FAQs on Imperviousness
What does Impervious mean?
Impervious means that water cannot penetrate the ground surface - instead it flows over the surface directly into catch basins, streams, and wetlands. Nonporous pavement is one example. Development in this area has created a significant amount of impervious surface, including parking lots, buildings and rooftops. New home development, stores and other services are the major cause of increasing imperviousness.
What is Water Quality?
Water quality is determined by the ability of a specific water body to serve its intended use, e.g. drinking, habitat, fishing, swimming, etc. 70% of Yorktown has streams, ponds or lakes that drain into the Croton Watershed which supplies New York City with drinking water.
Why is imperviousness affecting the environment?
When rain water falls onto an impervious surface, it can no longer seep into the ground and be naturally filtered by vegetation and soil. Instead, the water moves over hard impervious surfaces at a much faster rate. Because the water is moving off quicker, it can overwhelm drainage ditches and streams causing flooding. As storm water travels over roads and parking lots, it also picks up pollutants such as oil, grease, bacteria and sediment. Sediment in particular captures harmful elements. These pollutants, now in the stormwater runoff, are delivered directly to streams, lakes and reservoirs.
What effects do we see from stormwater runoff of impervious areas?
The following impacts of imperviousness have been scientifically documented:
- Flooding as more water is delivered directly to water bodies without being slowed down by vegetation or absorbed into the soil.
- Erosion as stream banks are undercut and washed away due to higher and faster flows of water.
- Sedimentation due to upstream soil erosion, which is gradually filling in our lakes, harbors, bays and other water bodies.
- Water temperature increases due to heated stormwater runoff from impervious surfaces.
- Water quality degradation from increased pollution levels such as excessive phosphates and pathogens.
- Habitat loss of certain fish and wildlife species due to water temperature increases, sedimentation, and nitrogen and phosphate loading.
How can we reverse the negative impacts of urban sprawl and imperviousness?
There are some easy ways to alleviate the impacts of imperviousness:
- Divert roof gutters onto vegetated areas instead of paved surfaces or pipes. Minimize the amount of impervious area (e.g. driveways, parking lots, roads, patios, etc.) or use pervious materials.
- Plant trees and shrubs to minimize surface runoff. Create natural buffer areas around wetlands, ponds and streams by creating a "no-mow" zone that filters runoff. Use paving surfaces that allow rainwater to soak into the ground, i.e. wood decking, bricks, or interlocking stones or porous asphalt for driveways.
- Select plants and trees that grow naturally in this area and are not exotic imported plants that may overwhelm a site, such as phragmites. Phragmites is that 8' high grass which grows in wet disturbed areas everywhere and displaces cat-o-nine tails, which muskrats need to eat. Instead put in plants that don't need a great deal of water or fertilizer to survive.
- Use fertilizers, herbicides and pesticides sparingly (or not at all) and according to directions. Use car washes that treat and recycle the wastewater.
- Wash your car on the lawn, instead of over asphalt.
- Check automobiles for leaking oil and other fluids and make repairs, if needed.
- Pick up and properly dispose of pet waste. Biological waste can not only add nutrients, but bacteria to water bodies.
