Environmental Engineering Reference
In-Depth Information
with the Brandywine Conservancy EMC, was retained to develop this con-
cept, analyze the existing water cycle, identify the limits of water and land use,
and formulate a land use/management program that would give the municipal-
ities the ability to manage their land and water resources into the future. The
program was supported by grants from the William Penn Foundation and the
Pennsylvania Department of Conservation and Natural Resources, as well as local
municipalities.
The primary goal was to sustain the essential values that distinguish these
watersheds, in the face of the wave of development pressures overtaking the
region. Because land use decisions directly affect water resources, and because
land use decisions are made at the municipal level, a critical ingredient of
this study was to work directly with the municipalities. Nine of the townships
comprised the Northern Chester County Federation, and a model stormwater
ordinance was developed for adoption, along with a review of planning and
zoning for consistency, as well as water and sewer infrastructure systems and
plans. One major concern was that the expansion of development would greatly
increase groundwater withdrawals and export effluent, leading to a dewatering
of the natural stream flows, with impervious surfaces creating severe ground-
and surface-water quality degradation. A computer-based geographic informa-
tion system was developed and used to predict future land development and
water resource impacts, including a low-flow maintenance model (Figure B-11)
and a dry year nitrate impact model, to ensure that unsafe nitrate levels, espe-
cially stemming from land application of wastewater effluent, did not contaminate
water supplies. Technical results from these models constituted the legal basis
for land management guidelines.
Valley Creek Stormwater Management Program with Reduction
and Prevention of Urban Non-Point Source Pollution (1998)
The Valley Creek, Schuylkill River basin, of Chester County, is the most highly
urbanized watershed in Pennsylvania with a stream classification of “exceptional
value,” usually applied to pristine rural watersheds. This apparent contradiction
is the result of strong community interest and concern for water quality in this
relatively small stream valley, which flows through Valley Forge National Park.
In a sense, this watershed represents all of the small streams that lie in the
path of expanding (or diffusing) urban regions which have been altered by the
changing patterns of transportation, land use, and economic development. As
new highways have reached out into the countryside surrounding every urban
center, carrying both residents and employment into valleys that were farmland
some 30 years ago, they have covered over the land with impervious struc-
tures and surfaces. In this watershed, the impervious cover was some 20% of
the total watershed in 1998, with about 65% comprised of roadway surfaces
and parking lots, serving the automobile. This produced a significant increase
in runoff and the pollution generated from these impervious (and pervious)
surfaces.
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