Abstract
The middle Arakawa River has large flood plains, about 2.5km in maximum width. Flood storage functions of the middle Arakawa River had been strengthened by installing cross-levees which extend at right angles to levees and the Arakawa 1st retarding basin on the flood plains. New three retarding basins have been planed in the middle Arakawa River. This paper investigate the storage functions of the middle Arakawa River against the design flood hydrographs by numerical flood simulations based on the accurate flood flow model. The cross-levees increase the flood plain storage and delay the peak occurrence time of rate of storage. However, the large flood plains are filled with flood water at early stage of rising limb of the flood flows and do not have the sufficient storage space at the flood peak of the design hydrographs. For this reason, the peak discharge of the Iwabuchi control point exceeds the design discharge (6300m3/s).
