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Pennswood Village Regional Stormwater Management System

Landscape Performance Benefits

Environmental

  • Reduced the rate of peak stormwater runoff by 53%, 64%, and 69% for the 2, 10, and 100 year storms.
  • Sequesters 11,700 lbs of carbon dioxide annually in the 205 new trees planted onsite.
  • Achieved ecological quality 13.8 times that of a standard stormwater detention/retention basin, as measured by the Plant Stewardship Index.
  • Provides habitat for at least 73 bird species, based on cumulative data from counts by residents.

Social

  • Increased satisfaction with Pennswood as a home or workplace, with 63% of survey respondents saying that the wetland landscape increased their satisfaction.
  • Improves the mood of residents and staff, with 61%, of survey respondents saying that their mood was more positive after being in the wetland landscape.
  • Serves as an educational tool for residents and staff, with 79% of survey respondents saying that they were aware that the wetland landscape captures and treats stormwater from on and off site, greatly reducing impacts to Neshaminy Creek.
  • Serves as an educational tool for university students and public agencies. Over 300 university landscape architecture students and 12 public agencies have visited the site to learn about non-traditional approaches to stormwater management. Over 100 general university students have learned about the project from lectures by the landscape architect.

At a Glance

  • Designer

    Wells Appel Land Strategies

  • Project Type

    Nature preserve
    Stormwater management facility
    Wetland creation/restoration

  • Former Land Use

    Institutional

  • Location

    1382 Newtown Langhorne Road
    Newtown, Pennsylvania 18940

    Map it

  • Climate Zone

    Humid continental

  • Size

    20 acres

  • Budget

    $2 million

  • Completion Date

    2000

Pennswood Village is a retirement community situated on 82 acres in suburban Pennsylvania. Born of a public-private partnership, the 1999 Pennswood Village redevelopment and expansion was planned to address local traffic safety and regional stormwater management issues. Faithful to the community’s founding on Quaker values, the redevelopment expresses the Friends’ respect for all individuals, sanctity of life, and stewardship of the land as a wetlands park shared with neighbors and wildlife. The sinuous topography mimics the function of a natural riparian stream corridor channel, managing not only the site’s runoff, but also that of adjacent properties and the highly developed outlying watershed areas. Swales, wetlands, and meadows with carefully selected native grasses, shrubs and trees slow runoff, create a pollutant removal train, and recharge groundwater, as well as create a place of serene beauty.

  • 13 acres of wet meadows and bioswales manage large volumes of stormwater from on and off site, mimicking the function of a riparian corridor floodplain.
  • The stormwater management system begins with a semicircular outfall structure constructed from local Bucks County brownstone, reflecting the building traditions of the region. A series of pipes direct runoff here from Route 413 and the contributing watershed.
  • The stormwater empties into a stone-lined sedimentation basin with a weir of boulders, which slows the water, settles out gross particulate matter, and contains the majority of the trash and road debris conveyed along with the runoff. The basin is easily accessed for maintenance, but screened from direct view by a landscape buffer.
  • From the sedimentation basin runoff flows into a grass swale that runs alongside the entrance road and is intermittently visible through the trees.
  • The swale directs the water into an infiltration basin with highly permeable soils with depths of at least 6 ft to both the seasonal high water table and bedrock layer. The infiltration basin is sized to manage the first flush runoff volume of a storm event. Runoff beyond the infiltration basin’s capacity flows over a broad weir into a long, winding vegetated swale.
  • The vegetated swale consists of a series of shallow, stepped channels, each designed to detain runoff from increasingly larger storm events. On either side of the swale is a broad, flat meadow that is graded to function like a riparian corridor or floodplain. The meadow includes native grasses, shrubs, and trees with varying flood and drought tolerances.
  • The system terminates in a constructed treatment wetland (CTW) and small wet pond. Water flows from the swale into the wet pond where outflow is controlled by an outlet structure designed to safely pass the 100-year storm. When the need arises, the outlet control structure allows water to flood back into the CTW. Excess water will back up further, eventually overflowing into the broad meadow and the created riparian corridor.
  • ADA- accessible paths wind through the swales, wetlands, and meadows, providing Pennswood residents with an inspiring setting for exercise, photography, and nature observation.
  • The road was relocated to accommodate the stormwater system, which now serves as an aesthetic entry feature welcoming residents and guests to the site.

Challenge

Pennswood Village is located in a rapidly suburbanizing area between New York City and Philadelphia, where development has increased stormwater problems. In 1996, heavy rains caused Pennswood’s 17-ft deep detention basin to overflow, flooding properties downstream. In 1999, Middletown Township asked Pennswood to help by incorporating regional stormwater management on their site. The design had to manage not only the site’s runoff, but that of the adjacent George School properties and much of the runoff from the highly developed outlying watershed area. Additionally, due to the democratic values of the Quaker client, all decisions had to be made by consensus, with all 300 members of the Quaker community agreeing to the design. This lengthened the process to two years.

Solution

The landscape architect and client wished to use a biological/ecological approach to stormwater that was more in line with the client’s land stewardship values than a standard engineering approach. Though special waivers were required, the system was designed to work with rather than against the land, using 13 acres of wet meadows and bioswales to manage large volumes of stormwater. Existing wetlands and grasslands were retained and became the basis for a riparian corridor concept developed in conjunction with wetland ecologists, which determined the ideal configuration and grading of the linked wetlands. Designers enthusiastically accepted the democratic consensus process and invested more time up front to explain and educate the client about this design approach.

  • The cost of maintaining the 20-acre wetland meadow landscape is approximately $7,000 per year, substantially less than the $54,000 annual cost of maintaining an equivalent area of traditional lawn with ornamental plantings.
  • Continuity of management is a key success factor in maintaining landscapes in accordance with the original design goals and intent. Pennswood has had the same landscape manager since its inception. Since this type of continuity may not always be possible, the designer‘s scope of work should include a document that clearly outlines design intentions and long-term management policy and goals in layman’s terms. This document could require annual reports from the site manager to the designer.
  • Designers should establish a plan to manage invasive species over time with site managers. On an annual or biannual basis, the landscape architects and ecologists should walk the site with the landscape manager to inspect, identify threats, and discuss steps already taken or yet to be taken. They should use their combined expertise to understand what type and how many (if any) invasive species will be tolerated.

Project Team

Landscape Architect/Land Planner: Wells Appel Land Strategies
Civil Engineer: Pickering, Corts & Summerson, Inc
Hydrologist and Ecologist: Princeton Hydro
Wetlands Specialist: Mellon Biological Services
Arborist: Morris Arboretum Consultants

Role of the Landscape Architect

Wells Appel assembled a team of plant ecologists, wildlife biologists, environmental planners and civil engineers. The firm developed the riparian corridor concept and determined the ideal configuration of and grading of the system, as well as the selection and utilization of plant materials. Wells Appel provided the master plan for the entire site and oversaw the project through construction.

Case Study Prepared By

Research Fellow: Mary Myers, PhD, FCELA, FASLA, Associate Professor, Temple University
Research Assistant: Allison Arnold, MLA Candidate, Temple University
August 2012

Topics

Stormwater management, Habitat quality, Populations & species richness, Carbon sequestration & avoidance, Health & well-being, Educational value, Bioretention, Native Plants, Rainwater harvesting, Trail, Trees, Wetland, Aging, Green communities

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