New Urbanism & ‘low-impact’ infrastructure

by Philip Langdon
Courtesy New Urban News

Natural drainage systems and other ecologically advanced technologies are coming to walkable communities.

A new urbanist-led charrette in November 2006 recommended that New Orleans be redeveloped with “natural drainage systems” — techniques allowing stormwater to soak into the ground rather than be piped, sometimes full of pollutants, to bodies of water like Lake Pontchartrain.The recommendation, intended for the Gentilly section of the flood-ravaged city, is a sign of new urbanists’ emerging interest in engineering and landscape systems based on processes found in nature.

In recent years, environmental activists have argued that rain should be handled in a more natural fashion — through “rain gardens,” bioswales, and other ecological features — instead of relying heavily on underground pipes and other conventional engineering mechanisms. A growing number of new urbanists are moving toward this ecological approach.Inquiries by New Urban News found nature-based environmental techniques being incorporated into projects and plans ranging from Traditional Neighborhood Developments (TNDs) in North Carolina and Pennsylvania to urban neighborhoods and HOPE VI public housing redevelopments in Portland, Oregon, and Seattle. (An article on using stormwater management to enhance civic spaces is on page 5 of the December 2006 issue.)

The approach is known by many names, including high-performance infrastructure, natural drainage systems, bioretention, low-impact development, and sustainable stormwater management. “’Laying lightly on the land’ is perhaps the best term we have,” says Tom Low, the Charlotte, North Carolina-based director of town planning for Duany Plater-Zyberk & Company (DPZ). “It basically means using less pipe. The water sheets across the surface. The amount of surface pavement per dwelling unit is reduced.”

Low led a group that last month completed a study of a TND called Griffin Park, to be built in Greenville County, South Carolina. The study looks at building Griffin Park as a TND with conventional engineering versus building it as a TND with a more nature-based system. The natural approach envisions less pavement, fewer curbs and gutters, less storm sewer pipe, and fewer storm sewer inlets, thereby reducing some of the development’s costs. The study is expected to be used to promote natural drainage options among new urbanists.

THE NATURAL APPROACH

For Woodsong, a 22-acre TND in Shallotte, North Carolina, developer Buddy Milliken insisted on natural methods of handling rainwater. In front of a series of cottages on narrow lots is a concrete street 300 feet long and 10 feet (one lane) wide. The center of the street consists of a three-foot-wide strip of pervious concrete. Rain seeps through the porous pavement and a rock subbase and enters the ground, rather than being concentrated in storm drains and pipes. The narrow, curbless street, passing within about seven feet of the houses, helps replenish an aquifer. At the same time, it helps create a more relaxed and intimate setting, making the properties more valuable.

A ditch that cut across the mostly wooded property prior to development has been modified by installing “small check dams or gabions to slow the water down,” Milliken says. Advocates of natural drainage often sum up the basic principles in these words: “Slow the water down, spread it around, and get it into the ground.” Rain from roofs may be captured in cisterns or directed into rain gardens — mild depressions filled with natural material that absorbs the water and gives it time to percolate into the soil. “These are very, very simple things,” says Milliken.

Low devised Woodsong’s neighborhood plan, which includes a man-made wetland in one area and a pond in another. Milliken says that in a conventional development the pond might have been dug in an out-of-the-way spot and then ringed by a chain-link fence. The detention and retention ponds that have proliferated in recent decades are often unsightly and hard to maintain — a waste of valuable real estate. Milliken chose instead to place the pond in a prominent location, in front of a group of houses, forming a neighborhood centerpiece which helps to control rainwater and let it soak into the ground.

At the edges of the pond are four small constructed wetland bays that slow and filter the water before it enters the pond. Mary Vogel, principal in PlanGreen in Washington DC advises against ponds because, among other things, their water may heat up, harming fish life. However, Peg Staeheli, principal in SvR Design Company in Seattle, says a detention pond is needed in some situations to control the water flow. Woodsong’s pond is apparently an aesthetic plus, which has translated into stronger real estate values.“Everything we’ve done has been with the intent to get a financial return —not necessarily the next day,” Milliken says of Woodsong, which he has been building since 1999. “New Urbanism and the environment are mutually reinforcing.”The Oct. 29-Nov. 3 Gentilly charrette, led by Andres Duany and covering 17 New Orleans neighborhoods, recommended using natural drainage systems to absorb water, decrease flooding, and lessen pollution in the runoff, much of which goes into Lake Pontchartrain untreated. Vogel says one instrument is “roadside bioswales — concave gardens planted with native perennial plants and trees — [which] increase absorption and add beauty and resiliency to the environment.” These can be placed between streets and sidewalks.

New Orleans contains many road medians (New Orleanians call them “neutral ground”) that were damaged by last year’s flooding. The intention is to dig into some of these medians and install a mix of soil conditioners, organic mulches, and rock, capable of holding and gradually dispersing a large quantity of water. The economics are favorable, says Vogel. “Whereas conventional street and storm drain maintenance costs increase over time as the result of aging materials, pipes, and drains, natural drainage systems actually become more effective over time, as plants and trees mature.”

One city that is a leader in combining natural drainage with walkable streets and neighborhoods is Seattle, where sustainable stormwater management has been advocated by the Puget Sound Action Team and has been put into practice by firms such as SvR Design. SvR designed High Point, a mixed-income, 34-block, 1,600-unit Hope VI project that features vegetated and grassy swales, porous concrete sidewalks, and front-yard rain gardens. South Lake Union, a large mixed-use development to be built north of downtown Seattle, may also employ natural drainage. (For techniques at High Point, see www.thehighpoint.com or www.svrdesign.com.)