Author(s): Chukait Sapphaisal; Napaporn Piamsa-Nga; Keiji Nakatsuji
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Keywords: Flood analysis; Alternative measure; Simulation; Bangkok; The Chao Phraya River
Abstract: The present study has discussed flood protection and drainage network system of the Eastern Bangkok Metropolitan Area (650 km2) and some challenging drainage alternative utilizing klongs (canals), retention reservoirs and pumping stations. Owing to the human intervention greatly changed in land use in the last 2 decades, the hydrological and hydraulic water balance have greatly changed and storm flooding has frequently recorded either in the urban area or in the border area of the Eastern Bangkok Metropolitan Area. Based on the one-dimensional mathematical model representing of the situation in the actual natural system, the simulation of rainfall-runoff processes together with runoff hydrograph of the existing and improved drainage system in the area was examined. The simulation model has been applied to predict the storm flooding hydrograph with different return periods of the short and long duration of rainfall. The simulation results of storm flooding hydrograph of some challenging drainage alternative in the area were also presented. The simulation reveals that the present drainage system cannot cope with the 5-year return period of rainfall under the land use in 2016. During the formulation of the study, three alternatives are proposed; namely A-1 klong improvement works and increases in number of A-2 retention reservoir and A-3 underground tunnel. The alternative A-1 which uses only present reservoirs demonstrates that water level in Klong Lat Phrao becomes below the height of the klong bank if the klong bottom is excavated to the level of -5. 5 m MSL. The recommended alternative includes reservoirs; tunnels and setting the initial water level in the klongs are -1. 0 m MSL for avoiding the influence on water levels in the secondary klongs. The simulation result shows that the improved bottom level of Klong Lat Phrao is between -3. 0 and -3. 5 m MSL. The simulation results demonstrated that the flood drainage system in Bangkok is almost 5-year return period. Therefore, in order to make the drainage system more successful before or after the rainy seasons, the operations of klongs, reservoirs, and pumping stations must be systematically synchronized. 1181
Year: 2005