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<br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />'. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />J <br /> <br />SCS TR-55 Methodoloov <br />Q = (P-0,2S)'j(P+0.8S) <br />S=(1000ICN)-10 <br />qp = Q,AQ <br /> <br />Hvdroloav Calculations <br />Town of Granby <br />Basin A 1 <br /> <br />where: <br />Q = runoff depth (inches) <br />S = potential abstraction <br />CN = SCS Curve Number <br />A = drainage area (acres) <br />P = rainfall depth (inches) <br />Q, = Unit Peak Discharge (cfs/sm/in) <br /> <br />Catchment Data <br />Location Western Colorado (II) <br />Catchment ID = <br />Basin Area, A = <br />NRCS Soil Type = <br />Overland Flow Type Short Grass Pasture & Lawns <br />Runoff Depths <br />Storm <br />Rainfall Frequency (years) <br />Rainfall Duration (hours) <br />Rainfall Depth, P (inches) <br /> <br />Weighted Curve Numbers, CN <br />Sub-Area <br />1 <br />2 <br />3 <br />4 <br />Sum <br /> <br />Total Runoff <br /> <br /> <br />Description <br />Residential <br />Commercial <br />Pasture <br />Roads <br /> <br /> <br />Percent <br />10% <br />5% <br />83% <br />2% <br />100% <br /> <br />Storm 5 yr - 24 hr 10yr-24hr 50yr-24hr 100 yr- 24 hr <br />Potential Abstration, S 2.43 2.43 2.43 2.43 <br />Runoff Depth, Q (inches) 0.25 0.35 0.84 0.98 <br /> <br />Time of Concentration <br />Overland Flow <br />From Figure 3-1, TR-55 <br /> <br />Basin Calculation <br /> <br />Reach <br />A <br />B <br />C <br />D <br />Total <br /> <br />Peak Dlscharae <br /> <br />Channel Flow <br />T", = U(I.49/n)R213 S 1/2 <br /> <br />where: <br />R = Hydraulic Radius n = Roughness Coeff, <br />S = Channel Slope L = Length of Flow <br />T cc = Time of Concentration, Channel Flow <br /> <br /> <br />V rea Dr Tee <br />(IVs) (min) <br />1,2 8.8 <br />1.6 36.4 <br />5.2 8.0 <br />2.0 53.3 <br /> <br /> <br />5 yr - 24 hr <br />354 <br />0.19 <br /> <br />100 yr - 24 hr <br />354 <br />0.19 <br /> <br />10 yr - 24 hr <br />354 <br />0.19 <br /> <br />50 yr - 24 hr <br />354 <br />0.19 <br /> <br />Unit Peak Discharge (ofs/sm/inch) <br />Area sm <br />1?'JlkiD <br /> <br />8/20102 <br />TR55-hydrolo9y.xls <br /> <br />