The examination of the present flood control plan for the Yodo River System based on simulated flood damages by the recurrence of the largest recorded flood in Lake Biwa basin People living at Lake Biwa shoreline areas have suffered from inundation damages from the ancient time, they strongly desire to relieve themselves from these damages. The largest recorded flood in Lake Biwa basin after Meiji Restoration occurred in 1896, but it occurred long time ago so that little hydrological and hydraulic data such as rainfall data , discharge data of the rivers which are basic information for preparing a flood control plan are left. Therefore we can't take this flood into consideration when we make the flood control plan for Lake Biwa basin. Based on the importance of the analysis of the largest recorded flood, we tried to collect as much data as possible about this flood and simulate this flood correctly based on collected data. And we also analyzed the damage by this flood. Due to the results of the analysis, if this flood occurred now, the water level of Lake Biwa would be higher than the present design flood level even if Setagawa Barrage, which was constructed at the outlet of Lake Biwa, were totally opened. On the other hand , the precipitation in the Kizu and Katsura River basins would be not very large, so the present river-related facilities would be enough for the prevention of the flood damage even if Setagawa Barrage were totally opened. But for the Uji River basin, it is clear that further counter measures for this flood must be taken because the discharge in the river would exceed the actual capacity of flow .

In the Lake Biwa watershed as one of marginal regions of metropolitan area, the land-use transformation and the deterioration of water quality resulted mostly from the implementation of rapid urbanization in addition to a variety of regional developments plans such as the Lake Biwa Comprehensive Development Plan (LBCDP, 1972(LBCDP, -1997. During the last phase of the LBCDP, the government of Shiga Prefecture began to consider how to ensure the comprehensive conservation of the lake for future generations. Therefore the "Lake Biwa Comprehensive Conservation Plan (LBCCP, Mother Lake 21 Plan)" was started in March 2000. The LBCCP aims at turning Lake Biwa into a model for lake conservation in the 21 st century by pursuing a broad spectrum of activities to maintain water quality and to preserve the natural environment and scenic landscape. The purpose of this study is to introduce our challenges to environmental conservation at the river-basin level in LBCCP.