FLOOD02650 - Laserfiche WebLink

Home Browse Search

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . mile contributing drainage area using the hypothetical storm record in the HEC-I program. The duration depths required for the HEC-I analysis were computed using the methodology published in NOAA Atlas n, Volume m. The 24-hour rainfall was applied uniformly to each subarea in the watershed using a triangular (critical) distribution pattern which places the peak intensity at the center of the storm and the remaining increments so that they ascend in magnitude to the peak and descend in magnitude to the end of the storm. InfIltration Rate Calibration . To determine appropriate infiltration rates, the Albuquerque District generated a HEC-l watershed model for Bear Creek, a tributary to the Los Pmos River, and calibrated the HEC-I model to peak discharges calculated from regional equations presented in U.S. Geological Survey Water- Resources Investigations Report 96-4112, Analysis of the Magnitude and Frequency of Peak Discharge and Maximum Observed Peak Discharge in New Mexico (1996). The following regional equations presented in Report 96-4112 were developed for the northwest plateau region of New Mexico including the San Juan River watershed in southwestern Colorado: Q(50.0%)= 8.47 X 101 x A 0.47 Q(20.0%)= 1.97 X 102x A 0.46 Q(lo.O%)= 3.06 X 102x A 0.46 Q(4,0'/") = 4.86 x I 02X A 0.45 Q - 6 54 02 0.45 (2.0%) -. x I x A Q = 8 53 X 102x A 0.45 (1.0%) . Q(0.2%) = 1.45 x 101X A 0.45 To simulate a critical storm, the rainfall in the HEC-I was reduced for the 19-square-mile drainage area of Bear Creek. Based on this analysis, the Albuquerque District adopted infiltration amounts and applied the infiltration rates to the HEC-I model for the Los Pinos River watershed above Bayfield. The infiltration amounts for each frequency are listed in Table 2. TABLE 2 INFILTRATION RATES Initial Loss Rate Above Bayfield Uniform Loss Rate for Entire FREQUENCY Watershed (in/hr) (in/hr) 1O.0o/...Chance (10-year) 1.035 0.30 4.0%-Chance (25-year) 1.217 0.30 2.0o/...Chance (50-year) 1.340 0.30 1.0o/...Chance (IOO-year) \.379 0.30 0.2o/...Chance (500-year) 1.435 0.30 4