Runoff Detention for Flood Volume or Erosion Control

A simple design aid is presented for quick preliminary sizing of flood-control detention basins and outlet structures. The design objective is to control the postdevelopment flood volume rather than the peak discharge. Alternatively, the method can be used to control downstream channel erosion caused by postdevelopment flows. The detention basins considered have a single outlet, which can be of either orifice or weir type. The design aid is based on the predetermined solutions to the reservoir-routing equation. The hydrologic storage equation is used for this purpose. To evaluate the channel-erosion tendencies, a generic bed-load formula is employed. All the equations are written in dimensionless form, and the solutions are obtained in terms of a set of governing dimensionless parameters. The results are generalized using the concept of hydrologic similarity, and they are presented in chart form. These charts can be used to determine the required stage-storage relationship for a detention basin and the size of the outlet structure. Sample applications are included to illustrate the use of the charts.