Author(s): Tetsuya Sumi; Masahisa Okano; Yasufumi Takata
Linked Author(s): Tetsuya Sumi
Keywords: Reservoir sedimentation; Sediment bypass; Diversion tunnel; Abrasion damage
Abstract: This paper focuses on sediment bypass tunnels for reservoir sedimentation management. Worldwide, number of constructed sediment bypass tunnels is very small because of topographical, hydrological or economical conditions. Bypass tunnels, however, have many advantages such as they can be constructed even at existing dams and prevent a loss of stored reservoir water caused by the lowering of the reservoir water level. They are also considered to have a relatively small impact on environment downstream because inflow discharge In Japan, sediment bypass tunnels of the Nunobiki Dam completed in 1908, and of the Asahi Dam completed in1995, have been successfully introduced to realize sustainable reservoir management. Sediment bypasses of the Miwa Dam, Koshibu Dam and Matsukawa Dam on the Tenryu River are expected to be next leading projects in Japan. In this paper, we discuss design criteria and lessons learned from existing facilities, and future challenges of planning projects. The focus is on tunnel geometries such as diameter, slope, bottom shape etc., and an abrasion-resistance design of the tunnel invert.