Bioretention  - Transportation

 

Prince George's County, Maryland, Department of Public Works and Transportation designed and constructed a linear rain garden for the median along Adelphi Road in the late 90s. Originally planned as a raised curb section, the median was redesigned as a landscaped infiltration / bioretention swale. Designs such as this one make multifunctional use of the roadway for stormwater controls.

The Maryland State Highway Administration (MSHA) is currently involved in a multi-year research and demonstration project that will develop standards and specifications for LID strategies applied to state highways. A pilot project planned along  US 1 in Mt. Rainier, Maryland, will also use monitoring to demonstrate the effectiveness of selected LID techniques in meeting TMDL compliance requirements. Another portion of the project involves the rehabilitation of a 6-year old bioretention facility located in a restaurant parking lot in Colmar Manor, Maryland. Originally constructed by Prince George's County, the bioretention facility will be retrofit to comply with current bioretention technology standards. The facility will also include sampling ports for future demonstrations of pollutant removal efficiency.

In Seattle, Washington, as part of the Urban Creeks Legacy Projects, Seattle Public Utilities enacted a pilot project called SEA Streets (the Street Edge Alternatives project), which aims to reduce the impact that streetscapes have on local stream watersheds and  salmon habitat.^{1 ,2} SEA Streets is a comprehensive approach that manages stormwater, minimizes impervious surfaces, and eases traffic. It complements an ongoing effort by Seattle Public Utilities and Seattle Transportation to address street improvements in areas that do not have traditional piped drainage systems.

As shown here, the SEA Streets Project focused on Broadview, a residential section of northwest Seattle located in the Pipers Creek Watershed. The alternative streetscape is intended to change the paradigm that the traditional curb and gutter system is necessary. Vegetated swales, bioretention areas, and infiltration trenches are used in conjunction with traditional drainage infrastructure to collect and treat runoff close to its source. The designers worked with property owners to integrate SEA Streets bioretention areas into existing grades and achieve a functional transition between public and private property. As on other streets, property owners are responsible for maintaining most of the landscaping, even though it serves as a replacement infiltration/filtration system for the storm drains. Seattle Public Utilities' long term goal is to retrofit the ditch and culvert drainage system that currently dominates the northern part of the city using SEA Streets and other natural approaches to manage runoff.

Similarly, the City of Maplewood, Minnesota, has implemented a very successful program that uses bioretention in street drainage improvement projects for older neighborhoods. ^{3, 4} Instead of curb and gutter systems, neighborhood rain gardens (bioretention cells) are used to decrease the runoff volume, improve runoff water quality, reduce construction costs, and maintain the character of the neighborhood. To assist in the acceptance and construction of the neighborhood rain gardens, the City provides prototype layouts with such appealing themes as easy daylily garden, Minnesota prairie garden, butterflies and friends garden, etc.  Maplewood is able to recycle street material for the base aggregate of the gardens, obtain reasonably priced landscape plants from the County Correctional Facility's greenhouse, and engage neighborhood residents in the cell construction through a block-wide planting day/block party. Besides saving money and bringing the neighborhood together, the projects are also a hydrologic success. For example, an engineer with the City cites a mid-1990s pilot project that now generates no runoff, i.e. it is 100% contained in the neighborhood! For communities looking to implement similiar projects, Minnesota's Metropolitan Council Environmental Service⁵ provides alternative stormwater conveyance options grants to help communities use natural processes to do the work of stormwater management.

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