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• <br />2 BEST PORTALS <br />CULVERT DESIGN <br />North Area Undisturbed Drainage, 100-Year Event <br />2 West Portal Area, Powderhorn Coal Company <br />BASIN CHARACTERISTICS <br />~~ • <br /> <br />DRAINAGE AREA (SQ. MI.) = 0.040 <br />STREAM LENGTH (MI.) = 0.347 <br />ELEVATION DIFFERENCE (FT.) = 850.000 <br />RUNOFF CURVE NUMBER, CN = 78.000 <br />MINIMUM INFILTRATION LOSS (IN,/HR.) = 0.150 <br />PRECIPITATION FOR SPECIFIED STORM <br />ADJUSTED PRECIPITATION FOR SELECTED STORM (IN.) <br />UNIT HYDROGRAPH PARAMETERS <br />UNADJUSTED TIME OF CONCENTRATION (HR.) _ <br />ADJUSTED TIME OF CONCENTRATION (HR,) _ <br />DURATION OF EXCESS RAINFALL, D (HR.) _ <br />TIME TO PEAK (HR. ) _ <br />BASE TIME (HR. ) _ <br />QPEAK (PEAK FLOW IN CFS FOR UNIT HYDROGRAPH) _ <br />RESULTANT HYDROGRAPH VALUES <br />PEAK DISCHARGE (CFS) _ <br />RUNOFF VOLUME (ACRE-FEET) _ <br />TIME TO PEAK DISCHARGE (HR) _ <br />22.92 <br />0.62 <br />12.01 <br />USED SCS TYPE II 24-HOUR GFNFUar. STORM <br />Culvert Design <br />Reference: Figure 4-18, Inlet Control monogram for CMP, Page 161, <br />Handbook of Stee] Drainage & Highway Construction Products, <br />American Iron and Steel Institute, 1971 <br />An 18" Ct4P with end section conforming to fill slope and a 1.66 headwater <br />depth to diameter ratio will carry 12 CFS. Use 2 18" CMP <br />2.20 <br />0.06 <br />0.06 <br />0.01 <br />0.04 <br />0.11 <br />471.8 <br />fdISC - 2 (New 8-28-921 <br />