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Hydrology The data file of gage discharges was developed from the U.S. Geo- logical Survey, Water Resources Data for Colorado and Water Resources Data for Utah. The discharges for each location were obtained from the Surface Water Records. Water temperatures at each location were obtained from Water Quality Records. Additional water temperature and discharge information was obtained through the use of the USGS WATSTOR system. Published Temperature Data Smoothing Fifteen USGS gages within the study area provided some useful instream water temperature data. However, none of the gage data were developed from accurate 24-hour averages. The published temperatures were assumed to represent water temperatures somewhere between the minimum/maximum on the day recorded. Frequently, published temperature data were missing for several days a month at each gage. Therefore, monthly means of the average daily water temperature for a specific year at any given gage were difficult to obtain directly. A second-order, multiple regression model was used at each gage to generate estimates of the missing data. The published water tem- perature was treated as the dependent variable. Discharges at the selected sites and prevailing meterological parameters (obtained from published data for the Grand Junction weather station) were the independ- ent variables. The meterologic parameters were based upon those used in • the physical process model. Data from 1964 through 1977 was used for the regression. Water Temperature Screening, Black Rocks and Jensen Reaches The water temperature model was used to predict mean monthly tem- peratures across a range of discharges at the Black Rocks (Colorado River) and Jensen (Green River) observation points. The Black Rocks flow-temperature relationships were to be used in screening flow levels for temperature suitability for humpback chub and Colorado squawfish spawning. The Jensen predictions were to be used 1) to determine dif- ferences between Green and Colorado River temperatures and 2) to screen various flow levels during critical spawning months for temperature suitability. On both rivers the months of May, June July, and August were selected as potential spawning months for both species (May and June primarily for humpback chubs, June, July and August for Colorado squawfish). Flow Time Series Generation Mean monthly flow data for the six CRFP PHABSIM study sites were obtained for the three flow conditions (actual, present, and natural) specified in the Amendment to the MOU. The "actual" flows were based upon USGS gage records adjusted to the study sites by addition or subtraction of tributary flows,between the 12