Author(s): Makoto Umeda; Naoki Mizuta
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Abstract: We aimed to elucidate the detailed hydraulic mechanism of long term persistance of turbidity in reservoirs, since the phenomeman cause water quality problem in the downstream river of the dams. For that purpose, we made field measurements on velocity disribusion characteristic under a thermally stratified condition in Isawa Dam Reservoir in Japan. A current meter with high temporal resolution was used to measure the velocity distribution that could influence on long term suspension of fine grained sediment in the reservoi. From the obtained data, velocity distribution was analyzed as well as swaying condition of the current meter during the measurement. The grain size of the suspended sediment sampled in this study showed almost homogenious distribution from the upper layer to the middle layer and concentrated around 10um. The velocity distribution was rather uniform regardless of the depth. Therefore, we presumed that such velocity distribution and fluctuation could effect on keeping suspended sediment from falling and cause active diffusion in epilimnion in the reservoir.
Year: 2018