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Cook Inletkeeper
Salmon Stream Monitoring Program
Impervious Cover
NEW Report!
Press Release &
Report
On March 19, 2007,
Cook Inletkeeper released an important new report, entitled
Mapping Impervious Cover to Correlate Land Use Activities with
Salmon Health & Habitat on the Lower Kenai Peninsula, which
documents how much impervious cover exists in the Deep Creek,
Ninilchik River, Stariski Creek, and Anchor River watersheds.
The amount of impervious cover in a watershed provides a good
estimate of potential development pressures on local waterbodies,
and national studies show that impervious surfaces are reliable
indicators of fish habitat and water quality. See the
Press Release and
the Report.
BACKGROUND
Impervious
surfaces are exposed areas where vegetation has been removed and
barren soil and/or gravel is obvious. Impervious surfaces
include roads, buildings, clustered cars, driveways, and gravel
pits. As the amount of impervious surface cover in a landscape
increases, a chain of events begins that alters the way water is
transported and stored, thereby affecting the entire local water
cycle. Once this chain of events commences, the effects are
far-reaching, and can result in degraded fish and wildlife
habitat, decreased water quality, and impacts to nearshore
estuarine habitat.
National
studies show that impervious surfaces are reliable indicators of
fish habitat and water quality. In many regions of the country,
as little as 10% impervious cover in a watershed has been linked
to stream degradation, with the degradation becoming more severe
as impervious cover increases. A more recent urbanization study
conducted by the U. S. Geological Survey in five watersheds in
Anchorage, Alaska, however, found cause for concern from
impervious cover at much lower levels: 4.4 –5.8% impervious
area (Ourso and Frenzel, 2003).
INLETKEEPER STRATEGIES
Cook
Inletkeeper, with GIS-support from the Kenai Watershed Forum,
has determined how much impervious cover there is in the
Deep
Creek, Ninilchik River,
Stariski Creek, and
Anchor River
watersheds. The results are hot off the press: these watersheds
have less than 2.6% impervious cover presently. The Ninilchik
and Anchor Point areas have the greatest concentration of hard
surfaces; the upper reaches of Deep Creek have the least. In
this analysis, seismic lines and trails were not included in the
impervious cover calculations.
The results
of this analysis provide important baseline information to
understand future population and economic growth. We now
understand where we are on the curve of development, which
provides unique insights for natural resource planning, and
habitat and water quality monitoring. In 2006, Inletkeeper
analyzed differences in water quality, water quantity and macroinvertebrate data between developed and undeveloped
portions of the watersheds. The results of this work can
be found in Inletkeeper's report,
Mapping Impervious Cover to Correlate Land Use Activities
with Salmon Health & Habitat on the Lower Kenai Peninsula.
Importantly, we used new methodology for obtaining GIS
impervious cover data. Traditionally, such data has been
obtained through the laborious task of hand-held digitizing.
This project relied on new GIS software which identifies unique
attributes of raster data in satellite imagery, and which
translates this data to reliable impervious surface coverages.
As satellite imagery improves, this method will become an
important and accessible tool for communities throughout
Alaska.
FUTURE
WORK
This effort
provides resource agencies with a clear understanding as to
where impervious cover currently exists and gives them a tool to
track this environmental indicator and help prevent the loss of
sensitive and necessary habitat. Impervious cover analysis
should be undertaken again in 5 – 10 years in this fast-growing
region, and monitoring work should be planned to provide data
for the same time period as the new imagery.
ADDITIONAL RESOURCES & LINKS
(links open in new window)
Ourso, R.T.,
and S.A. Frenzel. 2003. Identification of linear and threshold
responses in streams along a gradient of urbanization in
Anchorage, Alaska. Hydrobiologia 501(July):117-131.
Abstract available at
http://dx.doi.org/10.1023/A:1026211808745
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