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Puget Sound Georgia Basin Ecosystem |  |
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 What
is Urbanization? |
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Urbanization is defined as the transformation
of natural landscapes, such as wetlands and forests, to
built environments. These built environments typically contain
large amounts of impervious surfaces such as concrete, asphalt,
roofs, lawns and other materials which quickly carry pollutants
to the inland waters of the Puget Sound Georgia Basin. |
During the same period, urbanization increased across many low elevation watersheds and shoreline areas. Low elevation watersheds are typically 2,000 ft (609 meters) and lower. They contain valuable low gradient aquatic habitats for important species and provide water quality and flood buffering functions.
One hundred fifty-eight local watersheds gained impervious
surfaces by between 0.7 and 2 percent of their total
area. Another 58 local watersheds showed increases
in urban land cover of between 2 and 19 percent of
their total drainage area. While these percentages may seem small, they represent fairly dramatic change over a relatively short period of time.
Little or no change in urban land cover was observed in approximately 90 percent of the 2,725 assessed watersheds within the basin. Most of these watersheds were largely forested with small urban areas.
Research has shown that once watersheds have developed roughly 10 percent of their drainage area into an impervious or paved condition, there is a high potential for physical, chemical, and biological impairments to both water quality conditions and other aquatic resources such as erosion, flooding and extreme peak storm events, and scoured and smothered fish eggs.
Impervious surfaces heat the water that falls upon it. The heated, polluted runoff raises stream temperatures and this rise in temperature combined with pollutants decreases fish egg survival, impairs growth of the fry and smolt, increases susceptibility of disease and decreases the ability of young fish to compete for food and avoid predators.2
These adverse results occur because rainfall cannot seep (infiltrate) back into the aquifer where it is cooled and cleansed by soil microorganisms and slowly recharges the ground water table and flow levels in streams and rivers. When water cannot infiltrate, we lose the portion of the water fed by ground water that would otherwise be available for streams, lakes, wetlands and other uses including drinking water and irrigation.
Source: CommEn Space
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Urbanization
and Forest Change
Within the 5-7 year assessment
period, 452 watersheds had at least one percent
of their total area converted from mature forest
cover to some other land cover, often bare
ground, immature vegetation, or industrial/urban uses. At the same time, another group
of 205 watersheds, mostly occurring above
2,000 feet in elevation and generally within
public ownership, indicated a net increase in
forest cover as young stands or cleared areas
re-grow into more mature forest cover. 