Dual-Purpose Detention Basins

Design criteria for small detention basins, which are being built in large numbers to reduce flooding in rapidly urbanizing areas, may be modified to serve additionally the purpose of reducing runoff pollution, which also accompanies urbanization. Only slight reduction in local flood-control effectiveness will be entailed by the modification, and the dual-purpose basins will be more useful in aid of flood control further downstream than the single purpose locally oriented structures. Runoff pollution from urbanizing areas is important to water-quality planning, and occurs largely in particulate form. However, the trap effectiveness of detention basins for different kinds of pollutant, retained in storage for various periods, has not yet been determined by research or practical experience; so that design criteria for dual-purpose detention basins cannot be stated with any degree of precision. Tentative criteria for interim use are suggested.