Mimikawa River with seven dams and power stations in operation runs in the eastern area of Kyushu. With a total output of 341MW, the river basin is an important hydro-energy source in the Kyushu region. Typhoon No. 14 in 2005 brought record-breaking heavy rainfall, causing severe slope failures in approximately 500 locations. This experience raised awareness of the potential risk of slope failures which might occur in Mimikawa River Basin. Kyushu Electric Power owns hydroelectric power stations distributed over a wide area in this basin. From the viewpoint of appropriate dam operation, facility maintenance, and medium-long term installation, it is essential to understand the future risk of disaster due to slope failures, in advance, and optimally control this risk. However, because the slope failure phenomenon is very complex, and occurs over a wide area of the Mimikawa River Basin, there are no established methods to predict or manage these failures. The unprecedented Typhoon No. 14 disaster experience has provided key data for future slope failure prediction. By carrying out investigations such as a wide-area survey of slope failures, characteristics of slope failures including the locations, scales, failure mechanism and the level of rainfall that causes failure were clarified. In addition, through the use of information obtained from records of past disasters, a simplified method for wide-area slope failure prediction based on the characteristics of the river basin was structured. And through the use of this information and this method, the authors sought to identify slopes for which failures might occur and the level of rainfall that would cause failure (risk map). One example of specific hydroelectric installation risk management was also considered.