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Downingtown Borough and its vicinity have been plagued with serious
flooding and water quality impairment problems. In a 2003 report, the
U.S. Army Corps of Engineers determined that the extensive flooding in
Downingtown is due to the continued construction of residential
development in the area since the early 1990s. According to the
Pennsylvania Department of Environmental Protection (PA DEP),
Downingtown is considered a major water quality impairment area within
the Brandywine Creek watershed. The main culprit provoking this
designation is the impervious surface that is associated with land
development.
In 2002, the Borough of Downingtown replaced a dated piping system and
narrow stream channel located on Tech Center property, an acre in size,
with a detention basin and wetland to ameliorate conditions within the
Borough. Construction on the project began in Spring 2002 and was
completed by December 2002. The Borough took out a parking lot at the
Tech Center to make way for the basin and trees were removed from the
site. The outlet structure on the western side of Chestnut Street was
graded, culverts were built, and the depth of the basins was dug out.
Gabion baskets around the basin were built, topsoil was deposited, basin
end walls were installed, erosion control methods were implemented, and
overall rough grading of the basin was completed. The trench was
excavated and all storm water pipes across Chestnut Street to the Tech
Center were laid down. Depressions were made where the Borough’s
employees would plant native wetland species. 50 shrub species and
2,400 landscape plugs were planted. For a plant list, please click
here. The plants
within the wetland cell remove pollutants but also absorb more water
from their surroundings than typical sod. Evidence exists that
pollutants like nitrogen, phosphorus, and metals like chromium, copper,
lead and zinc are removed from stormwater by native vegetation.
The enhanced detention basin receives runoff from a culvert located
beneath the Alcoa facility, which runs through an open conveyance
channel, then underneath the Downingtown Tech Center. During a storm
event, the basin collects and retains run-off for a period of 24 hours
through a release control system. A 36” stormwater drain lets
stormwater constantly flow from the basin into Parke Run. This constant
output helps support aquatic life downstream. During periods of heavy
rain, water is discharged in a controlled manner, preventing property
damage, flooding, storm sewer system backups and erosion of the stream
banks. For a detail of structural plans, click
here. For a conservation plan, click
here. For an erosion control plan, click
here. For a construction improvements plan, click
here.
Repairs made on the
structure of the basin include curbing, berms, and a spillway. Though
the Tech Center Basin has helped mitigate flooding, additional methods
of controlling the area’s flooding were required. The Borough
negotiated a well-suited piece of land east of Tech Center Basin owned
by the company Alcoa and a larger retention basin was installed. It is
called the “Alcoa Project” or the “Lincoln Avenue Project,” and has the
capacity to support the 100-year storm.
Parameters to test water
quality improvements and pollutant removal rates as outlined by the
National Urban Runoff Program will be utilized by the Township to
determine the effectiveness of the system. The Borough monitored stream
quality throughout the whole project’s completion, while conducting
“Watershed Watch,” the Brandywine Valley Association’s $83,810 training
program. The Brandywine Valley Association has been involved with the
public education and outreach aspects of this project. The Association
has involved students from Bishop Shanahan High School. |
