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Rational Method Problems

Rational Method Problems. Last 3 pages include reference info. needed to solve problems. Given 8.2 acre industrial plant 4.4 acres relatively flat lawn with a silt loam soil 2.8 acres of pavement 1.0 acres of roof surface Find Peak rate of runoff for this drainage area

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Rational Method Problems

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  1. Rational Method Problems Last 3 pages include reference info. needed to solve problems

  2. Given 8.2 acre industrial plant 4.4 acres relatively flat lawn with a silt loam soil 2.8 acres of pavement 1.0 acres of roof surfaceFindPeak rate of runoff forthis drainage area Use rainfall intensity of 2 iph q = CiA

  3. Given 1.5 acres in NJ 0.14 acres pavement 0.20 acres woodland 1.16 lawnSoil is ‘Silt loam’ Slope ranges from 0 to 5%FindPeak rate of runoff leaving the site at the southwest corner Use 10-year design storm q = CiA

  4. Given 95 acre drainage area in NJCompletely wooded Soil is ‘Silt loam’ Drainage area avg. slope = 6%Stream slope = 2% Hydraulically most remote point is ‘A’FindPeak rate of runoff needed to design a road culvert Use 50-year design storm q = CiA

  5. Recommended Runoff Coefficients, C

  6. Tc Nomographs Overland Flowp. 181 Channel Flowp. 182

  7. Rainfall Intensity Curvesfor NJ Rainfall Intensity (in/hr) Duration of Storm (min)

  8. ~Examples 11.6, 11.8, and 11.9

  9. Given 15 acre drainage area in Boston areaRunoff Coefficient, C = 0.30Time of Concentration, Tc=25 minutes100-year storm frequencyFind 1) The 10-, 25-, and 50-minute hydrographs2) The volume of runoff for each3) Assume the proposed development outflow for the 25-minute storm cannot exceed the predevelopment rate. Find the volume of storm water storage necessary if:C = 0.75 Tc = 15 minutes qmax = CCAiA qmax = CCAiA(DUR/Tc)

  10. CA Recommendations Hydrograph Types A & B Hydrograph Type C qmax = CCAiA qmax = CCAiA(DUR/Tc) Storm Frequency 2 to 10 25 50 100 CA 1.0 1.1 1.2 1.25 Note: C x CA must never exceed 1.0

  11. Rainfall Intensity CurvesforBoston Boston Rainfall Intensity (in/hr) (minutes) (hours) Duration of Storm

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