Modeling Shasta Dam operations to regulate temperatures for Chinook salmon under extreme climate and climate change

Wednesday, 17 December 2014
Arthur Dai1, Laurel Saito2, Joseph R Sapin2, Balaji Rajagopalan3, R. Blair Hanna4 and Derek L Kauneckis5, (1)University of Arizona, Tucson, AZ, United States, (2)Univ of Nevada Reno, Natural Resources and Environmental Science and Graduate Program of Hydrologic Sciences, Reno, NV, United States, (3)Univ Colorado, Civil, Environmental, and Architectural Engineering and Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (4)Water and Earth Technologies, Inc, Fort Collins, CO, United States, (5)University of Nevada Reno, Reno, NV, United States
Chinook salmon populations have declined significantly after the construction of Shasta Dam on the Sacramento River in 1945 prevented them from spawning in the cold waters upstream. In 1994, the winter-run Chinook were listed under the Endangered Species Act and 3 years later the US Bureau of Reclamation began operating a temperature control device (TCD) on the dam that allows for selective withdrawal for downstream temperature control to promote salmon spawning while also maximizing power generation. However, dam operators are responsible to other interests that depend on the reservoir for water such as agriculture, municipalities, industry, and recreation. An increase in temperatures due to climate change may place additional strain on the ability of dam operations to maintain spawning habitat for salmon downstream of the dam. We examined the capability of Shasta Dam to regulate downstream temperatures under extreme climates and climate change by using stochastically generated streamflow, stream temperature, and weather inputs with a two-dimensional CE-QUAL-W2 model under several operational options. Operation performance was evaluated using degree days and cold pool volume (volume of water below a temperature threshold). Model results indicated that a generalized operations release schedule, in which release elevations varied over the year to match downstream temperature targets, performed best overall in meeting temperature targets while preserving cold pool volume. Releasing all water out the bottom throughout the year tended to meet temperature targets at the expense of depleting the cold pool, and releasing all water out uppermost gates preserved the cold pool, but released water that was too warm during the critical spawning period. With higher air temperatures due to climate change, both degree day and cold pool volume metrics were worse than baseline conditions, which suggests that Chinook salmon may be more negatively affected under climate change.