Urban
Waterways
Designing Rain Gardens
(Bio-Retention Areas)
Distributed in furtherance
of the Acts of Congress
of May 8 and June 30, 1914.
Employment and program
opportunities are offered to
all people regardless of
race, color, national origin,
sex, age, or disability. North
Carolina State University,
North Carolina A&T State
University, U.S. Department
of Agriculture, and local
governments cooperating.
As communities in North Carolina
develop, more and more land is
converted into impermeable sur¬
faces, which do not allow water to
infiltrate. These include driveways,
parking lots, homes, offices, schools,
highways, and paved walkways.
Much of this expanding infrastruc¬
ture is needed to maintain a desired
quality of life. Everything from a dry
place to work, eat, and sleep to easy
access to hospitals depends on a
system of impervious surfaces.
However, without careful consider¬
ation, impermeable land can dra¬
matically harm the quality of the
state's waters, adjacent wetlands and
forests, and other natural areas.
Water that once soaked into the
ground — or infiltrated — now runs on
top of roads or through gutters, often
heading straight to nearby streams
and lakes and carrying potentially
harmful pollutants. Often a network
of impervious surfaces serves as a
"stormwater superhighway" that
quickly conveys stormwater and
associated pollutants into streams.
Increased stormwater runoff
introduces many undesirable effects:
1) More flooding during storms
and less groundwater (or base
flow) during dry weather.
2) Increased erosion and subse¬
quent sedimentation (settling) of
eroded particles in streams or
flood plains.
3) Streambank erosion resulting
from high stream velocities.
STATE UNIVERSITY
AAT STATE UNIVERSITY
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College of Agric«tare and Life Sdaco, NC State Uiilventty
School of Agriculture ud Environment*! and Allied Science»,
NC A&T State Unbentt?
4) More chemicals and metals being
deposited by vehicles and equipment,
eventually reaching streams.
5) Nutrients, such as nitrogen and phos¬
phorus, gaining easier access to natural
water bodies via an "efficient" storm
sewer.
6) Increased numbers of potentially
harmful bacteria and other pathogens
from humans, pets, and wildlife enter¬
ing the state's waters.
7) All the pollutants — from sediment to
toxic chemicals to bacteria — harming
plants and animals living in or near
North Carolina's streams, lakes, and
estuaries.
Fortunately, there are techniques that can
minimize flooding, erosion, and the amount
of metals, nutrients, and bacteria that enter
the state's waters. These measures are often
called stormwater Best Management Prac¬
tices (BMPs). BMPs can include relatively
simple changes in homeowner actions, such
as proper application of fertilizer. Others
involve reduction at the source through site
design or mitigation measures, such as
preserving vegetation along streams or other
sensitive areas. Still other BMPs are struc¬
tural; that is, they are built. The most well-
known structural BMP is the pond or
reservoir, but many others are becoming
more common, such as stormwater wet¬
lands, sand filters, grassy swales, and, more
recently, rain gardens. These BMPs tend to
disrupt the "stormwater superhighway,"
allowing for infiltration or retention of the
water. For a more detailed survey of several
structural BMPs, please refer to the first
publication in the Urban Waterways series,
