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They save lots of money - and that's just their most obvious benefit.

Andy Wible’s backyard in Washington, D.C.’s Petworth neighborhood doesn’t look much like a sewerage drain. But his Bayberry, Bee Balm, Iris and Golden Ragwort plants get the job done – and then some. Dug 30 inches* down and filled with a mixture of sand, topsoil and compost, Wible's rain garden draws raindrops tumbling off the roof deep into the soil, purifying them and recharging the groundwater.

The backyard patch is part of RiverSmart Washington, a new network of rain gardens that seek to mimic a natural ecosystem and end the scourge of sewerage overflows that have long befouled the country’s waterways.

"We’re seeing a paradigm shift in this country on how we think of urban runoff," says Nathan Gardner-Andrews, general counsel for the National Association of Clean Water Agencies. The group represents about 280 public water utilities around the country, more than a third of which are under court order to reduce polluted runoff and bring local waterways in line with federal clean water standards.

Once, cities were built to channel storm water away from building foundations and roadways. But as urban areas have grown, rooftops, streets and other impervious surfaces have disrupted cities' natural hydrology. Today, everyone from water authorities to home gardeners are looking to absorb rain where it falls, eschewing traditional treatment plants and underground sewerage tunnels that effectively neutralize runoff, but don’t do much else.

The first of these projects matured in Portland, Oregon, and Prince George's County, Maryland. Now, dozens of cities including Washington, Philadelphia, and Louisville have embarked on their own overhauls. 

They are attracted, in part, by the lower cost of planting trees and gardens and retrofitting streets, parking lots and roofs. But it's also a matter of pay-off. Taxpayers never see the underground fixes. But green infrastructure is something people can use and enjoy, says Joan Furlong, program manager at the Rock Creek Conservancy, a D.C. nonprofit group working with city officials to recruit residents and business owners to the RiverSmart Program.

"It’s become a really hot topic in the last five years or so. Before that green fixes weren’t really accepted by the regulatory agencies," Gardner-Andrews says, particularly the EPA, which first publicly endorsed green infrastructure just five years ago.

The agency now endorses planting greenery to absorb rainfall as an important tool for adapting to rising sea levels and more extreme storms.

Wildlife also benefits. For instance, if you live in Maryland, planting White Turtleheads in your rain garden can provide much needed habitat for the state butterfly, the Baltimore Checkerspot, which will only lay its eggs on Turtlehead leaves, says Carole Barth, an environmental planner with the Department of Environmental Resources in Prince George's County, Md.

But doing a rain garden requires careful site planning, experts say. If planted too close to buildings, they can exacerbate rather than alleviate basement flooding. And it's important to find a patch of land where water percolates well through the soil, which is not necessarily the case everywhere. Researchers have found years of mowing and other activities sometimes leaves the ground so compacted that its about as permeable as concrete.

One U.S. city that's mastered the art of the rain garden is Portland, Oregon. Over the last decade, the city has added nearly 300 eco-roofs and more than 700 other types of "Green Streets facilities" - things like rain gardens and planters running along curbsides and wedged into street corners where the storm water naturally collects.

The Green Streets improvements deliver an annual volume reduction of more than 80 percent of storm water runoff, says Linda M. Dobson, a division manager in Portland’s Bureau of Environmental Services.

"We’ve found that green infrastructure works best when you management it right at the source. The natural system can function very well on its own, if you don't overwhelm it," Dobson says.

In terms of savings, she points to one of Portland’s sub-basin initially estimated to cost $144 million in old-school sewer upgrades. By substituting a greener approach, the city shaved $63 million off the cost. "Now our whole capital improvement plan recognizes both the gray and the green infrastructure as tools in our toolbox," Dobson says.

D.C. officials hope to follow in Portland’s footsteps, reducing storm water flows while cutting back on planned underground construction. But retrofitting existing places like Andy Wible’s Washington, D.C. neighborhood is a tricky business, particularly when homeowners and businesses are involved.

The $3.5 million RiverSmart pilot (which includes a $700,000 grant from National Fish and Wildlife Foundation) targeted homeowners and businesses in two small sewer sheds that feed into a single spot each where excess runoff overflows into Rock Creek, making results easier to monitor.

More than a third of the homeowners targeted, 51 in all, signed on for the grants. City contractors installed 30 rain gardens, planted trees and made other green fixes. Officials are now working on the next phase of the project, which includes adding similar greenery to city owned alleyways and curbsides and recruiting local businesses to green their roofs and parking lots. If data collected next year shows big reductions in runoff, the city is likely to expand the garden approach in other neighborhoods.

City contractors took pains to select plants that would require as little gardening as possible. The wetland plants usually don’t need to be watered once they take root and tend to crowd out most weeds, Furlong says. Nevertheless, how well the gardens hold up over decades in which houses are sold and businesses change hands is one of the chief unknowns, Gardner-Andrews says.

“It’s pretty easy to calculate the costs of tunnels over time but green infrastructure must maintained over a 20 or 30 year period,” he says. “We know (green infrastructure) can be effective, but how effective over time?”

Wible, who moved into his house with his wife Stacey Fahrner in 2008 and hadn’t gotten around to doing anything about the patchy crabgrass in the yard, has only praise for the program that has allowed him to be a good citizen and, he thinks, has improved his property’s value – not to mention its aesthetic one.

“In addition to helping reduce pollution and stormwater runoff,” he says, “we really love our yard now. It looks great.”

*An earlier version of this story incorrectly stated the depth of the rain garden plot.

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