Demonstration of Integrated Reservoir Operations and Extreme Hydroclimate Modeling of Water Temperatures for Fish Sustainability below Shasta Lake

Abstract

Construction of Shasta Dam on the Sacramento River in 1945 prevented anadromous fish from accessing their natural cold-water spawning habitat above the dam and is one of the factors that caused population declines in Chinook salmon and other species. To address listing of winter-run Chinook salmon under the Endangered Species Act, the U.S. Bureau of Reclamation began operating a temperature-control device (TCD) on Shasta Dam in 1997 that enabled selective withdrawal of reservoir outflows for control of downstream water temperatures while maximizing power generation. However, effectiveness of TCD operations for addressing fisheries concerns under hydroclimate variability is unknown. Stochastic methods to generate synthetic extreme hydroclimate conditions were combined with hydrodynamic modeling of reservoir operations and interactions with reservoir managers to examine the TCD’s ability to meet downstream temperature objectives. Model simulations suggest that TCD withdrawal schedules could reduce outflow temperature target exceedances when compared with more traditional dam operations such as solely hypolimnetic or epilimnetic releases. However, constraints imposed by multipurpose operational considerations, especially under extreme climate conditions, and the Sacramento–San Joaquin system’s complex regulatory environment limit use of reservoir management to provide optimal thermal conditions best for Chinook salmon spawning and recruitment.