Flood risk analysis for determining optimal flood protection levels in urban river management

The objective of the paper is to present a specific risk-analysis method for the assessment of optimal flood protection levels in urban flood risk management using intensity-duration-frequency relationships. Risk herein is understood as the product of flood damage potential and its occurrence probability. The risk analysis is based on a geographic information system-based flood damage prediction model to calculate flood damage for design storms with different return periods. Estimation of the monetary damages for these design storms and their return periods is the prerequisite for quantifying flood risk based on an annual risk density curve. The risk-analysis method is applied to determine optimal flood protection levels for the Kanda River basin in Tokyo, Japan. It shows how two cost curves can be used: risk cost reduction curves and capital cost curves.