An analysis of the flood mitigation function of a reservoir for irrigation purpose: - the cases of the release from the Ohsako Dam during floods -

摘要

An irrigation dam is considered to show flood mitigation function that reduces the peak flow of flood with its storage function in the course of being utilized as water source for irrigation. Consequently, we investigate the actual conditions of inflow and discharge during floods in the Ohsako Dam and clarify that peak discharge decreases as against peak inflow and that there are some cases of floods where peak discharge does not decrease very much. Further, we analyze discharge as against inflow concerning flood mitigation function of dam by using hydraulics and make it clear that flood mitigation function is created by cutting flood with storage capacity or temporary storage above spillway crest.