Evaluation of Head-of-Reservoir Conditions for Downstream Migration of Juvenile Chinook Salmon and Steelhead at Shasta Lake, California

Abstract:

Since completion of Shasta Dam, migration of Chinook salmon and steelhead trout in the Sacramento River has been blocked, causing loss of spawning and rearing habitat. This has been a factor leading to population declines of these fish species over several decades. Winter-run Chinook salmon, spring-run Chinook salmon and steelhead trout are now listed under the Endangered Species Act. A habitat assessment of the tributaries upstream of Shasta Dam showed that the Sacramento and McCloud tributaries have suitable habitat for reintroduction of adult salmon and steelhead for spawning. Such reintroduction would require downstream passage of juvenile Chinook salmon and steelhead past Shasta Dam. To evaluate the possibility of collecting and transporting juvenile Chinook salmon and steelhead past Shasta Dam, a CE-QUAL-W2 model of Shasta Lake and the Sacramento River, McCloud River, Pit River and Squaw Creek tributaries was used to assess where and when conditions were favorable at head-of-reservoir locations upstream of proposed temperature curtains to collect juvenile fish. Head-of-reservoir is the zone of transition between the river and the upstream end of the reservoir. Criteria for evaluating locations suitable to collect these fish included water temperature and velocities in the Sacramento and McCloud tributaries. Model output was analyzed during months of downstream migration under dry, median and wet year conditions. Potential for proposed temperature curtains, anchored and floating, to improve conditions for fish migration was also evaluated with the CE-QUAL-W2 model. Use of temperature curtains to assist fish migration is a novel approach that to our knowledge has not previously been assessed for recovery of Chinook salmon and steelhead populations. Providing safe passage conditions is challenging, however the study findings may assist in formulation of a juvenile fish passage alternative that is suitable for Shasta Lake.