“It’s our cities’ most dirty little secret that our stormwater is being routed directly into our sewer systems,” explains Tom Barrett, owner of Green Water Infrastructure, an Indianapolis-based landscape consulting company that integrates water resources for sustainable site development. “It doesn’t take an extremely hard rainfall to overwhelm our sewer system. Almost any rainfall over .25 inch overwhelms it.”
Barrett receives dozens of Raw Sewage Overflow Warnings issued by the city of Indianapolis every month.
Yet, Indianapolis is just one of 180 U.S. cities identified by the EPA for stormwater sewage overflow problems. “It’s going to cost the city of Indianapolis $1.7 billion to build a deep enough tunnel to separate the stormwater from the sewer to prevent overflow during heavy rains,” says Barrett. “Yet, if enough rain gardens and bioswales were built to handle the stormwater runoff, cities like Indianapolis could save 60 percent of that cost, eliminating the need for building massive curbs, gutters, storm drains and retention ponds.”
What exactly are rain gardens and bioswales, and why have they become one of the tried-and-true methods of alleviating the problem of stormwater?
Rain gardens, typically 100 to 300 square feet, remain dry yet retain water during storms. These modestly sized depressions are generally planted with shrubs, grasses and other attractive native and adapted plants. Although they may look like regular perennial garden under most conditions, they’re much more. A rain garden collects and holds rainwater runoff from impervious surfaces like rooftops, parking lots, roadways, driveways, sidewalks and even lawns, and allows it to soak into the soil instead of running into storm drains. Compared to a patch of lawn, a rain garden allows about 30 percent more water to soak into the ground. In most cases it takes just a day or two for the rainwater to soak into the soil.
Bioswales, similar to rain gardens, have an additional element of a subsurface underdrain—usually a corrugated pipe that feeds into the stormwater system. The key difference between the two is that bioswales are a conveyance system designed more for cleaning and processing water as well as redirecting it (usually away from a road or lot), while rain gardens are collectors designed to absorb stormwater. You can even have a rain garden at the end of a bioswale—they can work in tandem.
New greenscaping opportunity
Rain gardens, bioswales and other rain water harvesting technologies like permeable pavers, green roofs and xeriscapes are exciting “green” opportunities for landscapers. The entire country is buzzing about water conservancy, with many states and municipalities implanting mandatory water restrictions and offering incentives. Adding a rain garden gives concerned customers the opportunity to make a difference within their communities.
“The old days of corralling stormwater to channel it off-site are over,” says Barrett. “Contemporary designs demand that homeowners and businesses hold onto their water—for as long as 48 hours—to avoid overwhelming natural wetlands, estuaries, lakes, streams and sewer systems.”
Cities such as Portland, Seattle, Philadelphia, New York, Kansas City, Washington, D.C., Nashville and Indianapolis are coming up with aggressive greenscaping programs that include rain gardens and bioswales. Although most of these programs are too new to gather and calculate precise dollars-and-cents savings, some of the early returns are promising.
Rain gardens are collectors designed to absorb stormwater. When they’re planted with appropriate water-loving ornamentals they can be quite attractive, as well as capturing rainwater before it becomes runoff.
Photo courtesy of Landscapes Solutions.
Indianapolis is implementing a massive bioretention rain garden program in its central city area that’s expected to retain and store 100 percent of all stormwater when rainfall amounts are an inch or less. The goal is to keep the water out of the storm sewer. On average, the bioretention areas for all rain events are projected to hold 240,000 gallons of rain runoff annually, equating to keeping 91 percent of all annual rainfall runoff from the combined sewer system.
The Yard Fairy, San Diego, installed this rain garden, a great example of a landscape in tune with its climate.
Photo courtesy of The Yard Fairy.
This is not a new idea. In one experimental area, Seattle has already reduced runoff by 97 percent the year after converting an open ditch stormwater drain to an attractive roadside bioswale garden.
Landscapers seizing the rain garden and bioswale opportunity with municipal, commercial or residential properties aren’t finding it exactly a cakewalk when it comes to maintenance and performance issues. Seasoned rain garden installers agree it’s not like you can just find a depressed area, plunk down some pretty perennials near a downspout and watch the water magically disappear after the next downpour.
Three bioswales on this site attest to the commitment of Kum & Go, Fairfield, Iowa, the only convenience store chain in America participating in the USGBC’s LEED certification.
Photo courtesy of Greenwater Infrastructure.
“Every situation in creating a rain garden is different depending on various factors,” says Jerry Orkin, Landscapes Solutions in Nashville. “Is it in the sun or shade? What is the soil type? It depends on so many environmental factors.” Landscape Solutions has been installing rain gardens within a 10-mile radius of downtown Nashville in conjunction with two local nonprofits: Cumberland River Compact and Hands on Nashville.
Photo courtesy of Greenwater Infrastructure.
Diane Downey, owner of Yard Fairy in arid San Diego, started installing rain gardens in her customers’ yards because they wanted to save water from rushing off their properties during the city’s infrequent yet intense downpours, while at the same time creating beautiful spaces.
The Windridge community of 221 homes located in a natural setting in Indianapolis features a groundbreaking rain garden to alleviate existing flooding and moisture issues in the neighborhood.
“Before I jumped in, I learned all I could about the science of rainwater harvesting including how our local soils behave, making calculations on how much water each rain garden surface could handle and knowing which plants benefit most form an influx of water,” says Downey. “I would advise others to do the same.”
Sabrina Schweyer of Salsbury-Schweyer, Akron, Ohio, agrees with Downey that landscapers need to acquire knowledge before offering greenscaping options to customers. Being unprepared can reflect poorly on the entire industry, she adds. Her landscape design firm installed its first residential bioswale 10 years ago.
“Improper installations of rain gardens are extremely detrimental to our industry,” says Schweyer. “The public will embrace these nature-based systems only if they work well and add beauty to their properties long-term. If unsuccessful, then they will lose trust in our profession and abilities.
“These systems must be designed not only to function correctly, but to be beautiful and sustainable years from now. You’ll need an in-depth understanding of natural systems (particularly water and soils), herbaceous and woody plants, excellent design talents, plus knowledge of how to maintain rain gardens and fix them if there are problems.”
Schweyer adds that rain gardens and bioswales are best designed by multidisciplinary teams (landscape architects, landscapers and environmental engineers) because these projects are usually more aesthetic and successful.
Many university extension offices and professional landscaping associations now offer classes on rain garden and bioswale installation and maintenance. Rutgers University Extension in partnership with USDA National Water Program offers one-and-a-half day training classes in eight mid-Atlantic and New England states.
Rain garden and bioswale projects are not just a hit-and-run artifice for landscapers.
Rutgers University Cooperative Extension tells their rain garden and bioswale students that just as the design of rain gardens follows traditional principles, so, too, should their maintenance. You have to cut back growth in the spring and remove debris and mulch. The systems need a bit more attention after their initial installation. Topsoil erosion and plant establishment are very important to make sure the system takes root successfully. Weeding is critical in the first few months after planting; pruning of any dense shrub growth is necessary; regular mowing down to 6 to 8 inches of top growth is recommended early on in spring as is the removal of any excess sediment.
“Maintenance is required, but there’s not any maintenance plan specific to a rain garden,” says Orkin. “We go in and prune once a year. If the rain garden has an overflow pipe, you might have to keep the overflow basin cleared.”
Greenscape manufacturers have been promoting permeable pavers and green roofs for years, but now many, including ABS Materials, Aquascapes and Filtrexx, are starting to feature new systems, additives, designs and educational materials specifically for rain gardens. That’s a good sign for the growing niche of rain garden and bioswale installation and maintenance.