Impervious Areas

Impervious vs. Pervious

Impervious Areas are man-made areas that cannot absorb water from rain or snow.

Impervious Area Examples:

  • Roofs
  • Roads
  • Driveways
  • Parking Lots
  • Sidewalks

Pervious Areas, on the other hand, absorb water from rain or snow.

How Impervious Areas Affect Your Watershed

Water from Impervious Areas can no longer soak into the soil. Usually it is directed somewhere else to drain, such as: a Road Ditch, Stream, Property Line, etc…

This has negative impacts:

  • Aquifers don’t get replenished.
  • Water reaches streams much faster, which forces the stream to adjust to handle the additional water, often leading to streambank erosion and flooding.

Why is the Stormwater Program Important?

The Stormwater Program works with permit applicants on how to properly direct water from newly constructed Impervious Areas.

Applicants needing residential permits are encouraged to direct the water to drain on their own property. This allows their soil to absorb some of the water, which slows it down before it reaches streams. This also minimizes streambank erosion and flooding.

Commercial permits can create significantly large amounts of impervious areas with one project. This is why these applicants must have an engineered plan to make sure their stormwater runoff is released at a controlled rate.

Impervious Areas Maps

Since 2000, the District has administered the County Stormwater Permit Program. A portion of the data collected from the program includes the amount of Impervious Areas that have been added in the County.

This information has been broken down by Watershed and incorporated into an interactive map!

Not sure which watershed you’re in?

NOTE: Information has only been collected from 2000 to 2021, therefore the maps do not reflect the Impervious Areas prior to 2000.

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