Froude Number

The Froude Number (F
r
) represents the ratio of inertial forces to gravitational forces and is calculated using Equation 6‑14.
EquationObject208229
Equation 6-14.
where:
  • v
     = mean velocity (fps or m/s)
  • g
     = acceleration of gravity (32.2 ft/ s
    2
     or 9.81 m/s
    2
    )
  • d
    m
    = hydraulic mean depth = A / T (ft. or m)
  • A
     = cross-sectional area of flow (sq. ft. or m
    2
    )
  • T
     = channel top width at the water surface (ft. or m).
The expression for the Froude Number applies to any single section of channel. The Froude Number at critical depth is always 1.0.