Many LID practices, including bioretention, are well-suited for urban retrofit
projects since they are easily integrated into existing infrastructure (roads,
parking areas, buildings etc.) and use only a small amount of land on any
given site.
Bioretention techniques have been successfully applied to
retrofits of such high profile ultra-urban areas as the Naval District
Washington.1 As part of an overall initiative to help maintain and
restore the water quality of the Chesapeake Bay and the Anacostia and Potomac
Rivers, bioretention areas were installed along parking lot perimeters and
between the parking stalls in various lots at the Washington Navy Yard. Such
bioretention strips as the one in the photograph to the right required minimal
disturbance and maintained parking spaces at existing numbers. All of the
bioretention areas were designed to intercept preferential stormwater pathways
and to treat, at a minimum, the first one-half inch of rain from approximately
half acre segments of impervious parking surface. Pollutants are filtered and
runoff volume and timing are controlled before discharge of the water to the
Anacostia River occurs through the existing storm sewers. Bioretention strips
between parking stalls have also been successfully implemented as part of a
stormwater control plan for an 11.5 acre asphalt and concrete parking area
that serves 700,000 visitors per year at The Florida Aquarium in Tampa,
Florida.2
In general, bioretention techniques are proven to meet stormwater management
criteria in large office park and commercial parking facilities - both as new
designs and as retrofit projects.
The Greenbelt example3 above was constructed when an existing
shopping center was converted to an indoor mall, which required additional
stormwater management facilities due to the expansion. Primarily for economic
reasons, the developer chose to manage stormwater by channeling runoff from
the parking areas into bioretention islands located throughout the lot. The
cells were designed to infiltrate/filter large volumes of stormwater that were
then collected in perforated pipes and transported to the county's storm drain
system. With this design, the developer was able to fulfill not only the
stormwater management requirements, but also a significant portion of the
landscape requirements. The property managers have since reported that
maintenance costs are approximately the same as what would be expected with
conventional systems, while the maintenance procedures are comparable to those
of traditional commercial landscaping.
The Inglewood photo shows another landscaped island that was retrofit to treat
approximately one-half acre of almost entirely impervious surface using
bioretention.4 The island was excavated and filled to a depth of 4
feet with bioretention soil mix. In the interior of the island, the fill
extended to about 12 inches below the top of the curb, allowing for
approximately 6 inches of ponding within the island before backwater gets
generated at the curb opening. This opening is a 4-foot slot cut into
the curb immediately before the inlet to the municipal storm drain system. An
underdrain was installed and tied into the bottom of the existing storm drain
inlet. The retrofit cost approximately $4,500 to construct compared to other
proprietary devices that would treat the same volume of runoff and cost about
$15,000 to $20,000. Despite their higher construction and maintenance
costs, these other devices would not significantly reduce runoff volume or
temperature. The bioretention retrofit also had the additional benefit of
providing aesthetic enhancement with minimal watering requirements. For
example, after the installation of the plants a drought occurred during which
many of the other plants in the parking lot died or experienced severe stress.
The plants in the bioretention facility survived, however, because of the
retained water supply.
Bioretention can also serve as an effective urban revitalization tool.
Here, a bioretention area was incorporated into a sidewalk design to retrofit
an urban streetscape for an economic revitalization project in the Port Town
of Blandensburg, Maryland.5 Out of 300 candidates, the Port Towns
revitalization project received one of 24 national awards by Renew America and
the National Awards Council for Environmental Sustainability. Cited in the
award was the project's Rain Garden at Port Towns Shopping Center and the
streetscaping efforts to clean up the Anacostia River through natural
filtering methods.
4 United States Environmental Protection Agency, 2000:
Bioretention applications: Inglewood Demonstration Project, Largo,
Maryland, and Florida Aquarium, Tampa, Florida. Office of Water,
Washington, D.C., EPA-841-B-00-005A.
5 Port Towns Community Development Corporation for the
revitalization of the Port Towns of Blandensburg, Colmar Manor and Cottage
City
http://www.porttowns.org/
Bioretention techniques have been successfully applied to
retrofits of such high profile ultra-urban areas as the Naval District
Washington.
Bioretention can also serve as an effective urban revitalization tool.
Here, a bioretention area was incorporated into a sidewalk design to retrofit
an urban streetscape for an economic revitalization project in the Port Town
of Blandensburg, Maryland.
