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Urban or rural, publicly or privately owned, big or small—across the board, more new and redevelopment projects today are incorporating vegetation for storm water management.
Every day the Earth becomes increasingly developed, and thus more impervious surface-dominated. The space covered by roads, parking lots, buildings and other solid structures in the contiguous U.S. is about equal to the size of the state of Ohio, according to a 2004 National Oceanic and Atmospheric Administration study.
As water-loving plants and trees are stripped from land, the timely infiltration of rainwater and snowmelt constitutes a pressing challenge—one further aggravated by population growth, climate change and aging infrastructure. In addition to the clear-cut flooding threat it poses, excess runoff carries pollutants into water bodies, degrading their quality. The U.S. Environmental Protection Agency has estimated that roughly 40% of the nation’s surveyed rivers, lakes and estuaries are too contaminated for fishing and recreation due primarily to such nonpoint source pollution.
By mimicking nature to keep water quantity and quality in check, and toting a host of additional benefits—aesthetic, economic and social among them—natural wet-weather management solutions such as rain gardens and green roofs continue to gain popularity among innovative site owners as well as design, engineering and consulting professionals.
Though generally small in size, rain gardens can pack a big punch in terms of storm water management. Comprised of strategically selected soils and plants, these areas are situated—often in tandem—so as to intercept runoff before it travels downhill or into a water body. At the very least, rain gardens slow incoming storm water streams, diminishing their erosive capacity and extracting pollutants such as nitrogen and phosphorus; the ultimate goal, however, is flood control via complete infiltration or delivery to a conventional storm sewer system.
In addition to their water-related benefits, rain gardens offer aesthetic appeal; habitat creation; inexpensive installation costs; minimal upkeep requirements; and an attractive safety ranking (retention alternatives can pose drowning and mosquito-breeding risks).
Kicking the concept of rain gardens up a notch, literally, are green roofs, otherwise known as vegetated or living roofs. These manmade structure-topping systems incorporate specially chosen vegetation over drainage layers and underlying structural support. As with rain gardens, the goal of a green roof installation is to slow and filter runoff, decreasing loads to overburdened sewer systems, or ideally, to soak up rain and snow in the first place.
During summer months, a rain garden has the potential to retain 70% to 90% of the precipitation that falls on it, according to the nonprofit association Green Roofs for Healthy Cities. The group has estimated that this level can maintain a range of 25% to 40% in winter.
Other benefits of green roofs include their contributions to improved air quality and reduction of the urban heat-island effect, plus the social, recreation and food production potential that systems offer through the addition of green space.
Case No. 1: Gardens Galore
Nonprofit group West Michigan Environmental Action Council (WMEAC) and its Rain Gardens of West Michigan program promote citizen-based environmental advocacy and education, and they practice what they preach. In Spring 2005, WMEAC moved into two units of a new facility—East Hills Center, fondly dubbed Center of the Universe—in Grand Rapids’ East Hills neighborhood.
Green builder Bazzani Associates worked with the East Hills Neighborhood Association to transform a vacant, contaminated brownfield into the grounds for the 7,200-sq-ft multiuse complex—the world’s first U.S. Green Building Council LEED double-Gold- certified building.
“The storm water aspects really shot us to the moon,” said Patricia Pennell, rain gardens and low-impact development program manager for WMEAC. The site is Grand Rapids’ first zero-storm-water-discharge commercial site.
“All storm water is contained, naturally filtered and discharged back to the water table on site,” said Nathan Gillette, principal architect for Bazzani. “This is accomplished by the site’s vegetated green roof and rain garden.”
A sedum-populated green roof atop East Hills Center takes in nearly all of the precipitation that descends upon it each year. Any overflow—as well as all runoff generated by the facility’s parking lot—is routed to the Center of the Universe rain garden, which is comprised of thirsty soil and a variety of native and nonnative plants. In 2008, WMEAC also designed and installed the Paddock Street rain garden at the east end of the building. The group has estimated that it infiltrates approximately 11,000 gal of storm water per year.
“We’ve found that when people come and see these smaller rain gardens,” Pennell said, “they look at them and say, ‘I can do that,’ increasing the likelihood that they will build and maintain one at home.”
Together, the East Hills Center green roof and all onsite rain gardens manage about 580,000 gal of precipitation annually, according to WMEAC.
Case No. 2: Reigning Rooftop
When it comes to managing storm water beautifully, the 909 Walnut Fidelity Tower Building—Missouri’s tallest apartment building, located in Kansas City—is a crown-jewel example. The building’s eight-story parking garage features a lush 17,000-sq-ft green roof designed by area landscape architecture and planning firm Jeffrey L. Bruce & Co.
At a construction cost of about $40 per sq ft, the property developer wholly funded the green roof installation. The design team relied heavily on low-maintenance plants and grasses found in a Midwest prairie environment, promoting one of the garage topper’s primary benefits—storm water management. In a city with a combined sewer system dating back to the early 1800s, this green roof is expected to capture 75% of the annual rainfall and reduce peak runoff events by 25%.
“One unique aspect of the engineered soil design was to passively harvest rainwater in the growing media profile, thereby making it available to the lawn and plants,” said Jeffrey L. Bruce, president of the project’s landscaping firm. “This passive rainwater harvesting system has the capability of capturing a 2-in. rain event without runoff, then over time supplying moisture to the landscape without the use of cisterns or pumps.”
In addition to enjoying its storm water benefits (mindfully or not), residents and their pets utilize the space’s landscape and cabanas for daily recreation and relaxation. The green roof also has boosted investments in nearby buildings, provided nesting opportunities for local birds and reduced the urban heat-island effect around the condominium structures, among other benefits.
The award-winning 909 Walnut site has generated significant media buzz and hosted more than 150 professional, civic, public and social events, educating tens of thousands of visitors on the benefits of green roof technology—perhaps a testament to the dozens of look-alikes popping up across Kansas City’s rapidly developing downtown.
Planting Seeds of Change
Of the U.S. land deemed “urban” in 2004, 42% is likely to undergo redevelopment by 2030, according to Brookings Institution, an independent research and policy organization. Following the example of successful, organic wet-weather management projects such as those profiled here, tomorrow’s revamped spaces and structures have the potential to plant seeds for drier land and healthier water bodies.