| Many large dams in Japan have been constructed as multipurpose dams combining water utilization and flood control functions in order to supply water to the downstream river and to maintain the river environment in excellent condition. Recently, social conditions have increased the number of dam redevelopment projects carried out instead of new dam construction projects. The construction of stream type flood control dams, a type that stores only water discharged by floods has similarly increased. This thesis summarizes characteristics of the stream type dam and introduces some actual projects of it in Japan. It also evaluates the stream type dam, particularly its impact on sediment management in watersheds and reservoirs by numerical simulation of sediment transport in typical stream type dams. From the results of simulation, it is confirmed that gravel and sand are not discharged while the reservoir water level is rising, but they are discharged rapidly when the water level has fallen. When a stream type dam stores a flood discharge, the properties of the outflow sediment discharge unavoidably change more than the natural state. The degree of change varies according to flood control plans, inflow sediment properties, and scale of the flood, so stream type dam projects must be studied individually. |
