Index:

Channel Flow

This form helps determine the normal depth
of water in a trapezoidal channel.
Input Data:

Flow Rate = cfs
Bottom Width = ft
First Sideslope Factor = :1
Second Sideslope Factor = :1
Longitudinal Slope = ft/ft
Mannings 'n' =
Results:

Normal Depth = ft
Area = ft2
Velocity = ft/s
Top Width = ft
Hydraulic Radius =

MANNING'S FORMULA

Q = A * 1.486/n * R2/3 * S1/2

  • Q = Discharge (cu. ft./sec.)
  • A = Cross-sectional Area of Flow (sq. ft.)
  • n = Coefficient of Roughness
  • R = Hydraulic Radius (ft.)
  • S = Slope of Pipe (ft./ft.)

Hydraulic Radius

R = A / P

  • R = Hydraulic Radius (ft.)
  • A = Cross-sectional Area of Flow (sq. ft.)
  • P = Wetted perimeter (ft.)

Area of a Trapezoid

A = B * D + [(Z1+Z2)/2] * D2

  • A = Cross-sectional Area of Flow (sq. ft.)
  • B = Bottom width (ft.)
  • D = Depth of flow
  • Z1 = Left side slope (z:1)
  • Z2 = Right side slope (z:1)

Wetted Perimeter of a Trapezoid

P = B + [(Z1*D)2 + D2]1/2 + [(Z2*D)2 + D2]1/2

  • P = Wetted perimeter (ft.)
  • B = Bottom width (ft.)
  • D = Depth of flow
  • Z1 = Left side slope (z:1)
  • Z2 = Right side slope (z:1)
Material Manning's n
Metals
Brass 0.011
Cast Iron 0.013
Smooth Steel 0.012
Corrugated Metal 0.022
Non-Metals
Glass 0.010
Clay Tile 0.014
Brickwork 0.015
Asphalt 0.016
Masonry 0.025
Finished Concrete 0.012
Unfinished Concrete 0.014
Gravel 0.029
Earth 0.025
Planed Wood 0.012
Unplaned Wood 0.013
Corrugated Polyethylene (PE) with smooth inner walls 0.009-0.015
Corrugated Polyethylene (PE) with corrugated inner walls 0.018-0.025
Polyvinyl Chloride (PVC) with smooth inner walls 0.009-0.011
Excavated Earth Channels
Clean 0.022
Gravelly 0.025
Weedy 0.030
Stony, Cobbles 0.035
Natural Streams
Clean and Straight 0.030
Major Rivers 0.035
Sluggish with Deep Pools 0.040
Floodplains
Pasture, Farmland 0.035
Light Brush 0.050
Heavy Brush 0.075
Trees 0.15