§ 7.3.3. Velocity and Grade Considerations

The minimum cleaning velocity for a storm drain line is three (3) fps for a 5 year event is recommended. Use the following formula to determine the minimum slope required for a velocity of three (3) fps.

(Equation: 7.3.3)

S = pipe slope (ft./ft.)
K _u = 2.87
n = Manning's N
V = Cleaning velocity (ft./sec.)
D = diameter of conduit (ft.)

The maximum velocity for a storm drain line in a twenty-five (25)-year event should follow Table 7.3 below. Velocities above the maximum shall be approved by the Director of TCI.

Table 7.3 - Maximum Velocity

Type	Maximum Permissible Velocity
Laterals	No limit
Main trunk lines	15 fps

 

The minimum slope for the storm drain line is 0.3% or as approved by the Director of TCI.