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The main stem Trinity River provides critical habitat for numerous fish species, including chinook and coho salmon, and steelhead. These anadromous salmonid species have particular water temperature requirements for spawning and egg incubation, holding habitat, juvenile rearing, emigration of smolts, and immigration of spawning adults. The quality and quantity of water released from Trinity Reservoir define important upstream conditions for Lewiston Reservoir, releases to the Trinity River, and diversions to the Sacramento River Basin. Extra-basin diversions and releases to the Trinity River help maintain cool water temperatures for anadromous fishes in the Sacramento River and Trinity River, respectively.

 

This project updates and extends previous water temperature modeling efforts for Trinity Reservoir to define the water temperature regime of reservoir and reservoir releases for various hydrologic, climatic, and operational conditions. The completed Trinity Reservoir water temperature simulation model provides a practical tool that can be used to simulate release temperatures and assess temperature control alternatives in the Trinity and Sacramento River systems.

 

Principal project tasks included reviewing the computer models HEC-5Q and WQRRS to determine which model should be employed; model calibration and verification; formulating EIS year-type data sets; creating a framework for interpreting model output; and model application. This project report outlines each of these tasks as well as conclusions and recommendations for future work.

 

Initial strategies for switching to HEC-5Q were abandoned after determining that WQRRS was more flexible, easier to operate, provided a short development and application time, and produced numerically equivalent results. Model calibration and verification were completed for water year 1994 and 1993, respectively (water year extends from October 1 through September 30). Sufficient measured water temperature profile data for Trinity Reservoir were available for these periods and they were independent of the five hydrology based year-types selected for the Trinity River Mainstem Fisheries Restoration Environmental Impact Statement and Report (EIS). Model calibration and verification results were typically within l°F to 2°F of measured values. Additional measured profiles from 1986, 1989, and 1990 were compared with simulated values to expand the range of available hydrologic, climatic and operation conditions. Computed results effectively reproduced field conditions for these additional simulations and increased confidence in the ability of the model to represent Trinity Reservoir.

 

To improve interpretation of model results, spreadsheets were designed to post-process model output. WQRRS was modified to produce a new output file for transfer into Microsoft Excel® spreadsheets. This output file contained semi-monthly data including reservoir surface elevation and associated water temperature profiles. When imported to the spreadsheet, water temperature profiles and time series of storage and water temperature at selected elevations are plotted. Semi-monthly reservoir storage and surface elevation, and water temperatures at selected elevations are tabulated as well. Figures, tables, and raw data can be copied from these spreadsheets to other software packages.