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HYDROLOGIC DOCUMENTATION <br />SMALL AREA EXEMPTION <br />BEAR CREEK FAN SI'TE -TOPSOIL <br />The following calculations demonstrate the amount of silt fence or straw bale surface area required to adequately <br />handle the runoff from the Bear Creek Fan Site. <br />Runoff volume and peak discharge calculations were performed using the SEDCAD 4 computer model consistent <br />with the methodology previously discussed in this Exhibit. The sediment control structure was designed using the <br />pond routine in SEDCAD 4 to handle the peak discharge from a 10-year, 24-hour storm event. Length of the silt <br />fence and straw bales was determined from the topography of the site and from the necessary sediment storage to <br />comply with a settable solids limit of 0.5 ml/l. Input discharge rates for the Sedcad model were calculated from a <br />rate of 5.6 gpm/ft2 for straw bales and a rate of 10.0 gpm/ftz for a silt fence. Printouts of the Sedcad designs for a <br />silt fence and a straw bale boundary are provided below. <br />Hydrology Inputs <br />All hydrology inputs are shown on the SEDCAD computer printouts. <br />The CN numbers used for the SAE watershed were obtained from Procedures for Determining Peak <br />Flows in Colorado and Technical Release No. 55 (USDA-SCS, 1986) and consistent with previously <br />approved hydrology reports. Based on the soil type and vegetation cover, curve numbers were determined <br />using Table 2-2a and 202d, USDA-SCS TR-55, for the following conditions: <br />Disturbed: <br />Soil Type: C <br />Ground Gover: Poor <br />Cover Type: Herbaceous <br />CN: 87 <br />Area: 0.1 acres <br />2. Hydrology Results <br />Peak Discharge -Silt Fence or Straw Bales 0.15 cfs <br />10-year, 24-hour event <br />3. Hydraulic Structure Inputs <br />Assumed Length of Silt Fence or Straw Bales 36.0 ft <br />Assumed Height of Silt Fence or Straw Bales 1.5 ft <br />Assumed Slope behind Silt Fence or Straw Bales 10.0 <br />