Management of rainfall-related environmental risks in urban area

Abstract

Rainfall brings urban residents both benefits, such as water resources, but also adverse risks such as flooding. Additionally, it has been recognized that wet weather run-off discharges pollutants and transfers chemicals and pathogen bacteria into the aquatic ecosystem. This causes not only deterioration of water quality but also environmental pollution risk. Both the flood risk and environmental pollution risk are treated here as ‘rainfall-related environmental risks’. Although these two kinds of risks are quite different in their characteristics, the main purpose of urban wet weather flow management is how to decrease these risks. Furthermore, these risks have a similar background which is concerned with both the urban structure and the life-style of urban residents. Recently, flood disaster has occurred in the Japanese urban area with increasing frequency causing damage due not only to rainfall intensity, but also the vulnerability of urban structures against heavy storms. Although there has been urban area expansion and a decline in substrate permeability, wet weather flow management in Japan is aimed simply to drain the increased run-off volume quickly. As for the management of hazardous chemicals which might be discharged together with rainfall run-off, this has not been implemented sufficiently. It is necessary to develop a methodology to reduce rainfall-related environmental risks in urban wet weather flow management. In this paper, the possible risk management process and control options of rainfall-related risks will be discussed after a summary of both the similar and differing points between inundation risk and environmental pollution risk. As a result, it is deemed necessary to operate a scheme to raise the rainfall-related environmental risk perception level of urban residents to ensure their participation in risk management.