A Monitoring Method for Sediment Movement in Mountain Watershed with an Index of Turbidity

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The purpose of this research is to establish a method of monitoring sediment movement in a mountainous watershed with an index of turbidity. The turbidity and water discharge were continuously measured at an experimental dam section that is in the Ashiarai-dani experimental watershed of Hodaka Sabo Observatory of Kyoto University. The point of the study is to clarify whether the sediment movement in the upstream reach of the observation point is indirectly watched with the data. To observe the situation of sediment movement in the torrent, a video camera system set up in a headwater area in the observation reach. Also, the grain size distributions of the produced sediment, the sediment deposit and the turbidity material were investigated. The result is summarized as follows:1. Turbid water contains the sediments and organic matter. The percentage of the organic matter was 14 to 22%. The grain size of the sediment in the turbid water is less than 0.2mm and 5 to 10 percents of the fresh sediment produced at the source are those sediments. The turbidity materials are washed out of the fresh sediment under movement. As a result, the turbidity materials were not contained in the sediment brought up to the dam section.2. The amount of the sediment supplied from the source is estimated from the accumulated load of turbidity materials at the dam section.3. The hysteresis curves of turbidity and water discharge represent the situation of sediment movement.4. A method for monitoring sediment movement in mountain streams with an index of turbidity is promising.