The National Green Values™ Calculator is a tool provided by the Center for Neighborhood Technology for quickly comparing the performance, costs, and benefits of Green Infrastructure, or Low Impact Development (LID), to conventional stormwater practices. The GVC is designed to take you step-by-step through a process of determining the average precipitation at your site, choosing a stormwater runoff volume reduction goal, defining the impervious areas of your site under a conventional development scheme, and then choosing from various practices to find the combination that meets the necessary runoff volume reduction goal in a cost-effective way.
A few important points to keep in mind:
The National GVC is currently focused on runoff volume reduction. It does not produce any peak flow results. Volume reduction in this context implies infiltration, evapotranspiration and reuse, and does not include detention in ponds or vaults. All runoff volume captured is assumed to be kept on site.
The National GVC is meant for a single site or a campus of buildings contained on a single site. If you are interested in looking at the performance and cost/benefit analysis of Green Infrastructure BMPs applied on a neighborhood or watershed scale, consider using other stormwater tools provided by the Center for Neighborhood Technology, or other sources.