Effect of Large Scale Dams on Hydrological Regime in the Chao Phraya River Basin, Kingdom of Thailand. 2 Chanchai Suvanpimol 3

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1 Chao Phraya Effect of Large Scale Dams on Hydrological Regime in the Chao Phraya River Basin, Kingdom of Thailand 1 2 Chanchai Suvanpimol 3 Taichi TEBAKARI, Junichi YOSHITANI and Chanchai SUVANPIMOL 1 JST/CREST Ms. Eng Ms. Eng.Hydrology Division, Royal Irrigation Department (811 Samsen Road, Dusit, Bangkok 10300, Thailand) The purpose of this paper is to evaluate the effect of the human activities on water resources and hydrological cycle. The Chao Phraya River basin was selected for this study. The Chao Phraya River basin, the largest basin in Kingdom of Thailand is located in central and northern part of Thailand. This basin has two large-scale dams named Bhumibol Dam across the Ping River and Sirikit Dam across the Nan River. This large storage dams are beneficial to the country for generating electricity and discharging water for the irrigation project areas and flood mitigation on both banks of the Ping, Nan and the Chao Phraya rivers. There is no the long-term increase and decrease tendency of the precipitation. As the results of comparing the annual change of monthly runoff before and after dam construction, the minimum runoff increased and the maximum runoff degreased. As the results of spectrum analysis using FFT, after the Bhumibol dam was constructed, the daily runoff in Nakhon Sawan had period characteristics in 3.5 days and 7 days and the released water from the Bhumibol dam had period characteristics in 2.5 days, 3.5 days and 7 days. Dam operation effected on the hydrological cycle considerably. Key Words: large scale dam, Chao Phraya River Basin, water resources 1350 Ayutthaya Chao Phraya Tha Chin Mae Klong Bang Pakong Chao Phraya Chao Phraya 1) Chao Phraya 3,000 Chao Phraya 38GDP 58 Chao Phraya Greater Chao Phraya Project GDP

2 Chao Phraya Chao Phraya Ayutthaya ) Chao Phraya Yehonman vander Heide 1902 Canal Department 1964 Bhumibol 1977 Sirikit Chao Phraya Chao Phraya Pasak Ping Wang Yom Nan Chao Phraya River 1893 Ayutthaya Ayutthaya Chao Phraya Pasak Lop Buri 51.4 k Ayutthaya 1914 Krom Thod Nam or Barrages Department 1927 Royal Irrigation Department RID Chao Phraya 9 30 Ministry of Water Resources and Environment 2002 Chao Phraya

3 Bhumibol Sirikit Nakhon Sawan Bhumibol Dam Bhumibol P.12 Basin1 Bhumibol P.12 5 Chao Phraya 157, Chao Phraya Nakhon Sawan Ping 36,018k Wang 11,708k Yom 24,720k Nan 34,557k Nakhon Sawan 3) Ayutthaya Pasak 1957 Ping Bhumibol 1961 Nan 1977 Nan Sirikit RID Nakhon Sawan Ping 2 Nan Wang 1 Yom Wang Yom EGAT(Electricity Generating Authority of Thailand: )

4 Bhumibol Sirikit N.12A Basin Bhumibol 4km P Bhumibol Sirikit 3km P.12 P N.12A Nakhon Swan Ping Nan Chao

5 Bhumibol Dam Sirikit Dam Rainfall No Data Sirikit N.12A Nakhon Sawan Phraya Nakhon Sawan Bhumibol 225kmSirikit 325km C.2 N f(1)f(2)f(n) Bhumibol N ( n 1)( k 1) F( n) = ( ) ( ) f k W n = 1,2, L, N Bhumibol W = exp( i2π N ) Nakhon Sawan 2mm Bhumibol Sirikit Wang Yom FFT FFT Nakhon Sawan k=

6 Nakhon Sawan Bhumibol FFT Nakhon Sawan 5) Bhumibol Bhumibol Chao Phraya Chao Phraya 1957 Bhumibol 1977 Sirikit 2 1) ) Royal Irrigation Department (2002): History of water Resources development in Thailand, pp Chao Phraya 58 Bhumibol pp ) 2003Chao Phraya 47 4) pp pp.574 Sirikit 5) 2002GAME-T 202 pp Chao Phraya Ping Nan Nakhon SawanC.2 6) 7) Bhumibol 8) 1995 Wang Yom Bhumibol