Successful Operation of an Innovative Retrofitted Energy Dissipation Solution for Reservoir Filling

January 7, 2026

The Site C Clean Energy Project is an 1,100 MW hydroelectric generating station with a 60 m high dam on the Peace River near Fort St. John, BC, Canada. During earthfill dam construction, the Peace River was diverted through two fully submerged concrete lined diversion tunnels; each 10.8 m in diameter with gated inlet structures. Upon completion of the required diversion period, the tunnels needed to be used to pass minimum flow downstream during the initial stage of the reservoir filling process. Even with one diversion tunnel closed, the capacity of a single tunnel would have been too high to start filling the reservoir with normal river inflow. The capacity of the diversion tunnels needed to be reduced during reservoir filling to allow the reservoir to fill with normal inflows from upstream. Restricting the outflow using the inlet gates was considered but was deemed a risky alternative during a critical phase of the project. The final selected alternative was to install a series of four in-line orifices in one of the diversion tunnels prior to reservoir filling. The design process involved physical hydraulic modelling (PHM) and computational fluid dynamics (CFD) modelling. The orifices were installed in Summer 2023 and were completed on schedule. Reservoir filling was successfully completed in Fall 2024 and the design team had the opportunity to inspect the retrofitted orifice tunnel after it was dewatered to confirm the success of this innovative design. This paper will focus on design, construction, and operation of the in-line orifice solution.

Bruce, J., Chan, K. 2025 “Successful Operation of an Innovative Retrofitted Energy Dissipation Solution for Reservoir Filling,” in Proceedings of the NZSOLD/ANCOLD Conference 2025, 19 – 21 November 2025, Ōtautahi Christchurch, New Zealand: NZSOLD/ANCOLD