, 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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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.
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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
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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;
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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.
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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,
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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
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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.
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Figure 3: Tumnub Luok Catchment
Catchment area: 291 km2
Stream length: 29,000 m
H85: 100 m elevation
H10: 50 m elevation
Tumnub Luok
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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
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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
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 12 Flood Damage Emergency Reconstruction Project – Additional Financing
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.
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Flood Damage Emergency Reconstruction Project – Additional Financing Page 13
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.
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 14 Flood Damage Emergency Reconstruction Project – Additional Financing
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
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)
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 15
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
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Page 16 Flood Damage Emergency Reconstruction Project – Additional Financing
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.
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Flood Damage Emergency Reconstruction Project – Additional Financing Page 17
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.
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 18 Flood Damage Emergency Reconstruction Project – Additional Financing
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.
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 19
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.
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 20 Flood Damage Emergency Reconstruction Project – Additional Financing
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.
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 21
Fig
ure
10:
Ave
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ater
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Apr
Ma
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Jul
Aug
Sep
Oct
No
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Jan
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1.3
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Egis Eau Design Report: Tumnub Luok Irrigation System
Page 22 Flood Damage Emergency Reconstruction Project – Additional Financing
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Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 23
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
Large river flow into Reservoir
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
Normal irrigation releases
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
Large river flow into Reservoir
Continue to record reservoir water level
Go to Signal 2 when reservoir begins to fall
Normal irrigation releases
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
Large river flow into Reservoir
Continue to record reservoir water level
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.
Go to Signal 4 when reservoir begins to fall
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 24 Flood Damage Emergency Reconstruction Project – Additional Financing
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.
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 25
Figure 12: Arrangement of Tumnub Luok Irrigation System
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 26 Flood Damage Emergency Reconstruction Project – Additional Financing
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
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Flood Damage Emergency Reconstruction Project – Additional Financing Page 27
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
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Page 28 Flood Damage Emergency Reconstruction Project – Additional Financing
(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
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 29
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.
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 30 Flood Damage Emergency Reconstruction Project – Additional Financing
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.
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Flood Damage Emergency Reconstruction Project – Additional Financing Page 31
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.
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Page 32 Flood Damage Emergency Reconstruction Project – Additional Financing
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
0+980 Off-take Right bank 1 1.00 - 16.696
1+000 Check Canal 2 1.50 0.75 16.690
1+350 Off-take Right bank 1 0.80 - 16.576
1+640 Off-take Left bank 1 0.80 - 16.479
1+640 Off-take Right bank 1 0.80 - 16.479
1+685 Bridge Type A Canal 1 1.80 1.50 16.464
1+875 Off-take Right bank 1 0.80 - 16.400
1+900 Check Canal 2 1.50 0.75 16.392
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Flood Damage Emergency Reconstruction Project – Additional Financing Page 33
Station Type of
structure Supplying
Number of gates/spans
Diameter/ height
Width Invert
(m) (m) (m) (m) (m elv)
2+270 Off-take Right bank 1 0.80 - 16.123
2+655 Off-take Left bank 1 0.80 - 15.992
2+655 Off-take Right bank 1 0.60 - 15.992
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+870 Off-take Left bank 1 0.80 - 15.594
3+870 Off-take Right bank 1 0.60 - 15.594
3+900 Check Canal 2 1.50 0.75 15.584
4+375 Off-take Right bank 1 0.60 - 14.821
4+385 Bridge Type B Canal 1 1.80 1.50 14.812
4+395 Off-take Right bank 1 0.60 - 14.803
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.
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 34 Flood Damage Emergency Reconstruction Project – Additional Financing
Table 11: Structures along Main Canal MC3
Station Type of
structure Supplying
Number of gates/spans
Diameter/ height
Width Invert
(m) (m) (m) (m) (m elv)
0+070 Off-take Right bank 1 0.80 - 16.979
0+080 Off-take Left bank 1 0.80 - 16.976
0+085 Drop structure Canal 1 1.40 1.50 16.975/16.675
0+510 Off-take Left bank 1 0.80 - 16.547
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 35
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
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Page 36 Flood Damage Emergency Reconstruction Project – Additional Financing
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
Upstream water depth 2.20m
Upstream water depth 1.00m
Upstream water depth 0.20m
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
Upstream water depth 3.50m
Upstream water depth 2.20m
Upstream water depth 1.00m
Upstream water depth 0.20m
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Flood Damage Emergency Reconstruction Project – Additional Financing Page 37
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
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
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.
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Page 38 Flood Damage Emergency Reconstruction Project – Additional Financing
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
Upstream water depth 1.94m
Upstream water depth 1.50m
Upstream water depth 1.00m
Upstream water depth 0.20m
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
Upstream water depth 3.50m
Upstream water depth 2.20m
Upstream water depth 1.00m
Upstream water depth 0.20m
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Flood Damage Emergency Reconstruction Project – Additional Financing Page 39
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 RESERVOIR DAM CH.0+300 TO CH.0+500 TL-CS-002
CROSS SECTION OF RESERVOIR DAM CH.0+567 TO CH.0+780 TL-CS-003
CROSS SECTION OF RESERVOIR DAM CH.0+800 TO CH.0+900 TL-CS-004
CROSS SECTION OF RESERVOIR DAM CH.1+000 TO CH.1+090 TL-CS-005
CROSS SECTION OF RESERVOIR DAM CH.1+100 TO CH.1+334 TL-CS-006
CROSS SECTION OF RESERVOIR DAM CH.1+340 TO CH.1+400 TL-CS-007
CROSS SECTION OF RESERVOIR DAM CH.1+500 TO CH.1+600 TL-CS-008
CROSS SECTION OF RESERVOIR DAM CH.1+700 TO CH.1+825 TL-CS-009
CROSS SECTION OF RESERVOIR DAM CH.1+857 TO CH.2+070 TL-CS-010
CROSS SECTION OF RESERVOIR DAM CH.2+100 TO CH.2+192 TL-CS-011
CROSS SECTION OF RESERVOIR DAM CH.2+200 TO CH.2+500 TL-CS-012
CROSS SECTION OF RESERVOIR DAM CH.2+600 TO CH.2+742 TL-CS-013
CROSS SECTION OF RESERVOIR DAM CH.2+755 TO CH.2+775 TL-CS-014
CROSS SECTION OF MAIN CANAL MC CH.0+000 TO CH.0+300 TL-CS-015
CROSS SECTION OF MAIN CANAL MC CH.0+400 TO CH.0+700 TL-CS-016
CROSS SECTION OF MAIN CANAL MC CH.0+800 TO CH.1+100 TL-CS-017
CROSS SECTION OF MAIN CANAL MC CH.1+200 TO CH.1+500 TL-CS-018
CROSS SECTION OF MAIN CANAL MC CH.1+600 TO CH.1+900 TL-CS-019
CROSS SECTION OF MAIN CANAL MC CH.2+000 TO CH.2+300 TL-CS-020
CROSS SECTION OF MAIN CANAL MC CH.2+400 TO CH.2+700 TL-CS-021
CROSS SECTION OF MAIN CANAL MC CH.2+800 TO CH.3+100 TL-CS-022
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Page 40 Flood Damage Emergency Reconstruction Project – Additional Financing
Drawing List. Stage 2: Contract package FDERP-AF-MOWRAM-CW04 Part A
Drawing Title Drawing No.
CROSS SECTION OF MAIN CANAL MC CH.3+200 TO CH.3+500 TL-CS-023
CROSS SECTION OF MAIN CANAL MC CH.3+600 TO CH.3+900 TL-CS-024
CROSS SECTION OF MAIN CANAL MC CH.4+000 TO CH.4+300 TL-CS-025
CROSS SECTION OF MAIN CANAL MC CH.4+400 TO CH.4+700 TL-CS-026
CROSS SECTION OF MAIN CANAL MC CH.4+800 TO CH.5+000 TL-CS-027
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
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Flood Damage Emergency Reconstruction Project – Additional Financing Page 41
4.2. Stage 3 As-Built Drawing List
Drawing List. Stage 3: Contract package FDERP-AF-MOWRAM-CW07 Part A
Drawing Title Drawing No.
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
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-002
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-003
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-004
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-005
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-006
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-007
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-008
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-009
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-010
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-011
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-012
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-013
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF RESERVOIR DAM RD-CS-014
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
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-002
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-003
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-004
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-005
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-006
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-007
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-008
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Page 42 Flood Damage Emergency Reconstruction Project – Additional Financing
Drawing List. Stage 3: Contract package FDERP-AF-MOWRAM-CW07 Part A
Drawing Title Drawing No.
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-009
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-010
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-011
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-012
CROSS SECTION OF GRASS SODDING ON THE SIDE SLOPE OF MAIN CANAL MC1 MC1-CS-013
PLAN AND PROFILE OF MAIN CANAL MC3 MC3-PP-001
CROSS SECTION OF MAIN CANAL MC3 MC3-CS-001
CROSS SECTION OF MAIN CANAL MC3 MC3-CS-002
CROSS SECTION OF MAIN CANAL MC3 MC3-CS-003
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
CROSS SECTION OF RAISING THE EMBANKMENT DAM 1M DAM-CS-002
CROSS SECTION OF RAISING THE EMBANKMENT DAM 1M DAM-CS-003
CROSS SECTION OF RAISING THE EMBANKMENT DAM 1M DAM-CS-004
CROSS SECTION OF RAISING THE EMBANKMENT DAM 1M DAM-CS-005
CROSS SECTION OF RAISING THE EMBANKMENT DAM 1M DAM-CS-006
CROSS SECTION OF RAISING THE EMBANKMENT DAM 1M DAM-CS-007
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
PLAN VIEW AND SECTION OF GATE INSTALLATION FOR PIPE CULVERT (DIA. 800mm) ON MAIN CANAL MC1
MC1-GI-004
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Flood Damage Emergency Reconstruction Project – Additional Financing Page 43
Drawing List. Stage 3: Contract package FDERP-AF-MOWRAM-CW07 Part A
Drawing Title Drawing No.
GATE PLAN, SECTION AND DETAIL OF GATE INSTALLATION FOR PIPE CULVERT (DIA. 800mm) ON MAIN CANAL MC1
MC1-GI-005
GATE HANDLE GEAR DETAIL OF GATE INSTALLATION FOR PIPE CULVERT (DIA. 800mm) ON MAIN CANAL MC1
MC1-GI-006
PLAN VIEW AND SECTION OF GATE INSTALLATION FOR PIPE CULVERT (DIA. 1000mm) ON MAIN CANAL MC1
MC1-GI-007
GATE PLAN, SECTION AND DETAIL OF GATE INSTALLATION FOR PIPE CULVERT (DIA. 1000mm) ON MAIN CANAL MC1
MC1-GI-008
GATE HANDLE GEAR DETAIL OF GATE INSTALLATION FOR PIPE CULVERT (DIA. 1000mm) ON MAIN CANAL MC1
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
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Page 44 Flood Damage Emergency Reconstruction Project – Additional Financing
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
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Flood Damage Emergency Reconstruction Project – Additional Financing Page 45
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.
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Page 46 Flood Damage Emergency Reconstruction Project – Additional Financing
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).
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Flood Damage Emergency Reconstruction Project – Additional Financing Page 47
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.
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 48 Flood Damage Emergency Reconstruction Project – Additional Financing
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 49
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.
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 50 Flood Damage Emergency Reconstruction Project – Additional Financing
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.
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 51
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 52 Flood Damage Emergency Reconstruction Project – Additional Financing
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%
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 53
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 54 Flood Damage Emergency Reconstruction Project – Additional Financing
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 55
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)
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 56 Flood Damage Emergency Reconstruction Project – Additional Financing
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 57
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)
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 58 Flood Damage Emergency Reconstruction Project – Additional Financing
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 59
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 60 Flood Damage Emergency Reconstruction Project – Additional Financing
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 61
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 62 Flood Damage Emergency Reconstruction Project – Additional Financing
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
1.40 90.00 Open Channel 0.0003 0.030 Canal Section
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
1.40 310.00 Open Channel 0.0003 0.102 Canal Section
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
1.40 300.00 Open Channel 0.0003 0.098 Canal Section
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
1.40 80.00 Open Channel 0.0003 0.026 Canal Section
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)
1.40 15.00 Open Channel 0.0003 0.005 Canal Section
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
1.40 195.00 Open Channel 0.0003 0.064 Canal Section
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
1.40 150.00 Open Channel 0.0003 0.049 Canal Section
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)
1.40 290.00 Open Channel 0.0003 0.095 Canal Section
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)
1.40 40.00 Open Channel 0.0003 0.013 Canal Section
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
1.40 185.00 Open Channel 0.0003 0.061 Canal Section
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®
1.40 20.00 Open Channel 0.0003 0.007 Canal Section
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
CK-2 1 + 900.00 1.40 10.00 1900.00 Check Structure 0.0003 0.003 Check -2
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
1.40 95.00 Open Channel 0.0003 0.031 Canal Section
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®
1.40 330.00 Open Channel 0.0003 0.108 Canal Section
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
1.40 65.00 Open Channel 0.0003 0.021 Canal Section
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
CK-3 2 + 700.00 1.40 10.00 2700.00 Check Structure 0.0003 0.003 Check -3
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
1.40 295.00 Open Channel 0.0003 0.097 Canal Section
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
1.40 75.00 Open Channel 0.0003 0.025 Canal Section
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
OX-2 3 + 80.00 1.40 10.00 3080.00 Oxcart Bridge-2 0.0003 0.003 Oxcart Bridge-2
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
1.40 715.00 Open Channel 0.0003 0.234 Canal Section
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)
1.40 25.00 Open Channel 0.0003 0.008 Canal Section
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
1.40 95.00 Open Channel 0.0003 0.031 Canal Section
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
1.40 380.00 Open Channel 0.0003 0.125 Canal Section
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
OX-3 4 + 385.00 1.40 10.00 4385.00 Oxcart Bridge-3 0.0003 0.003 Oxcart Bridge-3
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
1.40 210.00 Open Channel 0.0003 0.069 Canal Section
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
OX-4 4 + 615.00 1.40 20.00 4615.00 Oxcart Bridge-4 0.0003 0.007 Oxcart Bridge-4
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
1.40 180.00 Open Channel 0.0003 0.059 Canal Section
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
OX-5 4 + 823.00 1.40 28.00 4823.00 Oxcart Bridge-5 0.0003 0.009 Oxcart Bridge-5
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
1.40 179.00 Open Channel 0.0003 0.059 Canal Section
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 63
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 64 Flood Damage Emergency Reconstruction Project – Additional Financing
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
0.12 40.00 Open Channel 0.0003 0.012 Canal Section
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
0.12 20.00 Open Channel 0.0003 0.006 Canal Section
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®
0.12 10.00 Open Channel 0.0003 0.003 Canal Section
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)
0.12 3.00 Open Channel 0.0003 0.001 Canal Section
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
0.12 413.00 Open Channel 0.0003 0.125 Canal Section
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
0.12 10.00 Open Channel 0.0003 0.003 Canal Section
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
0.12 69.00 Open Channel 0.0003 0.021 Canal Section
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
0.12 400.00 Open Channel 0.0003 0.121 Canal Section
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
0.12 23.00 Open Channel 0.0003 0.007 Canal Section
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 65
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/.
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 66 Flood Damage Emergency Reconstruction Project – Additional Financing
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
Flow litres per second
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 67
Head Regulator at Station 1+413 (MC1)
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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
0Fu
lly o
pen
0.6
10
.48
03
.98
31
3.9
40
0.7
51
10
,45
52
20
,91
0
1.5
01
7.0
0-1
5.5
0.1
0Fu
lly o
pen
0.6
10
.60
13
.95
20
.39
50
.75
12
96
25
93
19
.20
17
.00
2.2
0.2
51
.95
0.6
10
.58
93
.87
40
.96
80
.75
17
26
21
,45
2
19
.20
17
.00
2.2
0.5
01
.70
0.6
10
.57
13
.75
41
.87
70
.75
11
,40
82
2,8
16
19
.20
17
.00
2.2
0.7
51
.45
0.6
10
.55
53
.64
52
.73
40
.75
12
,05
12
4,1
01
19
.20
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
.20
17
.00
2.2
1.5
00
.70
0.6
10
.51
23
.36
75
.05
00
.75
13
,78
82
7,5
75
19
.20
17
.00
2.2
2.0
00
.20
0.6
10
.48
93
.21
36
.42
70
.75
14
,82
02
9,6
41
19
.20
17
.00
2.2
2.2
0Fu
lly o
pen
0.6
10
.48
03
.15
76
.94
70
.75
15
,21
02
10
,42
1
17
.00
-17
.00
0.1
0Fu
lly o
pen
0.6
10
.59
22
.62
20
.26
20
.75
11
97
23
93
18
.00
17
.00
1.0
00
.25
0.7
50
.61
0.5
68
2.5
16
0.6
29
0.7
51
47
22
94
4
18
.00
17
.00
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
18
.00
17
.00
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
18
.00
17
.00
1.0
01
.00
0.0
00
.61
0.4
80
2.1
29
2.1
29
0.7
51
1,5
97
23
,19
4
17
.20
17
.00
0.2
00
.10
0.1
00
.61
0.5
33
1.0
57
0.1
05
0.7
51
79
21
58
17
.20
17
.00
0.2
00
.20
Fully
op
en0
.61
0.4
80
0.9
52
0.1
90
0.7
51
14
32
28
5
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 68 Flood Damage Emergency Reconstruction Project – Additional Financing
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5G
ate
op
en
ing
(m
)
Discharge (m3/s)
Head Regulator MC1 using one gate only
Upstream water depth 3.50m
Upstream water depth 2.20m
Upstream water depth 1.00m
Upstream water depth 0.20m
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
Upstream water depth 3.50m
Upstream water depth 2.20m
Upstream water depth 1.00m
Upstream water depth 0.20m
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)
Head Regulator MC1 using one gate only
Gate opening Upstream water depth Discharge
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 69
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
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 70 Flood Damage Emergency Reconstruction Project – Additional Financing
Cross Regulator on Main Canal MC1 (Station 1+000, three other similar)
Ap
ple
tA
pp
let
Ap
ple
t
Up
stre
am
wat
er le
vel
Sill
leve
lU
pst
ream
dep
th
Gat
e o
pen
ing
Gat
e in
wat
erC
on
trac
tio
n
coef
fici
ent
Dis
char
ge
coef
fici
ent
Gat
e ve
loci
tyG
ate
un
it
dis
char
ge
Gat
e w
idth
Nu
mb
er o
f
gate
s
Dis
char
geN
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
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
Egis Eau Design Report: Tumnub Luok Irrigation System
Flood Damage Emergency Reconstruction Project – Additional Financing Page 71
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
Upstream water depth 1.94m
Upstream water depth 1.50m
Upstream water depth 1.00m
Upstream water depth 0.20m
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
Upstream water depth 3.50m
Upstream water depth 2.20m
Upstream water depth 1.00m
Upstream water depth 0.20m
Egis Eau Design Report: Tumnub Luok Irrigation System
Page 72 Flood Damage Emergency Reconstruction Project – Additional Financing
References
1 Subproject Profile Tumnub Luok, Egis Eau in association with KCC for MOWRAM. ADB Loan No.
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
System Subproject, Egis Eau in association with KCC for MOWRAM. ADB Loan No. 3125-CAM(SF)
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.
4 Nordic Development Fund/Asian Development Bank Climate Change Adaptation Project, RRP.CAM
42334, Ministry of Rural Development.
5 Report on Water Availability, Tonle Sap Lowland Stabilization Project, Fraser Thomas with SDC. TA
No. 4756-CAM, ADB, Manila, September 2006.
6 Cambodian Water Resources Profile, Water Resources Management Sector Development Program,
Egis Eau for MOWRAM. ADB Loan 2673-CAM and TA 7610-CAM, Phnom Penh, April 2014.
7 Sir William Halcrow & Partners Ltd. Annex A Hydrology, Irrigation Rehabilitation Study in
Cambodia, Final Report, Sir Wiiliam Halcrow & Partners Ltd in association with Mandala Agricultural
Development Corporation, 1994
8 Farquharson F, Green C, Meigh J and Sutcliffe J. Regional Flood Frequency Analysis, Ed V P
Singh, D Reidel, 1986.
9 Lacey G (1946). A General Theory of Flow in Alluvium, Journal of the Institution of Civil Engineers,
London, 27, 16-47.
10 Watkins L H and Fiddes D. Highway and Urban Hydrology in the Tropics, Pentech Press, London,
92-100 (1984).