Reference
Effects of Pasak reservoir on the flood levels of the lower Chao Phraya
river from Ayutthaya to Bangkok, Master of engineering thesis, AIT,
April, 1997.
Authors :
Surachai Laikarnchanapaiboon
Summary :
The flood problems in the lower Chao Phraya river basin cause severe
damages in the lower Chao Phraya flood plain and especially in Bangkok. The Pasak
reservoir is constructed on the Pasak river for multipurpose including flood control,
irrigation and water supply. The Pasak reservoir regulates the flood inflow and releases
the stored flood volume into the Pasak river before joining with the Chao Phraya river at
Ayutthaya province. In this study, two mathematical models namely the HEC-5 model for
reservoir flood control and water conservation system and the MIKE 11 hydrodynamic model
for flood routing are used.
The HEC-5 model is applied to route the design flood inflow of 100, 500 and 1 000 year
return periods to downstream of the Pasak river. The MIKE-11 model is applied to route the
release from the Pasak dam along the Pasak river to its confluence with the Chao Phraya
river at Ayutthaya and from Ayutthaya along the Chao Phraya through Bangkok to the river
mouth at Fort Chula. The flood hydrographs at various station along both rivers are
computed for the cases with and without the Pasak reservoir.
The MIKE-11 model was calibrated successfully using the hourly flood data from 10 Sep to
30 Nov, 1987 and verified using hourly flood data from 1 to 30 Nov, 1995. The results of
model applications shown that the flood peak levels in the Pasak river are decreased by
0.27 m (at station S26) to 0.55 m (at station S9) along the river for the 500 year return
period flood with a delay in the time peak from 8-24 hours, and by 0.35 m (at station S26)
to 0.68 m (at station S9) for the 1 000 year return period flood and time delay in flood
peak is about 1 day. For the Chao Phraya river, the effects of the Pasak reservoir on the
flood peak levels is negligible due to small flood volume of the Pasak river (1 000 year
return period) compared to that of the Chao Phraya river of 20 year return period.
However, there is a significant delay in the time to peak of 1 to 2 days due to the
routing effect of the Pasak reservoir.
Keywords :
Chao Phraya river / Flood modelling / Pasak reservoir / Pasak river /
Contacts :
Asian Institute of Technology
http://www.ait.ac.th/
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