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Thamnop Irrigation and Natural Hydrology in Northeast Thailand

PNC 2011 Annual Conference and Joint Meetings. Thamnop Irrigation and Natural Hydrology in Northeast Thailand. HOSHIKAWA Keisuke Center for Integrated Area Studies Kyoto University, Japan. FUKUI Hayao Faculty of Agriculture Khon Kaen University, Thailand.

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Thamnop Irrigation and Natural Hydrology in Northeast Thailand

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  1. PNC 2011 Annual Conference and Joint Meetings Thamnop Irrigation and Natural Hydrology in Northeast Thailand HOSHIKAWA Keisuke Center for Integrated Area Studies Kyoto University, Japan FUKUI Hayao Faculty of Agriculture KhonKaen University, Thailand

  2. Northeast Thailand:a rain-fed rice cultivation area Rice production Rice planted 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. Irrigation project area/rice cultivation area

  3. How is Thamnopirrigation? “…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…” Thamnop (ทำนบ): dike, dam, embankment, weir “Structures that block stream flow and prevent water from flowing downstream (สิ่งก่อสร้างกั้นลำน้ำไม่ใหลผ่าน)” Report of Ministry of Agriculture in 1912 (KS13/743 ) How is the thamnopirrigaion that played important roles in rice cultivation in the past?

  4. Topics • How is thamnop irrigation? • How does it work? • Structure and function different from “ordinary” irrigation weirs • Why thamnop? • Local hydrological environment and thamnop

  5. How is Thamop? Earthen weir that block up rivers completely Especially seen in Southern part of Northeast Thai and around Siemriap, Cambodia Thamnop Nonburi Surin Province, Thailand

  6. Thamnop Khon Muang Nakhon Ratchasima Province, Thailand

  7. Blocked rivers sometimes make a detour channels Buriram Province Thailand

  8. Former river channel

  9. Thumnup (Thamnop) around Ankor Wat East Barai West Barai Angkor Wat

  10. North of West Barai

  11. Characteristics of Thamnop Stream flow is blocked completely with an embankment longer than width of river channel Almost whole stream water directly flows into paddy fields around thamnop Flooded water reaches sometimes several kilometers from a thamnop

  12. Characteristics of Thamnopirrigation systems Structure • They block up streams completelywithembankments 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.

  13. Characteristics of Thamnop They sometimes cause flood damage on rice plants.

  14. Image search for “weir” “Ordinary” weir File:Revin Meuse weir 20041230- 024.jpg From Wikipedia, the free encyclopedia “Ordinary” weirs: raise and maintain river water level, but not block flow completely (allow overflow)

  15. “Ordinary” weir “Ordinary” diversion weir Water gate that regulate quantity of water intake Diversion channel to send water to paddy fields Weir that can release excess water Spillway along a diversion canal to discharge excess water in a channel Sophisticated system to take stable (or intended) amount of water from rivers

  16. Traditional weir irrigation system “Ordinary” weir Design and functions are basically same. Myanmar, Jan 2003

  17. Spatial distribution of Thamnop irrigation 0m Weir irrigation 900m thamnop Thamnop are constructed along “montainless” rivers

  18. Hydrology of mountainless rivers Why thamnop? Rainfall Runoff ratio = Runoff/Rainfall Evaporation Runoff (initial) Runoff (observed)

  19. Hydrology of mountainless rivers Why thamnop? Precipitation Mun Riv., Northeast Thai (thamnop) 390km2 (M101) Annual prec:1180mm Annual runoff:233mm Runoff ratio:0.20 Runoff Daily runoff (m3/s) Precipitation (mm/d) Ping Riv., North Thai (weir irrigation) 515 km2 (P021) Annual prec:1180mm Annual runoff:369mm Runoff ratio:0.31 1995

  20. Why thamnop? Quick runoff and slow runoff Rainfall Rainfall Quick runoff (surface runoff) Peak runoff Stream Runoff Slow runoff (subsurface) Base runoff

  21. 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.

  22. 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

  23. 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.

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