IN Brentwood-Baldwin-Whitehall Spring 2020 | Page 80

EPA 841-F-03-003
Clean Water Is Everybody’s Business
I
n urban and suburban areas, much
of the land surface is covered
by buildings and pavement, which
do not allow rain and snowmelt
to soak into the ground. Instead,
most developed areas rely on storm
drains to carry large amounts of
runoff from roofs and paved areas to
nearby waterways. The stormwater
runoff carries pollutants such as oil,
dirt, chemicals, and lawn fertilizers
directly to streams and rivers, where
they seriously harm water quality.
To protect surface water quality and
groundwater resources, development
should be designed and built to
minimize increases in runoff.
How Urbanized Areas
Affect Water Quality
Increased Runoff
The porous and varied terrain of
natural landscapes like forests,
wetlands, and grasslands traps
rainwater and snowmelt and allows
them to filter slowly into the ground.
In contrast, impervious (nonporous)
surfaces like roads, parking lots, and
rooftops prevent rain and snowmelt
from infiltrating, or soaking, into
the ground. Most of the rainfall
The most recent National Water Quality Inventory reports that runoff
from urbanized areas is the leading source of water quality impairments
to surveyed estuaries and the third-largest source of impairments to
surveyed lakes.
Did you know that because of impervious surfaces like pave-
ment and rooftops, a typical city block generates more than
5 times more runoff than a woodland area of the same size?
and snowmelt remains above the
surface, where it runs off rapidly in
unnaturally large amounts.
Storm sewer systems concentrate
runoff into smooth, straight
conduits. This runoff gathers speed
and erosional power as it travels
underground. When this runoff
leaves the storm drains and empties
into a stream, its excessive volume
and power blast out streambanks,
damaging streamside vegetation and
wiping out aquatic habitat. These
increased storm flows carry sediment
loads from construction sites and
other denuded surfaces and eroded
streambanks. They often carry
higher water temperatures from
streets, roof tops, and parking lots,
which are harmful to the health and
reproduction of aquatic life.
The loss of infiltration from
urbanization may also cause profound
groundwater changes. Although
urbanization leads to great increases
in flooding during and immediately
after wet weather, in many instances
it results in lower stream flows
during dry weather. Many native fish
and other aquatic life cannot survive
when these conditions prevail.
Increased Pollutant Loads
Urbanization increases the variety
and amount of pollutants carried
into streams, rivers, and lakes. The
pollutants include:
• Sediment
• Oil, grease, and toxic chemicals
from motor vehicles
• Pesticides and nutrients from
lawns and gardens
• Viruses, bacteria, and nutrients
from pet waste and failing septic
systems
• Road salts
• Heavy metals from roof shingles,
motor vehicles, and other sources
• Thermal pollution from dark
impervious surfaces such as streets
and rooftops
These pollutants can harm fish and
wildlife populations, kill native
vegetation, foul drinking water
supplies, and make recreational areas
unsafe and unpleasant.
Relationship between impervious cover and surface runoff. Impervious cover in a watershed results in increased
surface ruunoff. As little as 10 percent impervious cover in a watershed can result in stream degradation.
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