This study discusses the feasibility of maintaining storage capacity for small-scale hydropower generation by operating flood control dams flexibly.Currently in Japan, shortages in electrical supply have been a concern. It is hoped that this study will mitigate such shortages.For flexible dam operation, it is necessary to recover the dam's flood control capacity by releasing dam water ahead of predicted flooding. To obtain water for small-scale hydropower, a flexible dam operation using the cumulative forecasted rainfall for pre-releasing was considered. We examined such release by using the flood date of previous years. It was found that recovering flood control capacity of a dam is possible before the start of storing flood water. It was found that by using appropriate dam operation, there is a possibility for securing dam water for small-scale hydropower.