| For the purpose of understanding the thickness of riverbed material exchange at multiple places with different bed topography, we conducted cross-section surveys, gravel size surveys and buried markers surveys in the Toyohira River before and after snowmelt flooding. The surveys showed that the thicknesses of the bed material that is exchanged are more diverse around gravel bars than at narrowed sections of the river, and that the thicknesses increase at places with high flow rate and decrease at the middle and upper areas of each gravel bar front. At the narrowed river sections and at the gravel bars that were exposed to high flow rate where a thick layer of bed material was exchanged, scouring at the time of peak flood and deposition at the time of floodwater recession were considered to be key factors of bed material exchange. Deep scouring due to the presence of dune also affects bed material exchange. At
places around the gravel bar front where the thickness of the exchanged bed material was successfully obtained, the thickness is likely to have been affected mainly by deep scouring during the time of peak flood and by deposition during time of floodwater recession |
