Impervious Surfaces

What Are Impervious Surfaces?

Perviousness refers to the ability of a surface to allow water to flow through a substance. Sand is pervious, pavement is impervious. Since water cannot soak into an impervious surface, it will run off that surface until it reaches a pervious surface (such as a lawn). In addition, as water runs over some impervious surfaces (such as roadways and driveways); it will pick up pollutants such as oil, grit, and salt.

In some cases, even dirt and gravel compacted by vehicles will not allow water to percolate through.

Imperviousness & Stormwater Management

Since the amount of impervious surface directly affects the amount and quality of water runoff from a site, the ponds in Westgate were designed to handle a certain amount of runoff from the new development. If this amount of impervious area is increased, it will exceed the capacity of the ponds which will lead to less infiltration and more water being sent downstream. If the amount of impervious surface exceeds that which the facilities are designed to handle, several problems may occur. They include:
  • Decrease in amount of groundwater
  • Decrease in water quality
  • Diminished habitats for various species
  • Increased erosion
  • Increased flooding

Lot Surface Limitations

Within the Township Zoning Ordinance, the amount of impervious surface on a lot is limited, usually to a certain percentage cover.

In the case of the Westgate development, the developer has designed the facilities to handle a maximum area of 2,300 square feet of impervious surface per building lot. In order for the Township to ensure that the residents were aware of this requirement before they bought their homes, the Township required that the developer include a note within your deeds.

Surface Classifications

We have compiled a helpful guide to classification of surfaces that the Township considers when determining the amount of imperviousness on a lot:

Impervious Surfaces
  • Bricks (walkway)
  • Compacted gravel (depending on the degree of compaction)
  • Compacted sand (depending on the degree of compaction)
  • Concrete Block
  • Houses, sheds, and other buildings
  • Pavement
  • Pavers
  • Plastic Tarp
  • Poured Concrete
  • Sidewalks (all sidewalks, not just the ones along the street)
Pervious Surfaces
  • Decks with grass or dirt underneath (the water will seep through the cracks in the deck and reach the ground)
  • Landscape Fabric (woven or mesh type - not impermeable plastic)
  • Large stones (depending on percentage of area taken up)
  • Mulch
  • Pool surface area with pervious cover that allows water to seep through (does not include sidewalk around pool)