Flood routing in reservoirs using synthetic unit hydrograph: The case of Bung Takreng Reservoir in Yom Basin, Thailand

摘要

The disastrous flood that inundated many areas of the Chao Phraya basin in 2011 caused many detrimental effects on the country's economy and society. It is vital for all concerned to better plan and manage these effects in order to minimize future disasters areas. Flood reduction requires water flow detention or deceleration of during the storm water season. The construction of water detention ponds is one solution that should be taken into account. This study investigated the reduction of water flow in Yom basin (a sub-basin of Chao Phraya basin) using the synthetic unit hydrograph to synthesize deluge parameters. The objectives of this case study are to utilize natural lowland areas upstream of Yom Basin, namely Bung Takreng, Bung Kheerang, and Bung Raman. These three swamps are adjacent to one another, so one detention pond system could be constructed. The relationship between volume (S) and height (H) of the detention pond system was found to be S=18866224.8H~(1.15) based on the analysis of elevation data using Geographic Information System (GIS). The estimated inflow to the detention pond at different return periods was based on the synthetic unit hydrograph. The maximum flow rate was analyzed by flood routing through a modeled reservoir system. The reservoir system was assigned a 3 m height dyke over the spillways, dividing into 2 m for the peak drainage and 1 m freeboard. Flood routing was performed at the return periods of 2, 5, 10, 25, 50, and 100 years. We obtained the following safe lengths of spillway: 30, 70, 100, 140, 175, and 210 m, respectively. The detention pond system can detain water for 4 hr and reduce the peak flow in Yom River to 81.83, 84.44, 77.26, 81.00, 90.81, and 89.81m~3/sec or 9.37, 5.75, 4.08, 3.30, 3.15, and 2.71 percent, respectively. Findings of this study can be applied in decision making regarding the construction size of the reservoirs. In addition, the results can be applied in developing other areas into detention ponds.