Figure 10-11 shows the interdependence of inlet location, drainage area, discharge, and ponded width. A tentative inlet location is selected, drainage area determined for that location, discharge established, and ponded width calculated. Once the ponded width has been calculated for a tentative location, it must be compared to the allowable ponded width and depth.

If the ponded width is exceeded, the design must be adjusted by relocating the inlet to a point upstream in the curb and gutter section which will reduce the watershed area, the peak discharge, and thus the ponded width. This process is repeated until the ponded width is at or below the allowable ponded width.

If the calculated ponded width is less than or equal to the allowable ponded width, the hydraulic designer must decide if the design is efficient. If all or most of the allowable ponded width is used, the location is probably efficient. If only a small portion of the allowable ponded width is used, a more efficient location may be possible. In extensive storm drain systems, a design objective should be to minimize the number of inlets without violating allowable ponded widths anywhere in the system. (See for guidelines on allowable ponding.)