EVALUATION OF FLOOD CONTROL FUNCTION OF IRRIGATION PONDS IN THE ROKKAKU RIVER WATERSHED

Abstract

 To advance the flood control in the Rokkaku River basin, we examined the effectiveness of irrigation ponds as a measure against flood inundation inside the levee. The flood control function of irrigation ponds was evaluated by applying a distributed rainfall-runoff-inundation model (RRI model) and adopting data of the heavy rainfall in August 2019. The result found that the existing irrigation ponds reduced the floodwater volume by 150,000 m³. Furthermore, we evaluated the flood control function of the ponds, considering the pre-release of water from the ponds in the same rainfall condition. As a result, we found that the flood water volume decreased by 383,000 m³ compared with the case of no irrigation ponds and its prerelease. Besides, the pre-release of water from ponds reduced the inundation depth in the area many houses exist. In conclusion, irrigation ponds have a flood control function that mitigates the flood inundation inside levees.