Watersheds benefit from new urban development

Researchers in North Carolina have found that in greenfield development, New Urbanism is far better than conventional development at protecting watersheds, mitigating the impact of runoff, and restoring degraded streams. “New Urbanism offers a greener and more compact alternative to sprawl on the suburban fringe,” says a report by Philip R. Berke, Nancy White, Dan Line, Michael Holmes, Joe MacDonald, Kat Oury, and Rhonda Ryznar. The researchers are affiliated with the Center for Urban and Regional Studies at the University of North Carolina at Chapel Hill and with North Carolina State University at Raleigh. The researchers compared 50 new urban developments and 50 conventional developments to see how New Urbanism performs on environmental matters. They discovered that in greenfields, “new urban developments are more effective in incorporating watershed protection techniques than conventional developments.” They were especially impressed by the frequency with which new urban development protects “hydrologically sensitive areas” such as forested lands, steep slopes, and terrain with porous soils. Even though the greenfield new urban developments studied by the North Carolina team had average gross housing densities more than 2.5 times those of the conventional developments (7.2 versus 2.8 units per acre), the new urban developments were more likely to restore degraded streams, incorporate practices that mitigate the impact of runoff, and use techniques that pave over less land. “Despite high densities, New Urbanism holds considerable promise for reducing environmental degradation caused by development,” the researchers concluded. “Low-impact design techniques for protecting sensitive open space, reducing impervious cover, and infiltrating polluted runoff may allow new urban developments to become a more environmentally compatible alternative to sprawl.” The report, “Greening Development to Protect Watersheds: Is New Urbanism the Answer?,” looks at matched pairs of conventional and new urban developments in Georgia, Maryland, North Carolina, South Carolina, and Virginia. On infill sites, as opposed to greenfield sites, the results are not as dramatically favorable to New Urbanism. New urban infill developments are more likely than conventional developments to restore damaged stream environments and to incorporate techniques that limit impervious surfaces. However, new urban and conventional developments are about equal in the degree of protection they give to sensitive areas and in their use of detention and infiltration techniques. In the researchers’ view, the findings suggest that infill development practices need more attention. Berke says the full report will be posted at www.unc.edu.