Abstract
There are many old small dams for irrigation in Japan. Most of them were constructed by primitive method before the Meiji era, and have much lower spillway volume than that of modern design criteria. In this study, we tried to apply the mean variance model (MVM) to small dam repair works for maximization of benefit by cost (B/C) and its stability with the works. In this application, 1) small dam repair works were considered as a portfolio, 2) return of each small dam repair work was calculated as IRR (internal rate of return) in its life cycle period with each probable flood, 3) an expected return rate and a standard deviation of each small dam repair work were calculated by approximated probabilities of scenario to probabilities of exceedence with floods. It was cleared from this application that each weight or order of priority with repair works is able to be decided by the sharp ratios and expected return rates with them.
