Hydraulics Flow Rates and Slope

Slope Design

Neutral Slope:

Straight linear, no pitch, no rate of change

Step Slope:

External rate of change with different externalchannel depths

Continuous Slope:

Constant rate of change, typical slopes are .5%, .7%, 1%, 1.5% and 2.0% Swiftslope by Swiftdrain is a continous slope of .05% - 2.0%

Water Flow Design

Flow Rate Calculations:

Required water flow = Qr

  • Qr = CIA
  • Qr = C*I*A
  • Let C = surface constant (pavement use 0.9)
  • Let I = water fall intensity

Channel Flow Capacity = Qc

  • Qc = A*(1.49/n)*(R)^2/3*(S)^1/2
  • Let A = cross sectional area of the trench drain in square feet
  • Let n = the coefficient of friction of the trench drain body
  • concrete forming systems = 0.013
  • polymer concrete systems = 0.010
  • fiberglass & GFRPC systems = 0.009
  • Let R = the hydraulic radius which is calculated by
  • Hydraulic raidius = A / P
  • A = the cross sectional area found above the trench
  • P = the perimeter surface of the trench
  • Let S = bottom effective slope of the trench
  • Effective slope=site slope + built in slope of trench drain

Resources

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