Water Quality Scorecard : Incorporating Green Infrastructure Practices at Municipal, Neighborhood, and Site Scales Page: 4 of 56
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Many communities are already struggling with degraded water bodies and
failing infrastructure. For example, EPA 's National Water Quality Inventory:
1996 Report to Congress indicated that 36 percent of total river miles assessed
were impaired.3 In EPA's 2004 Report to Congress, that percentage increased
to 44 percent.4 Further, a report by the National Academy of Sciences found
urban stormwater is estimated to be the primary source of impairment for 13
percent of assessed rivers, 18 percent of lakes, and 32 percent of estuaries-
significant numbers given that urban areas cover only 3 percent of the land
mass of the United States.'
Urban runoff also affects existing wastewater and drinking water systems.
EPA estimates that between 23,000 and 75,000 sanitary sewer overflows
occur each year in the United States, releasing between 3 and 10 billion
gallons of sewage annually.6 Many of these overflow problems stem from
poor stormwater management. Many municipalities-both large and
small-must address the impact of existing impervious areas, such as parking
lots, buildings, and streets and roads, that have limited or no stormwater
management while at the same time trying to find effective and appropriate
solutions for new development.
These water quality impairments exist, in part, because historically stormwater
management and indeed stormwater regulation-has focused primarily at
the site level. The reasoning was sound: manage stormwater well at the site,
and water bodies in the community will be protected. However, as the findings
of EPA's National Water Quality Inventory demonstrated, this strategy has not
been effective for two main reasons.
First, the site-level approach does not take into account the amount of off-
site impervious surfaces. During the development boom from 1995-2005,
rain-absorbing landscapes, such as forests, wetlands, and meadows, were
transformed into large areas of houses, roads, office buildings, and retail
centers. This development created vast areas of impervious cover, which
3 U.S. EPA National Water Quality Inventory: 1996 Report to Congress: http://www.epa.
gov/305b/96report/index.html
4 U.S. EPA National Water Quality Inventory: 2004 Report to Congress: http://www.epa.
gov/owow/305b/2004report/
5 Urban Stormwater Management in the United States, National Research Council of the
NationalAcademy of Sciences, 2008: http://dels.nas.edu/dels/rpt briefs/stormwaterdis-
chargefinal.pdf
6 U.S. EPA National Water Quality Inventory: 2004 Report to Congress: http://www.epa.
gov/owow/305b/2004report/generated significant increases in stormwater runoff. However, the amount
of development in the watershed is not simply the sum of the sites within it.
Rather, total impervious area in a watershed is the sum of sites developed plus
the impervious surface of associated infrastructure supporting those sites, such
as roads and parking lots.
Second, federal stormwater regulations focus on reducing pollutants in the
runoff-the sediments from roads, fertilizers from lawns, etc.-and not on
the amount of stormwater coming from a site. Nevertheless, the increased
volume of runoff coming into a municipality's water bodies scours streams,
dumps sediments, and pushes existing infrastructure past its capacity limits.
Failure to consider the cumulative impact-this loss of natural land, increased
imperviousness, and resulting stormwater runoff volumes- on regional
water quality and watershed health has led communities to seek stormwater
solutions that look beyond site-level approaches.
Communities are recognizing the importance of managing water quality
impacts of development at a variety of scales, including the municipal, the
neighborhood, and site levels. A range of planning and development strategies
at the municipal and neighborhood scales is necessary to address stormwater
management comprehensively and systematically. At the same time that
stormwater management is moving beyond the site level, it is also evolving
beyond hardscaped, engineered solutions, such as basins and curb-and-gutter
conveyance, to an approach that manages stormwater through natural processes.
A green infrastructure approach provides a solution to thinking at all three
scales as well as addresses the need to change the specific types of practices
used on the site. Green infrastructure is a comprehensive approach to water
quality protection defined by a range of natural and built systems that can
occur at the regional, community, and site scales. At the larger regional
or watershed scale, green infrastructure is the interconnected network
of preserved or restored natural lands and waters that provide essential
environmental functions. Large-scale green infrastructure may include habitat
corridors and water resource protection. At the community and neighborhood
scale, green infrastructure incorporates planning and design approaches such
as compact, mixed-use development, parking reductions strategies and urban
forestry that reduces impervious surfaces and creates walkable, attractive
communities. At the site scale, green infrastructure mimics natural systems
by absorbing stormwater back into the ground (infiltration), using trees and
other natural vegetation to convert it to water vapor (evapotranspiration), and
using rain barrels or cisterns to capture and reuse stormwater. These natural
processes manage stormwater runoff in a way that maintains or restores the
site's natural hydrology.I
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United States. Environmental Protection Agency. Water Quality Scorecard : Incorporating Green Infrastructure Practices at Municipal, Neighborhood, and Site Scales, report, October 2009; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc948849/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.