Effects of flood mitigation policies under climate change scenarios based on the cost-benefit perspective in the mountainous Korean basin

This study aimed to evaluate the effects of combined flood mitigation measures on flood mitigation, cost-benefit, and hydrological system changes in forecasted future floods. Sewer enlargement was implemented in all mitigation scenarios, and two LID (Low Impact Development) measures, green roofs and permeable pavement, were implemented with fractions. Implementing green roofs affected two hydrologic components more, namely, evaporation loss and surface runoff, whereas permeable pavements affected infiltration loss more. Similar to infiltration loss, flood components were more affected by permeable pavements than by green roofs, whereas external outflow increased when implementing only sewer enlargement without LID measures, which may increase downstream damage. The flood damage reduction effects per cost in peak flow and external outflow were clearly better when green roofs were not implemented, which showed higher costs but less impact vis-à-vis flood mitigation. Implementing only sewer enlargement showed the best damage reduction per cost in flooding loss, whereas the amount of flooding loss was significantly larger than that of other scenarios with additional LID measures.