Storm‐Water Detention Storage Design under Random Pollutant Loading

Abstract

A set of equations for computing storm‐water detention storage‐capacity‐treatment‐rate combinations as a function of pollutant trap efficiency and relevant hydrologic statistics is provided. The hydrologic variables of runoff event depth, duration, and interevent time are treated as independent, exponentially distributed random variables. With the aid of a mass balance relationship at the detention unit and a first‐order pollutant load model, an expression for the expected pollutant wash‐off load is derived. This is used to obtain closed‐form expressions for the pollutant‐control isoquants in terms of the detention storage capacity, the treatment rate, the pollutant trap efficiency, and the statistics of the runoff process. For specified values of the treatment rate and pollutant trap efficiency, the isoquants are solved to obtain values of the required storage capacity. In addition, the expressions yield lower‐ and upper‐bound estimates of the storage capacity estimators. An illustrative example using data from a catchment in Minneapolis, Minnesota, is provided.