NEW
SATELLITE MAPS PROVIDE PLANNERS IMPROVED URBAN SPRAWL INSIGHT
A major advance
in satellite-based land surface mapping has led to the creation
of more accurate and detailed maps of our cities. These maps
provide urban planners with a better understanding of city
growth and how rainfall runoff over paved surfaces impact
regional water quality.
Maps taken from
space are invaluable to city planners and state agencies monitoring
water quality in urban areas, and are replacing the more expensive
and time-consuming traditional aerial photography.
These space-based
maps of buildings and paved surfaces, such as roads and parking
lots, which are impervious to water, can indicate where large
storm water runoffs occur. Concentrated amounts of runoffs
lead to erosion and elevated amounts of soil and chemical
discharge into rivers, streams and ground water.
Scott Goetz,
Project Manager of the NASA-sponsored Mid-Atlantic Regional
Earth Science Applications Center (RESAC) at the University
of Maryland, presented these highly detailed surface maps
today at the American Geophysical Union spring meeting, Boston,
MA.
Andrew Smith,
a faculty research assistant working with Goetz at the Mid-Atlantic
RESAC, developed a faster and less expensive capability, utilizing
Landsat 7 and Space Imaging's Ikonos satellite data, to generate
accurate maps of paved surfaces. "It's a major advance
in monitoring capability because aerial photo mapping can't
keep up with the pace of change," Goetz said. "Our
maps of counties and cities capture new development and can
be repeated much more quickly than the tedious and expensive
traditional photo interpretation work."
Urban sprawl
results in more paved surfaces and less area for water to
drain into soils.
Reduced drainage
areas bring more water into fewer drainage systems at a faster
rate, eroding the banks of streams and rivers, and adding
more sediment into the water. "If you increase an impervious
surface near a stream by creating a paved parking lot, for
example, you directly affect the quality of life in the stream
because of the runoff that surface will generate," Goetz
said.
Smith cites previous
researchers who have shown a relationship between the amounts
of impervious surface cover within a watershed and the quality
of surface water within that watershed. Generally, when 10
percent to 15 percent of an area is covered by impervious
surfaces, the increased sediment and chemical pollutants in
runoff have a measurable effect on water quality. When 15
percent to 25 percent of a watershed is paved or impervious
to drainage, increased runoff leads to reduced oxygen levels
and harms stream life. When more than 25 percent of surfaces
are paved, many types of macro and microorganisms in streams
die from concentrated runoff and sediments.
Impervious surface
maps also are useful in mapping urban sprawl. Sprawl is indicated
on the maps by increases in land consumption and housing construction.
By monitoring an area over time, maps can show the progress
of residential development. Currently, the RESAC team is working
with planning departments to add the data from the maps into
future urban planning models.
Smith has produced
a map of the Washington-Baltimore area that quantifies how
much impervious surface there is across the entire region.
Baltimore and the counties that border it have at least 20
percent, and up to 40 percent, impervious surface area, indicating
that pollution from runoff could be a problem. The District
of Columbia and surrounding watersheds in Virginia and Maryland
have levels of impervious surfaces between 20 percent and
30 percent percent. Areas between and beyond the Baltimore-Washington
corridor are more "green" with levels that range
from 0 percent to 20 percent impervious surface areas.
The RESAC team
has provided maps to the Chesapeake Bay Program, Maryland's
Departments of Planning and Natural Resources and Montgomery
County Department of Environment, among others, to monitor
water quality and changes in residential land use. These organizations
incorporate the impervious surface area data into models that
predict water quality, future land use and the potential effectiveness
of various "smart growth" policies.
NASA launched
Landsat 7 in April, 1999. Images are archived, processed,
and distributed by the U.S. Geological Survey, which is also
responsible for day-to-day operations of the satellite.
This research is being conducted as part of NASA's Earth
Science Enterprise, a long-term study of how natural and human-induced
change affects our global environment.
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