When a heavy rainstorm hits D.C., it’s bad news for the city’s rivers.
The city just finished a major component of a multibillion dollar tunnel system to intercept that storm water, but it’s also turning to a far simpler and cheaper solution: rain gardens.
These features, which are built below street level and host a variety of plantings, have been popping up across the country as cities seek to manage more extreme storms.
In San Francisco, officials built a twelve-block span of 30 rain gardens capable of managing over 5 million gallons of storm water every year, or the equivalent of five Olympic pools. Milwaukee has been installing rain gardens in parking lots, streets, and schoolyards, and so has Philadelphia, which has launched a years-long project to reduce combined sewer overflows.
Projects like these can’t handle storm water on the scale of D.C.’s huge new tunnel, but experts say that cities will need all the tools they can get to weather heavier rainstorms, which are expected to become more common and intense with climate change.
“If storms are getting bigger, we need more of everything,” said Trey Sherard, with the nonprofit Anacostia Riverkeeper group.
Managing storm waterD.C. has been struggling with its storm water for decades, well before the more intense rainfall we’re seeing today. Combined sewer systems are common in cities with aging infrastructure.
After being sued for polluting the river, the District agreed to implement a long-term project to reduce combined sewer overflows. The tunnels are part of this effort, preventing overflows by catching excess wastewater and bringing it to a treatment plant.
The agreement was amended in 2016 to include the use of “green infrastructure,” which manages storm water using natural processes. When water is captured by a rain garden, it infiltrates into the ground, evaporates, or is absorbed by plants and eventually returns to the atmosphere. The city is also installing permeable pavement.
The goal is to slowly absorb storm water to keep it out of the combined sewer, said Seth Charde, D.C. Water’s green infrastructure manager.
It’s like “draining a bathtub through a straw,” he said. “If we keep enough volume out of the system, then you can reduce those downstream overflows.”
One rain garden project to control storm water that flows into Rock Creek cost about $25 million. It’s built to manage the equivalent of 20 acres of hard surfaces like pavement and roofs, capturing the first 1.2 inches of storm water. A second project in the area is planned to be finished in January and cost $16 million.
Gardens everywhereD.C. is promoting rain gardens in other ways. For $100, the city will design and install a rain garden through an incentive program for homeowners. The city is also helping private projects get federal money.
Less than half a mile from the White House, the streets of the Golden Triangle district are lined with restaurants, businesses, and lots of greenery. The wide sidewalks host tree boxes, pollinator plants, and enough rain gardens to capture 48,000 gallons of water.
Cutouts in the curb allow water rushing down the road to flow into these gardens, which are set below the sidewalk level. The largest are the size of several parking spots, and they’re filled with trees, bushes, flowers and layers of soil. An underdrain sits below them to capture any excess water.
The project cost $2 million, according to Miranda Woolston, a spokesperson for the Golden Triangle Business Improvement District, which installed the gardens. The Department of Energy and Environment and the Environmental Protection Agency put up most of the money.
Intercepting pollutantsIn addition to keeping storm water from overwhelming combined sewers, rain gardens can intercept pollutants before they reach rivers. Sediment picked up by storm water can carry toxic compounds and cloud river water, harming aquatic plants and fish, Sherard said. Dog waste and trash can also get washed into local waterways. Rain gardens also create green spaces in cities.
“As our climate continues to change rapidly, I think that it’s just one more bonus of green infrastructure,” said Jennifer Cotting, director of the University of Maryland’s Environmental Finance Center. “It’s gonna be able to deliver some benefits that are addressing the impacts of climate change.”
Charde, with D.C. Water, wants rain gardens to become a normal sight on city streets.
“We’re looking for a future state where green infrastructure is just part of the fabric of the streetscape, you know, just like a stop sign,” he said