Abstract
Since 2002, Kamihayashi district in Niigata prefecture has been undertaking flood mitigation measures using paddy fields by installing runoff control devices in drainage pits. The purpose of this study is to evaluate the flood mitigation performance of a paddy field with runoff control devices by using combined hydrologic analyses and flood routing. The model constructed for runoff analysis is composed of the following three modules; mountain-urban module where the overland flow was estimated by the Kinematic Wave method, paddy field module where runoff from paddy fields was calculated by water balance analysis, and river/canal module where flood routing was performed by the one-dimensional unsteady flow model. The output of the first two modules represents the input of the third module. The result of the simulation shows that the main river and canal discharge would be decreased by 25% to 29% and water level would be lowered by 0.17 to 0.23m in the case of all the paddy fields being installed with runoff control devices. From these outcomes, it is confirmed that the runoff control measure in the study area is functioning effectively.
