The National Green Values Calculator is a stormwater management calculator developed by the Center for Neighborhood Technology as a tool for quickly comparing the performance, costs, and benefits of green infrastructure or low impact development to conventional grey infrastructure practices. The tool is intended for a non-technical audience to evaluate the environmental improvement that can be achieved with green infrastructure. In addition, the calculator provides users with planning-level cost estimates.
The calculator uses a simple web interface to walk the user step-by-step through a planning process to identify the right combination of green infrastructure practices to meet stormwater management goals in a cost-effective way. Users can enter a stormwater runoff volume reduction goal (typically a standard established by the regulating government agency) to tailor results to local requirements. Inputs to the calculator consist of the following:
- Project location (used for rainfall input data)
- Lot size
- Predevelopment conditions (land cover)
- Runoff reduction goal (for New Jersey, select 1.25 inches to comply with current regulations [NJAC 7:8])
- Proposed development characteristics (roof size, parking lot size, etc.)
- Proposed green infrastructure improvements
- Advanced options (such as life cycle length, discount rate, etc.)
The calculator determines cost and benefit results based on the pre- and post-development site conditions and what types of green infrastructure were selected. Costs of green and traditional infrastructure are presented side-by-side for comparative purposes. Stormwater management, pollution reduction, energy savings, and groundwater replenishment values of green infrastructure are also presented. Click here to try the calculator.