Green and Stormwater Calculators
A number of agencies and organizations have developed stormwater and green infrastructure calculators to assist design professionals in stormwater management and green infrastructure planning, costing and comparison of various best management practices. We've included calculators from the U.S. Environmental Protection Agency, Center for Neighborhood Technologies, Sustainable Technologies Evaluation Program and the Water Environment Research Foundation.
State, regional or municipal calculators and programs by educational institutions are also being developed and will be listed as they become available.
Environmental Protection Agency National Stormwater Calculator
The EPA has released their National Stormwater Calculator, a desktop application that estimates the annual amount of rainwater and frequency of runoff from a specific site anywhere in the United States (including Puerto Rico). Estimates are based on local soil conditions, land cover, and historic rainfall records.
It is designed to be used by anyone interested in reducing runoff from a property, including:
- site developers
- landscape architects
- urban planners
The Calculator accesses several national databases that provide soil, topography, rainfall, and evaporation information for the chosen site. The user supplies information about the site’s land cover and selects the types of low impact development (LID) controls they would like to use. The LID controls that the user can choose are seven green infrastructure practices:
It is based on the EPA’s SWMM program which has been used for over 40 years and is widely accepted. The SWMM program is the basis of the PC-SWMM PP that was developed by Bill James of Computational Hydraulics for UNI-GROUP U.S.A. It is a free program.
National Green Values Calculator by the Center for Neighborhood Technologies
The Center for Neighborhood Technology (CNT) is an award-winning innovations laboratory for urban sustainability. CNT works across disciplines and issues, including transportation and community development, energy, water, and climate change. These stormwater management calculators are quite detailed with parameters for site information including annual rainfall by zip code, design storm, rainfall in inches, soil type, impervious cover, percentages of types of land cover, runoff reduction goals, green improvements, life cycle, curve numbers, coefficients, costs and benefits.
Sustainable Technologies Evaluation Program
This worksheet was developed by the Sustainable Technologies Evaluation Program, Toronto and Region Conservation Authority who have tested UNI® pavers in a number of projects. The worksheet is based on local costs and design for that area, though it may be useful from a comparison standpoint as it features a number of stormwater management practices that can be compared and there are separate costing sheets for bioretention, grass swales, green roof, infiltration chambers, infiltration trench, PICP and rainwater harvesting. When you select a specific stormwater practice, it opens other sheets for that practice that include design and cost information, maintenance and life cycle costs.
Water Environment Research Federation BMP and LID Cost Tools
In a climate of increasingly smaller budgets and competing needs, calculating the whole-life cost of a BMP or LID approach can be key to making decisions about the most appropriate and cost-effective options – and ultimately moving a project forward. WERF’s suite of modeling tools provides a framework to ease cost estimation for various solutions, factoring in items such as capital expenses, long-term maintenance, and the potential value a project will deliver. These tools, which supply planning-level estimates and can serve as a format for cost reporting, are available for a variety of BMPs and LID options, including green roofs, rainwater cisterns, bioretention facilities, retention ponds, extended detention basins, swales, rain gardens, and permeable pavement.
State, Regional and Municipal Calculators
State, regional or municipal calculators, as well as programs by educational institutions are also being developed and will be listed as they become available. Please visit our State and Municipal Stormwater and Green Infrastructure Guidance and Incentives and Credit Programs pages for additional information, references and guidance.
Minnesota Minimal Impact Design Standards Calculator
Volume and pollutant reductions given in the MIDS calculator are based on the assumption that the BMP is properly designed, constructed and maintained. Guidance and recommendations for design, construction and maintenance are contained within the individual BMP sections of the Minnesota Stormwater Manual.
Santa Rosa, CA Stormwater Calculator
This is an Excel-based calculator is to be used by the designer to determine the quantity of storm water that will need to be treated and/or infiltrated to meet the permit requirements.
North Carolina State University Biological & Agricultural Engineering - Stormwater
NCSU BAE has developed a number of hydrologic models for permeable pavements, bioretention, green roofs and rainwater harvesting.