BY BRADFORD MCKEE

Gray infrastructure has given way to green to prevent sewer overflows into Washington, D.C.’s waters.

FROM “THE RIVER BENEATH THE RIVER,” IN THE NOVEMBER 2018 ISSUE OF LANDSCAPE ARCHITECTURE MAGAZINE.

Green infrastructure is now an important part of the Clean Rivers Project. The colossal Anacostia River tunnel remains a fixture in the effort on the east side of the city to hold and carry stormwater to DC Water’s Blue Plains Advanced Wastewater Treatment Plant. But to the west, the introduction of green infrastructure is allowing the elimination of one smaller tunnel for a combined sewer network above Rock Creek, which drains into the Potomac River, and the scaling back of another large tunnel along the Potomac itself.

The notion of complementing gray infrastructure with green was a priority of George Hawkins when he became general manager of DC Water in 2009. It was not an easy sell. Clean-water advocates were skeptical of green infrastructure’s performance capability and also feared delays in achieving the goals of the Clean Rivers Project—to end 96 percent of the District of Columbia’s combined sewer overflows. Hawkins was able to make a case for the efficacy of green infrastructure and also to show that significant improvements to water quality would occur well before the tunnels’ projected completion.

The Clean Rivers program is deploying a mix of bioretention, porous pavements, rain barrels, and downspout disconnection from combined sewers. In the Rock Creek sewershed, enough green infrastructure is planned to manage 1.2 inches of rainfall on the equivalent of 365 impervious acres; in the Potomac sewershed, it will manage 1.2 inches on the equivalent of 133 impervious acres. “We are volume-driven,” says Seth Charde, a landscape architect who is DC Water’s program manager for green infrastructure construction. “It’s all about keeping water out of the combined sewer to prevent overflow.”

Image courtesy Rhodeside & Harwell.

Above Rock Creek, the landscape architecture office of Rhodeside & Harwell, based in Alexandria, Virginia, is designing 40 bioretention facilities in residential areas for DC Water as a consultant to Nitsch Engineering and AKRF Inc., the prime contractors. The plan will place regional plants in tree panels and curb bump outs. The firm is taking a similar approach in the watershed of Klingle Creek, a tributary of Rock Creek, for the District of Columbia’s Department of Transportation. “It’s one of the first projects of its scale in being systematic in this approach to identifying green infrastructure opportunities in the watershed,” says Faye Harwell, FASLA. She noted a New York Times article about neighborhood resistance in New York City to new bioretention installations. In the District, she says, “We haven’t seen anything in protest.”

One staple of green infrastructure in the Clean Rivers Project for Washington, D.C., is porous pavements in upland portions of the city. Much of the absorption required to meet clean-water goals will need to occur in public rights-of-way. Along with tree-panel and curbside bioretention and sponge parks, there will be new porous surfacing in parking strips and in a new system of green alleys. “That’s really the bread and butter of the program” to spare waterways the overflows of sewage, says Seth Charde of DC Water. “It’s where we’re going to get the bulk of our volume.” (In addition to these measures, the RiverSmart programs administered by the District’s Department of Energy and Environment subsidize green infrastructure on non-city-owned lots.)

Image courtesy Rhodeside & Harwell.

In a location above the Potomac combined outflows, Rhodeside & Harwell, as a prime contractor to the District of Columbia Department of Transportation (the District is a party along with DC Water to the Clean Rivers Project), has developed a prototype for a green alley behind Q Street NW in the Foxhall Village neighborhood. It had been a typical asphalt alley, prone to flooding in low points. The prototype design, directed by Elliot Rhodeside, FASLA, brought in pervious pavers, porous concrete, and bioretention plantings with check dams. “It’s basically a rill system,” says Faye Harwell.

DC Water is committed to maintaining all new green infrastructure projects, Charde says, “for the duration of their lifetime.”

Photo by Sahar Coston-Hardy, Affiliate ASLA.