Assessing Impact of Discharge Control on Mitigating Peak Discharge from Paddy Plot

— A case study of Yamato Plain Area in Nara Prefecture, Japan —

Abstract

Integrated flood control in the entire basin has been focused as a flood control. The flood mitigating function of rice paddy fields is expected to reduce direct runoff during rainfall events, and the installation of discharge control plate in a paddy-plot drainage tank has been attracting attention to enhance this function. In this study, we quantified the peak runoff mitigation effect of the installation of discharge control plates at paddy plots in the Yamato Plain, Nara Prefecture. As a result, the peak runoff mitigation effect was 30% and 21% for the non-irrigation and irrigation periods, respectively, when the 10-year return period rainfall was input to the runoff model. The sensitivity analysis of the model parameters related to the plot characteristics showed that the peak runoff mitigation effect by the discharge control depended on the ponding water depth at a plot at the beginning of rainfall, the factors that determine the amount of water flowing out over the weir board at the outlet of a plot, the infiltration rate of a plot, and the height of the top of the weir board. The peak discharge was stably reduced, indicating the effectiveness of the discharge control plate in the peak runoff mitigation.