STORMWATER MANAGEMENT
APPLICATION
Conventional stormwater management infrastructure has been engineered
to move the largest volume of water from a site as quickly as possible,
collecting surface runoff in subsurface structures.2 Sustainable stormwater management
captures water closer to the source, reducing combined sewer overflows (CSOs),
ponding, and roadway flooding. In the process, rain water issued as an asset to
improve urban ecology, microclimates, air quality, and the aesthetic quality of
the public realm.
Sustainable
stormwater management aims to achieve the following goals:
Improve
water quality
Vegetated strips and swales filter
and reduce sediment and filter pollutants through settling, physical filtration
in the soil matrix, biological breakdown by microbes, and nutrient uptake by
plants.
Detain
stormwater flows
Stormwater runoff is detained in facilities such as flow-through planters, pervious pavements, and bioswales.
Detaining the flows mitigates the peak flow rates from the rain event, which in
turn helps reduce erosion, loss of nutrients, scouring, and load-carrying
capacity.
Reduce stormwater
volumes
Overall stormwater runoff volumes may be reduced by designing facilities
that absorb and infiltrate rain water in place. Water-tolerant plant root
systems maintain the porosity of the soil while taking up excess water in the
stormwater facility.
Relieve burden on
municipal waste systems
Sustainable stormwater systems reduce the amount of stress on a city’s
wastewater treatment facilities, and may reduce long-term costs if applied at a
citywide scale.4 Unlike
traditional infrastructure, which does not add any additional value beyond its
stormwater conveyance function, green infrastructure can be incorporated into
neighborhood parks and landscaping.
Benefits and
Considerations
Sustainable stormwater management can prove less costly than
upgrading large sub-grade pipe networks, and allows for flexible, modular
installation.
A 2007 U.S. EPA study found lower total costs for 11 of 12
green infrastructure projects when compared to equivalent grey infrastructure
projects. The EPA study found the reliance on natural conveyance systems
significantly reduced structural costs throughout the stormwater management
chain. The opportunity to incorporate green infrastructure into other
structures and landscaping also reduces the overall footprint of stormwater
management infrastructure. Jeffrey Odefey et al., Banking On Green: A Look at
How Green Infrastructure Can Save Municipalities Money and Provide Economic
Benefits Community-wide (American Rivers, Water Environment Federation,
American Society of Landscape Architects, and ECONorthwest, 2012).
Maintenance agreements are necessary to establish
responsibility for the upkeep of the facility. Agreements may be secured
through a specific city agency, neighborhood or business association, or be
assumed by the adjacent business or property owner.
Facility design must account for the physical constraints of
the site, the presence of subsurface utilities, the local climate, and the
feasibility of maintenance agreements. An experienced geotechnical engineer
should verify partial or full infiltration conditions of the native soils.
Native soil conditions, site slopes, native plantings, and location within the
existing watershed should all be considered in the design process. Infiltration
facilities should only be located in Class A or B soils.
Footnotes
“Low Impact
Development (LID),” U.S. Environmental Protection Agency, accessed June 3,
2013.
Noah Garrison and Karen Hobbs, Rooftops to Rivers II: Green
strategies for controlling stormwater and combined sewer overflows (Washington,
D.C.: National Resources Defense Council, 2011).
“Managing Urban Runoff,” U.S. Environmental Protection
Agency, accessed June 3, 2013.
“Chapter 3: Fundamentals of Stormwater Management,”
New Hampshire Stormwater Manual (Concord: New Hampshire Department of
Environmental Services, 2006).
“Deconstructing Green Infrastructure,” Erosion Control,
accessed June 3, 2013.
“Why Green Infrastructure,” U.S. Environmental Protection
Agency, accessed June 3, 2013.
Jeffrey Odefey et al., Banking On Green: A Look at How Green
Infrastructure Can Save Municipalities Money and Provide Economic Benefits
Community-wide (American Rivers, Water Environment Federation, American Society
of Landscape Architects, and ECONorthwest, 2012).
Green City, Clean Waters: Green Infrastructure Maintenance
Manual Development Process Plan (Philadelphia: Philadelphia Water Department,
2012).
Evaluation of Urban Soils: Suitability for Green
Infrastructure or Urban Agriculture, (Washington, D.C.: U.S. Environmental
Protection Agency, 2011).