10.4122/1.1000001523 Morita, M. Yamashita, K. Decision support system for storm design level based on inundation damage simulation and risk analysis using GIS DTU Library, Technical University of Denmark (DTU) 2005 Risk analysis inundation simulation inundation damage storm design level Shibaura Institute of Technology, Department of Civil Engineering en Conference presentation 10.4122/1.1000001524 text/xml 1 To decide a storm design level for flood prevention in urban areas is a crucial task for local governmental engineers. The objective of this study is to present a risk analysis method for storm design level decisions. The concept of \342\200\234risk\342\200\235 is defined as the product of flood damage and its occurrence probability. The study also presents a flood damage prediction system using GIS to calculate flood damages for any design storms with different return periods. The calculated monetary damages for the design storms with their occurrence probabilities enable us to quantify flood inundation risk based on the concept of \342\200\234risk.\342\200\235 The Tokyo Metropolitan Government has adopted a storm design level of 15-year return period, 75 mm/hr. The government constructed in 1997 a flood control reservoir, Loop-7 Reservoir, for flood risk reduction in the Kanda river basin. Through the risk analysis method, the relation between storm design level and annual risk density is calculated for two cases: with and without the flood control reservoir. The design level of the government, 75 mm/hr, is discussed on the basis of the annual risk density curves and the risk reduction effect of the reservoir is clarified by the results of the risk analysis.