The Use of Temperature Models in the Evaluation and Refinement of Proposed Trinity River Restoration Act Flow Alternatives

Reservoir temperature models of Trinity and Lewiston Lakes and a river temperature model of the mainstem Trinity River were used to evaluate the impacts of five proposed Trinity River Basin Fish and Wildlife Restoration Act flow alternatives. Initial results of temperature modeling indicate that most flow alternatives result in water temperatures that exceed downstream temperature requirements. The reasons for these results lie in the complex "plumbing" and operations of the Trinity Division. Temperature model simulations were then initiated to investigate and develop proposed mitigations for elevated release temperatures. Promising solutions include: shifting CVP diversion patterns so that the highest diversion rates occur during the summer period; maintaining higher carry-over storage capacity of Trinity Lake into the late summer; decreasing summer release temperatures to the Trinity Fish Hatchery; and using an auxiliary outlet to draw upon the deeper cool-water pool of Trinity Lake. Many of these temperature mitigation strategies provide benefits to other Trinity River stakeholders (e.g. higher summer-time lake levels for recreation, higher CVP diversions during peak power generation periods, and more timely diversions that will help meet summer-time Sacramento River and Bay-Delta flow and water quality objectives).