Abstract
Since the elevation of flood plains in the lower Ota River floodway is located in the intertidal zone, tidal flats formed on the flood plains have become important as one of river functions. However, the tidal flats are gradually reducing in size due to bed scouring year by year. So, the cross-sectional shape in the lower floodway has changed gradually and naturally to the ship-bottom shaped channels at present from compound channels in the beginning by flood flows. Therefore, it is necessary to design the riprap for protecting against the erosion of the tidal flats. In this study, we evaluate effects of ripraps on the topographic changes and provide appropriately ripraps design by using numerical simulation for flood flows and bed variations in the lower Ota River floodway. Finally, issues to be considered in the design of a ship-bottom shaped channel which are found in the present study are summarized.
