Manning'sMANNING'S CHEAT SHEET FOR CIRCULAR PIPE - full flow conditions123456789materialAddnl.Pipe MaterialroughnessDiameterAreaR2/3AR2/3QVelQdn1.49 / n(inches)(sf)(ft)capacity(ft/s)(cfs)Lucite0.008186.2510.0050.0760.00041--1.840.010glass0.009165.5620.0220.1200.00262535%2.920.064pvc, asphalted cmp0.010149.0040.0870.1910.01665535%4.640.405concrete - trowel, smooth0.012124.1760.1960.2500.04909195%6.081.194Welded steel, smooth HDPE0.012124.1780.3490.3030.106115%7.362.570clay drainage tiles0.012124.17100.5450.3510.19281%8.544.661rcp,vcp,cmp-helical0.013114.62120.7850.3970.31263%9.657.58clean uncoated cast iron0.014106.43151.2270.4610.56581%11.2013.74brick lined w/mortar, Corrugated HDPE with smooth liner0.01599.33181.7670.5200.91963%12.6422.34riveted steel, rough asphalt0.01693.13212.4050.5761.38651%14.0133.70unfinished concrete, poor joints0.01787.65243.1420.6301.97943%15.3248.120.01882.78273.9760.6812.70937%16.5765.880.01978.42304.9090.7313.58832%17.7787.25dirty tuberculated c.i.0.02074.50367.0690.8255.83563%20.07141.880.02364.78429.6210.9158.80251%22.24214.01cmp -2 2/3 by 1/2" annular correg.0.02462.084812.5661.00012.56643%24.31305.556 by 1" corregations0.02559.605415.9041.08217.20437%26.30418.300.02755.196019.6351.16022.78432%28.21553.99cmp - 3" by 1" in correg.0.02853.216623.7581.23729.37829%30.07714.310.03049.677228.2741.31037.05026%31.86900.859 by 2 1/2 inch structural plate0.03542.578438.4851.45255.88751%35.311358.870.06024.83The Manning's equation determines the maximum gravity flow capacity of a pipe or conveyance. Maximum capacity is a function of a pipe's roughness(n), size (diameter or surface area), hydraulic radius (area/wetted perimeter) and slope. To use this calculator, enter the constant multiplier from thelist above and choose the pipe's slope. The calculator will perform the remaining calculations.1.49 / nSlope114.620.045Vel = col 2 x col 5 x S^.5 = fpsQ = col 2 x col 6 x S^.5 = cfsVel = Pipe Velocity, Q = Max Pipe DischargeD theor = 16{Qn/S^.5} ^.375D (inches), Q(cfs), S(ft/ft)Vel = 1.49/nR2/3 S0.5 ; Q = VA, A = (Pi/4)D2Hydraulic radius: R = A / wetted perimeter (pi x D) which reduces to D/4 for circular pipeApplicability - Although the Manning's equation is only applicable where flow is steady and uniform, (and discharge does vary during thepassage of a flood wave), during the specific time around the peak, the flow is essentially steady.Hint: When comparing pipes of similar material installed at the same slope, it is only necessary to compare the product of each pipe's (Area x HydraulicRadius) to compare capacities. Columns 6 and 7 gives the "carrying capacity" when comparing pipes that differ only by size. Cxample #1: A two-inchpipe can carry 535% more flow than a one-inch pipe (of the same material, installed at same slope) Example #2: If a 15 inch pipe is installed in abasin that requires an 18 inch pipe, as much as 37% (1-63%) of the drainage basin's flows won't be conveyed by the underdesigned 15" system.

n valuesmaterialmaterialFLOW TYPEroughnessFLOW TYPEroughnessnnPIPE & CHANNEL FLOW - concentratedChannels, Swalescmp - completely asphalted0.0104" stone lined channel0.028pvc, abs plastic0.010grass, sod, grouted rip-rap0.030smooth concrete0.0119" stone lined channel0.032hdpe, welded steel0.012ungrouted rip-rap0.035rcp,vcp,cmp-helical0.013channels w/stones & weeds0.035concrete - avg. value0.01318" stone lined channel0.036curb0.014very poor natural channel0.060concrete - float finish0.015Unmaintained brushy channel0.080street gutter or paved channel0.015brick, riveted steel0.016OVERLAND FLOW - thin sheet flowunfinished conc.0.017Smooth surfaces (concrete, asphalt, bare soil, gravel)0.011concrete - poor joints, rough walls0.017Fallow0.05smooth earth0.018Smooth surfaces - very shallow.10 - .15dirty tuberculated cast iron0.020Prairie grass - short.10 - .20firm gravel0.023Lawns.20 - .30cmp - 2 2/3 by 1/2 in annular correg.0.024Pasture.30 - .40cmp - 6 by 1 in correg.0.025Dense Growth/Light underbrush.40 - .50earth- straight & uniform0.027Dense Underbrush0.8cmp - 3 by 1 in correg.0.028Underdrain pipes for bioretention etc.4 and 6" single-wall corrugarted plastic.014 - .0154 and 6" smooth-wall plastic.01 - .0118" single-wall corrugated plastic.015 - .016has larger corrugations thus rougher

Rational formulaDrainage Area #1Contrib.Drainage Area #2Contrib.Drainage Area #3Contrib.DischargeDischargeDischargeCIAQiCIAQiCIAQirunoff coeff(in/hr)(acres)(cfs)runoff coeff(in/hr)(acres)(cfs)runoff coeff(in/hr)(acres)(cfs)0.988.5433.320.5564.514.850.5564.514.85Drainage Area #4Contrib.Drainage Area #5Contrib.Drainage Area #6Contrib.DischargeDischargeDischargeCIAQiCIAQiCIAQirunoff coeff(in/hr)(acres)(cfs)runoff coeff(in/hr)(acres)(cfs)runoff coeff(in/hr)(acres)(cfs)0.5564.514.850.5564.514.850.5564.514.85ft2acres% totalCCwroofs/drive/patio35000.0810.980.98lawn0.980trees0.220businesses0.70streets0.9800.081.00