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Page 1 of 3 <br /> <br />1• <br /> <br />1 <br />1 <br /> <br />1_ l <br /> <br />~~ <br /> <br /> <br />1 <br /> <br /> <br />1 <br />1 <br />A <br />FIGURE 2.05.3(3)(c)(i) <br />CALCULATIONS AND PEAK FLOWS FOR 18" AND 9" CULVERTS <br />18" CULVEP.T <br />P9ethod of determining peak flows: SCS. <br />Determine precipitation: <br />Design for 25 year, 24 hour storm (from NOAA Precipitation <br />Frequency Atlas of the Western United States, Volume III - <br />Colorado 2.2") <br />Choose CN = Curve Number s ('re ~ R~RayC ~~ <br />Soils: Beenom - Absarokee 1008 <br />Hyrologic Soil Group C <br />Cover 958 Oak Brush <br />AMC -II, CN=35 (from United States Bureau of Reclamation <br />Design of Small Dams, page 539) <br />The amount of rain necessary to initiate runoff is P=0.25, where <br />S = lONO _ 10 = 1000 _. 10 = 18.57 <br />0.?.S = 0.2(18.57) = 3.71 <br />From NOAP_, 25 year - 24 hour P = 2.2" <br />Since 3.71 inches of rain is necessary to initiate runoff, <br />no runoff will occur in this channel due to a 25 year, 24 <br />hour storm. <br />9" CULVEF.T <br />Precipitation for a 25 year, 24 hour storm = 2.2" <br />Choose CN = 80 (see above reference) <br />Soils: Breece Loam <br />Hydrologic Soil Group B <br />Cover 08 <br />AMC - II, (see above reference) <br />(see above) <br />' REVISED May 15, 1981 <br />