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I I I I I I I I I I I I I I I I I I I Calibration of the UDSWM2 Model The Colorado Urban Hydrograph Procedure for cal ibrating the UDSWM2 model was completed utilizing the computerized model CUHPB, as currently approved by the UDFCD. The basin areas, lengths (L), and lengths to centroid (Lea) were measured on the U.S.G.S. quadrangle. The coefficient reflecting time to peak (Ct), and the coefficient related to the peak rate of runoff (Cp), were calculated using the most current data determined by the UDFCD. The coefficient Ct was adjusted for use in the computer program using the equation Ct = Cto ((LLca).18/So.24). The percent of impervious covers and basin parameters deal ing with rainfall losses due to infiltration, depression storage, and decay rate were all taken from the UDSWM2 runs. The CUHPB input data for the Quail Creek and McKay Lake basins are shown in Table 7. The total I-hour rainfall depth for the 100-year storm was calculated from the rainfall hyetograph used in the UDSWM2 runs, and distributed to produce the 100-year design storm, following the procedure outlined in the rainfall section of the USDCM. The 100-year storm event was used to calibrate the UDSWM2 model. This provides calibrated flows for the 100-year design. For designs that involve the 2-, 5-, or 10-year events, the UDSWM2 model should be calibrated using the 2, 5, or 10-year rainfall. TABLE 8 UDSWM2 versus CUHPB Are!! Design Point (miZ) Qua il Creek L Lea (mi) (mi) TABLE 7 CUHPB INPUT DATA Dep. Storage Initial Perv.lmperv. Infl. %I Cto Ct* ~ (in) (in) (in/hr) Quail Creek 100-year Discharges Design Pt. 302 306 13 304 302 (cfs) UDSWM2 1540 2990 3530 1180 1920 CUHPB 1730 3120 3250 1200 2050 So Decay Rate (per/see) F i na 1 Infl. ( in/hr) McKay Lake 302 1.05 1.48 0.63 0.019 40 0.093 0.24 0.53 .40 .10 3.0 .0018 .50 306 2.64 3.03 1.14 0.017 40 0.093 0.31 0.61 .40 .10 3.0 .0018 .50 13 3.71 4.20 2.00 0.014 40 0.093 0.38 0.64 .40 .10 3.0 .0018 .50 McKay Lake 304 1.11 1.88 1.16 0,007 40 0.093 0.35 0.53 .40 .10 3.0 .0018 .50 302 1.94 2.96 1.64 0.006 51 0.087 0.40 0.69 .40 .10 3.0 .0018 .50 Calibrating the UDSWM2 model can be accomplished using a number of methods. The original UDSWM2 results for the Quail Creek basin were significantly lower than the CUHPB values. To increase the discharges calculated by the UDSWM2 model, the flows in the basin were accelerated by decreasing the basin overland flow length and by widening the basin tributary widths. * - Adjusted using Ct = Cto ((LLca).18/So.24) where Cto is the coefficient found in the USDCM, and Ct is the coefficient used in the UDSWM2 model to convert the tp equation in the program (i.e., tp = Ct(LLca).3) to give results equal to those found in the USDCM 1982 revision. Table 9 presents a summary of the peak discharges developed from the final cal ibrated UDSWM2 runs for Quail Creek, the Tributaries to Quail Creek and the McKay Lake drainageways. Discharge profiles for the Quail Creek basin are shown in Figures 2 and 3. Similar information for the McKay Lake watershed is shown in Figure 4. Typical flood hydrographs are shown in Figures 5 and 6 for the Quail Creek and McKay Lake basins, respectively. Discharges for the 100-year event were calculated at three design points in the Quail Creek basin and at two design points in the McKay Lake basin (see Figure 1). Composite CUHPB runs were made to each of these points. The results of these runs, and how they compare to the calibrated UDSWM2 runs, are shown in Table 8. As Table 8 indicates, a close correlation exists between the results of the two models. It should be noted that the hydrologic analysis in the McKay Lake basin was evaluated assuming two main channel branches crossing 1-25 under future developed conditions. Discharges at Interstate-25, given in Table 9, relate to this condition. The existing configuration of 1-25 causes all of the flow to be combined in a backwater area west of the highway. 11