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Modeling Head-of-Reservoir Conditions at Shasta Lake, California to Evaluate Downstream Juvenile Fish Passage
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Restoration of Chinook salmon and steelhead is a priority in the Sacramento River Basin because they were listed under the Endangered Species Act in 1989 and 1998, respectively. Shasta Dam and Reservoir, constructed in 1945, obstructed fish migration, causing loss of spawning and rearing habitat that has been a factor in population declines of these fish species over several decades. In an effort to increase salmon populations, an interagency committee has been evaluating the feasibility of reintroducing fish to tributaries upstream of Shasta Dam to provide cold water habitat for spawning and rearing of salmon. Such reintroduction would require downstream passage of juvenile Chinook salmon and steelhead at Shasta Dam. To evaluate the possibility of collecting and transporting juvenile Chinook salmon and steelhead upstream of Shasta Dam, a CE-QUAL-W2 model of Shasta Lake and its main tributaries was used to assess where and when conditions were favorable at head-of-reservoir locations on the McCloud River to collect juvenile fish. Water temperatures were evaluated to determine locations suitable to collect these fish during months of downstream migration under dry, median and wet year conditions. Use of anchored and floating temperature curtains (i.e., flexible fabric flow barriers) to improve conditions for fish migration was also evaluated with the CE-QUAL-W2 model. Potential for these temperature curtains to assist juvenile fish migration is a novel approach that to our knowledge has not previously been assessed for recovery of Chinook salmon and steelhead populations. Water temperatures were evaluated upstream of the temperature curtains over the periods of concern for juvenile migration. Model results indicated that the use of temperature curtains, especially a long floating curtain, at the head-of-reservoir on the McCloud River would be helpful to improve conditions for winter-run and late fall-run Chinook salmon by reducing or eliminating harmful water temperatures. Model results also indicated that temporary use of a temperature curtain or multiple placement of curtains may improve conditions for winter-run and late fall-run Chinook salmon. CE-QUAL-W2 served as a useful tool to assess head-of-reservoir conditions with and without temperature curtains at Shasta Lake, but several limitations were encountered with the Shasta model that include the model’s dimensions, bathymetry, resolution of layers and segments, extents, and capability to simulate floating temperature curtains and temporary placement of curtains. These limitations require results to be interpreted carefully. Although providing safe passage conditions is challenging, the study findings may assist in formulation of a juvenile fish passage alternative that is suitable for Shasta Lake.