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Abstract

She-Zih is a low-lying area in Taipei City where the Tanshui River and Keelung River meet. Average elevation is about 2.5 m. Perennial flood events occur very often. The only flood prevention facility is the 6 m levee built around the perimeter to overcome 20-yr flood events. The main cause of the flooding problem is the instantaneous extreme high rainfall events that often exceed the drainage capacity of She-Zih. Current solutions to relieve this water hazard, suggested by the Water Resources Agency, include channel widening and many water pumping installations. At present, all emergency facilities are insufficient to combat unexpected heavy storms. Therefore, this study attempts to design drainage systems using the available limited land space, along with rainwater catchment systems, in order to achieve the expected flood prevention goal. These study results may provide adequate references for residents and government agencies to design future flood prevention management plans and strategies. This study gathers information from previous literatures to understand initially the effect of storm runoff in this low-lying area, the flood mitigation benefits of building rooftop catchment systems and the drainage systems. Scaled-down rooftop simulation experiments are then conducted with different rainfall intensities and retention rates to evaluate their effects on flood mitigation. Study results indicate that for low intensity rain, a 55% and 69% flood retention efficiency may be obtained using the lower capping device (2.5 cm) and the higher capping device (5.0 cm), respectively. For medium intensity rain, a 58% and 70% flood retention efficiency may be obtained using the lower capping device and the higher capping device, respectively. For high intensity rain, a 46% and 63% flood retention efficiency may be obtained using the lower capping device and the higher capping device, respectively. In addition, eight locations are selected for temporary retention ponds construction in order to enhance the flood mitigation effect. Stored flood water may then be drained out through pumping or connecting drainages ditches.

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