IMPERVIOUS SURFACES IN SOUTH MIDDLETON TOWNSHIP
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 and 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.
o Increased erosion
o Increased flooding
o Decrease in amount of groundwater
o Decrease in water quality
o Diminished habitats for various species
Within the Township Zoning Ordinance, the amount of impervious
surface on a lot is limited, usually to a certain percentage
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.
For further information on impervious surfaces and their
effects, visit Towson Universitys website about the Chesapeake
Below is a classification of surfaces that the Township
considers when determining the amount of imperviousness on a
Houses, sheds, and other buildings
Compacted sand (depending on the degree of compaction)
Compacted gravel (depending on the degree of compaction)
Sidewalks (All sidewalks, not just the ones along the street)
Decks with grass or dirt underneath (the water will seep
through the cracks in the deck and reach the ground)
Large stones (depending on percentage of area taken up)
Landscape Fabric (woven or mesh type not impermeable
Pool surface area with pervious cover that allows water to
seep through (does not include sidewalk around pool)