www.epa.gov/research
                          science    in   ACTION
                           INNOVATIVE RESEARCH FOR A SUSTAINABLE  FUTURE

                  (1) Green Infrastructure

             (2) Traditional Infrastructure
The National Stormwater Calculator shows
users how land use decisions and green
infrastructure controls affect the amount
of Stormwater runoff  produced. Green
infrastructure, such as the street planter
and porous pavers shown in the image (1)
above, promotes the  natural  movement of
water within an ecosystem or watershed,
instead of allowing it to wash into streets
and down storm drains as shown in the
traditional infrastructure  image (2).
These practices allow the Stormwater
(rainfall) to be used as a  resource
rather than a waste product. Having
less water run off into storm drains and
roadways can help prevent contamination
of waterways, water infrastructure
degradation, flooding, and overwhelming
of wastewater treatment plants.
  www.eDa.gov/nrmrl/wswrd/wa/models/swc/
          Contact: SWC@EPA.sov
Office of Research and Development
National Stormwater Calculator (SWC)

A desktop tool that helps users control runoff to promote
the natural movement of water

Stormwater discharges continue to cause impairment of our Nation's
waterbodies. Regulations that require the retention and/or treatment of
frequent, small storms that dominate runoff volumes and pollutant loads
are becoming more common. EPA has  developed the National Stormwater
Calculator (SWC) to help support local, state, and national Stormwater
management objectives to  reduce runoff through infiltration  and retention
(i.e., green infrastructure). The primary focus of the SWC is to inform site
developers on how well they can meet  a desired Stormwater retention target
with and without the use of green infrastructure. It can also  be used by
landscapers and homeowners.
The SWC estimates runoff  at a site based on available information such as
soil type, landscape and land-use information, and weather.  This update to
SWC will allow users to consider how runoff may vary based  both on
historical weather and potential future  climate. To better inform decisions, it
is recommended that the user develop  a range of SWC results with various
assumptions about model inputs such  as percent of impervious surface, soil
type, sizing of green infrastructure, as  well as historical weather and future
climate scenarios. Please check with local authorities about whether and
how use of these tools may support local Stormwater management goals.

The SWC is comprised of ten pages:
Page 1-Location. This step has an address lookup feature that allows the
user to easily navigate to a site selected anywhere within the United States.
Page 2-Soil Type. The type of soil on the site is identified and is used to
infer infiltration properties. The soil type can be selected based on local
knowledge or by retrieving  a soil map overlay from the online database.
Page 3-Soil Drainage. This step is used to identify how quickly standing
water drains into the soil. The user can select the site's soil conductivity
based on local  knowledge or retrieve it  from the online database.
Page 4-Topography.  Here,  the site's  surface topography is characterized, as
measured by the surface slope. The  user can rely on the slope data display
as a guide or can use local knowledge to describe the site's topography.
Page 5-Precipitation. A National Weather Service rain gauge, which supplies
rainfall data for the site, is selected. A  long-term rainfall  record is used to
replicate the full scope of storm events that might occur.
Page 6-Evaporation. This step is used  to select a nearby weather station that
will supply evaporation rates for the  site.
Page 7-Climate Change. Users can elect to apply different future climate
change scenarios that modify the  historical precipitation  events and
evaporation rates normally used by the calculator. These scenarios are based
on future outcomes produced by well accepted  global circulation models of
the earth's weather systems.
Page 8-Land Cover. For this step, impervious land cover and the different
types of pervious land cover are assigned to the site for the condition the
user wants to analyze: pre-development, current, or  post-development.
Page 9-Low Impact Development (LID) Controls. To help control  runoff,
seven different LID controls can be selected for use throughout the site.
These controls are green infrastructure practices that help the user
determine the best way to mimic natural water  flow  processes to retain
rainfall onsite.
Page 10-Runoff. A hydrologic analysis of the site is run and the results are
displayed for review.
                             EPA/600/F-13/095b  Revised January  2014

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