The Risk-Based Floodplain Regulation of Shiga Prefecture in Japan

This study shows the overview of the risk-based floodplain regulation implemented by the Shiga Prefectural Government. Shiga, located near Kyoto in central Japan, is home to Lake Biwa, the largest lake in the country. Approximately 500 rivers flow into Lake Biwa from the steep surrounding mountains. The population is concentrated in alluvial cones and alluvial plains. The Shiga Prefectural Government enacted the integrated flood management ordinance in March 2014. This ordinance includes land use and building regulation measures in order to promote flood risk reduction for excessive flood events based on the newly developed risk evaluation method, which is the first in Japan. The goal of the risk-based floodplain regulation is to make use of existing legal framework for effective land use and building regulations, based on comprehensive flood hazard risk maps, to indicate both the damage levels and occurrence probabilities of various floods at all sites in a flood plain.