Compilation of technical material on reservoir sedimentation mitigation: with particular focus on SBT-related content

There are few comprehensive resources available in Japan regarding reservoir sediment management. In particular, sediment bypass tunnels (SBTs) have been constructed at only six dams (with one under construction) across Japan, resulting in limited availability of technical information on SBTs. To address this issue, the Water Resources Environment Center (WEC) published the "Technical Guideline for SBT Planning" in 2023. However, this guideline serves primarily as a technical reference for assessing the feasibility of SBT implementation. To further address this, WEC prepared the "Technical Material on Reservoir Sedimentation Mitigation" to disseminate key information widely on the characteristics and challenges of sediment management techniques to engineers engaged in dam management. We introduce the key aspects of this technical material, with a particular focus on sections related to SBTs. The sections related to SBTs cover various aspects, including: (1) the specifications of existing and those under construction SBTs, (2) the background and process leading to the installation of an SBT at Miwa dam, along with an overview of the facility, (3) the effectiveness of the Miwa dam SBT in reducing sediment inflow into the reservoir, (4) the effectiveness of the Asahi dam SBT in mitigating prolonged turbidity, (5) case studies of tunnel damage and restoration efforts at Koshibu dam, (6) the observed environmental improvements in downstream rivers at Matsukawa and Koshibu dams, and (7) abrasion countermeasures implemented at Koshibu dam and other sites. By widely disseminating this technical material, we aim to facilitate the appropriate and effective implementation of sustainable reservoir sediment management strategies. All information is reorganized from existing publications, and no new field data are presented.