Author(s): Hiroki Takaoka; Haruyuki Hashimoto; Kichan Park; Natsuki Hisaoka
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Keywords: Bed erosion; Bank erosion; Lateral erosion; Bank failure; Erosion rate; Landslide; Debris flow
Abstract: There occur sometimes landslides on mountain slopes during heavy rains. Some of the landslides change into debris flows and move down a mountain river. The debris flow erodes river bed and bank simultaneously during the movements in steep river reach. In the downstream reach at mild slope the debris flow deposits a large amount of sediment. The result makes the debris flows overflow riverbanks and does great damage to many houses along the river. When we plan the countermeasures, it becomes necessary to predict the hydrograph of debris flow. The prediction of the hydrograph requires the knowledge of river bed variation, such as the bed and bank erosions during the movements of debris flows. The purpose of this study is to investigate bed and bank erosion rate and develop the prediction method of river bed variation. Firstly, we make experiments on bed and bank erosions in a steep open channel. Substituting the measurements of channel bed level and channel width into one-dimensional basic equations of unsteady flow, we calculate flow velocity and sediment concentration at any positions of the channel. As a result we obtain the relationship of the bed and bank erosion rate and hydraulic quantities, such as flow velocity and sediment concentration. We apply the erosion rate equations to a natural river erosion problem caused by debris flow.
Year: 2005