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amec~ <br />Subjed LaFargeH&H MaaeM ACR gab 4271-716054 <br />Ft. Lupton Drainage cberxea M ~~ <br />!J ' Date 10/11/04 <br />Perimeter Channel Design Approved by sheet 2 of 2 <br />• See Table 1 for Tc calculations. For calculation purposes, assume Tc = 60 minutes. <br />• Runoff calculations performed using the Rational Method: Q =CIA = 0.44 * 80ac * 2.71 in/hr = 45.4 cfs <br />Where: Q =Peak flow for the design intensity (cfs) <br /># 23ac * 57ac _ <br />C = runoffcoefficient(Appendix 20.A Lindeburg,2001) _ (0.8) + (0.3) - 0.44 <br />80ac 80ac <br />I =Intensity (in/hr) (p.15 NOAH 1973) = Y,~ =1.897 + 0.439 * ~x; # I x' JJ - 0.0082 =2.71 in/hr <br />l x* <br />Where: Ytoa = 100-yr, 1-hr precipitation <br />X3 = 100-yr, 6-hr precipitation depth = 3.4 in (NOAA 1973) <br />Xo = 100-yr, 24-hr precipitation depth = 4.2 in (NOAA 1973) <br />Z =point elevation (hundreds of feet) = 49.4 (site is 4940 ft amsl) <br />A =watershed area (ac) = 80ac <br />• Channel Sizing based on Manning's formula. See Table 2 for calculations. <br />CO NCLUSIONS/RES ULTS: <br />A grass-lined trapezoidal channel at 0.3% longitudinal slope with the dimensions below will convey the 100-year storm <br />event across the east side of the Rittenhouse property to the South Platte River while maintaining 1 foot of freeboazd. <br />Refer to Table 1 for hydraulic pazameters, and Sheets 1 and 2 for channel details and location information, respectively. <br />3.01 ft <br />~--- 1(ll ft -~ <br />Urban Drainage and Flood Control District. 2001. Urban storm drainage criteria manual [in three volumes]. Denver CO: <br />Wright Water Engineers. <br />U.S. National Oceanic and Atmospheric Administration (NOAA). 1973. Precipitation Frequency Atlas ojthe Western <br />US, Atlas No. 2, volume 111-Colorado. Silver Spring MD : US Department of Commerce. <br />