Author(s): Yusuke Hayashi; Tatsuhiko Uchida; Yoshihisa Kawahara
Linked Author(s): Tatsuhiko Uchida, Yoshihisa Kawahara
Keywords: Volume variation; Sediment sorting; Packing model; Porosity; Sediment mixture
Abstract: It is necessary to develop a calculation method for the topographical riverbed changes due to the variations in grain size distributions, to evaluate the deposition, sediment-flushing mechanism in the reservoir, and the effect of sediment supply downstream of the river. However, the conventional method, which is based on the concept of active layers, has limitations in evaluating the change in sediment porosity and thickness of the layer. In this study, an experiment was conducted in a straight horizontal channel to clarify the change in sediment volume and porosity using sediment sorting. The sediment, which was well mixed with a wide grain size distribution, was installed in the channel. For a constant flow rate, the depth of the downstream end was reduced in stages. It was discovered that the porosity increased in the flow direction. Although the change in volume associated with the variation in grain size distribution was large at the initial stage, it decreased rapidly, approaching asymptotically to about 1.1 times of the erosion volume in this experiment. The experimental porosity in a finite thickness was reproduced by the Eulerian deposition model. A calculation method for evaluating riverbed height is proposed based on the model and was validated through the comparisons with the experimental results.
Year: 2020