2019年台風19号時における小渋・美和ダムの排砂トンネル操作 --ダム貯水位に関係した排砂の制限--

Abstract

We reported here on the operation of sediment bypass tunnel (SBT) and reservoir sedimentation in Koshibu and Miwa dams during Typhoon-19, October, 2019. In Koshibu, sediment release by SBT started late, which was relevant to a recovery of reservoir water level for water demands, and stopped soon due to an accident in gates. In Miwa, reservoir water level increased rapidly and got close to a full water stage. To avoid overflow of water from the reservoir to SBT, SBT had to stop soon after the commencement. As a consequency, SBTs transported less than 10% of the sediment inflow. Reservoir sedimentation was nearly 900, 000m3 for each of Koshibu and Miwa dams, and the difference in elevation between the conduit gates and bottom sediment was only a few meter for Koshibu. To use SBT more effectively and increase sediment transport efficiency, operation strategies that use SBT much actively and steadily during large floods, and keeping a certain pocket for sediment in the diversion weir pond by a consistent SBT release during every floods are needed.