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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Dolores LO\\'cr (Dolores River from the confluence of the West Dolores to the Dolores River at <br /> <br />Dolores gage), and Lost Canyon Creek at gage (Table 6). <br /> <br />6,4 Loss Rates. The Initial and Constant Loss Rate method was used in both Ihe HEC-I <br /> <br />and IIMS models. Flood optimiz.ation flEe-I runs made in 1976 sho\',.'ed that the basin initial <br />loss could vary from as great as 2.S inches, for at least two weeks of antecedent dry conditions, to <br /> <br />as low as 0.7 inch for continuous antecedent slonns. The oplimized range for constant loss was <br /> <br />O.IS to 0.20 inch per hour. These loss rates are basically Ihe same as those from other regional <br /> <br />studies conducted by the Corps, Los Angeles Dislrict and the U,S. Bureau of Reclamation <br /> <br />(USBR). In the IIMS model an initial loss orO.8 inch and constant loss of 0.19 inch per hour <br />'....erc used to reconstitute the observed hydrograph at the Dolores gage and the observed peak <br /> <br />now at the "bclo\l': Rico" gage on 6 September 1970. The Dolores basin received between 2 and <br /> <br />4.S inches of rainfall during AugUSI with most occurring Iwo weeks before the September 6 <br /> <br />slonn. This is slightly above average lor the basin (see Table 3) and sets up a loss rate at the lower <br /> <br />range for initial loss. <br /> <br />6.S Baseflow. The R-cession method 'vas used to compute basetlow for bolh the IIEC-I <br /> <br />and IIMS models. This method is suitable for watersheds where precipitation events strongly <br /> <br />influence Ihe volume and time of base flow. The paramclers are: initial bascflow (initial Q). <br /> <br />recession constant, and threshold basetlow (threshold Q). Initial basetlow is the subbasin now at <br /> <br />the start of the flood event. in cfs per square mile (ds/mi2). The initial baseflow of 0.6 for the <br /> <br />1970 tlood reproduction is based on a flow around 300 cfs observed at the Dolores gage at the <br /> <br />start ofS September 1970. The recession constant, describing the rale of bas ell ow decay, is the <br /> <br />r..ltio of present bascflow to basellow one day earlier. Threshold Q, the point on the recession <br /> <br />limb of the hydrograph ",,'here bascflO\\." replaces overland flow as source of !low for the subbasin, <br /> <br />18 <br />