Economic Assessment of Storm Drainage Planning

Factors that planners must consider in the economic evaluation of storm drainage system alternatives include the scale of development, the degree of protection, and the option for including detention storage. A planning tool that requires a limited data base is presented for use in evaluating various possible designs and the effect on total cost of imperviousness, design return period, and the time of concentration. The utility of the above planning tool is demonstrated for the Washington, D.C., Dallas, Tex., and Los Angeles, Calif. areas. Improvement in the efficiency of storm drainage systems will reduce both the total cost and the hydrologic impact of development. Both structural measures like detention storage, and nonstructural measures, like open space ponding and grass-lined swales, improve the efficiency of storm drainage systems. The effect on cost of increases in the time-of-concentration is examined as an indicator of the efficiency of storm drainage alternatives.