July 12, 2001

Stormwater problems? Put a LID on it

  • Low impact development techniques help protect local waters as the region grows.
    Puget Sound Quality Action Team

    Graphic courtesy of Prince George’s County Department of Environmental Resources
    Low impact development practices on a single-family home site.

    By the year 2020, the Puget Sound region is expected to grow by another 1 million people. Protecting natural resources and maintaining a high quality of life while experiencing this population growth will provide many challenges for our region. One challenge is how to develop land and manage stormwater so that Puget Sound streams, salmon and other water resources remain healthy.

    To help meet this challenge, the Puget Sound Water Quality Action Team is actively promoting innovative land development and stormwater management techniques known as “low impact development practices.”

    Quick LID facts
    A cost comparison for a 21-acre single-family subdivision in Prince George’s County, Md., showed that development costs for a low impact development subdivision design were almost 30 percent lower than a conventional approach.

    As part of its street reconstruction program for residential neighborhoods, the city of Seattle is installing narrower streets and replacing curb and gutter road sections with open swales and bioretention swales. You can visit the first green street project at Second Avenue Northwest between Northwest 117th and 120th streets.

    The Built Green Program, developed by the Master Builders Association of King and Snohomish Counties, provides the development community with a model program for developing greener, more sustainably built homes.

    Last month, the Action Team, along with numerous co-sponsors, presented a two-day conference called “Low Impact Development in Puget Sound.” It was the first forum in Puget Sound for local elected officials and their staff, natural resource managers, developers, builders, landscape architects, stormwater engineers, academics, and others to learn about and share ideas on low impact development practices.

    “The conference was extremely successful,” said Nancy McKay, chair of the Action Team. “Information shared by regional and national experts helped create momentum for bringing these innovative practices to Puget Sound.”

    The Action Team is going to follow up on the conference with regional, more in-depth workshops around the Puget Sound.

    An educational brochure and a CD-ROM that contains dozens of Web links, a Power Point presentation, downloadable documents, and conference abstracts and biographies are available from the Action Team.

    Why do we need low impact development?

    Studies show that traditional development and stormwater management practices cannot fully mitigate the cumulative effects of growth on the environment. During development and construction, many natural landscape features are severely altered. Soils are compacted by construction equipment and grading, and trees and other vegetation are replaced by extensive stretches of impervious surfaces, such as roofs and pavement. The result is that less water soaks into the ground and more water runs off.

    Most conventional stormwater management techniques used in traditional developments do not adequately address these issues. Too many land grading and storm drain systems are designed to remove water from the site as quickly and efficiently as possible. Conventional stormwater management systems are generally designed to only control the peak runoff rate of stormwater for a few large storm events. These systems often are not designed to mitigate for the runoff rate and increased volume from frequently occurring smaller storms, which are common in our area.

    The result is often severe damage to fish and wildlife habitat and less aquifer recharge for drinking water.

    What is low impact development?

    Low impact development, or LID, is an eco-friendly approach to land development and stormwater management designed to reduce impacts on watershed hydrology and aquatic resources. Watershed hydrology is the relationship between rainfall, evaporation, groundwater infiltration and flow of surface water.

    LID is based on the premise that nature knows best. Forests and other natural areas are extremely effective groundwater recharge areas. For example, there is very little runoff in a forested area — most rainfall infiltrates to the ground, is taken up by vegetation, or evaporates to the atmosphere. So rather than collecting and conveying stormwater off-site through pipes and other conveyance systems, a LID-designed site uses vegetation and small-scale hydrologic controls to capture, treat and infiltrate stormwater on site.

    To design using LID practices, a site’s natural runoff patterns are noted and sensitive areas and natural drainages (such as streams and wetlands) are protected. A portion of the site’s trees and other native vegetation is set aside to help store and infiltrate water runoff. Specially designed landscaped areas (called bioretention cells or rain gardens) are then built to treat and infiltrate stormwater. Roads are narrowed, and parking lots, driveways and other impervious surfaces are reduced to allow and improve infiltration. Runoff is also directed from impervious surfaces onto vegetated areas with porous soils. Soils compacted during construction are amended with compost or other organic material to restore their capacity to infiltrate runoff.

    Together, these controls help maintain watershed hydrology and reduce runoff, while also reducing overall development costs, making communities greener and more attractive, and helping ensure that our drinking water supplies are replenished.

    Other benefits of low impact development

    In addition to better protecting the environment, low impact development also provides economic and community benefits. Developers using LID practices potentially increase developable land by reducing size requirements for stormwater ponds. A reduced need for stormwater drainage facilities means lower infrastructure costs. And stormwater utility fees may be lower due to the reduced amount of impervious areas.

    Local governments and communities benefit by better protecting streams and habitat for endangered salmon, shellfish growing areas, and other natural resources. As neighborhoods, homes and businesses grow greener, they become more attractive and property values can increase. Stormwater facilities can be easier to oversee and less costly to maintain. Drinking water supplies can be better maintained. And low impact development provides new tools for cost-effective retrofit as well — something many communities are concerned with.

    Next steps

    Low impact development is part of the state strategy to protect Puget Sound. The Puget Sound Water Quality Management Plan calls on all local governments in the basin to adopt new or revise existing ordinances to allow low impact development practices on new and redevelopment projects. The Action Team urges developers, local governments and others to partner on low impact development projects.

    For more information on low impact development and the Puget Sound Management Plan, or to request copies of conference materials, call the Puget Sound Water Quality Action Team at (800) 54-SOUND or visit its Web site at

    Bruce Wulkan is a technical and policy specialist at the Puget Sound Water Quality Action Team.

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