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I <br /> The reclamation drainage plan includes a network of terraces and ditches designed to convey <br /> runoff from the graded and reclaimed slopes to the existing sediment control structures previously <br /> described. Terraces will collect sheet flow occurring on the reclaimed slope and divert it to <br /> armored ditches on the edge of the reclamation slope. <br /> Design of the channels and calculation of run off quantities were carried out using SEDCAD <br /> Version 4, a commercially available software package that calculates the runoff response to a <br /> given precipitation event for specific surface topography, soil, and vegetative cover conditions <br /> using subroutines from TR-55 (USDA-SCS, 1986). Application of the SEDCAD 4 program <br /> involves subdividing the drainage area into sub-watersheds with relatively uniform surface <br /> characteristics. SEDCAD utilities were used to determine surface areas, storage capacities, <br /> routing parameters, and storm runoff for the proposed ditches and sediment basins. <br /> a. Site Climate <br /> Precipitation data for the Colorado Springs area are available from NOAA Atlas 14, point <br /> precipitation values for site area (NOAA 2013). Table G-1 shows the 24-hour storm event data. <br /> Table G-1 <br /> Storm Event Estimates <br /> Return 24-hour Rainfall <br /> Period (in) <br /> 2 Years 2.06 <br /> 10 Years 3.19 <br /> 100 Years 5.64 <br /> A Natural Resource Conservation Service (NRCS, formerly the Soil Conservation Service)Type <br /> II rainfall distribution was applied to the 24-hour storm. The Type II distribution applies to mid- <br /> continent locations where there are intense localized storms. <br /> The 100-year, 24-hour storm event was used to model runoff and design the ditches for the final, <br /> reclaimed condition. The SEDCAD result model reports are included in Appendix G-1 for <br /> reference. <br /> b. Site Curve Numbers <br /> The modeled runoff volume is a function of the curve number (CN), watershed area, and storm <br /> size, with the soil curve numbers used to define the runoff from soils in the model. Runoff curve <br /> Pikeview Quarry Amendment 4 <br /> 2019 <br /> G-4 <br />