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Paving the Watershed

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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