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1960-1982 Data Base The original data base was used to model the Green River from below Flaming Gorge Dam; the Greendale gage was used to estimate initial flows and temperatures. The White River was modeled from the gage near Watson, Utah, and the Yampa was modeled from the gage near Maybell, Colorado. The Colorado River was modeled from the Gage near Cameo, Colorado. The Gunnison was modeled from the gage near Grand Junction, Colorado. Other tributaries were modeled from gages near the mainstem rivers. A total of 15 USGS gaging stations were used for data input (Table 1). Irrigation demands were approximated at a single node on the Colorado River at river mile 199 (Grand Valley). A constant demand of 1,610 cfs was used from May through October, and 0 cfs was used for the other months. Another irrigation demand node was placed on the Green River (RM 125), but a zero year-round demand was used here (Prewitt, et. al., 1981). Figure 1 shows the basin-wide network, the gaging stations used, and the two irrigation demand nodes. A separate hydrology program called COLHYD was used to distribute the gage flows throughout the network. COLHYD uses the mean monthly discharge from the 15 USGS gaging stations to determine discharge values at additional hydrology nodes located in the temperature model network. Discharge in the model is assumed to vary linearly between USGS gaging stations. As a result, • discharge at intermediate nodes is based on simple mass balance. In addition, the model assumes a constant 70% return flow from irrigation diversions (Guy and Theurer, 1984). Climatological data was developed from the U.S. Department of Commerce, National Oceanic and Atmospheric Administration records, Grand Junction, Colorado. Local Climatological Data (Annual Summary, 1950-1982) were used for average daily information on air temperature, wind speed, percent possible sunshine, and relative humidity. Normals for the period of record were also taken from the Annual Summary. Time Period Extension One goal of this task was to extend the 'baseline' data period to cover the additional time period of water year 1930 to 1959. Most data sources were identical to those used by Theurer, namely published United States Geological Survey and computerized WATSTOR data for the system hydrology and water temperatures and the National Oceanic and Atmospheric Administration's Local Climatological Data from Grand Junction, Colorado, for the meteorological data. Internal system hydrology was synthesized using solution techniques developed by Guy and Theurer (Guy and . Theurer, 1984). The stream geometry data assembled by Theurer remained unchanged. 3