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<br /> <br />' PROBABLE MAXIMUM FLOOD DISCHARGES <br />' The expected discharge from probable maximum magnitude floods has been a <br />combined effort of AWA, Wheeler, and Steffens. AWA has performed asite-specific <br />evaluation of the hydrometeorological parameters and has provided precipitation depth- <br />duration values, or Probable Maximum Precipitation (PMP) depths. The report describing <br />the results of this analysis is included herein as Appendix A. Based on the rr~sults of the <br />AWA analysis, a design storm depth of 5.6 inches of rainfall in a 6-hour period was <br />' used in this analysis. <br />' The AWA PMP depths were used to model the Probable Maximum Flood (PMF) <br />by integrating them with soil and hydrologic parameters. Wheeler perforred a flood <br />analysis for the tailing basin in 1996 using Corps of Engineers HEC1 and I'MP depths <br />' prescribed by NOAA Hydro-Meteorological Report (HMR)-49. Green-Ampt infiltration <br />models and unit hydrographs were used to conform as much as possible to the Colorado <br />' State Engineer's recommended procedures for evaluating storage dams. The unit <br />hydrographs used in the model were developed based on the methodology ~jescribed in <br />' the USBR Flood Hydrology Manual. The table below summarizes the basin input data <br />that was used in the HEC-1 model. Figure 1 shows the basin and facility configuration <br />' at the Henderson Mill. The Initial Loss and Volumetric Moisture Deficit parameters for <br />L.J <br /> <br /> <br />1 <br /> <br /> <br />all of the basins were set to zero. <br />BASIN INPUT PARAMETERS <br /> <br /> <br /> <br />asin <br /> <br />Area <br />(Sq. Mi.) Wetting <br />Front <br />Suction <br />(in.) <br />Hydraulic <br />Conductivity <br />(inJhr.) <br /> <br />Percent <br />Impervious <br />UCR 1.64 6.88 0.19 17.5 <br />HC 0.61 6.24 0.24 17.5 <br />EBRB 0.90 5.01 0.41 9.5 <br />EBRT 1.63 6.82 0.19 21 <br />TPB 4.20 5.33 0.35 6.5 <br />TPT 2.54 5.33 0.35 75 <br />' 5 <br />