Low Impact Development

What is Low Impact Development?

Low Impact Development (LID) comprises a set of design approaches and small-scale management practices that are designed to reduce runoff and associated pollutants from the site at which they are generated. By means of infiltration, evapotranspiration, and reuse of rainwater, LID techniques manager water and water pollutants at the source and thereby prevent or reduce the impact of development on rivers, streams, lakes, coastal waters, and ground water.

Why is Low Impact Development Important?

LID is needed to reduce the water quality impacts caused by land development and construction. Roofs, pavement, and other impervious surfaces displace vegetation and blanket the soil causing less storm water to soak into the ground and more to run off the land surface. Small tributaries and even larger streams cannot accommodate the increased water volume and flow that occur immediately following rainfall and snowmelt events, leading to eroded streambanks, incised channels, streams choked with sediment, destroyed aquatic life and aquatic habitat, and increased flooding and property damage. In addition, storm water carried a broad mix of toxic chemicals, bacteria, sediment, fertilizers, oil and grease to nearby streams.

How Does Low Impact Development Work?

LID is based on the premise that a natural approach to storm water management is best. In forests and other natural areas, most rainfall percolates through the soil, is absorbed by vegetation, or evaporates to the atmosphere. LID is a means of enabling developed areas to simulate nature to preserve predevelopment flow conditions. When the natural landscape is replaced by roads, parking lots, roofs and other impervious surfaces, rainfall can no longer soak into the ground. This results in tremendous increase in polluted runoff. Rather than employing the traditional storm water management approaches that uses miles of costly pipes and acres of storm water ponds to deal with this additional runoff, LID uses natural vegetation and small-scale treatment systems to treat and infiltrate storm water runoff close to where it originates. Reducing the amount of storm water runoff generated in the first place reduces the impact on streams carrying storm water.

Reduce Runoff: Slow It Down, Spread It Out, Soak It In video
The U.S. Environmental Protection Agency and the U.S. Botanic Garden produced this 9-minute on-line video, “Reduce Runoff: Slow It Down, Spread It Out, Soak It In,” that highlights green techniques such as rain gardens, green roofs and rain barrels to help manage storm water runoff.

The film showcases green techniques that are being used in urban areas to reduce the effects of storm water runoff on the quality of downstream receiving waters. The goal is to mimic the natural way water moves through an area before development by using design techniques that infiltrate, evaporate, and reuse runoff close to its source.

The techniques are innovative storm water management practices that manage urban storm water runoff at its source, and are very effective at reducing the volume of storm water runoff and capturing harmful pollutants. Using vegetated areas that capture runoff also improves air quality, mitigates the effects of urban heat islands and reduces a community’s overall carbon footprint.

The video highlights green techniques on display in 2008 at the U.S. Botanic Garden’s “One Planet – Ours!” Exhibit" and at the U.S. EPA in Washington, D.C., including recently completed cisterns.

*Information and video provided by the United States Environmental Protection Agency website http://www.epa.gov/owow/nps/lid/costs07/q-and-a.html