Designing Bioretention Areas for Stormwater Management

Abstract

Governing equations for designing bioretention areas for both flood control and water-quality control are developed, and a design protocol for applying these equations is also presented. Factors taken into account include the flood-control return period, the local intensity-duration-frequency (IDF) function, the catchment volumetric runoff coefficient, and the depth and infiltration capacity of the bioretention-area bowl. It is shown that the IDF functions nested within the conventional Natural Resources Conservation Service (NRCS) rainfall distributions can be described by a common functional form, with different parameters for each of the four rainfall types. These extracted IDF functions are used to show that designing bioretention areas for flood control is more feasible in the western part of the United States that have Type I rainfall, compared to other parts of the county that have Types IA, II, and III rainfall. It is demonstrated that practical bioretention areas that are sized for water-quality control can also meet flood-control regulations in some areas. A design example is provided to demonstrate the typical sizing of bioretention areas for both flood control and water-quality control.