Drawing No.

ABBREVIATION OF TUMNUB LUOK -

LAYOUT MAP TUMNUB LUOK -

PLAN AND PROFILE OF RESERVOIR DAM CH.0+000 - CH.2+775 TL-PP-001

PLAN AND PROFILE OF MAIN CANAL CH.0+000 - CH.3+000 TL-PP-002

PLAN AND PROFILE OF MAIN CANAL CH.3+000 - CH.5+007 TL-PP-003

CROSS SECTION OF RESERVOIR DAM CH.0+000 TO CH.0+200 TL-CS-001














CROSS SECTION OF MAIN CANAL MC CH.0+000 TO CH.0+300 TL-CS-015

















TYPICAL GRASS SODDING ON SIDE SLOPE OF RESERVOIR DAM TL-CS-028

TYICAL CROSS SECTION OF ACCESS ROAD CONNECTED FROM NR.68 TL-CS-029

PLAN VIEW OF HEAD REGULATOR ON MC STA.0+000 TL-HR-001

SECTION VIEW OF HEAD REGULATOR ON MC STA.0+000 TL-HR-002

REINFORCING BAR ARRANGEMENT OF HEAD REGULATOR ON MC TL-HR-003

GATE PLAN SECTION & DETAIL OF HEAD REGULATOR ON MC TL-HR-004

PLAN VIEW FOR REPAIRING THE SPILLWAY STRUCTURE TL-SP-01

REPAIR CROSS SECTION OF THE SPILLWAY STRUCTURE TL-SP-02



4.2. Stage 3 As-Built Drawing List



LOCATION MAP OF FLOOD DAMAGE EMERGENCY RECONSTRUCTION PROJECT-ADDITIONAL FINANCING -

ABBREVIATION AND SYMBOL -

LAYOUT MAP OF TUMNUB LUOK IRRIGATION SYSTEM SUBPROJECT -

LAYOUT OF TUMNUB LUOK IRRIGATION SYSTEM SUBPROJECT -

DRAINAGE FLOW DIAGRAM FOR TUMNUB LUOK -

A. EARTHWORKS

PLAN AND PROFILE OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-PP-001

CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-001














PLAN AND PROFILE OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-PP-001

PLAN AND PROFILE OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-PP-002

CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-001

















PLAN AND PROFILE OF MAIN CANAL MC3 MC3-PP-001

CROSS SECTION OF MAIN CANAL MC3 MC3-CS-001



PLAN VIEW AND PROFILE OF RAISING THE EMBANKMENT DAM 1M FOR THE RESERVOIR DAM DAM-PP-001

PLAN VIEW AND PROFILE OF RAISING THE EMBANKMENT DAM 1M FOR THE RESERVOIR DAM DAM-PP-002

CROSS SECTION OF RAISING THE EMBANKMENT DAM 1M DAM-CS-001







B. STRUCTURES

PLAN VIEW OF NEW SPILLWAY (BROAD CREST WEIR) ON RESERVOIR DAM RD-SW-001

FRONT VIEW OF NEW SPILLWAY (BROAD CREST WEIR) ON RESERVOIR DAM RD-SW-002

REINFORCEMENT BAR ARRANGEMENT OF NEW SPILLWAY (BROAD CREST WEIR) ON RESERVOIR DAM RD-SW-003

PLAN VIEW OF NEW HEAD REGULATOR AT STA.2+380 RD-HR-001

SECTION AND DETAIL OF NEW HEAD REGULATOR AT STA. 2+380 RD-HR-002

REINFORCING BAR OF NEW HEAD REGULATOR AT STA. 2+380 RD-HR-003

GATE PLAN SECTION AND DETAIL OF NEW HEAD REGULATOR AT STA. 2+380 RD-HR-004

GATE HANDLE GEAR DETAIL OF NEW HEAD REGULATOR AT STA. 2+380 RD-HR-005

LADDER OF NEW HEAD REGULATOR AT STA. 2+380 RD-HR-006

PLAN VIEW AND SECTION OF GATE INSTALLATION FOR PIPE CULVERT (DIA. 600mm) ON MAIN CANAL MC1

MC1-GI-001

GATE PLAN, SECTION AND DETAIL OF GATE INSTALLATION FOR PIPE CULVERT (DIA. 600mm) ON MAIN CANAL MC1

MC1-GI-002

GATE HANDLE GEAR DETAIL OF GATE INSTALLATION FOR PIPE CULVERT (DIA. 600mm) ON MAIN CANAL MC1

MC1-GI-003


MC1-GI-004






MC1-GI-005


MC1-GI-006


MC1-GI-007


MC1-GI-008


MC1-GI-009

PLAN VIEW OF OFF-TAKE (DIA 800mm) ON MAIN CANAL MC1, MC3 MC-OT-OO1

SECTION AND DETAIL OF OFF-TAKE (DIA 800mm) ON MAIN CANAL MC1, MC3 MC-OT-OO2

REINFORCING BAR OF OFF-TAKE (DIA 800mm) ON MAIN CANAL MC1, MC3 MC-OT-OO3

GATE DETAIL OF OFF-TAKE (DIA 800mm) ON MAIN CANAL MC1, MC3 MC-OT-OO4

GATE HANDLE GEAR DETAIL OF OFF-TAKE (DIA 800mm) ON MAIN CANAL MC1, MC3 MC-OT-OO5

PLAN VIEW, SECTION, DETAIL AND REINFORCING BAR OF OXCART BRIDGE TYPE A MC-OX-001

PLAN VIEW, SECTION, DETAIL AND REINFORCING BAR OF OXCART BRIDGE TYPE B MC-OX-001

PLAN VIEW AND SECTION OF DROP STRUCTURE (DP) ON MAIN CANAL MC3 STA.0+530 MC3-DP-001

REINFORCING BAR OF DROP STRUCTURE (DP) ON MAIN CANAL MC3 STA.0+530 MC3-DP-002

PLAN VIEW AND SECTION OF TERMINAL STRUCTURE (TS) ON MAIN CANAL MC3 STA.1+000 MC3-TS-001

REINFORCING BAR OF TERMINAL STRUCTURE (TS) ON MAIN CANAL MC3 STA.1+000 MC3-TS-002

PLAN VIEW, SECTION AND DETAIL OF CHECK STRUCTURE O MAIN CANAL MC1 MC1-CK-001

REINFORCING BAR OF CHECK STRUCTURE O MAIN CANAL MC1 MC1-CK-002

GATE PLAN, SECTION AND DETAIL OF CHECK STRUCTURE O MAIN CANAL MC1 MC1-CK-003

C. SIGNBOARD

PLAN VIEW OF SIGNBOARD TL-SB-001

REINFORCING BAR ARRANGEMENT OF SIGNBOARD TL-SB-002

D. FWUC BUILDING

PLAN VIEW OF FARMER WATER USER COMMUNITY BUILDING (FWUC BUILDING) TL-FWUC-001

SECTION AND DETAIL OF FARMER WATER USER COMMUNITY BUILDING (FWUC BUILDING) TL-FWUC-002

REINFORCING BAR ARRANGEMENT AND DETAIL OF FARMER WATER USER COMMUNITY BUILDING

(FWUC BUILDING)

TL-FWUC-003



Appendix 1: Hydrological Methods

Peak Discharge Estimates

Modified IRS Method

The Modified Irrigation Rehabilitation Study (IRS) Method is a refinement of the original IRS Method 7 8

based on regional flood frequency analysis for Cambodian catchments. The mean annual flood (MAF)

is estimated from the following equation:

9.03981.0 AREAMAF

Where MAF = mean Annual Flood (i.e. the maximum flood expected in an average

year)

AREA = catchment area (km2)

The growth factors for the 1 in 50 and 100 years’ floods are 2.0 and 2.2 respectively.

Applied for Tumnub Luok catchment area of 127 km2 the Modified IRS method yields a MAF of the

order 190 m3/s:

smMAF /662913981.0 39.0

And the 1 in 50 and 100 years’ floods are respectively:

smMAF /1316622 3

smMAF /145312.22.2 3

Assuming an additional 20% for climate change in the future the Q100 might increase to 173 m3/s.

However, the Modified IRS Method is limited to catchments at elevations below 100 m, basically

catchments which are large low-lying plains. The Dangrek escarpment locally rises to 269 m and the

catchment slope is steep in the upper part. This could cause larger peak discharges than predicted by

the Modified IRS Method.

Direct Estimate of MAF: Regime Theory

It is clearly stated for the IRS Method that for detailed design for a particular site it will generally be

possible to make an estimate of MAF from local records or memories of flood water levels and the

application of hydraulic principles. Hydraulic principles can be applied using the slope-area method

and Regime Theory to estimate the in-bank discharge of the existing river channel. Under Regime

Theory this provides an indication of the MAF.

Regime Theory was developed in the 19th Century for the design of earthen irrigation canals in India.

It is an empirical method based on the hypothesis that for a steady discharge a channel has an

equilibrium elliptical cross section depending on the channel slope and the soils forming the bed and

bank. There are a number of empirical equations used to estimate the width of a channel between top

of bank, the depth from top of bank to the deepest point, the cross-section flow area when flowing full,

and the bed slope. Although rivers are subject to very variable discharge it has been found that the

width and depth of channels are generally those for the dominant discharge which is normally similar

to the MAF. This is reasonable because in nature a river forms a channel to accommodate normal



seasonal flows and will only flood out of bank when there are abnormally large flows or some external

interference such as a too small bridge. Hence the width of a channel between top of banks, and the

depth, can be used to estimate the MAF.

River channels in the Cambodian lowlands are generally formed in small to fine grained sandy and

silty soils. The Lacey equations9 are most appropriate for these soils. The Lacey equation are:

5.08.4 QB

3/1

3/1473.0

f

Qy

3/1

6/5

28.2f

QAR

6/1

3/5

3170Q

fSR

Where B = regime channel width (m)

Q = equivalent steady flow which would generate the same channel

geometry (m3/s)

Y = mean regime depth of flow (m)

F = A silt factor for which recommended values are given in Table 13.

AR = cross sectional area of regime channel (m2)

SR = regime gradient to which the channel can expect to adjust when

regime conditions are achieved

Table 13: Silt factor f for Lacey Equations

Material Mean grain size (mm) Silt factor (f)

Silt

very fine 0.081 0.50

fine 0.120 0.60

medium 0.233 0.85

standard 0.323 1.00

Sand

medium 0.505 1.25

coarse 0.725 1.50

The river channel at Tumnub Louk is braded and meandering. In places, there is a top of bank width

about 18 m. This width would suggest a MAF of the order 49 m3/s and applying the IRS growth

factors the Q50 is 98 m3/s and Q100 is 107 m3/s. Assuming an additional 20% for climate change in the

future the Q100 might increase to 129 m3/s.



Flood Transposition

The hypothesis is that the discharge in an ungauged catchment can be estimated from the discharge

in an adjacent gauged catchment proportional to the ratio of the catchment areas raised to a power

0.5 to 0.8 depending on the relative catchment areas. This is done by application of the following

formula.

n

A

AQQ

2

121

Where Q = mean Annual Flood (i.e. the maximum flood expected in an average

year)

A = catchment area (km2)

n = a constant

1 and 2 = 1 and 2 refer to the catchment being estimated and the catchment

with records respectively

Values of n of 0.5 to 0.8 have been suggested by various researchers with 0.8 applying to small

catchments (up to 100 km2) and 0.5 for large catchments (over 1,000 km2). The ratio of areas should

not exceed 2.

For Tumnub Louk there is only one gauged catchments of similar size and with characteristic

mountainous headwaters. The Prasat Keo catchment area is 178 km2 so the ratio of the areas is 1:1.4

and well with the limit of 2. The calculation was using a value n = 0.75.

smQQ asatKeoMAFasatKeoMAF /84178

291 3

75.0

PrPr

The calculation estimates the MAF to be 84 m3/s. Applying the IRS growth factors the Q50 is 168 m3/s

and Q100 is 184 m3/s. Assuming an additional 20% for climate change in the future the Q100 might

increase to 221 m3/s.

Generalised Tropical Flood Model

A further check was applied using the Generalised Tropical Flood Model (GTFM). This is a rainfall-

runoff model which has been used extensively in Cambodia. It takes account of catchment

characteristics including slopes, soil and land use and of rainfall intensity-duration-frequency.

The GTFM is expressed by the formula:

B

AR

T

ARFFAPCQ

360

Where QR = peak flow of return period R years (m3/s).

R = return period (years).

CA = is the runoff coefficient (%).

P = is the design storm rainfall (i.e. total rainfall in mm not intensity in

mm/h) of hydrograph base time (TB hours).



A = is the catchment area in km2.

F = is the peak flow factor to convert the average flow generated by the

model to peak flow.

ARF = is the area reduction factor.

TB = is the hydrograph base time (hours).

The values of the parameters required for the GTFM have been taken from the recommendations

contained in Watkins and Fiddes10. The values chosen can be seen in the GTFM Worksheet at

Appendix 2and are further described below.

The runoff coefficient CA is express by the formula:

LWSA CCCC

Where CS = is the standard value of contributing runoff coefficient (PRO),

dependant on Soil Class I and Slope Class S.

CW = is the catchment wetness factor which is dependent on soil moisture

recharge (SMR). Because Cambodia is within a wet zone (SMR >

75 mm) the value adopted should always be 1.0.

CL = is the land use factor.

It should be noted that the percentage runoff coefficient in the GTFM is different to that in the

(commonly used) Rational Method. This is because GTFM takes separate account of factors included

in the Rational Method runoff coefficient.

The contributing runoff coefficient PRO for humid zone catchments such as Cambodia is calculated

from the formula:

SIPRO 81253

Where PRO = is the contributing runoff coefficient (%).

I = is the Soil Class.

S = is the Slope Class.

Soil Classes are listed in Table 14. Because of the large area of flooded rice paddy during the peak

flood season which equates to poorly drained soils, a Soil Class of 2.5 has be assumed for design:

Table 14: Soil Class I

Soil Class I Description

1 Impermeable – rock surface

2 Very low permeability. Clay soils with high swelling potential, shallow soils over largely

impermeable layer, very high water table.

3 Low permeability. Drainage slightly impede when soil fully wetted.

4 Fairly permeable. Deep soils of relatively high infiltration rate even when wetted.

5 Very permeable. Soils with high infiltration rates such as sands, gravels and aggregated clays.



It has been found that for the flat or very gently sloping catchments characteristic of Cambodia using

the tabulated Slope Class S in reference 10 are too coarse tending to overestimate flow. The flow

estimate is very sensitive to the slope class because it not only affects the runoff coefficient CA but

also the base time TB. It was found that presenting the slope classification in graphical form (Figure

19) and using fractional slope classes to remove the abrupt change between bands significantly

improved estimates predicting flows generally consistent with field observations.

Figure 19: Slope Class S

0123456789

101112131415161718192021222324252627

1 2 3 4 5 6

Slope Class (S)

Avera

ge c

atc

hm

en

t slo

pe (

%)

A high SMR (> 75 mm) and wet zone can be assumed for Cambodia because design is for large

rainfalls that occur in the wetter months.

Land use factors CL are listed in Table 15. For Tumnub Luok the mix of cultivation, grass cover,

scrub and degraded woodland indicate an aggregate CL of 1.25 is most appropriate.

Table 15: Land use factor CL

Catchment type CL

Semi arid zone 1.00

Urban 1.50

Largely bare soil (humid zone) 1.50

Intensive cultivation 1.50



Grass cover 1.00

Dense vegetation (particularly in valleys) 0.50

Forest

(a) shallow impermeable soils 1.00

(b) very steep (S5, S6) permeable soils 0.67

(c) other 0.33

The design rainfall P is the total rainfall with the same duration of the hydrograph base time TB. It can

be determined from the rainfall-intensity-duration curves, in the case of Tumnub Luok the curves at

Figure 6 were used.

The hydrograph base time TB can be thought of as being made up of three components: the storm

duration, the time taken for the surface runoff to drain into the stream system; and the flow time down

to the culvert or bridge site. Base time TB is expressed by the formula:

SB TS

ACT

2

5.0

Where C = a constant, which is 30 for humid zone catchments such as

Cambodia.

A = the catchment area (km2).

S = the Slope Class S.

TS = the surface cover flow time.

The recommended peak flow factor F in a humid zone such as Cambodia is 2.5.

The area reduction factor ARF is introduced to account for the spatial variability of point rainfall over

the catchment. In simple terms, the average rainfall intensity at any instant for a catchment will be

less than the rainfall measured at a single point (rain gauge) in the catchment, and the difference

increases with increasing size of catchment. Therefore, this is not significant for small catchments but

becomes so as catchment size increases. The relationship adopted for ARF is suitable for the

convective rainfall‡‡ that occurs in Cambodia:

50.033.004.01 ATARF

Where T = Is duration in hours.

A = the catchment area in km2.

This equation applies for storms of up to 8 hours’ duration. For longer durations on large catchments

the value calculated for T = 8 hours should be used.

‡‡ Convective rainfall occurs where there is low pressure and air movement is mostly vertical.

Evaporation is high early in the day and moisture is carried high by vertical currents and precipitated in

the afternoon.



Baseflow is the normal river flow prior to a flood and therefore must be added to the peak flood flow to

determine the total peak flow. In Cambodia, most watercourses are ephemeral (seasonally dry), and

perennial streams have small dry season flow. Design flows will however occur in the rainy season

when base-flow may be more significant. Even then, flows will be flashy§§ and high discharges are not

sustained over long periods. For design purposes, it is a reasonable assumption that large floods will

occur during the wettest months of September and October. Therefore, baseflow can be assumed to

be the monthly average flow for either of these months, whichever is the greater, for Tumnub Louk the

highest average flow is during October at 18 m3/s, which is therefore assumed as the baseflow.

The GTFM estimates are MAF 55 m3/s, Q50 109 m3/s and Q100 120 m3/s. These take no account of

climate change so the Q100 might increase to peak discharge to 144 m3/s.

§§ ‘Flashy’ means that flow increases in size very quickly and also stops very quickly.



Appendix 2: Hydrological Calculations

Peak Discharge Estimates

Structure Station Catchment Stream 85% 10% Effective Return Peak

Area Length Elevation Elevation Elevation Period Discharge

Difference

A L H 85 H 10 H 85 - H 10 T Q

(km2) 130.0 (m) (years) (m

3/s)

Tumnub Luok NA 291.0 29,000 100 50 50 2.33 66

Tumnub Luok NA 291.0 29,000 100 50 50 50 131

Tumnub Luok NA 291.0 29,000 100 50 50 100 145

173Design Q100 = 20%

Modified IRS Method

Channel dimensions based on GTFM Estimates Flow estimates based on actual channel dimensions

Structure Regime Regime Regime Regime SR% Actual Actual Actual Estimate Estimate GTFM

0 Width Depth Area Gradient Width Depth Area Regime 100 yr flood 100 yr flood

0 B y A R S R S R % Flow Q 100 Q 100

(m) (m) (m2) (%) (m) (m) (m

2) (m

3/s)

Tumnub Luok 35.6 1.7 59.8 0.000235 0.023% 18 3 54 49 106.0 120

Q50 98

Q100 107

Q100+20% 129

Regime Theory Check Calculation

Tumnub

Luok

Tumnub

Luok

Catchment Areas km2

291.00 291.00

l/s/km2

m3/s m

3/s m

3/s m

3/s/km

2m

3/s

Mean 92.25 16 27 Q50 Q100 Q100+20%

Maximum 130.28 23 38 58 0.326 84 168 184 221

Data transposed from TSLSPSiem Reap River at

Prasat Keo

Annual maximum

daily discharge

178

Mean monthly

discharge

Siem Reap River at

Prasat Keo

178



Str

uctu

reS

tation

Catc

hm

ent

Str

eam

85%

10%

Eff

ective

Land

Slo

pe

Soil

Runoff

Catc

hm

ent

Land

Contr

ibuting

Wet S

eason

Baseflow

Surf

ace

Base

Are

al

Retu

rnR

ain

fall

Sto

rmP

eak

Are

aLength

Ele

vation

Ele

vation

Ele

vation

Slo

pe

Cla

ss

Cla

ss

Coeff

icie

nt

Wetn

ess

Use

Are

aM

onth

ly

Cove

r F

low

Tim

eR

eduction

Period

Dura

tion T

BD

epth

Dis

charg

e

Diffe

rence

Facto

rF

acto

rR

ain

fall

Tim

eF

acto

r

AL

H85

H10

H85 -

H10

(H85 -

H10)/

.75L

SI

CS

Cw

CL

CA

PM

QB

TS

TB

AR

FT

TB

PQ

(km

2)

(m)

(m)

(%)

(%)

(%)

(mm

)(m

3/s

)(h

)(h

)(y

ears

)(m

m)

(mm

)(m

3/s

)

Tum

nub L

uok

NA

291.0

29000

100

50

50

0.2

3%

1.1

02.0

38

1.5

1.0

57

281

18

2.0

425

0.9

12.3

3152

138.2

55

Tum

nub L

uok

NA

291.0

29000

100

50

50

0.2

3%

1.1

02.0

38

1.5

1.0

57

281

18

2.0

425

0.9

150

370

336.4

109

Tum

nub L

uok

NA

291.0

29000

100

50

50

0.2

3%

1.1

02.0

38

1.5

1.0

57

281

18

2.0

425

0.9

1100

416

378.2

120

144

GE

NE

RA

LIS

ED

TR

OP

ICA

L F

LO

OD

MO

DE

L W

OR

KS

HE

ET

Desig

n Q

100 =

20%



Reservoir Flood Routing Over Spillway

PROGRAM SI ROUTING

This program will route an inflow hydrograph through a reservoir using the

Storage-Indication method. Values for the Q vs (2S/dt + Q) table must

be entered. The more accurately that these values are entered, the more

accurate the results will be.

To run the program, please enter the following parameters

in the highlighted boxes:

Flow unit selection: (E for English, M for Metric) M

Time unit selection: (H for Hours, M for Minutes) H

Starting time of the inflow hydrograph: 0

Ending time of the inflow hydrograph: 45

Time step dt: 1

Number of SI curve ordinates: 13

Initial storage S0: 0

Initial outflow Q0: 0

Inflow hydrograph ordinates: Sheet2

Storage indication curve ordinates: Sheet2

Click "Create Template" to create inflow

hydrograph and SI curve ordinate templates

in Sheet2. Click Sheet1 or Sheet2 to switch

between the two sheets.

Click "Clear Sheet2" to clear the inflow

hydrpgraph and SI curve in Sheet2.

Click the "Run Program" button to

run the program.

Click the "Clear Results" button to

clear the results before starting a

new run.

The results are shown below. Click the "Chart 1" or "Sheet 1" tab

at the bottom of the Excel window to switch between the chart

and the worksheet.

Add Baseflow 17.900

Time Qin Qout Time Qin Qout

0 0 0 0 17.9 17.9

1 4 0 1 21.7 18.2

2 16 2 2 34.2 19.7

3 35 5 3 52.6 23.3

4 60 15 4 78.0 33.1

5 91 33 5 108.8 50.7

6 124 58 6 141.6 76.0

7 150 87 7 167.6 105.1

8 167 115 8 184.6 132.6

9 173 137 9 191.3 154.6

10 169 151 10 186.7 168.6

11 156 156 11 174.4 173.5

12 140 153 12 158.4 170.6

13 123 144 13 141.0 162.1

14 105 132 14 122.7 149.8

15 89 118 15 106.9 135.9

16 76 104 16 93.4 121.9

17 65 91 17 83.0 109.0

18 55 79 18 73.4 97.3

19 48 69 19 65.7 87.1

20 40 60 20 58.0 77.9

21 35 52 21 52.6 69.8

22 29 45 22 46.8 62.9

23 24 39 23 42.4 56.7

24 20 33 24 37.6 51.2

25 18 29 25 35.5 46.7

26 15 25 26 32.4 42.8

27 13 22 27 30.9 39.4

28 11 19 28 28.7 36.6

29 10 17 29 27.9 34.5

30 8 15 30 26.4 32.6

31 7 13 31 24.9 30.8

32 5 11 32 23.4 29.1

33 4 10 33 21.9 27.5

34 5 8 34 22.4 26.1

35 4 7 35 21.7 25.1

36 3 6 36 21.0 24.4

37 2 6 37 20.3 23.8

38 2 5 38 19.6 23.2

39 2 5 39 20.0 22.7

40 2 4 40 19.6 22.3

41 1 4 41 19.3 21.8

42 1 4 42 18.9 21.4

43 1 3 43 18.6 21.0

44 1 3 44 18.8 20.7

45 1 2 45 18.6 20.3



Inflow Hydrograph Ordinates S-I Curve Ordinates

(Enter Time in column B, I n in (Enter Q in column I, 2S/dt+Q

column C): in column J):

Time In Q 2S/dt + Q

0 0.0 0.0 0.0

1 3.8 6.9 89.6

2 16.3 19.5 188.1

3 34.7 35.7 294.5

4 60.1 55.0 407.3

5 90.9 76.9 527.2

6 123.7 101.1 654.3

7 149.7 127.4 788.2

8 166.7 155.6 927.1

9 173.4 185.7 1076.8

10 168.8 217.5 1229.0

11 156.5 250.9 1387.2

12 140.5 285.9 1550.5

13 123.1 322.4 1715.3

14 104.8

15 89.0

16 75.5

17 65.1

18 55.5

19 47.8

20 40.1

21 34.7

22 28.9

23 24.5

24 19.7

25 17.6

26 14.5

27 13.0

28 10.8

29 10.0

30 8.5

31 7.0

32 5.5

33 4.0

34 4.5

35 3.8

36 3.1

37 2.4

38 1.7

39 2.1

40 1.7

41 1.4

42 1.0

43 0.7

44 0.9

45 0.7

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

200.0

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45

Flo

w (

m3 /

s)

Time (h)

Inflow/Outflow Hydrographs

Inflow Outflow



Average Year Water Balance

Month

Decadal

Rain

fall

Seepage

Eva

pora

tion

Irrigation

Recessio

nV

illage

Net lo

sses

Inflow

fro

mC

hange in

Spill

Leve

lA

rea

Volu

me

actu

al

Off

-take

Cro

pw

ate

r supply

and d

em

ands

catc

hm

ent

volu

me

(m)

(ha)

(MC

M)

(mm

)(m

m)

(mm

)(m

m)

(m3)

(MC

M)

(MC

M)

(MC

M)

(MC

M)

(MC

M)

(MC

M)

(MC

M)

(MC

M)

12

34

56

78

910

11

12

13

14

15

16

Gra

ph

Gra

ph

Bala

nce

Rain

fall

ET

4-5

-62*7

Cro

p R

eq

Cro

p R

eq

30 l/c

/d9-1

0-1

1-1

2F

low

13+

14

Flo

w

Apr

115.0

05

0.0

10

22.2

22.9

14.4

-15.1

-754

0.0

00.2

34

0.0

012

-0.2

40.0

4-0

.20

0.0

00

215.5

06

0.0

10

13.7

22.9

13.1

-22.2

-1,3

35

0.0

00.2

23

0.0

012

-0.2

30.0

5-0

.17

0.0

00

315.5

06

0.0

10

18.8

22.9

13.9

-17.9

-1,0

76

0.0

00.0

00

0.0

012

0.0

00.0

90.0

90.0

00

May

116.0

621.6

0.0

96

25.3

22.9

14.5

-12.1

-2,6

03

0.0

00.0

00

0.0

012

0.0

00.6

60.6

60.0

00

217.5

858.4

0.7

54

34.7

22.9

15.8

-3.9

-2,2

99

0.0

00.1

96

0.0

012

-0.2

00.9

90.7

90.0

00

318.6

3106.9

1.5

48

46.1

25.2

19.0

1.9

2,0

35

0.0

00.3

37

0.0

012

-0.3

41.6

51.3

20.0

00

Jun

119.1

5142.1

2.1

80

29.5

22.9

17.6

-11.0

-15,6

29

-0.0

20.1

34

0.0

012

-0.1

53.1

63.0

13.1

55

219.1

5142.1

2.1

80

34.7

22.9

17.9

-6.1

-8,6

28

-0.0

11.0

92

0.0

012

-1.1

03.6

92.5

83.4

86

319.1

5142.1

2.1

80

34.1

22.9

19.6

-8.4

-11,9

69

-0.0

11.7

96

0.0

012

-1.8

14.7

42.9

34.4

02

Jul

119.1

5142.1

2.1

80

45.2

22.9

18.9

3.4

4,8

36

0.0

01.2

59

0.0

012

-1.2

67.0

65.8

06.9

06

219.1

5142.1

2.1

80

25.8

22.9

18.1

-15.1

-21,5

01

-0.0

22.0

73

0.0

012

-2.1

06.0

53.9

54.9

48

319.1

5142.1

2.1

80

51.1

25.2

22.7

3.2

4,5

70

0.0

00.8

82

0.0

012

-0.8

87.0

66.1

85.2

48

Aug

119.1

5142.1

2.1

80

55.6

22.9

22.1

10.6

15,0

98

0.0

21.3

63

0.0

012

-1.3

511.8

010.4

510.5

41

219.1

5142.1

2.1

80

31.2

22.9

22.2

-13.9

-19,6

99

-0.0

21.8

17

0.0

012

-1.8

414.1

612.3

212.0

60

319.1

5142.1

2.1

80

42.1

25.2

28.3

-11.4

-16,1

76

-0.0

21.6

48

0.0

012

-1.6

621.2

319.5

720.3

55

Sep

119.1

5142.1

2.1

80

48.2

22.9

25.5

-0.2

-281

0.0

01.3

32

0.0

012

-1.3

321.5

620.2

320.2

12

219.1

5142.1

2.1

80

65.0

22.9

28.1

14.0

19,9

48

0.0

20.9

06

0.0

012

-0.8

922.2

321.3

520.3

97

319.1

5142.1

2.1

80

49.9

22.9

28.4

-1.4

-2,0

00

0.0

01.1

83

0.0

012

-1.1

923.5

822.4

021.9

17

Oct

119.1

5142.1

2.1

80

86.6

22.9

34.5

29.2

41,4

95

0.0

40.4

85

0.0

012

-0.4

536.5

636.1

235.2

29

219.1

5142.1

2.1

80

68.2

22.9

32.7

12.6

17,9

20

0.0

20.1

85

0.0

012

-0.1

731.9

931.8

231.1

05

319.1

5142.1

2.1

80

37.4

25.2

35.2

-22.9

-32,5

35

-0.0

30.7

83

0.0

012

-0.8

222.8

522.0

321.6

65

Nov

119.1

5142.1

2.1

80

6.7

22.9

25.7

-41.8

-59,4

51

-0.0

61.2

40

0.0

012

-1.3

020.2

618.9

619.8

14

219.1

5142.1

2.1

80

11.2

22.9

23.3

-35.0

-49,7

44

-0.0

50.6

93

0.0

012

-0.7

412.1

611.4

111.9

88

319.1

5142.1

2.1

80

6.3

22.9

23.0

-39.6

-56,2

27

-0.0

60.6

65

0.0

012

-0.7

28.1

07.3

87.2

87

Dec

119.1

5142.1

2.1

80

3.4

22.9

21.8

-41.3

-58,6

67

-0.0

60.7

50

0.0

012

-0.8

11.7

60.9

50.4

62

219.1

5142.1

2.1

80

2.9

22.9

20.7

-40.7

-57,8

89

-0.0

60.9

10

0.0

012

-0.9

71.0

60.0

90.3

14

319.1

5142.1

2.1

80

0.9

25.2

19.7

-44.0

-62,4

65

-0.0

61.0

15

0.0

012

-1.0

80.7

1-0

.37

0.0

00

Jan

118.7

2111.6

1.8

06

0.0

22.9

18.0

-40.9

-45,5

97

-0.0

50.3

07

0.0

012

-0.3

50.1

6-0

.19

0.0

00

218.7

2111.6

1.6

12

0.0

22.9

17.0

-39.9

-44,4

79

-0.0

40.3

19

0.0

012

-0.3

60.1

0-0

.41

0.0

00

318.2

084

1.2

04

0.9

25.2

18.5

-42.8

-35,9

49

-0.0

40.3

59

0.0

012

-0.4

00.0

6-0

.43

0.0

00

Feb

117.5

858.4

20.7

72

0.4

22.9

20.0

-42.5

-24,8

17

-0.0

20.3

54

0.0

012

-0.3

80.0

3-0

.41

0.0

00

216.7

233.0

30.3

67

9.7

22.9

21.0

-34.2

-11,3

08

-0.0

10.5

17

0.0

012

-0.5

30.0

3-0

.54

0.0

00

315.5

06

0.0

10

4.6

18.3

20.5

-34.2

-2,0

54

0.0

00.4

41

0.0

012

-0.4

40.0

3-0

.45

0.0

00

Mar

115.5

06

0.0

10

2.1

22.9

19.0

-39.8

-2,3

86

0.0

00.3

45

0.0

012

-0.3

50.0

3-0

.35

0.0

00

215.5

06

0.0

10

0.2

22.9

10.9

-33.5

-2,0

12

0.0

00.3

53

0.0

012

-0.3

60.0

3-0

.36

0.0

00

315.5

06.0

0.0

10

3.4

25.2

12.7

-34.5

-2,0

68

0.0

00.3

82

0.0

012

-0.3

90.0

3-0

.39

0.0

00

918.3

835.4

754.2

-671.4

-0.5

526.6

0.0

0.0

424

-27.1

6285.7

6258.1

2261.5

1450.0

Reserv

oir

Net gain

(sto

rage)



Apr

Ma

yJun

Jul

Aug

Sep

Oct

No

vD

ec

Jan

Feb

Ma

r

Re

se

rvoir

Vo

lum

e0

.010

0.0

10

0.0

10

0.0

96

0.7

54

1.5

48

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

1.8

06

1.6

12

1.2

04

0.7

72

0.3

67

0.0

10

0.0

10

0.0

10

0.0

10

Ra

in-s

ee

pa

ge-E

T0

.00

0.0

00

.00

0.0

00

.00

0.0

0-0

.02

-0.0

1-0

.01

0.0

0-0

.02

0.0

00

.02

-0.0

2-0

.02

0.0

00

.02

0.0

00

.04

0.0

2-0

.03

-0.0

6-0

.05

-0.0

6-0

.06

-0.0

6-0

.06

-0.0

5-0

.04

-0.0

4-0

.02

-0.0

10

.00

0.0

00

.00

0.0

0

Inflow

fro

m C

atc

hm

ent

0.0

40

.05

0.0

90

.66

0.9

91

.65

3.1

63

.69

4.7

47

.06

6.0

57

.06

11.8

01

4.1

62

1.2

32

1.5

62

2.2

32

3.5

83

6.5

63

1.9

92

2.8

52

0.2

61

2.1

68

.10

1.7

61

.06

0.7

10

.16

0.1

00

.06

0.0

30

.03

0.0

30

.03

0.0

30

.03

Irrig

atio

n0

.234

0.2

23

0.0

00

0.0

00

0.1

96

0.3

37

0.1

34

1.0

92

1.7

96

1.2

59

2.0

73

0.8

82

1.3

63

1.8

17

1.6

48

1.3

32

0.9

06

1.1

83

0.4

85

0.1

85

0.7

83

1.2

40

0.6

93

0.6

65

0.7

50

0.9

10

1.0

15

0.3

07

0.3

19

0.3

59

0.3

54

0.5

17

0.4

41

0.3

45

0.3

53

0.3

82

-5.0

00

0.0

00

5.0

00

10.0

00

15.0

00

20.0

00

25.0

00

30.0

00

35.0

00

40.0

00

Volumes (MCM)

Avera

ge Y

ear

Reserv

oir

Wate

r B

ala

nce



Dry Year Water Balance

Month

Decadal

Rain

fall

Seepage

Eva

pora

tion

Irrigation

Recessio

nV

illage

Net lo

sses

Inflow

fro

mC

hange in

Spill

Leve

lA

rea

Volu

me

actu

al

Off

-take

Cro

pw

ate

r supply

and d

em

ands

catc

hm

ent

volu

me

(m)

(ha)

(MC

M)

(mm

)(m

m)

(mm

)(m

m)

(m3)

(MC

M)

(MC

M)

(MC

M)

(MC

M)

(MC

M)

(MC

M)

(MC

M)

(MC

M)

12

34

56

78

910

11

12

13

14

15

16

Gra

ph

Gra

ph

Bala

nce

Rain

fall

ET

4-5

-62*7

Cro

p R

eq

Cro

p R

eq

30 l/c

/d9-1

0-1

1-1

2F

low

13+

14

Flo

w

Apr

115.0

05

0.0

10

19.0

22.9

14.4

-18.3

-914

0.0

00.0

47

0.0

012

-0.0

50.0

1-0

.04

0.0

00

215.5

06

0.0

10

11.7

22.9

13.1

-24.2

-1,4

53

0.0

00.0

45

0.0

012

-0.0

50.0

2-0

.03

0.0

00

315.5

06

0.0

10

16.1

22.9

13.9

-20.7

-1,2

39

0.0

00.0

00

0.0

012

0.0

00.0

30.0

30.0

00

May

115.5

06

0.0

39

21.7

22.9

14.5

-15.7

-943

0.0

00.0

00

0.0

012

0.0

00.0

20.0

10.0

00

215.5

06

0.0

53

29.7

22.9

15.8

-8.9

-536

0.0

00.0

00

0.0

012

0.0

00.0

20.0

20.0

00

315.9

218

0.0

75

39.4

25.2

19.0

-4.7

-841

0.0

00.0

00

0.0

012

0.0

00.0

40.0

40.0

00

Jun

116.1

223

0.1

12

25.3

22.9

17.6

-15.2

-3,5

78

0.0

00.0

00

0.0

012

0.0

00.0

50.0

40.0

00

216.1

223

0.1

56

29.7

22.9

17.9

-11.1

-2,5

97

0.0

00.0

00

0.0

012

0.0

00.0

60.0

50.0

00

316.0

020

0.2

08

29.2

22.9

19.6

-13.3

-2,6

66

0.0

00.0

00

0.0

012

0.0

00.0

70.0

70.0

00

Jul

116.0

020

0.2

76

38.7

22.9

18.9

-3.1

-621

0.0

00.0

00

0.0

012

0.0

01.0

31.0

30.0

00

218.2

084

1.3

04

22.1

22.9

18.1

-18.9

-15,8

39

-0.0

20.0

00

0.0

012

-0.0

20.8

80.8

70.0

00

319.1

5142

2.1

70

43.8

25.2

22.7

-4.1

-5,8

84

-0.0

10.0

00

0.0

012

-0.0

11.0

31.0

20.0

00

Aug

119.1

5142

2.1

80

47.6

22.9

22.1

2.6

3,7

33

0.0

01.4

54

0.0

012

-1.4

59.4

07.9

49.3

94

219.1

5142

2.1

80

26.7

22.9

22.2

-18.4

-26,0

89

-0.0

33.2

01

0.0

012

-3.2

311.2

88.0

511.2

58

319.1

5142

2.1

80

36.1

25.2

28.3

-17.5

-24,7

92

-0.0

20.9

75

0.0

012

-1.0

016.9

115.9

116.9

06

Sep

119.1

5142

2.1

80

41.3

22.9

25.5

-7.1

-10,1

46

-0.0

10.8

38

0.0

012

-0.8

522.6

421.7

921.1

93

219.1

5142

2.1

80

55.6

22.9

28.1

4.7

6,6

56

0.0

10.4

25

0.0

012

-0.4

223.3

522.9

320.1

24

319.1

5142

2.1

80

42.7

22.9

28.4

-8.6

-12,2

10

-0.0

11.9

05

0.0

012

-1.9

224.7

722.8

523.7

66

Oct

119.1

5142

2.1

80

74.1

22.9

34.5

16.7

23,7

91

0.0

21.2

11

0.0

012

-1.1

936.5

635.3

735.7

13

219.1

5142

2.1

80

58.4

22.9

32.7

2.8

3,9

67

0.0

01.4

84

0.0

012

-1.4

831.9

930.5

131.5

73

319.1

5142

2.1

80

32.0

25.2

35.2

-28.3

-40,1

90

-0.0

40.9

79

0.0

012

-1.0

222.8

521.8

320.9

33

Nov

119.1

5142

2.1

80

5.8

22.9

25.7

-42.8

-60,8

26

-0.0

61.5

78

0.0

012

-1.6

418.3

516.7

117.1

63

219.1

5142

2.1

80

9.6

22.9

23.3

-36.6

-52,0

36

-0.0

51.4

28

0.0

012

-1.4

85.5

14.0

24.0

24

319.1

5142

2.1

80

5.4

22.9

23.0

-40.5

-57,5

13

-0.0

61.3

30

0.0

012

-1.3

93.6

72.2

82.6

50

Dec

119.1

5142

2.1

80

2.9

22.9

21.8

-41.8

-59,3

55

-0.0

61.4

25

0.0

012

-1.4

90.3

5-1

.14

0.0

00

218.0

978

1.0

40

2.5

22.9

20.7

-41.2

-31,9

71

-0.0

31.3

29

0.0

012

-1.3

60.2

1-1

.16

0.0

00

315.5

06

0.0

10

0.8

25.2

19.7

-44.1

-2,6

46

0.0

01.2

23

0.0

012

-1.2

30.1

4-1

.09

0.0

00

Jan

115.5

06

0.0

10

0.0

22.9

18.0

-40.9

-2,4

51

0.0

00.0

61

0.0

012

-0.0

70.0

4-0

.02

0.0

00

215.5

06

0.0

10

0.0

22.9

17.0

-39.9

-2,3

91

0.0

00.0

64

0.0

012

-0.0

70.0

2-0

.07

0.0

00

315.5

06

0.0

10

0.7

25.2

18.5

-42.9

-2,5

75

0.0

00.0

72

0.0

012

-0.0

80.0

2-0

.08

0.0

00

Feb

115.5

06

0.0

10

0.3

22.9

20.0

-42.5

-2,5

52

0.0

00.0

71

0.0

012

-0.0

70.0

2-0

.08

0.0

00

215.5

06

0.0

10

8.3

22.9

21.0

-35.6

-2,1

38

0.0

00.1

03

0.0

012

-0.1

10.0

2-0

.11

0.0

00

315.5

06

0.0

10

3.9

18.3

20.5

-34.9

-2,0

94

0.0

00.0

88

0.0

012

-0.0

90.0

2-0

.09

0.0

00

Mar

115.5

06

0.0

10

1.8

22.9

19.0

-40.1

-2,4

05

0.0

00.0

69

0.0

012

-0.0

70.0

2-0

.07

0.0

00

215.5

06

0.0

10

0.2

22.9

10.9

-33.6

-2,0

15

0.0

00.0

71

0.0

012

-0.0

70.0

2-0

.08

0.0

00

315.5

06

0.0

10

2.9

25.2

12.7

-35.0

-2,0

97

0.0

00.0

76

0.0

012

-0.0

80.0

2-0

.08

0.0

00

786.1

835.4

754.2

-803.5

-0.4

021.6

0.0

0.0

424

-21.9

9231.4

4209.2

6214.7

1450.0

Reserv

oir

Net gain

(sto

rage)



Apr

Ma

yJun

Jul

Aug

Sep

Oct

No

vD

ec

Jan

Feb

Ma

r

Re

se

rvoir

Vo

lum

e0

.010

0.0

10

0.0

10

0.0

39

0.0

53

0.0

75

0.1

12

0.1

56

0.2

08

0.2

76

1.3

04

2.1

70

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

2.1

80

1.0

40

0.0

10

0.0

10

0.0

10

0.0

10

0.0

10

0.0

10

0.0

10

0.0

10

0.0

10

0.0

10

Ra

in-s

ee

pa

ge-E

T0

.00

0.0

00

.00

0.0

00

.00

0.0

00

.00

0.0

00

.00

0.0

0-0

.02

-0.0

10

.00

-0.0

3-0

.02

-0.0

10

.01

-0.0

10

.02

0.0

0-0

.04

-0.0

6-0

.05

-0.0

6-0

.06

-0.0

30

.00

0.0

00

.00

0.0

00

.00

0.0

00

.00

0.0

00

.00

0.0

0

Inflow

fro

m C

atc

hm

ent

0.0

10

.02

0.0

30

.02

0.0

20

.04

0.0

50

.06

0.0

71

.03

0.8

81

.03

9.4

01

1.2

81

6.9

12

2.6

42

3.3

52

4.7

73

6.5

63

1.9

92

2.8

51

8.3

55

.51

3.6

70

.35

0.2

10

.14

0.0

40

.02

0.0

20

.02

0.0

20

.02

0.0

20

.02

0.0

2

Irrig

atio

n0

.047

0.0

45

0.0

00

0.0

00

0.0

00

0.0

00

0.0

00

0.0

00

0.0

00

0.0

00

0.0

00

0.0

00

1.4

54

3.2

01

0.9

75

0.8

38

0.4

25

1.9

05

1.2

11

1.4

84

0.9

79

1.5

78

1.4

28

1.3

30

1.4

25

1.3

29

1.2

23

0.0

61

0.0

64

0.0

72

0.0

71

0.1

03

0.0

88

0.0

69

0.0

71

0.0

76

-5.0

00

0.0

00

5.0

00

10.0

00

15.0

00

20.0

00

25.0

00

30.0

00

35.0

00

40.0

00

Volumes (MCM)

Dry

Year

Reserv

oir

Wate

r B

ala

nce



Appendix 3: Hydraulic Calculations

Spillway and Stilling Basin

The spillway is a 150 m long broad crested weir with a USBR Type 1 Stilling Basin. The elevation of

the weir crest is 19.2 m and the crest level of the embankment dam is 20.5 m. The spillway provides a

6.0 m wide low-level vehicle crossing.

0 1 2 3

Hd dc

d1 d2

d3

HL

hz0

z1

HW

zw

Dimensions

U/S bed Weir elv

Height

U/S face

Design

flow

Width of

weir

Unit

discharge

Stilling

basin elv Drop

Depth

Stilling

basin

Depth

D/S (over

sill)

If d3 > d2

height of

upstand

sill

Required

length of

stilling

basin

Actual

length of

stilling

basin

zo zw h Q100 B z1 zw-z1 d2 d3 L Lact

(m) elv (m) elv (m) (m3/s) (m) (m

3/s) (m

3/s) (m) (m) (m) (m) (m) (m)

15.5 19.2 3.7 173 150 1.153333 14.8 4.4 1.530 0.776 0.754484 9.181 9.200

Downstream channel

W D A P s n Q

(m) (m) (m2) (m) (m

3/s)

150 1.47 223.7414 155.300 0.00025 0.035 128.933

Head over

weir

Discharge

He Q

(m) (m3/s)

0.000 0.00

0.050 2.50

0.100 7.07

0.150 12.98

0.200 19.99

0.250 27.56

0.300 35.74

0.400 55.40

0.500 76.90

0.600 101.08

0.700 127.38

0.800 155.63

0.900 185.70

1.000 217.50

1.100 250.93

1.200 285.91

1.300 322.38

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

0 25 50 75 100 125 150 175 200 225 250 275 300 325

Heig

ht

of

reserv

oir

ab

ove w

eir

cre

st

(m)

Discharge over spillway (m3/s)

Stillway rating curve

q Hd dc=(q2/g)

0.33vc

2/2g Drop EL + Drop E1=v1

2/2g+d1 d1 F1=q/d1(gd1)

0.5d2=(d1/2)((1+8F1

2)0.5

-1) L=6d2

(m3/s) (m) (m

3/s) (m) (m) (m) (m) (m) (m) (m)

1.153 0.776 0.517 0.253 3.900 4.671 4.671 0.12208 8.63 1.490 8.94

1.153 0.776 0.517 0.253 4.400 5.171 5.171 0.11581 9.34 1.530 9.18

Toggle until E1=EL + Drop



Hydraulic Design of Canal

The spreadsheets for the hydraulic design of main canals MC1 and MC3 are on the following pages.

The basis of the calculations is shown below.

Flow Calculation in Open Canals

Formula of Manning - Strickler : Q = 1/n x A x R2/3

x S1/2

Canal Cross - Section

zd B freeboard

1 d = water depth

z

b = w d

Canal parameters

z = side slope canal (hor. / vert.) ( - )

w = ratio : bottom width / water depth ( - )

d = water depth (m)

b = w x d (bottom width) (m)

A = d2 x (w + z) (wetted section) (m

2)

P = d x (w+ 2(z2 + 1)

1/2) (wetted perimeter) (m)

R = A / P (hydraulic radius) (m)

= d x (w + z) / (w + 2(z2 + 1)

1/2 )

n = canal roughness coefficient ( - )

S = canal slope (m/m)

Q = 1/n x A x R2/3

x S1/2 (canal flow) (m

3/s)

= 1/n x S1/2

x d8/3

x (w + z)5/3

x (w + 2(z2 +1)

1/2 )-2/3

D = (Q / (1/n x S1/2

))3/8

x (w + 2(z2 + 1)

1/2)1/4

x (w + z)-5/8



MC-1 MC-1 MC-1 MC-1 MC-1

Type of channel 0 -800 m 800-2000 m 2000-3000 m 3000-4000 m 4000-5007 m

Design discharge Q= 1.40 1.40 1.40 1.40 1.40

Bottom width B= 2.0 2.0 2.0 2.0 2.0

Side slope m= 1.50 1.50 1.50 1.50 1.50

Coef. of roughness n= 0.030 0.03 0.03 0.03 0.03

Bed slope I= 1/3050 1/3050 1/3050 1/3050 1/3050

0.0003 0.0003 0.0003 0.0003 0.0003

Canal dimension

Depth H= 0.952 0.952 0.952 0.952 0.952

Area A= 3.263 3.263 3.263 3.263 3.263

Wetted perimeter P= 5.432 5.432 5.432 5.432 5.432

Hydraulic m-depth R= 0.601 0.601 0.601 0.601 0.601

Velocity V= 0.430 0.430 0.430 0.430 0.430

Velocity head hv= 0.009 0.009 0.009 0.009 0.009

Frude number Fr= 0.141 0.141 0.141 0.141 0.141

Free board fb= 0.500 0.500 0.500 0.500 0.500

Channel height D1= 1.500 1.500 1.500 1.500 1.500

adopted 1.500 1.500 1.500 1.500 1.500

Ratio of B/H 2.101 2.101 2.101 2.101 2.101

Trial calculation

Depth h= 0.952 0.952 0.952 0.952 0.952

Area A= 3.263 3.263 3.263 3.263 3.263

Wetted perimeter P= 5.432 5.432 5.432 5.432 5.432

Hydraulic m-depth R= 0.601 0.601 0.601 0.601 0.601

R^2/3= 0.712 0.712 0.712 0.712 0.712

Velocity V= 0.430 0.430 0.430 0.430 0.430

Calculation dis. Q'= 1.403 1.403 1.403 1.403 1.403

Design discharge Q= 1.400 1.400 1.400 1.400 1.400

An error Q'-Q= 0.003 0.003 0.003 0.003 0.003

B/d 2.101 2.101 2.101 2.101 2.101

Tumnub Luok Irrigation System Subproject

CALCULATION OF UNIFORM FLOW



Canal Name :

Station HM Discharge Distance Accu. Works Energy Energy Energy Velocity Velocity Water Water Canal Canal Canal L-Inside R-Inside Roughness Free Canal

No. Distance Gradient Loss Elevation Head Surface Depth Bed EL Top EL Width Slope Slope Coefficient Board Height Remarks

(m3/sec) (m) (m) (i) (m) (m) (m/sec) (m) EL (m) (m) (m) (m) (m) (1:mL) (1:mR) (n) (m) (m)

INT.MC-1 0 + 0.00 1.40 0.00 Head Regulator-1 0.200 18.700 18.700 Intake

BP.MC-1 0 + 10.00 10.00 18.500 0.430 0.009 18.491 0.952 17.54 19.04 2.00 1.50 1.50 0.030 0.50 1.50 BP

1.40 90.00 Open Channel 0.0003 0.030 Canal Section

0 + 100.00 100.00 18.470 0.430 0.009 18.461 0.952 17.51 19.01 2.00 1.50 1.50 0.030 0.50 1.50


Off-take 1 (L+R) 0 + 190.00 190.00 OF-1 (L+R) 18.440 0.430 0.009 18.431 0.952 17.48 18.98 2.00 1.50 1.50 0.030 0.50 1.50


Off-take 2 (L) 0 + 500.00 500.00 OF-2 (L) 18.338 0.430 0.009 18.329 0.952 17.38 18.88 2.00 1.50 1.50 0.030 0.50 1.50


0 + 800.00 800.00 18.240 0.430 0.009 18.231 0.952 17.28 18.78 2.00 1.50 1.50 0.030 0.50 1.50

1 + 550.00 1.40 100.00 1550.00 Open Channel 0.0003 0.033 Canal Section

0 + 900.00 900.00 18.207 0.430 0.009 18.198 0.952 17.25 18.75 2.00 1.50 1.50 0.030 0.50 1.50


Off-take 3 (L+R) 0 + 980.00 980.00 OF-3 (L+R) 18.181 0.430 0.009 18.172 0.952 17.22 18.72 2.00 1.50 1.50 0.030 0.50 1.50 Off-take 3(R+L)


0 + 995.00 995.00 18.176 0.430 0.009 18.167 0.952 17.22 18.72 2.00 1.50 1.50 0.030 0.50 1.50

CK-1 1 + 0.00 1.40 10.00 1000.00 Check Structure 0.0003 0.003 Check -1

1 + 5.00 1005.00 18.173 0.430 0.009 18.164 0.952 17.21 18.71 2.00 1.50 1.50 0.030 0.50 1.50


1 + 200.00 1200.00 18.109 0.430 0.009 18.100 0.952 17.15 18.65 2.00 1.50 1.50 0.030 0.50 1.50


Off-take 4 ® 1 + 350.00 1350.00 OF-4 (R) 18.060 0.430 0.009 18.051 0.952 17.10 18.60 2.00 1.50 1.50 0.030 0.50 1.50 Offtake 4 (R)


Off-take 5 (L+R) 1 + 640.00 1640.00 OF-5 (R+L) 17.965 0.430 0.009 17.956 0.952 17.00 18.50 2.00 1.50 1.50 0.030 0.50 1.50 Offtake 5(R+L)


1 + 680.00 1680.00 17.952 0.430 0.009 17.943 0.952 16.99 18.49 2.00 1.50 1.50 0.030 0.50 1.50

OX-1 1 + 685.00 1.40 10.00 1685.00 Oxcart Bridge-1 0.0003 0.003 Oxcart Bridge-1

1 + 690.00 1690.00 17.949 0.430 0.009 17.940 0.952 16.99 18.49 2.00 1.50 1.50 0.030 0.50 1.50


Off-take 6 ® 1 + 875.00 1875.00 OF-6 ® 17.888 0.430 0.009 17.879 0.952 16.93 18.43 2.00 1.50 1.50 0.030 0.50 1.50 Off-take 6®


1 + 895.00 1895.00 17.881 0.430 0.009 17.872 0.952 16.92 18.42 2.00 1.50 1.50 0.030 0.50 1.50


1 + 905.00 1905.00 17.878 0.430 0.009 17.869 0.952 16.92 18.42 2.00 1.50 1.50 0.030 0.50 1.50


2 + 0.00 2000.00 0.180 17.667 0.430 0.009 17.658 0.952 16.71 18.21 2.00 1.50 1.50 0.030 0.50 1.50

200.00 Open Channel 0.0003 0.066 Canal Section

2 + 200.00 1.40 2200.00 17.601 0.430 0.009 17.592 0.952 16.64 18.14 2.00 1.50 1.50 0.030 0.50 1.50

70.00 Open Channel 0.0003 0.023 Canal Section

Off-take 7 ® 2 + 270.00 2270.00 OF-7 ® 17.578 0.430 0.009 17.569 0.952 16.62 18.12 2.00 1.50 1.50 0.030 0.50 1.50 Off-take 7®


2 + 600.00 2600.00 17.470 0.430 0.009 17.461 0.952 16.51 18.01 2.00 1.50 1.50 0.030 0.50 1.50


Off-take 8 (R+L) 2 + 665.00 2665.00 OF-8 (R+L) 17.449 0.430 0.009 17.440 0.952 16.49 17.99 2.00 1.50 1.50 0.030 0.50 1.50 Off-take 8 (R+L)

1.40 30.00 Open Channel 0.0003 0.010

2 + 695.00 2695.00 17.439 0.430 0.009 17.430 0.952 16.48 17.98 2.00 1.50 1.50 0.030 0.50 1.50


2 + 705.00 2705.00 17.436 0.430 0.009 17.427 0.952 16.48 17.98 2.00 1.50 1.50 0.030 0.50 1.50


3 + 0.00 3000.00 17.339 0.430 0.009 17.330 0.952 16.38 17.88 2.00 1.50 1.50 0.030 0.50 1.50


3 + 75.00 3075.00 17.314 0.430 0.009 17.305 0.952 16.35 17.85 2.00 1.50 1.50 0.030 0.50 1.50


3 + 85.00 3085.00 17.311 0.430 0.009 17.302 0.952 16.35 17.85 2.00 1.50 1.50 0.030 0.50 1.50


3 + 800.00 3800.00 17.077 0.430 0.009 17.068 0.952 16.12 17.62 2.00 1.50 1.50 0.030 0.50 1.50

1.40 70.00 Open Channel 0.0003 0.023

Off-take 9 (R+L) 3 + 870.00 3870.00 OF-9 (R+L) 17.054 0.430 0.009 17.045 0.952 16.09 17.59 2.00 1.50 1.50 0.030 0.50 1.50 Off-take 9 (R+L)


3 + 895.00 3895.00 17.046 0.430 0.009 17.037 0.952 16.09 17.59 2.00 1.50 1.50 0.030 0.50 1.50

CK-4 3 + 900.00 1.40 10.00 3900.00 Check Structure 0.0003 0.003 Check 4

3 + 905.00 3905.00 17.043 0.430 0.009 17.034 0.952 16.08 17.58 2.00 1.50 1.50 0.030 0.50 1.50


4 + 0.00 4000.00 0.400 16.612 0.430 0.009 16.603 0.952 15.65 17.15 2.00 1.50 1.50 0.030 0.50 1.50


4 + 380.00 4380.00 16.487 0.430 0.009 16.478 0.952 15.53 17.03 2.00 1.50 1.50 0.030 0.50 1.50


4 + 390.00 4390.00 16.484 0.430 0.009 16.475 0.952 15.52 17.02 2.00 1.50 1.50 0.030 0.50 1.50


4 + 600.00 4600.00 16.415 0.430 0.009 16.406 0.952 15.45 16.95 2.00 1.50 1.50 0.030 0.50 1.50


4 + 620.00 4620.00 16.408 0.430 0.009 16.399 0.952 15.45 16.95 2.00 1.50 1.50 0.030 0.50 1.50


4 + 800.00 4800.00 16.349 0.430 0.009 16.340 0.952 15.39 16.89 2.00 1.50 1.50 0.030 0.50 1.50


4 + 828.00 4828.00 16.340 0.430 0.009 16.331 0.952 15.38 16.88 2.00 1.50 1.50 0.030 0.50 1.50


EP.MC1 5 + 7.00 5007.00 16.281 0.430 0.009 16.272 0.952 15.32 16.82 2.00 1.50 1.50 0.030 0.50 1.50 Ending MC-1

CANAL HYDRAULIC CALCULATION SHEET

Design Calculation for the Main Canal MC-1TUMNUB LUOK IRRIGATION SYSTEM SUBPROJECT Main Canal MC-1



MC-3 MC-3

Type of channel 0 -530 m 530-1025 m

Design discharge Q= 0.12 0.12

Bottom width B= 1.5 1.5

Side slope m= 1.50 1.50

Coef. of roughness n= 0.030 0.03

Bed slope I= 1/3300 1/3300

0.000303 0.0003

Canal dimension

Depth H= 0.291 0.291

Area A= 0.564 0.564

Wetted perimeter P= 2.549 2.549

Hydraulic m-depth R= 0.221 0.221

Velocity V= 0.212 0.212

Velocity head hv= 0.002 0.002

Frude number Fr= 0.126 0.126

Free board fb= 0.400 0.400

Channel height D1= 0.700 0.700

adopted 0.700 0.700

Ratio of B/H 5.155 5.155

Trial calculation

Depth h= 0.291 0.291

Area A= 0.564 0.564

Wetted perimeter P= 2.549 2.549

Hydraulic m-depth R= 0.221 0.221

R^2/3= 0.366 0.366

Velocity V= 0.212 0.212

Calculation dis. Q'= 0.120 0.120

Design discharge Q= 0.120 0.120

An error Q'-Q= 0.000 0.000

B/d 5.155 5.155

Tumnub Luok Irrigation System Subproject

CALCULATION OF UNIFORM FLOW



Canal Name :

Station HM Discharge Distance Accu. Works Energy Energy Energy Velocity Velocity Water Water Canal Canal Canal L-Inside R-Inside Roughness Free Canal

No. Distance Gradient Loss Elevation Head Surface Depth Bed EL Top EL Width Slope Slope Coefficient Board Height Remarks

(m3/sec) (m) (m) (i) (m) (m) (m/sec) (m) EL (m) (m) (m) (m) (m) (1:mL) (1:mR) (n) (m) (m)

INT.MC-3 0 + 0.00 0.12 0.00 HR-MC3 0.160 18.150 18.150 Intake

BP.MC-3 0 + 10.00 10.00 17.990 0.212 0.002 17.988 0.291 17.70 18.40 1.50 1.50 1.50 0.030 0.40 0.70 BP


0 + 50.00 50.00 17.978 0.212 0.002 17.976 0.291 17.69 18.39 1.50 1.50 1.50 0.030 0.40 0.70


Off-take 1 (R) 0 + 70.00 70.00 OF-1 (R) 17.972 0.212 0.002 17.970 0.291 17.68 18.38 1.50 1.50 1.50 0.030 0.40 0.70 Off-take 1®


Off-take 2 (L) 0 + 80.00 80.00 OF-2 (L) 17.969 0.212 0.002 17.967 0.291 17.68 18.38 1.50 1.50 1.50 0.030 0.40 0.70 Off-take 2 (L)


0 + 83.00 83.00 17.968 0.212 0.002 17.966 0.291 17.68 18.38 1.50 1.50 1.50 0.030 0.40 0.70

CK-1 0 + 85.00 0.12 4.00 85.00 Check Structure 0.0003 0.001 Check Structure

0 + 87.00 87.00 17.967 0.212 0.002 17.965 0.291 17.67 18.37 1.50 1.50 1.50 0.030 0.40 0.70


0 + 500.00 500.00 17.842 0.212 0.002 17.840 0.291 17.55 18.25 1.50 1.50 1.50 0.030 0.40 0.70


Off-take 3 (L) 0 + 510.00 510.00 OF-3 (L) 17.839 0.212 0.002 17.837 0.291 17.55 18.25 1.50 1.50 1.50 0.030 0.40 0.70 Off-take 3 (L)

19.00 0.0003 0.006 Check -1

0 + 529.00 529.00 17.833 0.212 0.002 17.831 0.291 17.54 18.24 1.50 1.50 1.50 0.030 0.40 0.70

0.12 2.00 530.00 Drop in the bed 0.0003 0.001 Canal Section

0 + 531.00 531.00 0.300 17.532 0.212 0.002 17.530 0.291 17.24 17.94 1.50 1.50 1.50 0.030 0.40 0.70


0 + 600.00 600.00 17.511 0.212 0.002 17.509 0.291 17.22 17.92 1.50 1.50 1.50 0.030 0.40 0.70


1 + 0.00 1000.00 17.390 0.212 0.002 17.388 0.291 17.10 17.80 1.50 1.50 1.50 0.030 0.40 0.70


1 + 23.00 1023.00 17.383 0.212 0.002 17.381 0.291 17.09 17.79 1.50 1.50 1.50 0.030 0.40 0.70

TS 1 + 25.00 0.12 2.00 1025.00 Terminal Structure 0.0003 0.001 Terminal Structure

1 + 25.00 1025.00 17.382 0.212 0.002 17.380 0.291 17.09 17.79 1.50 1.50 1.50 0.030 0.40 0.70

0.12 0.00 Open Channel 0.0003 0.000

EP.MC3 1 + 25.00 1025.00 17.382 0.212 0.002 17.380 0.291 17.09 17.79 1.50 1.50 1.50 0.030 0.40 0.70 Ending MC-1

CANAL HYDRAULIC CALCULATION SHEET

Design Calculation for the Main Canal MC-3TUMNUB LUOK IRRIGATION SYSTEM SUBPROJECT Main Canal MC-3



Hydraulic Calculations and Operational Charts for Head Regulators

and Cross Regulators

Head Regulators at Culverts

Two of the three head regulators at Tumnub Luok are gates immediately upstream but not on the

upstream face of a culvert: at station 0+588 m a pipe culvert and at station 2+380 m a box culvert.

This affects the performance of the gate inlet but the flow condition will approximate to orifice flow at

the culvert entrance rather than undershot sluice gate flow. Under all but low head conditions flow will

be supercritical at the culvert inlet and remain supercritical throughout the culvert. If there is shallow

backwater from downstream a hydraulic jump may form at the outlet, or if there is a drop at the outlet

the flow will in most cases remain supercritical beyond the outlet, if there is deep backwater from

downstream the flow from the gate will be drowned and the gate open will need to be increased to

achieve the required flow. The critical case for design is when flow is not drowned and for which the

discharge equation for the head regulators is:

21 HHAnQ

Where Q = Discharge(m3/s)

µ = Discharge coefficient

n = Number of gate/culverts

A Cross-section of gate opening (m2)

H1 Head of water upstream of gate (m)

H2 Head of water downstream of gate (m)

Each calculation sheet is accompanied by operational charts. The charts plot discharge (flow) past

the gate for different gate openings; there are several curves for a range of upstream water levels

including upstream water level at dam crest level (the upper bound extreme flood case), and when

upstream water level is at the spillway level/full supply level (design case). The purpose of the charts

is to illustrate the performance of the gates for operational purposes.

Head and Cross Regulators on Open Channels

The head regulator at station 1+413 m (MC1) and the four cross regulators along main canal MC1 are

open channel sluice gates and the method of calculation is different to the head regulators which

discharge through culverts. For convenience, the calculation for the cross regulator made use of an

‘Applet’*** to calculate flow at the gate. The applet can be found at:

Discharge under a sluice gate http://onlinecalc.sdsu.edu/onlinechannel13.php.

*** The applets are free to use on the World Wide Web, courtesy Dr. Victor Miguel Ponce, Department

of Civil, Construction, and Environmental Engineering, San Diego State University, California,

http://ponce.sdsu.edu/.

http://onlinecalc.sdsu.edu/onlinechannel13.php

http://ponce.sdsu.edu/



Head Regulator at Station 0+588 Gate invert 17.350 m elv

Reservoir

level

Water level

d/s of gate

Gate

openning Dia µ Area Q 1 Gate 2 Gates

m elv m elv m m m2

l/s m3/s m

3/s

20.500 17.370 0.02 1.00 0.65 0.00 13 0.013 0.027

20.500 17.450 0.10 1.00 0.65 0.04 145 0.145 0.291

20.500 17.550 0.20 1.00 0.65 0.11 391 0.391 0.782

20.500 17.650 0.30 1.00 0.65 0.20 681 0.681 1.362

20.500 17.750 0.40 1.00 0.65 0.29 991 0.991 1.981

20.500 17.850 0.50 1.00 0.65 0.39 1,301 1.301 2.603

20.500 17.950 0.60 1.00 0.65 0.49 1,599 1.599 3.199

20.500 18.050 0.70 1.00 0.65 0.59 1,871 1.871 3.742

20.500 18.150 0.80 1.00 0.65 0.67 2,102 2.102 4.204

20.500 18.250 0.90 1.00 0.65 0.74 2,274 2.274 4.547

20.500 18.350 1.00 1.00 0.65 0.79 2,345 2.345 4.689

19.200 17.370 0.02 1.00 0.65 0.00 10 0.010 0.020

19.200 17.450 0.10 1.00 0.65 0.04 110 0.110 0.220

19.200 17.550 0.20 1.00 0.65 0.11 292 0.292 0.585

19.200 17.650 0.30 1.00 0.65 0.20 502 0.502 1.005

19.200 17.750 0.40 1.00 0.65 0.29 719 0.719 1.439

19.200 17.850 0.50 1.00 0.65 0.39 929 0.929 1.858

19.200 17.950 0.60 1.00 0.65 0.49 1,120 1.120 2.240

19.200 17.970 0.62 1.00 0.65 0.51 1,155 1.155 2.310

19.200 18.050 0.70 1.00 0.65 0.59 1,282 1.282 2.564

19.200 18.150 0.80 1.00 0.65 0.67 1,405 1.405 2.810

19.200 18.250 0.90 1.00 0.65 0.74 1,477 1.477 2.955

19.200 18.350 1.00 1.00 0.65 0.79 1,474 1.474 2.948

18.350 17.370 0.02 1.00 0.65 0.00 7 0.007 0.015

18.350 17.450 0.10 1.00 0.65 0.04 79 0.079 0.158

18.350 17.550 0.20 1.00 0.65 0.11 204 0.204 0.407

18.350 17.650 0.30 1.00 0.65 0.20 338 0.338 0.675

18.350 17.750 0.40 1.00 0.65 0.29 463 0.463 0.925

18.350 17.850 0.50 1.00 0.65 0.39 565 0.565 1.131

18.350 17.950 0.60 1.00 0.65 0.49 633 0.633 1.267

18.350 18.050 0.70 1.00 0.65 0.59 655 0.655 1.310

18.350 18.150 0.80 1.00 0.65 0.67 613 0.613 1.227

18.350 18.250 0.90 1.00 0.65 0.74 479 0.479 0.959

18.350 18.300 0.95 1.00 0.65 0.79 358 0.358 0.715

17.650 17.370 0.02 1.00 0.65 0.00 4 0.004 0.008

17.650 17.450 0.10 1.00 0.65 0.04 37 0.037 0.074

17.650 17.550 0.20 1.00 0.65 0.11 72 0.072 0.144

17.650 17.600 0.25 1.00 0.65 0.20 90 0.090 0.180

17.650 17.600 0.30 1.00 0.65 0.29 134 0.134 0.267

21 HHgbanQ

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

Gate

op

en

ing

metr

es


Head Regulator at Station 0+588

Reservoir at crest of dam, 1 gate open

Reservoir at full supply level, 1 gate open

Reservoir level with top of culvert, 1 gate open

Reservoir 0.3m above invert of culvert, 1 gate open

Reservoir at crest of dam, 2 gates open

Reservoir at full supply level, 2 gates open

Reservoir level with top of culvert, 2 gates open

Reservoir 0.3m above invert of culvert, 2 gates open



Head Regulator at Station 1+413 (MC1)

Ap

ple

tA

pp

let

Ap

ple

t

Up

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am

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un

it

dis

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idth

Nu

mb

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f

gate

s

Dis

char

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um

ber

of

gate

s

Dis

char

ge

Res

ervo

irG

ate

Y1

Y2

Cc

Cd

V2

q2

W

m e

lvm

elv

mm

mm

/sm

2/s

ml/

sl/

s

1.9

41

7.0

0-1

5.0

60

.10

Fully

op

en0

.61

0.6

04

5.0

10

0.5

01

0.7

51

37

62

75

2

20

.50

17

.00

3.5

0.2

53

.25

0.6

10

.59

74

.47

01

.23

60

.75

19

27

21

,85

4

20

.50

17

.00

3.5

0.5

03

.00

0.6

10

.58

54

.84

72

.42

30

.75

11

,81

72

3,6

35

20

.50

17

.00

3.5

0.7

52

.75

0.6

10

.57

34

.75

23

.56

40

.75

12

,67

32

5,3

46

20

.50

17

.00

3.5

1.0

02

.50

0.6

10

.56

24

.66

34

.66

30

.75

13

,49

72

6,9

95

20

.50

17

.00

3.5

1.5

02

.00

0.6

10

.54

34

.49

96

.74

90

.75

15

,06

22

10

,12

4

20

.50

17

.00

3.5

2.0

01

.50

0.6

10

.52

54

.35

08

.70

30

.75

16

,52

72

13

,05

5

20

.50

17

.00

3.5

2.5

01

.00

0.6

10

.50

94

.21

71

0.5

40

0.7

51

7,9

05

21

5,8

10

20

.50

17

.00

3.5

3.0

00

.50

0.6

10

.49

44

.09

51

2.2

80

0.7

51

9,2

10

21

8,4

20

20

.50

17

.00

3.5

3.5

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0.6

10

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03

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31

3.9

40

0.7

51

10

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52

20

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0

1.5

01

7.0

0-1

5.5

0.1

0Fu

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0.6

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13

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20

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50

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12

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25

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19

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0.2

51

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0.6

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40

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80

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17

26

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2

19

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2.2

0.5

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0.6

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13

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41

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70

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11

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2,8

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19

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17

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0.7

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0.6

10

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53

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52

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40

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12

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12

4,1

01

19

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17

.00

2.2

1.0

01

.20

0.6

10

.53

93

.54

53

.54

50

.75

12

,65

92

5,3

18

19

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17

.00

2.2

1.5

00

.70

0.6

10

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23

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75

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00

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13

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82

7,5

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19

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2.2

2.0

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0.6

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1.1

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0.7

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18

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17

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1.0

00

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0.2

50

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0.5

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1.6

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0.7

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2.1

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23

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0.2

00

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0.1

00

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0.5

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1.0

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0.1

05

0.7

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17

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17

.00

0.2

00

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op

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0.4

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0.9

52

0.1

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0.7

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14

32

28

5



0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5G

ate

op

en

ing

(m

)

Discharge (m3/s)






0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Gate

op

en

ing

(m

)

Discharge (m3/s)

Head Regulator MC1 using two gates





0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0

2,000

4,000

6,000

8,000

10,000

12,000

3.50 2.20 1.00 0.20

Up

stre

am w

ate

r d

epth

(m

)

Dis

char

ge (l

/s)

Gate opening (m)


Gate opening Upstream water depth Discharge



Head Regulator at Station 2+380 (MC3)

Gate invert 17.000 m elv

Reservoir

Level

Water level

d/s of gate

Gate

openning W µ Q Q

m elv m elv m m l/s m3/s

20.500 17.020 0.02 1.50 0.65 114 0.114

20.500 17.100 0.10 1.50 0.65 563 0.563

20.500 17.200 0.20 1.50 0.65 1,109 1.109

20.500 17.300 0.30 1.50 0.65 1,639 1.639

20.500 17.400 0.40 1.50 0.65 2,151 2.151

20.500 17.500 0.50 1.50 0.65 2,645 2.645

20.500 17.600 0.60 1.50 0.65 3,120 3.120

20.500 17.666 0.67 1.50 0.65 3,424 3.424

20.500 17.700 0.70 1.50 0.65 3,577 3.577

20.500 17.800 0.80 1.50 0.65 4,014 4.014

20.500 17.900 0.90 1.50 0.65 4,432 4.432

20.500 18.000 1.00 1.50 0.65 4,828 4.828

20.500 18.100 1.10 1.50 0.65 5,204 5.204

20.500 18.200 1.20 1.50 0.65 5,558 5.558

20.500 18.300 1.30 1.50 0.65 5,888 5.888

20.500 18.400 1.40 1.50 0.65 6,196 6.196

20.500 18.500 1.50 1.50 0.65 6,478 6.478

19.200 17.020 0.02 1.50 0.65 90 0.090

19.200 17.100 0.10 1.50 0.65 443 0.443

19.200 17.200 0.20 1.50 0.65 864 0.864

19.200 17.300 0.30 1.50 0.65 1,263 1.263

19.200 17.320 0.32 1.50 0.65 1,340 1.340

19.200 17.400 0.40 1.50 0.65 1,639 1.639

19.200 17.500 0.50 1.50 0.65 1,991 1.991

19.200 17.600 0.60 1.50 0.65 2,318 2.318

19.200 17.700 0.70 1.50 0.65 2,618 2.618

19.200 17.800 0.80 1.50 0.65 2,891 2.891

19.200 17.900 0.90 1.50 0.65 3,134 3.134

19.200 18.000 1.00 1.50 0.65 3,345 3.345

19.200 18.100 1.10 1.50 0.65 3,523 3.523

19.200 18.200 1.20 1.50 0.65 3,665 3.665

19.200 18.300 1.30 1.50 0.65 3,766 3.766

19.200 18.400 1.40 1.50 0.65 3,824 3.824

19.200 18.500 1.50 1.50 0.65 3,832 3.832

18.500 17.020 0.02 1.50 0.65 74 0.074

18.500 17.100 0.10 1.50 0.65 361 0.361

18.500 17.200 0.20 1.50 0.65 696 0.696

18.500 17.300 0.30 1.50 0.65 1,004 1.004

18.500 17.400 0.40 1.50 0.65 1,281 1.281

18.500 17.500 0.50 1.50 0.65 1,527 1.527

18.500 17.600 0.60 1.50 0.65 1,738 1.738

18.500 17.700 0.70 1.50 0.65 1,912 1.912

18.500 17.800 0.80 1.50 0.65 2,044 2.044

18.500 17.900 0.90 1.50 0.65 2,129 2.129

18.500 18.000 1.00 1.50 0.65 2,159 2.159

18.500 18.100 1.10 1.50 0.65 2,125 2.125

18.500 18.200 1.20 1.50 0.65 2,007 2.007

18.500 18.300 1.30 1.50 0.65 1,775 1.775

18.500 18.400 1.40 1.50 0.65 1,352 1.352

17.200 17.020 0.02 1.50 0.65 26 0.026

17.200 17.100 0.10 1.50 0.65 97 0.097

17.200 17.125 0.20 1.50 0.65 167 0.167

21 HHgbanQ

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

Gate

op

en

ing

metr

es









Cross Regulator on Main Canal MC1 (Station 1+000, three other similar)

Ap

ple

tA

pp

let

Ap

ple

t

Up

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vel

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it

dis

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ge

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idth

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mb

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f

gate

s

Dis

char

geN

um

ber

of

gate

s

Dis

char

ge

Res

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irG

ate

Y1

Y2

Cc

Cd

V2

q2

W

m e

lvm

elv

mm

mm

/sm

2/s

ml/

sl/

s

18

.63

16

.69

1.9

40

.10

1.8

40

.61

0.6

00

3.7

04

0.3

70

0.7

51

27

82

55

5

18

.63

16

.69

1.9

40

.25

1.6

90

.61

0.5

87

3.6

22

0.9

05

0.7

51

67

92

1,3

58

18

.63

16

.69

1.9

40

.50

1.4

40

.61

0.5

67

3.4

97

1.7

48

0.7

51

1,3

11

22

,62

2

18

.63

16

.69

1.9

40

.75

1.1

90

.61

0.5

48

3.3

84

2.5

38

0.7

51

1,9

04

23

,80

7

18

.63

16

.69

1.9

41

.00

0.9

40

.61

0.5

32

3.2

81

3.2

81

0.7

51

2,4

61

24

,92

2

18

.63

16

.69

1.9

41

.25

0.6

90

.61

0.5

16

3.1

87

3.9

84

0.7

51

2,9

88

25

,97

6

18

.63

16

.69

1.9

41

.50

0.4

40

.61

0.5

02

3.1

01

4.6

52

0.7

51

3,4

89

26

,97

8

18

.19

16

.69

1.5

00

.10

1.4

00

.61

0.5

97

3.2

43

0.3

24

0.7

51

24

32

48

6

18

.19

16

.69

1.5

00

.25

1.2

50

.61

0.5

81

3.1

52

0.7

88

0.7

51

59

12

1,1

82

18

.19

16

.69

1.5

00

.50

1.0

00

.61

0.5

56

3.0

16

1.5

08

0.7

51

1,1

31

22

,26

2

18

.19

16

.69

1.5

00

.75

0.7

50

.61

0.5

33

2.8

96

2.1

72

0.7

51

1,6

29

23

,25

8

18

.19

16

.69

1.5

01

.00

0.5

00

.61

0.5

14

2.7

89

2.7

89

0.7

51

2,0

92

24

,18

4

18

.19

16

.69

1.5

01

.25

0.2

50

.61

0.4

96

2.6

93

3.3

67

0.7

51

2,5

25

25

,05

1

18

.19

16

.69

1.5

01

.50

Fully

op

en0

.61

0.4

80

2.6

07

3.9

11

0.7

51

2,9

33

25

,86

7

17

.69

16

.69

1.0

00

.10

0.9

00

.61

0.5

92

2.6

22

0.2

62

0.7

51

19

72

39

3

17

.69

16

.69

1.0

00

.25

0.7

50

.61

0.5

68

2.5

16

0.6

29

0.7

51

47

22

94

4

17

.69

16

.69

1.0

00

.50

0.5

00

.61

0.5

33

2.3

64

1.1

82

0.7

51

88

72

1,7

73

17

.69

16

.69

1.0

00

.75

0.2

50

.61

0.5

05

2.2

37

1.6

78

0.7

51

1,2

59

22

,51

7

17

.69

16

.69

1.0

01

.01

Fully

op

en0

.61

0.4

80

2.1

29

2.1

29

0.7

51

1,5

97

23

,19

4

16

.89

16

.69

0.2

00

.10

0.1

00

.61

0.5

33

1.0

57

0.1

05

0.7

51

79

21

58

16

.89

16

.69

0.2

00

.20

Fully

op

en0

.61

0.4

80

0.9

52

0.1

90

0.7

51

14

32

28

5



0.00

0.25

0.50

0.75

1.00

1.25

1.50

Gate

op

en

ing

(m

)

Discharge (m3/s)

Cross Regulators MC1 using one gate only





0.00

0.25

0.50

0.75

1.00

1.25

1.50

Gate

op

en

ing

(m

)

Discharge (m3/s)

Cross Regulators MC1 using two gates







References

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3125-CAM(SF) and GoA (DFAT) Grant No. 0285-CAM(EF), Phnom Penh, January 2015.

2 Initial Environmental Examination Tumnub Luok Irrigation System Subproject, Basac Irrigation

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and GoA (DFAT) Grant No. 0285-CAM(EF), Phnom Penh, February 2015.

3 ADB. Safeguard Policy Statement, Policy Paper, Asian Development Bank, Manila, June 2009.

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