HOSHIKAWA KeisukeCenter for Integrated Area StudiesKyoto University, Japan

PNC 2011 Annual Conference and Joint Meetings

Thamnop Irrigation and Natural Hydrology in Northeast Thailand

FUKUI HayaoFaculty of AgricultureKhon Kaen University, Thailand

Northeast Thailand:a rain-fed rice cultivation area

Northeastern Region

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1933 1943 1953 1963 1973 1983 1993

rai

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ton

0 200km0 200km0 200km

Rice planted area

Rice production

0.0 - 0.10.1 - 0.20.2 - 0.30.3 - 0.40.4 - 0.50.5 - 0.60.6 - 0.70.7 - 0.80.8 - 0.90.9 -

Irrigation project area/rice cultivation area

However, Northeast Thailand also has history and tradition of irrigation for rice cultivation.It was widely practiced before the expansion of rice area.Still in use.

How is Thamnop irrigation?

“…paddy fields in Phanchana District mostly depend on water from thamnop as this district has many streams. Lam Chiang Krai River is one of the most important streams. Some thamnop on it are supplying water to paddy fields. If there are no thamnop in the district, rice cultivation should depend only on rainfall, and transplantation has not finished by until this month…”

Report of Ministry of Agriculture in 1912 (KS13/743 )

How is the thamnop irrigaion that played important roles in rice cultivation in the past?

Thamnop (ทำ�นบ): dike, dam, embankment, weir“Structures that block stream flow and prevent water from flowing downstream (สิง่ก่อสร�้งกัน้ลำ�นำ้�ไมใ่หลผ่�น)”

Topics

• How is thamnop irrigation?• How does it work?

– Structure and function different from “ordinary” irrigation weirs

• Why thamnop?– Local hydrological environment and thamnop

Earthen weir that block up rivers completely

How is Thamop?

Thamnop NonburiSurin Province, Thailand

Especially seen in Southern part of Northeast Thai and around Siemriap, Cambodia

Thamnop Khon MuangNakhon Ratchasima Province,Thailand

Blocked rivers sometimes make a detour channels

Buriram ProvinceThailand

Former river channel

Thumnup (Thamnop) around Ankor Wat

Angkor Wat

West Barai

East Barai

North of West Barai

Stream flow is blocked completely with an embankment longer than width of river channel

Characteristics of Thamnop

Almost whole stream water directly flows into paddy fields around thamnop

Flooded water reaches sometimes several kilometers from a thamnop

Characteristics of Thamnop irrigation systems

Structure• They block up streams completely with

embankments that are often several times longer than width of river channels.

• No water gate to regulate water intake.

Function• Quantity of water intake is not controllable.• It depends on amount of river runoff.• As a consequence, thamnop often make flood

damage on rice plants.

They sometimes cause flood damage on rice plants.

Characteristics of Thamnop

Image search for “weir”

File:Revin Meuse weir 20041230- 024.jpgFrom Wikipedia, the free encyclopedia

“Ordinary” weirs: raise and maintain river water level, but not block flow completely (allow overflow)

“Ordinary” weir

“Ordinary” diversion weir

Weir that can release excess water

Water gate that regulate quantity of water intake

Diversion channel to send water to paddy fields

Spillway along a diversion canal to discharge excess water in a channel

Sophisticated system to take stable (or intended) amount of water from rivers

“Ordinary” weir

Traditional weir irrigation system

“Ordinary” weir

Myanmar, Jan 2003

Design and functions are basically same.

Spatial distribution of Thamnop irrigation

0m

900m

Weir irrigation

thamnop

Thamnop are constructed along “montainless” rivers

Hydrology of mountainless riversRunoff velocity

Sensitivity to rainfall

Runoff ratio(runoff/rain)

Shape of peaks

Rivers in plain areas(thamnop)

Low Low Low Gradual low peaks

Rivers in mountainous areas(weir irrigation)

High High High Sharp high peaks

Why thamnop?

Evaporation

Runoff (observed)

Rainfall

Runoff (initial)

Runoff ratio =Runoff/Rainfall

Hydrology of mountainless riversRunoff velocity

Sensitivity to rainfall

Runoff ratio(runoff/rain)

Shape of peaks

Rivers in plain areas(thamnop)

Low Low Low Gradual low peaks

Rivers in mountainous areas(weir irrigation)

High High High Sharp high peaks

Daily

runo

ff (m

3/s)

Prec

ipita

tion

(mm

/d)

1995

Precipitation

Runoff

Mun Riv., Northeast Thai (thamnop)

390km2 (M101)Annual prec:1180mmAnnual runoff:233mm

Runoff ratio:0.20

Ping Riv., North Thai (weir irrigation)515 km2 (P021)

Annual prec:1180mmAnnual runoff:369mm

Runoff ratio:0.31

Why thamnop?

Quick runoff and slow runoffRainfall

Quick runoff (surface runoff)

Slow runoff(subsurface)

Stream

Base runoff

Peak runoff

Rainfall

Runoff

Why thamnop?

Hydrology of a weir irrigation river

• Runoff consists of peak flow and base flow.• Stable and rich base flow.

There is no reason to dare to use peak runoff, as peaks are sharp and short lasting.

Why thamnop?

Hydrology of a thamnop irrigation river

• Difficult to separate base flow and peak flow because of long lasting low peaks and unstable base flow

• Water resource is rather limited because of low runoff ratio.

It is better to take whole runoff at every moment

Why thamnop?

Conclusions

• Thamnop irrigation much depends on river runoff.

• This does not mean that thamnop irrigation is less efficient than weir irrigation.

• The thamnop irrigation system is well designed by local people for mountailess rivers.