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I I I I I I I I I I I I I I I I I I I 30 u au ah 1 au sf = S - - - - - - -- o g ax ax g at (3) where u is the mean velocity, x is the streamwise direction, and t is time. For flows that do not vary with time or vary slowly with time (steady flow), iJu/at = 0, hence the right-hand term in (3) can be eliminated. Peak spring and summer flows in the upper Colorado River are derived from snowmelt higher in the basin and the discharge does not change rapidly from one day to the next- the snowmelt hydrograph typically lasts for several months- and thus, for time steps of one day or so, it is reasonable to assume that the discharge is steady. Equation (3) can be solved iteratively for a series of cross sections where the bed slope, flow depth and velocity are known (Henderson, 1966; Dingman, 1984). Study Sites and Methods The field sites for this analysis are located near the Palisade gauge (-RM 184.2), near the Corn Lake boat launch (-RM 177.3), below the Redlands Parkway bridge (- RM 166), approximately half way between the Redlands Parkway and Fruita bridges (-RM 162.4) and at both the old (-RM 139.5) and new (-RM 134) sites of the USGS State-line gauge (Fig. 1). All of these sites are in single thread, relatively straight reaches of the river. Six or seven cross-sections were surveyed at each site during the spring and summer of1994 by the method described previously (Figures 12 through 17). The cross-sections were placed approximately one channel width apart. Water surface elevations at each cross-section were measured at several flows throughout the runoff season, and the elevation of the 1993 peak flow was estimated from high water marks. These measurements provide us with important information on both the depth and slope at each cross- section which is essential to an accurate calculation of the boundary shear stress.