Natural drainage systems can cut NU’s development costs

New Urban News Article with images, table, sidebar, 1/1/2007

In a South Carolina case study, “light-imprint” infrastructure reduced anticipated engineering expenses 31 percent.

In the December issue, we reported that new urbanist developers are increasingly turning to “natural drainage systems” — techniques that allow much of a community’s stormwater to soak into the ground rather than be piped to rivers, lakes, treatment plants, or large, unsightly detention ponds. A newly completed study led by Tom Low shows that these more natural methods could sharply reduce engineering costs for traditional neighborhood developments (TNDs).

Low, the Charlotte, North Carolina-based director of town planning for Duany Plater-Zyberk & Company (DPZ), organized a team that examined the financial effect of using natural drainage techniques in Griffin Park, a TND about to get under way in Greenville County, South Carolina. The techniques — sometimes described as “high-performance infrastructure” or “low-impact development” — have been dubbed “Light Imprint New Urbanism” by Low. Because they require less pipe, less paving, and less massive excavation, grading, and tree clearing, they could save developers a substantial sum of money.

Low’s team looked at the financial consequences of introducing a natural drainage system in the 42-acre first phase of the 300-acre project being developed by Jelks Little LLC. As the table to the right shows, this system would generate some extra expenses, such as $16,900 for a fence protecting existing mature trees during the erosion-control phase of the project. Twenty “rain gardens” — small, slightly depressed areas that can soak up stormwater — would cost $102,400, more than twice as much as the large detention pond that a conventional engineering approach would call for.