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Biodiversity

The Highest Form of Flattery: mimicking wetlands for stormwater management

Wetlands provide numerous ecosystem services that are often completely overridden by the urban environment and fabric of the city grid. Wetlands often exist at locations in the landscape that are competitively desired for anthropogenic uses, such as agriculture – for their fertility – or business -for their adjacency to navigable waters. Historically, wetlands were a scourge on the landscape – “worthless” land that could only be ameliorated by draining, which would utterly destroy the wetland’s functions. Most researchers included these ecological services and human-desired functions provided by wetlands:

·         groundwater recharge and discharge

·         pollutant sequestration and “polishing”

·         nutrient retention, removal, and transformation

·         wildlife habitat

·         biomass accumulation and carbon sequestration

·         flood control and storm buffering

·         sediment stabilization

Our economic system and cultural biases influence the way that we all attribute values to ecosystem services, like those from wetlands. The Kuznet’s Curve explains why a more developed country might be more active in protecting their environmental resources than a developing country. In the future, we may find it appropriate to compare the political progressiveness of local governments within a country with relation to their policy-based valuation of ecosystem services.

Constructed Wetland Design

Constructed Wetland Design

In Philadelphia, the Water Department has established a program called “Green City, Clean Waters” which aims to protect the cities watersheds with best management practices on multiple scales. One of the program’s Green Stormwater Infrastructure Tools is the stormwater treatment wetland: a man-made vegetated system that mimics a natural wetland, designed to management stormwater runoff and filter pollutants through natural landscaping.

Preserving, restoring, or constructing wetlands all aid in the balance of ecotones – the transitional zones between two biological communities, biomes, or regimes – and the built environment needs healthy, functioning transitional zones and interstitial spaces if it wish to retain any of the pre-existing ecological functions of the land within the urban form.

Stormwater wetlands collect runoff and store it – and the water-mobile pollutants – in a shallow basin, which allows the pollutants to either settle out of the water and into the sediment, or be processed by the hydrophytic vegetation. If attractively planted and maintained, constructed stormwater wetlands can provide green space amenity benefits to the surrounding area as an aesthetically pleasing part of the view and as wildlife habitat.

 

Through the “Green City, Clean Waters” program, Philadelphia has created three acres of stormwater wetland at the following sites:

  • Wises Mill Run Stormwater Wetland

    • Problem: stormwater flows from the fully developed 261 acres of neighborhoods discharge and erode the riverbed of Wises Mill Run

    • Solution: two-tiered stormwater wetland capable of holding 150,000 cubic feet of water, reducing peak flows. Each tier allows for settling. Surrounded by two acres of wet meadow habitat.

Wises Mill

Wises Mill

  • Saylor Grove Stormwater Wetland and Educational Site

    • Problem: 156 acre urbanized watershed yielded poor source water quality, drastic impacts of storm-related flows on the aquatic and structural integrity of the riparian ecosystem.

    • Solution: one acre wetland constructed with cascading rocks, vegetation,  to treat a portion of the 70 million gallons of urban stormwater generated in the storm sewershed per year before it is discharged into the Monoshone Creek.

Saylor Grove

Saylor Grove

  • Cathedral Run Stormwater Wetland

    • Problem: the collection area of 116 acres is 31% impervious, but Cathedral Run collects stormwater from and additional 40 acres by pipe. This has resulted in steep erosion of the creek bed, on average 8.5% slope.

    • Solution: multiple-pool forested wetland in natural depressions to remove sediment, slow flow, and reduce shear stress.


Wises Mill Run, Cathedral Run, and (Saylor Grove’s) Monoshone Creek are all within the Wissakickon Creek watershed, which is a source of drinking water for the city. Collaborators have included: Fairmount Park, Friends of the Monoshone, Friends of the Wissahickon, the Pennsylvania Department of Environmental Protection, the Wissahickon Restoration Volunteers, the Senior Environment Corps, and Chestnut Hill College.

Philadelphia  wetland

Sources and further information:
http://www.phillywatersheds.org/place-bmping-wises-mill-run-stormwater-wetland

http://www.csc.temple.edu/t-vssi/BMPSurvey/wises_wetland.htm

http://environment.transportation.org/environmental_issues/water_wetlands/recent_dev.aspx

http://www.phillywatersheds.org/what_were_doing/green_infrastructure/tools/stormwater_wetland

http://www.phillywatersheds.org/doc/ERU_3_Wetland_Creation.pdf

http://www.csc.temple.edu/t-vssi/BMPSurvey/saylor_grove.htm

http://www.phillyriverinfo.org/WICLibrary/Tour%20Guide2%20Compressed.pdf

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