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<br />000336 <br /> <br />Draft-Do Not Cite <br /> <br />12 <br /> <br />August 2003 <br /> <br />conditions, suspended loads can be a large portion of the total load in a river. For example, <br />Pitlick et al. (1999) state that suspended load in the Colorado River comprises more than 98% of <br />the river's total load. <br /> <br />Many correlations have been developed to evaluate suspended load, bed load, and wash <br />load. These correlations range from simple empirical formulas (e.g., the DuBuoys equation; <br />Henderson 1966), to Einstein's statistical model (1942), to multi-dimensional computer models <br />(Graf 2003). <br /> <br />2.3.1 Suspended Load Models <br /> <br />For this study, two suspended sediment load transport models for the Gunnison River <br />were considered-Van Steeter and Pitlick (1998) and Pitlick et al. (1999). Both of these models <br />are empirically derived from sediment load data for the Grand Junction gage and have a simple <br />form similar to a sediment-rating curve approach in which the suspended load is assumed to <br />follow a relationship of the form: <br /> <br />C =aQb (1) <br />where C is the sediment load, Q is the discharge, and a and b are constants to be determined <br />from field observations (Beschta 1987). These models were selected for the present analyses <br />because they were developed for the Gunnison River using site-specific load information. <br /> <br />2.3.1.1 Van Steeter and PitlickModel <br /> <br />For the Van Steeter and Pitlick model (1998), sediment concentrations in the Gunnison <br />River were represented with the following relationship for the period of time beginning in 1966: <br /> <br />C = 5(Q-1O)4 ~~eJ .r~ (2) <br />s Q3 ~ <br />where: Cs is the concentration of suspended sediment in mgIL and Q is the river flow in m3/s. <br />Total suspended sediment loads for the period of interest were obtained by integration, assuming <br />that the daily sediment load could be estimated as the load produced by the mean daily discharge <br />of the river. <br />