RELATIONSHIP BETWEEN WATER MANAGEMENT OF AN IRRIGATION POND DURING HEAVY RAINS AND FLOOD STORAGE

In irrigation ponds, water management protocols, such as reservoir water release, can be achieved during heavy rains using ditch riders. In this study, such water management practices used in O-pond, Kagawa Prefecture, during three frontal rainfall events in 2020 were investigated. Information collected from interviews after the rainfalls revealed that the dich rider operated the inflowing channel diversion gates during heavy rains based on an empirical method to ensure irrigation water storage but also prevent sediment inflow and/or overflow of the irrigation channel. Estimation of the O-pond flood storage rate from reservoir water level records further suggested that the gate-opening condition used impacted the flood storage outcome. Hence, in the O-pond catchment, most rainfall-runoff concentrated in the inflowing channel and, thus, the flood inflow was controlled by the gate operation. In summary, if the runoff pathway is similar for larger rainfall events, the flood control effect of O-pond will depend on the gate operations.