Impervious Surfaces
According to the Center for Watershed Protection, impervious coverage is the biggest problem facing urban watersheds and streams1. Impervious surfaces are mainly constructed surfaces—rooftops, sidewalks, roads and parking lots—covered by impenetrable materials such as asphalt, concrete and stone. Studies indicate the impervious surfaces are nearly 100% hydrologically active—meaning they generate surface runoff—and high percentages of such surfaces occur within urbanized areas containing commercial, industrial, transportation and medium to high-density residential uses2. The environmental impacts of impervious surfaces are not limited to increases in stormwater quantity. Instead, these impervious surfaces usually involve permanent impacts to the land that result in the land not being able to be returned to its natural state. Once an impervious surface is constructed, it will affect the quantity, velocity and quality of stormwater resulting in impacts to nearby water bodies.
Impervious surfaces collect and accumulate pollutants deposited from the atmosphere, leaked from vehicles or derived from other sources. During rainstorms or snowmelts, these accumulated pollutants wash off and make their way to nearby water bodies.
According to the EPA Mid-Course Review Recommendations, "[R]eduction] of impervious surfaces is a key component of good environmental design. Studies have shown that there is an "imperviousness" threshold at which no Best Management Practice (BMP) can mitigate the additional pollutant load resulting from development. EPA recommends that NYCDEP make it a priority to work with developers and town planning boards to limit the amount of impervious surfaces and to utilize the natural landscape as buffer."
1 WaterLaws.Com-Water Guest: Tom Schueler, Executive Director, Center for Watershed Protection. "We have met the enemy—imperviousness," 1998.
2 Novotny, V. and G. Chesters, Handbook of Urban Non-point Pollution: Sources and Management, New York: Van Nostrand Rheinhold Company, 1981.
Urban Sprawl
Land Acquisition
Protection by Conservation Easement
MAPS:
IMPERVIOUS COVER MAPS: City-owned Land, Land Use,
and Impervious Surfaces
Croton Watershed
Bog Brook Basin
Croton Falls Basin
Diverting Basin
East Branch Basin
Kensico Basin
Lake Gilead Basin
Muscoot Basin
Westbranch Basin
Delaware Catskill Watershed
Boyd's Corner Basin
Kensico Reservoir
Cannonsville Basin East
Cannonsville Basin West
Croton Basin
Ashokan Reservoir
Neversink/Rondout Basins
Scoharie Basin
Pepacton Basin
West Branch/Boyds Corner Basins
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