Cost-Benefit Allocation of Selected Low Impact Development Techniques versus the Conventional Method

Abstract

One of the most exciting new trends in stormwater management today is the movement by many cities, counties, states, and private-sector developers toward the increased use of Low Impact Development (LID) to help protect and restore water quality and reduce rainwater runoff rate. LID comprises a set of approaches and practices that are designed to reduce runoff rate and pollutants from the site at which they are generated. By using infiltration, evapotranspiration, and reuse of rainwater, LID techniques manage and control water at the source and prevent or reduce the impact of development on rivers, streams, lakes, coastal waters, and ground water. This paper includes the most commonly implemented LID techniques, the available unit cost for each LID technique, and case studies. The paper is focused on proving that low impact development techniques will reduce the stormwater management land requirement and the overall cost of stormwater mitigation, while also providing stormwater quality benefits and making the resulting land and building projects more aesthetically pleasing and marketable. A weighting/rating system was designed to show the tradeoffs and benefits between the LID development techniques versus the conventional construction method. Weighting factors such as site preparation, stormwater management, street paving, sidewalk paving, landscaping, aesthetics, quality, and the cost of meeting local and other rules and regulations were incorporated. The goal was to evaluate cost-benefit allocation for projects using selected LID techniques versus the conventional construction method. The allocation was tested with the eight LID case studies and worked well in final positive allocation values for six LID cases (where LID was clearly justified) and two negative allocation values (where the conventional construction method was selected).