Author(s): Shiro Okayama; Yuko Naito; Shoji Fukuoka; Takahisa Gotoh
Linked Author(s): Shoji Fukuoka
Keywords: Non-equilibrium flow and sediment; Upper sediment boundary condition; A large amount of sediments yields; Flood flow; Bed variation
Abstract: The Kamanashi River is a steep river with gravel grains, cobbles and boulders. In 1982, the record breaking largest flood occurred and the large amount of sediments yielding in the upstream mountainous area flowed into and deposited in the river channels. The depositions mainly occurred in the lower reaches where the bed slope was milder than the upper reaches. In addition, the grain size distributions became coarser in the upper reaches and finer in the lower reaches due to sorting during the flood. In this study, we developed and applied flood flow and bed variation analysis method considering the non-equilibrium sediment motions of boulders and gravel grains with large amount of suspended sediments for the 1982 flood. The upstream boundary condition of the bed variation analysis was given by estimating the large amount of sediment discharge from the upstream mountainous area. The calculation results clarified the process of the particle distributions fining in the lower reach and the process of the one becoming coarser in the upper reach. And the calculation results demonstrated the tendency of the deposition shown in the observed data in the lower reach after the flood.
Year: 2020