Landscape News:

Wetlands Restoration Is an Environmental Success Story

by Chris van de Velde, Project Manager

Origianlly published in Awbury’s Winter 2021 Leaflet quarterly newsletter

At the southwest corner of Awbury Arboretum there is a unique water feature consisting of a series of wetlands, bog gardens, two ponds, and a stone-lined stream channel. This area is the last remaining above-ground portion of the Wingohocking Creek. Beginning in the late 1800s, 21 miles of surface waters of the creek and its tributaries were enclosed in a combined sewer to make way for City expansion. This burial of the Wingohocking took approximately 40 years to complete—the City of Philadelphia’s most extensive stream enclosure project.

Awbury’s watercourse and ponds were incorporated in Arthur Westcott’s original 1916-19 master plan for the Arboretum. Cowell, a noted landscape architect credited with the establishment of the Department of Landscape Architecture at Pennsylvania State University, created at Awbury a fine example of Victorian-era Romantic landscape and incorporated progressive ideas for slowing and detaining water flows. Interestingly, his 100-year-old detailed design approach conforms to what we now consider best practices for stormwater management: renovation of a meandering stream with detention ponds rather than a channelized water corridor.

Over the past century, the ponds have degraded, turning into a sort of marshy, muddy area overgrown with invasive phragmites and filled with trash dumped illegally. By 2019, Field Studies groups could no longer visit, because there were hardly any living animals in the murky, smelly water.

With a grant of $310,000 from the Philadelphia Water Department and one of $75,000 from the Pennsylvania Department of Community and Economic Development, the reconstruction of the watercourse and ponds commenced last spring. The Water Department agreed that the restoration of the waterway and ponds on Awbury’s property could significantly alleviate the stormwater problems that regularly occur in the Washington Lane and Chew Avenue area. The project was supposed to be finished by early summer 2020, but then COVID-19 erupted. Early work was shut down during the initial pandemic lockdown. When work outdoors was permitted, the ponds were dredged; trash, invasive trees, and weeds were removed; a new waterproof mat material (Bentomat) was installed; and most of the stone edge walls were rebuilt.

When the initial work was complete, the construction team hit another COVID-19-related problem: the manufacturer of the sophisticated filter system that will clean the street runoff from Washington Lane could not resume operations until August, so delivery of this critical part was delayed until late September. Then the overflow inlets required to connect to the City’s sewer system had to be back-ordered and did not arrive until early December.

Now, final construction is expected to begin as weather permits. The digging, earth moving, and filter/sewer work will be done by late [May, and the final project work may not be complete until early summer 2021].  However, you can now see two ponds full of clear water and enjoy watching the final work as it progresses.

Did you know:

  • the additional capture areas from which stormwater will be directed towards the pond are calculated to be 13.2 acres, including pervious meadow and impervious paved streets;
  • the anticipated runoff will be more than 27,154 gallons per one inch of rainfall for every acre;
  • Philadelphia has an average annual rainfall of 41.45”, so one acre yields about 1,125,533 gallons of water annually;
  • the amount of water absorbed by a meadow depends on the amount of each rainfall and whether or not the ground is frozen or parched;
  • on an impervious surface, most of the water goes directly into the City’s sewer system;
  • so, while we can’t know the exact amount of stormwater the Awbury watercourse and ponds will capture, we are confident that more than 14,000,000 gallons will likely pass through our system annually.

In addition to the alleviation of the flooding that occurs on Washington Lane, drawing stormwater off Washington Lane will reduce the amount of pollutants that reaches the City’s sewer system. More than three-quarters of Philadelphia’s residents are served by the City’s combined sanitary/storm sewer system. This situation in especially true in the oldest and densest parts of the City, including the Germantown section where Awbury is located. As stormwater travels over roadways like Washington Lane, it picks up pollutants, and this polluted water mixes with raw sewage in the City’s combined sewer system. When heavy rainstorms produce unusually high overflows, sewage and other pollutants end up in our rivers and creeks, which impacts aquatic life, water quality and scours river and creek beds.

In addition to reducing the volume and velocity of stormwater to the City’s sewer system, this project also restores Awbury’s historical water feature to its former beauty and function. The finished project will provide valuable educational opportunities for the community and neighboring schools and will demonstrate to the Arboretum’s many visitors why and how stormwater management is so important to Philadelphia.

So, we believe this project will be a win-win-win: for Awbury’s visitors who will enjoy an attractive water feature not found in any other part of Northwest Philadealphia and who will learn something about stormwater management; for neighborhood residents who will see less flooding on Washington Lane; and for the City as it works to reduce the pollutants reaching our regional waterways. Come visit this spring!