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2 METHODS Model Description The instream water temperature model, developed by the Instream Flow and Aquatic Systems Group, Western Energy and Land Use Team (WELUT), U.S. Fish and Wildlife Service, was used to model water temper- atures in the Yampa River in Dinosaur National Monument. The model documentation (Theurer et al., 1984) provides a complete description of the model. The model predicts instream water temperatures from either historical or synthetic hydrology, meteorology, and stream geometry. The instream water temperature model has two major components for predicting water temperatures, a regression model and a physical process model. The regression model uses the same input parameters as the physical process model and is used to complete missing data and smooth existing data for headwaters and interior validation locations. The physical process model consists of six components: (1) a solar model to predict solar radiation penetrating the water surface; (2) a meteorology model that transfers meteorological data from a single station to each point in the stream system; (3) a heat flux model to predict energy balance between the water and surrounding environment; (4) a heat transport model to predict mean daily water temperatures and diurnal fluctuations in temperatures; (5) a shade model to predict solar radiation weighted shading from riparian and topographic shade; and (6) procedures to calibrate the model to known interior water temper- atures using certain physical parameters (Theurer and Voos 1982, Theurer 1983). Input Data Required input data for the model is meteorology, hydrology, and stream geometry. For the Yampa River modeling only historical meteorol- ogy data was used. The years modeled were 1975, 1976, 1977, 1981, 1982, and 1983. The first three years were chosen after reviewing meteorol- ogical records and are historical data for a colder than normal year (1975), a near normal historical year (1976), and a warmer than normal year (1977). The years 1981, 1982, and 1983 were included because they coincided with years that data were collected for the endangered Colorado squawfish in the Yampa Canyon. Weekly time periods from March 1 to August 15 were modeled each year. Meteorological data. Meteorological data for air temperature, wind speed, relative humidity, and percent possible sunshine was obtained from U.S. Weather Bureau records for the study area. Daily meteorol- ogical data were summarized to obtain a weekly mean for each parameter. National Park Service fire weather data collected at Dinosaur National Monument Quarry was used as input to the model as representing the meteorological conditions for the Yampa Canyon. The period of data