Lifecycle cost and benefit analysis for parcel-scale implementation of green stormwater infrastructure

Abstract

Green stormwater infrastructure (GSI) is commonly implemented to reduce excess stormwater runoff while also producing secondary environmental, health, and aesthetic benefits. However, GSI is sometimes perceived to be cost prohibitive for limited-budget site development projects. This study used lifecycle cost analysis (LCCA) and benefit-cost analysis (BCA) to investigate the cost-effectiveness of GSI combined with conventional stormwater infrastructure for a proposed parcel development site in Oxford, Mississippi, USA. Hydrologic modeling was conducted for a conventional underground detention facility as well as three GSIs (permeable pavement, rain garden, and grassy ditch), all of which met regulatory runoff attenuation targets for the site. The LCCA considered capital and operation and maintenance (O&M) costs. Benefits were estimated under six categories–water, energy, climate, air quality, health, and community–based on existing tools for economic analysis of low impact development (LID). Economic benefits and costs over different scenarios of project lifecycles were compared using the present value (PV) approach in the benefit cost analysis (BCA). The lifecycle costs of two of the three GSIs (rain garden and grassy ditch) were lower than for the conventional alternative alone. However, in all three GSI cases, the long-term benefits of GSI features outweighed the costs. The methodology presented can be adapted to other locations to inform analyses of lifecycle costs and benefits and identify GSI and hybrid infrastructure options that are financially and environmentally feasible.