Hydrologic Modeling and Capital Cost Analysis of Low-Impact Development1

Abstract

Urban development substantially increases the rate and volume of stormwater runoff. Conventional stormwater management focuses on peak rate control while overlooking the increased volume of urban runoff. Low impact development (LID) is a land planning and stormwater management approach that seeks to manage runoff as close as possible to its source by reducing both the rate and volume of runoff. It has been hypothesized that LID can be used to restore predevelopment hydrology. This study investigates if LID practices alone can maintain predevelopment hydrology, as well as how much LID is required, and provides a capital cost analysis of LID practices. Several different stormwater management scenarios were evaluated with the EPA Storm Water Management Model (SWMM) including two rainfall types and two soil types. Design storm and continuous simulation analyses were performed. Modeled LID elements include grassed swales, rain gardens, infiltration trenches, and permeable pavement. Results show that LID can restore predevelopment site hydrology but requires extensive implementation of LID to manage the 1-year storm. Finally, the cost comparison indicates that the extra expense for a 1-year LID system may be as much as 4–65% more than the cost of a conventional drainage system.