Kaid Benfield Archive


Green infrastructure in smart growth, beautifully illustrated

Kaid Benfield

Posted July 13, 2009 at 1:37PM

, , , , , , ,

My NRDC colleague Rachel Sohmer has produced a wonderful slide show illustrating how low-impact-development techniques for reducing stormwater runoff (sometimes called "green infrastructure") can successfully be integrated into the kinds of smart, urban environments that we need to revive cities and enable walkable, transit-oriented transportation patterns.  (Rachel last appeared on this site writing about a related topic, the importance of neighborhood streets that connect with each other.)  The slide show is below, but first let me set the context.

Sometimes well-intentioned bureaucrats do all the wrong things while trying to protect watersheds.  As I've written before, the biggest mistake is to look at the problem on a site-by-site basis, on the assumption that reducing runoff on each site, (photo of polluted runoff from roadway)generally by reducing on-site impervious surface, will collectively add up to reduced runoff in the watershed as a whole.  (This may be what the Commonwealth of Virginia, for example, is now attempting to do with new regulatory guidance.)

Unfortunately, it doesn't work that way: if builders respond to regulatory initiatives by reducing the development footprint on each site, the effect is to reduce average per-acre density, which has the unintended effect of spreading more, not less, impervious surface (generally in the form of pavement for public roads, for driveways, and for parking lots) around the watershed.  EPA research demonstrates that density - even though it may increase imperviousness on local sites - actually reduces runoff in the watershed as a whole.

So we absolutely need compact development, not large lots, to protect our waterways.  But how do we do our best to soften the localized impacts of density and deal with the stormwater that runs off of dense urban sites?  Pictures are worth thousands of words, and that's where the slideshow comes in.  Enjoy:


For more on low-impact development, see this introduction prepared by NRDC's water program.