Run-off process of suspended sediment in mountain rivers

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1. Stream flows and runoff process of suspended sedimentWe observed suspended sediment concentration, flow discharge and rainfall intensity simultaneously in the Takahara river basin and discussed their relationship. As a result, the following matters were found out. Suspended load concentration is strongly dependent on rainfall intensity, but the relation between them is not unique because the soil on slopes is quickly washed out. The relation between flow discharge and suspended load concentration is not also unique because of the same reason. This change in the situation of source areas should be studied in future.2. Diffusion theory of suspended sedimentAccording to previous study, the diffusion equation of suspended sediment which is generally used cannot explain a suspended sediment concentration in a steep channel with a large roughness without the much larger diffusion coefficient In this paper, we have presented a diffusion equation with a source term and shown the concentration in the above-mentioned channel can be expressed by means of the equation with the ordinary diffusion coefficient.3. Modeling of runoff process of suspended sedimentIf the boundary condition of suspended load concentration is given, the runoff process of suspended sediment in river systems can be analyzed by means of the presented diffusion theory. However, the boundary condition can not be easily evaluated because the sediment production process is too complex. We will study more about this point.