Ponding
The flow of water in the gutter should be restricted to a depth and corresponding width that will neither obstruct the roadway nor present a hazard to the motoring public at the design AEP. These restrictions are referred to as allowable depth and allowable ponded width. The depth and width of flow depend on the following:
- rate of flow
- longitudinal gutter slope
- transverse roadway slope
- roughness characteristics of the gutter and pavement
- inlet spacing.
Depth of flow should not exceed the curb height.
Ponded widths are limited to the following minimum acceptable standards for Department roadway design:
- Limit ponding to one-half the width of the outer lane for the main lanes of interstate and controlled access highways.
- Limit ponding to the width of the outer lane for major highways, which are highways with two or more lanes in each direction.
- Limit ponding to a width and depth that will allow the safe passage of one lane of traffic per direction for minor highways.
Inlets should be placed at all low points in the roadway and at suitable intervals along extended slopes as necessary to prevent excessive flow in the gutter or ponding on the roadway. An economical design uses a minimum number of inlets by allowing the ponded width and depth to approach the allowable limits. In instances such as a narrow shoulders or low grades, there may need to be a continuous removal of flow from the surface.