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The main culprit is “progress”: The concrete jungles of increasing urbanization interfere with the normal water cycle. When rainwater falls in forests or on vegetated lands, some of it is used by plants, some percolates through the soil and replenishes aquifers, and some of it evaporates; consequently, there’s little or no surface flow over these natural areas. In contrast, a whopping 70 to 90 percent of rainwater that falls on impervious surfaces ends up as runoff.

 

Wetlands are attractive. as well as functional, site elements.

As rainwater streams down city streets, it picks up sediment, oils, greases, metals, and airborne particulates. This cocktail of pollutants often flows untreated into natural bodies of water, and numerous studies show it’s a major cause of impaired water quality and harm to aquatic plants and wildlife. According to the Environmental Protection Agency (EPA), almost half of the nation’s waterways are compromised by polluted runoff. Even when there is a treatment program, large surges of runoff entering sewage treatment plants during storms stress these systems to their capacity.

But just as nature punishes, so it can accommodate. Intentionally constructed wetlands, implemented as part of site planning or landscaping, reduce the amount of runoff leaving a site while also cleansing it of harmful substances.

Granted, architects don’t design landscapes. Or wetlands. But they do design the buildings and cities that create runoff, meaning that their decisions have implications beyond the projects in their immediate control. Just as environmental laws are turning up the heat on clients to safeguard natural resources, they’re also compelling architects to learn strategies such as natural stormwater management to mitigate the overall environmental effects of their work.

Green machines

Flood control has long been the bailiwick of civil engineers, who study a building site and then design storm sewers and detention ponds to drain it. These strategies prevent short-term flooding, but they’ve contributed to the problems we face today. And engineered solutions for stormwater management tend to be, shall we say, clunky. “An eyesore” is what one architect termed them.

Constructed wetlands, on the other hand, are an organic form of infrastructure: They work with and by the laws of nature, not against them. Generally, wetlands—both natural and man-made—are areas that are filled or saturated with water for all or part of the year. These soggy conditions promote the development of hydric soils, which are characteristic of saturated areas, along with the growth of specially adapted plant species. A bog is a wetland. So are marshes, swamps, and creeks.

 

Case Study Herman Miller furniture plant, Cherokee County, Ga. Firm: Michael Van Valkenburgh Associates, Inc., New York Working with Mack Scogin Merrill Elam Architects, vanguard landscape architecture firm Michael Van Valkenburgh Associates designed the site for a new factory for the leading furniture mavens, located in pristine, hilly farm country north of Atlanta. The program called for an immense flat-roofed factory building, 550 parking spots, and a paved area for staging hundreds of storage trailers. The project team wanted to reduce the volume of runoff leaving the site. “Typically, you take care of the building program requirements, then shunt stormwater in pipes to a retention basin,” said Matthew Urbanski, a firm principal. “Instead, we used storm- water management to inform the landscape design, break up the parking areas structurally, and make an experience of going into the factory.” Rather than creating a single large parking lot, Urbanski designed a mosaic of smaller, triangular lots without curbs, which are interspersed with flat terraces planted with wetland vegetation in which water will pool during storms before percolating slowly through the soil. “They’re sort of like rice paddies,” he observes. One concern was that mosquitoes would breed in the standing water, but the terraces are designed to retain water for no more than seven days—less than the incubation time for a mosquito egg. Tight rows of small trees of varying species were planted along the terrace edges. Over time, the trees will grow and distinguish the parking areas as site features. Urbanski calls the scheme “a conflation of infrastructure, landscape, and program.” The landscape has a repetitive quality to it—a fitting solution for a factory. Also on the boards is the Athletic Center at the University of Iowa, in conjunction with this year’s aia-award-winning firm Herbert Lewis Kruse Blunck Architecture. The project will involve regrading a 50-acre site, with sculptural forms and grading around a new soccer field dictated by runoff management. Infiltration strips and wetlands will manage parking lot drainage.

Wetlands serve several important ecological functions: Their plants and aquatic life cleanse surface and groundwater; they reduce flooding by acting as natural sponges, storing stormwater and slowly releasing it back to natural waterways; they prevent erosion by stabilizing soil; and they serve as a critical feeding ground and habitat for fish, waterfowl, and other wildlife. As stormwater runoff enters a wetland system, its velocity decreases, which allows sediments and solids to settle out. Plants break down and synthesize organic pollutants, such as oils and greases, and also use metals and minerals in urban runoff as nutrients for growth.

The environmental benefits of wetlands extend beyond the mere site level. Ponds and plant life diminish the “urban heat island” effect, in which impervious surfaces, such as rooftops and parking lots, radiate sunlight back into the atmosphere, increasing the temperature over these regions—a phenomenon that contributes to global climate change.