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<br />METHODOLOGY AND ASSUMPTIONS <br />HYDROLOGY <br />In the original permit (1980) the "SCS Method" of determining runoff and <br />peak discharge values was used. Runoff volumes were computed using <br />equation 10.10 and the procedure outlined in Chapter 10 of the National <br />Engineering Handbook, Section 4 - Hydrology, (USDA-SCS, 1971). Peak <br />discharge values for each pond tributary area were calculated for the <br />10-year, 25-year, and 100-year. 24-hour duration precipitation events in <br />accordance with Procedures for Determining Peak Flows in Colorado, <br />(USDA-SCS, 1980). <br />The following parameters and factors are used to develop representative <br />values for each drainage basin and for structures within that basin: <br />• - Drainage Area <br />- Maximum drainage area (DA), planimetered on 1"=500' scale <br />map <br />- Maximum elevation - highest elevation of drainage area <br />- Minimum elevation - lowest elevation of drainage area <br />- Drainage height (Z) - difference between maximum and <br />minimum elevation <br />- Hydraulic length (L) - greatest flow length of drainage <br />area <br />- Average slope (S) - slope of drainage area calculated as <br />follows: <br />S Z/L <br />- Slope adjustment factor - adjustment factor taken from <br />Table 23-1, Slope Adjustment Factors by Drainage Areas. <br /> <br />23-11 <br />