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- CALlBRA TION Flood peak discharges were calibrated by making slight adjustments to Curve Numbers. As noted on Figure 2, a small portion of the watershed includes soils of Hydrologic Soils Group A, B, or C. Calibration was affected by substituting "A" soils for "0" soils in the high density forest category. The results of the curve number adjustment are shown in Table 3. Curve numbers were decreased by about 4 points in most catchments. The resulting average curve numbers are within the range used by previous hydrologic analysis in the study area. Table 3. Curve Number Adjustments for Calibration, Catchments 1-10, 1979 Land Use. eN 1 2 3 4 5 6 5962 3875 5208 490 1884 810 9.32 6.05 8.14 0.77 2.94 1.27 S 9 10 691 1552 1870 1.08 2.43 2.92 High. Density Forest, D soil 79 56% 40% 56% 41% 55% 2% 45% 32% 60% High Density Forest -A soil (calibration) Low Density Forest - D soil . Meadow Low Density Residential 36 9% 9% 8% 9% 10% 10% 3% 5% 9% 83 19% 31% 21% 25% 15% 45% 21% 4% 0% 75 16% 20% 10% 24% 20% 40% 31% 50% 23% 84 0% 0% 5% 0% 0% 0% 0% 0% 7% Med. Density Residential Conunercial Avera e eN 0% 0% 1% 0% 75 74 90 95 0% 0% 0% 0% 0% 0% 75 75 76 2% 0% 1% 0% 75 77 3% 0% 6% 1% 76 74 Note: See Figure 4 for Catchment location. RESULTS Flood peaks for the 1 DO-year flood obtained from the TR20 hydrologic analysis are compared to the flood peaks in the 1979 study in Table 4. The flood peak from the 1979 study did not include Silver Gulch, and the peak was adjusted using weighted area calculations for mountainous areas recommended by CWCB (McCain et aI., 1976). The results on Table 4 indicate this study has successfully reconstituted the 1979 flood peak estimates using 1979 data with the TR20 using only minor adjustments to curve numbers. Program output is found in the Appendix to this report. -9-