Curb extensions have historically been used to slow traffic and improve pedestrian safety. A new variation, called a stormwater landscaped curb extension, is landscaped with plants that help filter pollutants from stormwater runoff.

Landscaped curb extensions have similar benefits to the conventional curb extension but they also improve water quality, reduce stormwater flow, and are aesthetically pleasing. The extensions are essentially roadside rain gardens. 

Portland, Oregon is building sustainable "green street" stormwater management projects around the City to reduce the negative impacts of stormwater runoff. When it rains, combined sewer pipes fill to capacity and overflow to the Willamette River. Green Streets projects reduce the amount of stormwater that flows into the combined sewer system, remove pollutants from stormwater runoff, and help reduce combined sewer overflows (CSOs). 

The Northeast Siskiyou Green Street Project is Portland's first residential, on-street stormwater management project. The demonstration project involves the construction of two landscaped curb extensions in the parking zone on each side of Siskiyou just above the storm drain inlets. Stormwater slows when it enters the landscaped areas, the water soaks into the ground, and wetland plants help filter pollutants, mimicking natural conditions. The goal of the project is to demonstrate how Portland can build new streets or retrofit existing ones to manage stormwater flow and volume effectively and inexpensively. The project cost about $15,000. http://www.portlandonline.com/bes/index.cfm?c=degab 

Landscaped Curb Extension on NE Siskiyou Street, Portland, OR
Photo: Portland Bureau of Environmental Services

A series of Green Streets handbooks are available for a nominal charge from the Portland Metro Region Transportation Department at http://www.metro-region.org/article.cfm?ArticleID=262.

For more information on Landscaped Curb Extensions, rain gardens, stormwater BMPs, low-impact development, or other stormwater management issues, contact F. X. Browne, Inc. at info@fxbrowne.com.