1. Study on performance of dry season rotational irrigation for Mae Lao irrigation project, Thailand
Naritaka KUBO: Univ. of Tokyo, Japan
Takuya TAKEUCHI: Tokyo Univ. of Agri. & Tec., Japan
Unggoon WONGTRAGOON: Rajamangala Uni. of Tec., Thailand
Hajime TANJI: NIRE, NARO, Tsukuba, Japan

2. Back Ground In south east Asian countries…
Irrigation projects were developed primarily for supplemental supply during rainy season
Constructing new reservoirs makes irrigation possible during dry season
Water supply is not enough
Restricted irrigation areas because of scare water
Necessity of effective water use

3. Mae Lao irrigation scheme
Project site
Mae Lao irrigation scheme
Tributary of the Kok River belonging to Mekong River basin
Chiang Rai in North Thailand
Irrigation Area : ha

4. Mae Lao project site Right Main Canal （RMC） - RMC length ：about 50 km
Branch 3
4,848 ha
Branch 2
5,264 ha
Branch 1
7,968 ha
Branch 4
5,600 ha
Mae Lao river
Left Main Canal
Right Main Canal
Mae Lao weir
Mae Suai Dam
Laterals
Streams 5
10 km
Mae Suai Dam
Mae Lao Weir
Right Main Canal （RMC）
　- RMC length ：about 50 km
　- Secondary canals ： 23
　- Max Q： about 27 m3/s
18,080 ha

5. Water deficit in dry season
Interviews
Branch 1
　　・Water deficit occurs partially
Branch 2
　　・Irrigation area is expanded beyond allotted area
　　・Water deficit occurs in downstream areas
Branch 3
　　・Water deficit is serious
　　・No water comes to downstream areas

7. Summary of interviews Problem identification
Mae Suai Dam can store 73,000,000 m3
Low distribution efficiency
Unequal water distribution
Functional problems
Managerial problems
Illegal activities
　Problem identification

8. 　　Objectives
Quantitative analysis of effects of facilities　and water management on water distribution performance
1. Planning phase
Continuous irrigation by non-uniform flow model
Effects by physical causes of facilities & structures
2. Execution phase
Rotational irrigation simulated by UIWDC model
Effects by managerial & institutional causes

9. Methodology Numerical simulation by UIWDC model（Unggoon et al., 2010）
　（Unsteady Irrigation Water Distribution and Consumption）
Water movement in canal
⇒　1-D unsteady flow model
Water consumption in paddy field
⇒　Paddy Tank model
Saint-Venant Equations
inundated
Plow layer
A：Area, Q：Flow, q：side flow, h：depth, g：gravitational acceleration, S0：bed slope, Sf：friction slope, u：mean velocity
Ground
Water

10. Modeling of irrigation systemHW 1L 2L 3L 4L
Paddy field CK
Check structure PF
withdrawal
Direct
Branch 1
Branch 2
5L~12L
Branch 3
13L~22L

11. Modeling of FTOs and water distribution

12. Intake flow rate (IFR) 1. Based on water requirement Qs
2. Base on non-uniform flow calculation Qe （considering physical properties）
Assumptions for Calculation
Equal water distribution within a branch
Daily water consumption in paddy field:14.7 mm/day
Each branch is calculated independently
Total paddy field area in Branch i : Ai
Scheduled area to be irrigated in Branch i : Asi

13. 1. Calculation of scheduled IFR Qs
Exact water volume to irrigate area of Asi
　⇒　Scheduled Qsi for Branch i
Based on water requirement
　＝Paddy water consumption ×Asi
+ Seepage loss
Canal seepage losses are calculated assuming Full Supply Level PF
to be
irrigated
not to be

14. 2. Calculation of equilibrium IFR Qe
Calculated by numerical simulation for non-uniform flow
IFR at equilibrium
　（useless spillage＝deficit）　　
deficit
⇒Equilibrium Qei for Branch i　　
Paddy field
canal
Spillage
Canal seepage loss considering Non-uniform Flow Level
Inlet of FTO

15. Result (1) Scheduled area vs. IFR Q
Maximum Flow Rate 27 m3/sec
Scheduled Qsi & Equilibrium Qei
Scheduled area ratio (Asi/Ai)
Intake Flow Rate (m3/s)
No differences at no seepage losses
→ caused by seepage losses
Lower water level than that of FSL
Longer distance causes more losses

16. Result (2) Scheduled area vs. WSR
WSR = [Actually distributed water]/[Volume to be distributed]
(Water supply ratio)
WSR
Branch 1
Branch 2
Branch 3
Scheduled area ratio (SAR Asi/Ai)
Larger canal section
Lower water level
Higher threshold of FTO
More difficult withdrawal
Lower WSR
More upstream

17. Rotational irrigation （execution phase）
Intake Flow Rate Q : 10 m3/s
Field water supply : 3 times of daily water requirement
5 days
Observance of rotation :
Upstream branches do not withdraw water during off-turn
Strict application rule:
Water withdrawal stops when ponded water exceeds 100 mm depth, and irrigation re-starts at 80 ％ of soil moisture
5 days
5 days

18. Water management conditions
Planning water management （Type O）
Observance of rotation
Strict application rule
Possible water managements
Type A :
Direct FTOs use riparian right and application rule is strict
Type B :
All FTOs observe rotation and application rule is not strict
Type AB :
Direct FTOs use riparian right and application rule is not strict

19. Result (3) WSR corresponding to water management types
Along RMC
Along lateral canal
WSR
Branch 1
Branch 2
Branch 3
WSR
Branch 1
Branch 2
Branch 3
1. Low WSR for Branch 1 along RMC
2. High WSR for Branch 2 along RMC at AB type management
3. Low WSR for Branch 3 along lateral canal at AB type management

20. Result (4) Direct FTO WSR along RMC based on type O
Branch 2
Branch 3
Branch 1
Upstream
Downstream
WSR
Larger cross section
High inlet of FTO
Lower water level
Difficult withdrawal

21. Checks, Laterals and Spill ways along RMC

22. 　　 Result (5) Direct FTO WSR in Branches 2 and 3, along RMC based on types of O and AB
Sure water
withdrawal
Excessive
at off-rotation O
WSR
Branch 2
Branch 3 AB

23. Result (6) FTO WSR at laterals in Branch 3 based on types of O and AB
Excessive
withdrawal
at midstream
Water
deficit at
downstream
13L
14L
15L
17L
17La
18L
19L
20L
21L
22L
WSR AB

24. 　　Conclusion
Water distribution performance is influenced by structures and strictness of water management
Influence by structures
　　　Water withdrawal is restricted when water level is low.
Influence by strictness of water management
　　　One of two observances of rules improves water
distribution performance considerably
Other wise
　　　Excessive withdrawal at middle branch
　　　Serious water deficit at downstream branch