Bioretention  - Commercial / Industrial / Institutional
(Ultra-Urban Retrofits)

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.

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