Sprawl causes increased reliance on
automobiles because suburban developments are spread over larger land
areas. This results in more roads being built
over larger land areas. Roads are impervious surfaces. Impervious surfaces
prevent rain and other precipitation from naturally seeping into the
ground. As a result, the building of roads may contribute to the pollution
of the local waterways in a variety of ways:
- Thermal Pollution:
Impervious surfaces such as roads and buildings are heated by the
sun. When it rains, water flows over the heated surfaces and then
into storm water drains. Storm water drainage systems flow into surface
water systems such as a streams or rivers, resulting in increased
water temperature of the water body. This rise in temperature negatively
impacts dissolved oxygen levels - cold water holds more dissolved
oxygen than warm water - and may ultimately impact aquatic wildlife.
- Automobile Pollutants: Oil, gas, and other
substances related to maintaining cars leak onto roads, parking lots,
driveways, and other paved surfaces and are carried into surface water
systems, such as streams and rivers. These pollutants may be toxic
to organisms living within the surface water system.
- Erosion: Increasing
impervious surfaces, from road construction causes larger volumes
of water to be funneled into surface water systems. A stream reacts
to this increased volume of water by widening or deepening its channels
through the process of erosion.
- Sedimentation: Construction of roads causes
an increase in the amount of sediment exposed to the elements. Sediments
are carried by moving water and may enter a surface water system during
precipitation events. Once in the water system, sediments may either
be suspended in the water column or settle out of the water in slower
moving areas. A build up of sediment may damage fish and macroinvertebrate
habitats.
- Groundwater Recharge: Impervious surfaces
decrease the amount of land area capable of absorbing water and recharging
the ground water system and aquifers below the surface. Groundwater
recharge is essential for lessening the impact of drought conditions.
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