Cooling California Rivers: Using a spectral physically-based energy balance model to predict flow and river temperatures under current and future climates

Erin Bray, San Francisco State University

We propose to use the best-available science to further develop a physically-based spectral river energy balance model (FLUVIAL-EB) that not only accurately predicts water temperature, but incorporates the physics that are necessary to be able to attribute water temperature changes to the right mechanisms. The overarching question we aim to answer is: How does better understanding about the mechanics about how rivers warm help us to make decisions based on the best available science to sustain cool temperatures for salmon under a warming climate? We will accomplish this goal through a focused effort of (1) computational model development using FLUVIAL-EB which was first developed by the PI, (2) use of data from a field experiment of measured river temperatures, (3) and utilization of state-of-the-art GCM climate model datasets (CRCM Regional Climate Model) to conduct a strategic set of simulations under current and future climates.

The goal is to (1) generate quantitative knowledge for management of stream temperatures and river thermal regimes through a numerical model referred to as FLUVIAL-EB, and (2) conduct and design a series of model simulations to predict river temperature using a range of realistic flow releases together with current and future climate data. The results of this work can be used by water management agencies to establish a greater extent of coldwater refugia for salmon in California rivers. We will initially focus on the mainstem San Joaquin River between Friant Dam (River Mile 267) and the confluence of the Merced River (River Mile 118), managed by the U.S. Bureau of Reclamation (USBR) in cooperation with the San Joaquin River Restoration Program. We will make use of new scientific results that were developed and new equations that were derived in a beta version of the model (Bray, Dozier, and Dunne, 2017). The application of this research is to design implementation activities that are effective at cooling river temperatures during hot summer months and warming climates, so that the model may be used more broadly to plan and design water flow releases downstream of dams that improve the spatial extent and access to coldwater refugia in any river.