Adaptation strategy with public space for pluvial flood risk mitigation in a densely populated city: A case study in Huwei, Taiwan

Study region: Huwei Township is located in Yunlin County, Taiwan, and its urban planning district covers an area of 5.29 km2. The land development in the district is close to saturation, and most of the public facilities have been developed. The flat terrain and the uncompleted storm sewer system lead to frequent flooding.Study focus: This study presents an adaptation strategy of adopting public space to build flood retention facilities (FRF) for pluvial flood risk mitigation in a densely populated city. This study integrates risk and benefit-cost analysis to evaluate the proposed strategy's flood mitigation effect and economic benefit. Huwei is taken as a study region to compare this strategy with traditional storm sewer (SS) construction.New hydrological insights: SS construction reduces flooded areas more than building FRF, leading to more significant flood damage. Since public space is adjacent to residential areas, FRF can directly and effectively reduce residence-related flood damage. Additionally, building FRF is less expensive than building SS. The benefit-cost ratio of building FRF is 0.45, more than twice the 0.21 of building SS. Therefore, we recommend prioritizing the construction of FRF in Huwei rather than finishing the construction of SS. This adaptation strategy can be applied to densely populated cities facing the same problems.