TOPOGRAPHIC CHANGES OF TIDAL FLATS IN THE OTA RIVER FLOODWAY

Abstract

In the Ota River floodway there are extensive tidal flats along the riverside, which provide habitats for many creatures in the brackish river. Therefore, it is important to understand topographic changes of the tidal flats by flood flows for conservation of the tidal flats in the floodway. So, first we investigated changes over time in bed profiles of the tidal flats by using surveying data. The observed data indicates that the tidal flat elevations become lower by a series of flood events. For understanding the decreasing mechanism of the tidal flat areas, we applied the unsteady quasi three dimensional flood flows analysis and two dimensional bed variations analysis. As a result, it is found that the bed scouring on the tidal flats along the river side is induced by alternate bar movements by flood flows. This study gives the information for preservation of tidal flats along the river side in the Ota River floodway.