Method for predicting sediment runoff including sediment storing mechanism in stream channels

点击翻译按钮获取中文摘要

To develop a method for predicting sediment runoff at any cross section of stream channels in a drainage basin, the research was conducted with three sub-topics; 1. density of landslides' occurrences and transformation rate of landslides to debris flow, 2. sediment storing mechanism in channel reach due to sediment transportation by debris flow and 3. development of a method for predicting sediment runoff based on Egashira's method and the results of above sub-topics. The results are summarized as follows.1. The density of landslides occurrences caused by heavy rainfall is closely related to surface and intermediate flows on mountain slopes and can be explained using parameters such as the occupied ratio of surface and intermediate flows, slope gradient and thickness of surface soil layer. In Japanese topographic conditions, landslides more than eighty percent are transformed into debris flows through their run-out processes.2. Formulas for mass conservation with respect to total sediment as well as to each grain size class are proposed to treat an abnormal sediment runoff problem which takes place in stream channels where a large amount of sediment is transported by debris flows.3. A method is proposed for predicting sediment runoff due to rainfall, which is composed of drainage-and channel-model, sediment transport model and rainfall runoff model and can evaluate bed-loads, suspended loads and wash loads. To test validity of the method, predicted results are compared to the observed data for annual reservoir sedimentation and wash loads during several floods in the upper drainage of Kumano river, and accord well with the corresponding data.