Concurrent Potential for Flooding Risk Reduction of Decentralized Rainwater Management System

摘要

Centralized water management system has problems about water supplying and flood control as it manages rainwater only for single purpose. When rainfall occurs, the system discharges rainwater quickly to end of the basin as priority without consideration about using rainwater as a water resource on-site. It has negative effects as it consumes excessive energy to treat and supply water from water treatment plant. Above all, the centralized water management system increases flood risk occurrence potential by dealing only peak flow rate at end of basin. Climate change and urbanization makes centralized water management system worse. Accordingly, in this research, we introduce multi-purpose decentralized rainwater management system as a solution which supplies water and controls flood concurrently. First, design type and installation place of decentralized rainwater management system (DRMS) is suggested. Second, flooding risk reduction potential through evaluation of runoff reduction and flood occurrence is quantitatively measured using XP-SWMM. Third, potential for rainwater harvesting potential for water resources securement is quantitatively measured. Detail factors to measure the effects of water resources securement are usable water volumes, energy saving amount, and pollutants load. Finally, we suggest optimum design type of DRMS and analyze the effects of design improvement at existing drainage system. When total volume of the rainwater storage tank (RST) is same, study results showed more and smaller RSTs are installed the better runoff reduction at end of basin. This result means flooding risk reduction effect of DRMS. The effect of runoff reduction was most favorable in case of MWS-a type. These results mean that we can find optimum design type of DRMS to improve flood risk reduction potential. Also on-site control of rainwater through the DRMS affects water quality positively as catchment area changes. It is expected to use guideline to decide optimum volume of RST from a decision maker related to urban water management of a government.