REV94505 - Laserfiche WebLink

Home Browse Search

• Table 3-1 Summary of Basin Characteristics Basin ID Area (miles=) Average Slope Corrected Hydraulic Length (ft) Curve Number Lag Time (hr) Basin I 0.140 0.170 3674 74 0.261 Basin 2 0.025 0.249 1783 74 0.121 Basin 3 0.024 0.414 1629 79 0.231 Bazin 4 0.013 0.170 445 78 0.054 Basin 5 0.123 0.185 3567 74 0.244 Basin 6 0.142 0.211 4606 74 0.281 Basin 7 0.036 0.278 1529 74 0.101 Basin 8 0.021 0.365 292 74 0.023 Basin 9 0.007 0.415 496 74 0.034 Basin 10 0.006 0.297 218 74 0.021 Basin I1 0.002 0.307 375 74 0.031 Basin 12 0.002 0.319 293 74 0.025 Basin 13 0.049 0.184 3146 74 0.221 Basin 14 0.007 0.316 842 82 0.070 Basin I S 0.007 0.431 781 75 0.066 Basin 16 0.005 0215 646 87 0.077 Basin 17 0.013 0.301 707 87 0.085 Basin 18 0.037 0.328 2059 81 0.214 3.5.3 Method of Analyses 3.5.3.1 HEC-1 Model Watershed runoff and stream flow routing were modeled using the U.S. Army Corps of Engineers HEC-1 computer program. The 100-year, 24-hour storm event was distributed in the HEC-1 program using the SCS Type II distribution. From the U.S. Soil Conservation Service National Engineering Handbook (SCS, 1969), it was determined that the hydrologic condition of the soils in the area was classified to be group C. The soil is also assumed to have antecedent moisture condition (AMC) II, which represents an average condition of watershed wetness prior to the storm event. Based on the soil hydrologic condition (group B) and antecedent moist condition (II), conservative runoff curve numbers of 74 and 87 were determined for the native soil areas and the regraded areas, respectively. For areas of each basin that have both the native soil and the regraded areas, a weighted average curve number based on the areas was used in the • HEC-1 Model. Ba((!e Moun(ain Resources, /nc. DRaf7' Shepherd Miller, lnc. p:l100}6~eKpprrrd,~repw/.dac 3-5 Afay 71, /999