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National Stormwater Calculator

Screenshot of the national stormwater calculator

The Environmental Protection Agency (EPA)'s National Stormwater Calculator is a desktop application that estimates the annual amount of rainwater and frequency of runoff from a specific site anywhere in the United States. 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
  • homeowners

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:

  • Disconnection
  • Rain harvesting
  • Rain gardens
  • Green roofs
  • Street planters
  • Infiltration basins
  • Porous pavement

Learn more and install the calculator here.