Sedimentation in a narrow reservoir under climate change and sediment bypass tunnel operation scenarios

• Main Authors: Dahal, Sudesh, id_orcid:0 000-0003-3526-1051, Evers, Frederic M., id_orcid:0 000-0001-5181-8978, Boes, Robert, id_orcid:0 000-0002-0319-976X, Vetsch, David F., id_orcid:0 000-0003-3293-5831
• Other Authors: Albayrak, Ismail, Felder, Stefan, Crookston, Brian, Heller, Valentin
• Format: Conference Object
• Language: English
• Published: ETH Zurich 2024
• Subjects: Reservoir Sedimentation; Sediment Bypass Tunnel; Climate Scenarios; Numerical Modelling; permafrost
• Online Access: https://hdl.handle.net/20.500.11850/676029; https://doi.org/10.3929/ethz-b-000676029

Reservoir sedimentation is one of the main issues interfering with the sustainable operation of many hydropower reservoirs as it causes a reduction of storage capacity and may also affect dam safety. The rate of sedimentation is anticipated to change due to changes in flow following climate change. Although quantifying the variation of sedimentation is subject to high uncertainty, sediment yield is mainly expected to increase for Alpine catchments due to retreating glaciers and thawing permafrost. Sediment Bypass Tunnels (SBTs) are hydraulic structures to counteract sedimentation problems as they allow for bypassing incoming sediment (bedload and parts of the suspended load) around the dam into the tailwater reach. This study deals with the SBT in Solis reservoir (Switzerland) where an SBT has been operating for more than a decade to counteract sedimentation. The aim is to evaluate the performance of the Solis SBT under climate scenarios by conducting 1D numerical simulations. The HydroCH2018-Runoff ensemble is referred for the future projection of river inflows into the Solis reservoir. In absence of quantified impact on the sediment input, it is computed from calibrated sediment transport equations based on monitored data. The model is found useful to simulate future sedimentation and to compare scenarios of SBT operation during flood events. Considering the impact of SBT operation on energy generation due to water losses, SBT operation during two different floods is more effective than its operation in a single flood for a given total duration of operation.