Ponding on Continuous Grades

Excessive ponding on continuous grades can be avoided by proper placement of storm drain inlets. The gutter ponding at a specific location may be determined on a continuous grade using the following steps:
  1. Select a location of a proposed inlet. Start on the high point and work towards the low point. Take into consideration the discussion in
    Inlet Locations
    .
  2. Calculate the total discharge in the gutter based on the drainage area to the selected location. See
    Determination of Runoff
    for methods to calculate discharge.
  3. Determine the longitudinal slope, transverse slope and Manning's roughness coefficient of the gutter.
  4. Compute the ponded depth and width. For a constant transverse slope, compute the ponded depth using Equation 10-1 and the ponded width using Equation 10-2. For parabolic gutters or sections with more than one transverse slope, refer to the FHWA publication “
    Urban Drainage Design Manual
    " (
    HEC-22
    ).