Downingtown Tech Center Basin Stormwater Management Techniques

Description

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.

Location

County: Chester
Watershed: Brandywine Creek

Tech Center Basin is found within the 2.2 square mile borough of Downingtown, which is located in a low-lying urbanized area at the convergence of two waterways, the East Branch Brandywine Creek and Beaver Creek. The Tech Center Basin is downstream from the more recently added Alcoa Basin, and 4.2-acre Marinelli Park separates the two detention basins.

Partners

Borough of Downingtown
Brandywine Valley Association (BVA)
Bishop Shanahan High School 
D-Town Associates (owner of the Tech Center location: participated in a public-private partnership to help fund the design and construction of the project)  
D.L. Howell Engineering, Inc. (contractor)
D. Fickler (completed grading)
Land Studies (plant provider)

Cost

Pennsylvania Department of Environmental Protection Growing Greener Grant (2000): $239,811.
D-Town Associates (owners of the Tech Center location) paid remaining balance.

Contact

Thomas J. Yuhas, P.E., P.L.S.
(Downingtown Borough Engineer)
Director of Government Services
Horizon Engineering
200 Kelly Rd.
Quakertown, PA 18951
215-529-5300 x122
tyuhas@horizonengineers.com

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