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Calculator

Development

EPA Smart Growth

Getting Started

The National Green Values™ Calculator is a tool 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 a range of Green Infrastructure Best Management Practices (BMPs) 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 in BMPs 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 the original GVC and/or some of the other stormwater tools provided below.

To get started, select a tab at the top to enter site information. Default values (that can always be changed by the user) are provided throughout the calculator, so you can begin on any step. However, we recommend starting on the Lot Information page and proceeding through each step. Below is a brief description of the information you can provide on each page:

  • Lot Information
  • Predevelopment
  • Runoff Reduction Goal
  • Conventional Development
  • Green Improvements
  • Advanced Options

Results

The results statement at the bottom of the page continuously updates to reflect site conditions and BMPs defined by the user. The user does NOT need to click on a “Calculate” button to see the affect of different choices. The results are presented in detail on separate tabs. They include progress toward the specified runoff volume reduction goal, changes in the total runoff volume annually and for the average storm event for the predevelopment, conventional, and green scenarios, changes in the land use between the conventional and green scenarios, and detail on the lifecycle cost/benefit analysis.

For more information on the conceptual, hydrologic, and financial basis of this tool, please see the methodology link provided below.

Download Methodology

methodology.pdf (PDF, 505kb)

Other Resources

Original Green Values Stormwater Calculator

EPA Office of Water Managing Wet Weather with Green Infrastructure

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