Quantifying Green Infrastructure’s Stormwater Capture Potential

September 5, 2017, Department, by Serda Ozbenian

2017 September Conservation Quantifying Green Infrastructures Stormwater Capture Potential 410

When it rains in highly urbanized areas, water that would normally soak into the ground becomes runoff, picking up litter, sediment and various other pollutants as it travels over impervious surfaces. This stormwater runoff carries pollutants directly to streams and rivers, where it can cause flooding, water-quality issues and erosion. Public parks, which often contain large swaths of land, are great sites for green infrastructure stormwater management because they offer multiple opportunities for slowing and capturing the destructive force of stormwater runoff — cleansing it of pollutants with vegetation and infiltrating it back into the ground, thereby preventing flooding, recharging groundwater tables and protecting watersheds.

The amount of stormwater that can be captured and treated in a green infrastructure installation depends on several factors, including the permeability of the soil at the site and the placement and size of the green infrastructure features. With funding from NRPA’s 2016 Great Urban Parks Campaign, four grant recipients — Boone Park West in Atlanta, Georgia; McKinley Park in Pittsburgh, Pennsylvania; Ambrose Kennedy Park in Baltimore, Maryland; and Montbello Open Space in Denver, Colorado, are showing how they are improving the quality of the environment in their communities.

All four grant recipients are increasing the permeability of their sites by intentionally designing their projects to capture and hold stormwater flowing into their parks using a practice called bioretention. This type of design diverts stormwater into specially designed, low-lying drainage areas that contain native, deep-rooted plants in a specifically engineered soil mix (if necessary).

Bioretention areas can temporarily be flooded without damage, while the stormwater runoff from impervious surfaces either slowly percolates into the soil or slowly evaporates in a process called evapotranspiration, thereby mimicking natural areas. As the water soaks into the ground, it is taken up by plants, and evaporates into the air, pollutants from runoff are removed through natural processes, instead of just cycling into streams and drinking water supplies as it does with traditional ‘gray’ stormwater management.

Atlanta, Georgia
Project sponsor: Park Pride

Key stormwater management features/practices:

  • Infiltration lawns
  • Rain garden
  • Bioswales

Stormwater capture potential:

  • 7,450,000 gal./yr.

The Boone Park West project will establish a new 3.5-acre public park in the English Avenue neighborhood on the west side of the city of Atlanta in the Proctor Creek watershed. Proctor Creek, which empties into the Chattahoochee River, Atlanta’s main source for drinking water, was historically an asset and source of pride for the surrounding communities. Over many years, however, the creek’s upper watershed has become highly impervious from development, resulting in large volumes of stormwater runoff when it rains. This runoff is the biggest threat to water quality and habitat in Proctor Creek. Often, it is blamed for neighborhood flooding, and it puts a strain on the area’s sewer infrastructure. In recognition of these challenges, in 2013, the federal government designated Proctor Creek one of 11 priority waterways under the Urban Waters Federal Partnership.

The green infrastructure retrofits to Boone Park West, which includes the installation of two bioswales, two infiltration lawns and a rain garden, will reduce the negative impacts of an estimated 7,450,000 gallons of stormwater runoff annually from the surrounding streets and neighborhoods. Treating this volume of stormwater by green infrastructure methods demonstrates the significant potential for Boone Park West to relieve pressure on Atlanta’s combined sewer system and reduce localized flooding in the surrounding community.

Pittsburgh, Pennsylvania
Project sponsor: Pittsburgh Parks Conservancy

Key stormwater management features/practices:

  • Rain gardens
  • Bioswales
  • Subsurface stormwater storage

Stormwater capture potential:

  • 1,600,000 gal./yr.

McKinley Park is a 78.5-acre community park in the Beltzhoover neighborhood of Pittsburgh. It is the only park within walking distance for area residents and has been a public asset since the 1870s. However, the park’s steep topography, lack of accessible paths, poorly defined entrances and deferred maintenance issues discourage neighborhood access, limiting public use of the park. Stormwater runoff negatively impacts community use as well as the park’s ecology. This renovation project involves the installation of green infrastructure features in the upper portions of McKinley Park, in an area known as Chicken Hill, to reduce the volume of street runoff that discharges into the combined stormwater and sanitary sewer that flows underneath the park. Green infrastructure improvements will reduce flooding and other negative impacts from the deteriorating gray infrastructure and positively contribute to improving water quality and the health of the impaired Saw Mill Run watershed. The green infrastructure features are designed to route stormwater through treatment areas of rain gardens and bioswales prior to draining into slow-release, underground subsurface storage that will slowly release and infiltrate storm overflows. Complementary improvements, being implemented in partnership with the city of Pittsburgh, include accessible trails, a new shelter, a hill slide and overlooks. The anticipated annual stormwater capture potential for McKinley Park is approximately 1.6 million gallons throughout a typical year.

Baltimore, Maryland
Project Sponsor: Parks and People Foundation

Key stormwater management features/practices:

  • Large bioretention area
  • Removing impervious surfaces
  • Planting native trees and plants

Stormwater capture potential:

  • 232,960 gal./yr.

Ambrose Kennedy Park is a 1.75-acre community park located in the Jones Falls watershed of Baltimore City, in one of the high-priority neighborhoods identified in Baltimore’s Municipal Separate Storm Sewer System and Watershed Implementation Plan. This green infrastructure project calls for the removal of more than 17,600 square feet of impervious asphalt and replacing it with natural soils and native Maryland plants. These improvements will restore a natural landscape and eliminate 393,950 gallons of runoff annually from entering Jones Falls and eventually the Chesapeake Bay. A large bioretention area will treat runoff from an additional drainage area of 30,684 square feet. This equates to an annual capture volume of roughly 232,960 gallons per year. All the green infrastructure features in the park have been identified by the city as appropriate strategies to meet the city’s stormwater reduction requirements. The green infrastructure components of this project will also measurably reduce urban heat island effect in this park, cooling what is otherwise a hot, barren expanse of asphalt in a community where there is little shade.

Denver, Colorado
Project Sponsor: Environmental Learning for Kids

Key stormwater management features/practices:

  • Bioswale
  • Rain gardens
  • Impervious surface disconnections
  • Infiltration

Stormwater capture potential:

  • 2,228,734 gal./yr.

The Montbello Open Space project in the far northeast section of the city and county of Denver, Colorado, involves the restoration of 5 acres of undeveloped parkland in Montbello, one of the city’s largest neighborhoods. Current gray stormwater infrastructure in the neighborhood is unsafe and aging. The new park is designed specifically to mimic the native Colorado prairie ecosystem; employ green infrastructure techniques to improve stormwater flow; accommodate frequent storms; withstand a 100-year flood event; improve water and environmental quality; and improve wildlife habitat in this arid landscape. The design calls for regrading the site into a gently rolling prairie topography with a central arroyo, or broad drainage swale, to contain stormwater and reduce flow into the city’s stormwater management facilities. Surface drainage from parking areas and planned building roofs will be routed through a series of tiered rain gardens into a central rain garden and large 7,500-foot-long bioswale, the focal point of the park. To allow for additional infiltration, water will collect on the park site prior to releasing the flows into a detention pond on the health clinic site, thereby capturing and filtering all water that flows into the public storm sewer.

Three of the green infrastructure projects are slated for completion by the end of this year, with the fourth planned for completion in July 2018. NRPA will continue to use them as demonstrations for professional training and development purposes to show how park and recreation agencies, in partnership with private nonprofits and municipal water utilities, can achieve greater environmental benefits than traditional gray infrastructure by implementing green stormwater infrastructure installations in parks.

View the park illustrations that were included in the print edition of Parks & Recreation magazine.

Coming to the 2017 NRPA Conference?
Learn more about these projects and hear from the project sponsors themselves at the “Great Urban Parks Campaign: 4 Green Infrastructure Stormwater Management Projects in Parks,” Session 110, Tuesday, September 26, 1 p.m. - 2:15 p.m.

Serda Ozbenian, MS, is NRPA’s Conservation Program Manager.