PRECEDING DRAWDOWN OPERATION OF UNAZUKI DAM FOR THE IMPROVEMENT OF COOPERATIVE SEDIMENT FLUSHING IN THE KUROBE RIVER

Abstract

 In the Kurobe river, cooperative sediment flushing of Dashidaira and Unazuki dams have been executed since 2001 in order to maintain flood control and water utilization system. We studied improvement of dam operational method on the basis of numerical analysis and actual implementation both to reduce the deposited reservoir sediment volume and to lower suspended sediment concentrations just downstream of Unazuki dam. As the numerical analysis, “the preceding drawdown operation of Unazuki dam” seems to be effective where the Dashidaira dam starts to be lowered after the water level of Unazuki dam have been already drawdown to its half of an usual level. As the experiments in 2020, the deposited sediment volume of Unazuki dam in a year was 10,000 m³ equivalent to a 97% reduction and the maximum suspended sediment concentration was 37,000 mg/l equivalent to a 26% reduction in the conventional operation.