Development of Storm Drainage Cost Functions

Planners must have simple quantitative relationships to rapidly but accurately estimate the costs of urban drainage facilities. Using fundamental concepts of urban hydrology, engineering design, and cost estimation, relationships are derived between percent imperviousness of urban areas, return period of design storm, and the resulting cost of drainage facilities. Increasing design return periods demand greater storm sewer sizes and additional coverage of drainage basins by the sewer network. A case study demonstrates rapid increases in cost from 1-yr to 10-yr return periods, but reduced rates of increase from 10-yr to 100-yr designs. The relationships developed will be useful for tradeoff decisions between levels of urbanization, storm drain design criteria, and the resulting cost of facilities.