Understanding LID

Low-impact development (LID) techniques are becoming widespread throughout the country for a number of reasons. In some places, interest has been building for a long time, spurred by a desire—or a mandate—to “deal with the rain where it falls” and to mimic a site’s, or a watershed’s, predevelopment hydrology. A surging interest in green building and sustainable techniques has led other areas to join in and investigate LID where before they had relied mainly on large-scale infrastructure to handle stormwater volume and on end-of-pipe treatments for water quality.

In some cases, the so-called LID techniques are applied piecemeal with little consideration for the overall hydrology of the watershed. The original LID practices—developed over several decades, largely in Prince George’s County, MD—are now sometimes treated as a menu of choices: pick one from column A, two from column B, and you can say you have a “sustainable site.”

As Neil Weinstein, the executive director of the Low Impact Development Center in Beltsville, MD, points out in his white paper written for the Center’s 10th anniversary, many misconceptions still persist about just what constitutes low-impact development. It’s not just about infiltration, or about putting “a bunch of green practices” together on a lot. It isn’t even just about stormwater; it can provide other benefits as well. And, not surprisingly, it requires some work—developing an overall strategy and understanding the hydrology of the area. (You can read the full paper on the Center’s Web site at www.lowimpactdevelopment.org.)

And yet, the situation is not entirely bad. For all the partial applications and misconceptions still out there, an increasing familiarity with LID is leading to a greater understanding of the concept—and in some places, of course, the concept of LID is being put into practice extremely well.

As interest in the green building movement and Leadership in Energy and Environmental Design (LEED) grows, with some regions and some government agencies now requiring certain buildings to meet LEED standards, manufactured stormwater products and technologies come into play as well. For example, they are used to retain stormwater underground so that it can eventually infiltrate into an area’s less-permeable soils, and to provide pretreatment before infiltration, particularly in places where water tables are high and there is concern about pollutants reaching groundwater supplies. Particularly in retrofit areas where impervious surfaces abound, such technologies can make infiltration an option where limited space would otherwise not allow it.

With all of that said, in this issue of Stormwater, we offer several articles dealing with projects and practices commonly said to fall into the LID category. “University Roofs Go Green” examines the state of the art of green roofs in the US today, providing some basic definitions of their types and construction. The article also looks at how the United States compares to Europe, where green roofs are more widely used, and how some of the barriers, such as higher costs, are slowly being removed.

“A Paradox of Nature” looks at the now-familiar idea of the rain garden from a slightly different perspective, explaining how it can be used in drier climates. (The Low Impact Development Center’s Web site also has more information on rain gardens, including design templates for gardens in different climates and geographical regions.)

Finally, “Chicago’s Green Alleys” describes that city’s use of permeable surfaces and other techniques, providing stormwater management as well as other benefits like helping reduce the urban heat island effect.

We hope these articles provide information that fits into your larger understanding and use of LID, whatever that may be for your site or your community. You can comment on the articles and see what others are saying about them at www.stormh2o.com.          

Author's Bio: Janice Kaspersen is the editor of Stormwater magazine.