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National Stormwater Calculator Launched

The Environmental Protection Agency has designed and launched a national stormwater calculator to aid in reducing runoff.

The EPA has launched a 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).

It is designed for site developers, landscape architects, urban planners, homeowners, and anyone interested in reducing runoff from a property.

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:

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

The stormwater calculator (SWC), like any model, estimates an outcome based on available information such as soil type, landscape and land-use information, and historical weather. These estimates can be affected by limitations on site-specific information and uncertainties about future climate.

To better inform decisions, it is recommended that the user develop a range of results with various assumptions about model inputs such as percent of impervious surface, soil type, and sizing of green infrastructure.

The end of 2013 will release an update to the SWC, which will include the ability to link to several future climate scenarios.

For more information about EPA's SWC, please visit

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November 18, 2019, 11:58 am PDT

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