Preliminary Design Aid for Bioretention Filters

Abstract

A physically based mathematical model is developed in this study for the hydrologic process taking place in a bioretention filter. The hydrologic storage equation is adopted to determine the variation of water depth in the ponding area. The Green and Ampt equations are used to model the movement of water in the underlying storage zone, or soil filter, taking into account the finite depth of the filter. The perforated drain pipes placed at the bottom of a soil filter are represented by atmospheric pressure at this location. The ponding area and the soil filter equations are coupled through the infiltration term. The governing equations are written in terms of a set of dimensionless parameters and are solved numerically by using an explicit finite-difference scheme. The solutions to the dimensionless governing equations are also in terms of dimensionless parameters, and they can be generalized on the basis of the principle of hydrologic similarity. A series of solutions is obtained for numerous and systematically chosen combinations of filter size and hydrologic and soil conditions and is presented in chart form. These charts can be used as a design aid for quick preliminary sizing of new bioretention filters and quick evaluation of existing filters.