A Decision Support System for Mitigating Stream Temperature Impacts in the Sacramento River

Abstract:

Increasing demands on the limited and variable water supply across the West can result in insufficient streamflow to sustain healthy fish habitat. We develop an integrated decision support system (DSS) for modeling and mitigating stream temperature impacts and demonstrate it on the Sacramento River system in California. Water management in the Sacramento River is a complex task with a diverse set of demands ranging from municipal supply to mitigation of fisheries impacts due to high water temperatures. Current operations utilize the temperature control device (TCD) structure at Shasta Dam to mitigate these high water temperatures downstream at designated compliance points. The TCD structure at Shasta Dam offers a rather unique opportunity to mitigate water temperature violations through adjustments to both release volume and temperature. In this study, we develop and evaluate a model-based DSS with four broad components that are coupled to produce the decision tool for stream temperature mitigation: (i) a suite of statistical models for modeling stream temperature attributes using hydrology and climate variables of critical importance to fish habitat; (ii) a reservoir thermal model for modeling the thermal structure and, consequently, the water release temperature, (iii) a stochastic weather generator to simulate weather sequences consistent with seasonal outlooks; and, (iv) a set of decision rules (i.e., ‘rubric’) for reservoir water releases in response to outputs from the above components. Multiple options for modifying releases at Shasta Dam were considered in the DSS, including mixing water from multiple elevations through the TCD and using different acceptable levels of risk. The DSS also incorporates forecast uncertainties and reservoir operating options to help mitigate stream temperature impacts for fish habitat, while efficiently using the reservoir water supply and cold pool storage. The use of these coupled tools in simulating impacts of future climate on stream temperature variability is also demonstrated. Results indicate that the DSS could substantially reduce the number of violations of thermal criteria, while ensuring maintenance of the cold pool storage throughout the summer.