The effectiveness of detention pond for reducing properties flood damage

Flood frequently occurs in the raining seasons. Basically, the flood is occurred caused by the inflow discharge is bigger than river capacity. The properties under inundation areas will be damaged. The value of properties damage depends on the depth and area of inundation. Therefore, it is necessary to reduce the inundation area to minimize the properties damaged. The effectiveness of detention pond is applied to reduce the inundation area. This scenario was applied to Kali Lamong River. This river is occupied 714.654 km² watershed area and the outlet located in Surabaya city, Indonesia. The Nakayasu Synthetic Unit Hydrograph was used to analyze the runoff discharge. This runoff data was used as main input data to predict the water level in the river. Based on the water level produced from HEC-RAS, the inundation area was plotted on the topographic map. The property loss was analyzed base on the high resolution satellite remote sensing image overlaid with inundation map. The property loss was calculated by the price of unit area for each land cover type time the inundated area. The detention ponds were set up in the upper stream area to reduce the properties damaged caused by the flood. From the simulating result, it can be concluded that 3,914,000 m³ detention pond can be reduced the damaged properties equal to the US $ 2,850,000. From this research, it can be shown that the detention pond is effective to reduce the properties damage caused by the flood.