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r <br /> 'f : Transit Mix Concrete Co. <br /> runoff peak flows from the major (100-year) storm event. The UDFCD result tables presenting <br /> these calculations are included in Attachment G-1. <br /> Curve Number Method <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 ponds. The curve <br /> number method flow calculations are included as Attachment G-1. <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. Table G-2 shows the 24-hour storm event data. <br /> Table G-2 <br /> Storm Event Estimates <br /> Return 24-hour Rainfall <br /> Period (in) <br /> 2 Years 1.93 <br /> 10 Years 2.99 <br /> 100 Years 5.38 <br /> The data in DCM Volume 1 are based on NOAA Atlas 2, which has been superseded by NOAA <br /> Atlas 14; however, the data referenced in the DCM Volume were utilized for these calculations <br /> following El Paso County rules and regulations. <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 modeled for the design of culverts and ditches, and for <br /> the design of all sediment ponds in accordance with state and county regulations. The SEDCAD <br /> result model reports are included in Appendix G-1 for reference. <br /> Hitch Rack Ranch Quarry Permit Application M-2016-010 <br /> September 15, 2016 G-12 <br />