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~ L_ Instream Tesperature Model " '•DRAFT..R. Page 3 March 27, 1989 validation nodes and are usually U. S. Geological Service gaging stations where water temperatures are measured. R_e g r_e s_s__o n .,_M o d_e 1 The regression model is used to fill in missing water temperatures at headwater and validation nodes. Two regression model options are available in the temperature model. The standard regression model is a simple linear multiple regression model that predicts water temperature as a function of air temperature, wind speed, relative humidity, sunshine ratios, solar radiation, and discharge. The transformed regression model is a physical-process model where meterologic data are used to determine the equilibrium temperature and the first-order thermal exchange coefficient. These parameters are matched with corresponding discharges as independent variables to determine the regression coefficients for estimating water temperature. The regression model does not fill in missing discharges at nodes within the network. If some flow data are missing, the model fills in these missing points with the average flow for the time period in question. LITERATURE REVIEMI The model programs were originally written for execution on a Cyber mainframe computer. The Aquatic Systems Group, Fort Collins, Colorado, recently modified these programs for execution on IBM-AT compatible microcomputers (Bartholow, 1987). The model predicts mean daily (24-hour average), minimum night-time, and maximum daily water temperatures. The U.S. Fish and Wildlife Service previously used the temperature model to predict tempera- tures within the Upper Colorado River Basin, including the mainstem Colorado and Green Rivers, the Yampa River, and associated tributar- ies, The final model network included 78 nodes; a monthly time period was used. The absolute difference between observed and predicted average daily temperatures was 1.32°C for the entire network on an annual basis (Brewer, 1985). Theurer and Voos (1982) verified the model solution techniques and validated the temperature model using a network analogous to the one used by the Service (1984). Theurer et al. (1982) also used this network and calibrated the model to observed temperatures in the Upper Colorado River Basin. O'Brien and Miller (1984) used the temperature model to simulate weekly river temperatures throughout the Yampa River. The average mean error for all time periods after calibration was 0.14°C.