Open Channel Calculator

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Open Channel Calculator

Required Information
Enter the Slope: Enter the Channel Top Width (feet):
Enter the Channel Bottom Width (feet): Enter the Channel Height (feet):
Enter the Flow Depth (feet): Enter the n value:

The wetted perimeter is Feet.

The flow area is Square Feet.

The hydraulic radius is Feet.

The C value is

The flow is CFS.

The flow is GPM.

The velocity is FPS.

Design Use Values of Manning's n
Channel Material n
clean, uncoated cast iron 0.013-0.015
clean, coated cast iron 0.012-0.014
dirty, tuberculed cast iron 0.015-0.035
riveted steel 0.015-0.017
lock-bar and welded 0.012-0.013
galvanized iron 0.015-0.017
brass and glass 0.009-0.013
wood stave
  • small diameter
  • 0.011-0.012
  • large diameter
  • 0.012-0.013
  • with rough joints
  • 0.016-0.017
  • dry mix, rough forms
  • 0.015-0.016
  • wet mix, steel forms
  • 0.012-0.014
  • very smooth, finished
  • 0.011-0.012
    vitrified sewer 0.013-0.015
    common-clay drainage tile 0.012-0.014
    asbestos 0.011
    planed timber 0.011
    canvas 0.012
    unplaned timber 0.014
    brick 0.016
    rubble masonry 0.017
    smooth earth 0.018
    firm gravel 0.023
    corrugated metal pipe 0.022
    natural channels, good condition 0.025
    natural channels with stones and weeds 0.035
    very poor natural channels 0.060
    Copyright 1998 Donald R.Milam, PE