Green streets drive runoff in the right direction

Its name may evoke something out of a children’s story, but green streets are entirely concrete.

The green street is one of the innovative ways that the Montgomery County Department of Environmental Protection (DEP) is working to minimize rain and snow runoff—and the pollution it can pick up in places like roads and parking lots—and keep it from reaching waterways. In the process, green streets are making even the grayest landscapes a little greener.

“The idea of the green street is to work in a neighborhood, treating runoff closer to the source of origin,” said Craig Carson, manager of DEP’s watershed restoration program. “We put them in older areas that do not meet the current requirements to treat stormwater.” In addition to the green street projects, DEP also works with individual property owners in these neighborhoods through the RainScapes program, to reduce runoff that might otherwise enter the right of way.

A Green Street bioretention retrofit in Silver Spring.

How They’re Made

Though they may look simple, green streets are sophisticated pieces of landscape architecture. In this way, they have a lot in common with rain gardens and many of the other stormwater management projects championed by DEP’s RainScapes program.

Asters and Helianthus in a bioretention garden on Dennis Avenue in Silver Spring.

Green streets, which are typically located in grassy areas between a curb and a sidewalk, employ what are referred to as low-impact development techniques to managestormwater runoff. These techniques include bioretention, or depressed planting areas with vegetation and soil mixtures specifically intended for water filtration; special tree boxes that capture and filter precipitation; bioswales and grass swales that physically slow stormwater flow rates and create temporary ponding areas; and permeable pavers that allow stormwater to infiltrate through the spaces between pavers into the ground below.

“Green streets are usually comprised of bioretention areas or rain gardens,” Carson noted. “This way, when stormwater hits the ground, it can infiltrate directly through the plant roots and soil, filtering pollutants all the way down.”

Dennis Avenue step pools.

The Road to Cleaner Waterways

As many Montgomery County residents know, the Chesapeake Bay is fed by the Potomac, Anacostia and Patuxent Rivers, which meander through a slew of local watersheds and subwatersheds in the county. Some of the most problematic pollutants that travel into these waterways from urban and suburban areas are nitrogen, sediment and heavy metals. As it happens, the infiltration that green streets provide is excellent for filtering pollutants, such as heavy metals like zinc, from stormwater.

That makes green streets critical to any runoff prevention strategy in the county, but it’s not their only benefit. Once installed, green streets help create more attractive streetscapes, provide natural habitat for pollinators and birds and help visually connect neighborhoods and other areas.

A map showing completed green streets projects and those that are currently in the design phase.

Since DEP began installing green streets in 2011, nine green street projects have been installed in neighborhoods around the county, concentrated primarily in Silver Spring. Six more green streets are currently in the works for other locations around the county. The areas currently in design are neighborhoods in Wheaton, Glenmont, Kensington and Silver Spring.

Is a Green Street Right for You?

Carson and other DEP staff members work with colleagues within the county, as well as local agencies like the Montgomery County Department of Transportation (MCDOT), to incorporate green streets, whenever circumstances allow, such as when existing roads are being resurfaced.

Officials use a variety of technical factors to determine whether a given area is appropriate for a green street. With so many variables involved, every project is truly one of a kind.

Permeable paver parking areas are a green street practice.

“Neighborhoods are initially screened based upon road and right of way width, road slope, tree coverage, drainage patterns and existing stormwater treatment. Every neighborhood layout is different, which makes every situation unique,” Carson said.

Would you like to learn more about green streets? Visit the DEP Green Streets web page or email askdep@montgomerycountymd.gov.

Scroll down the page for more photos of green streets throughout the County.

By Scott Harris, Freelance Writer. Read Scott’s other posts on the benefits of environmental peer pressure, birds and climate change, eco-friendly ice rinks, residential solar, and congregational rain gardens.

Planting the Dennis Avenue step pools in Silver Spring.

Special areas catch debris and are inspected and maintained monthly by DEP.

Treating water and looking beautiful.

This is what it takes to build a bioswale on Dennis Avenue.

The just constructed step pools on Dennis Avenue.

Lanark Walk in Silver Spring, near Dennis Anenue – before construction

Lanark Walk under construction.