Prince William Conservation Alliance

Low Impact Development: Keeping a LID on Stormwater Run Off

Stormwater program requirements include a variety of ecosystem and human health protection goals. Unfortunately, conventional stormwater technology is not meeting many of these goals and communities are faced with the challenge of funding upgrades and refurbishing an expanding network of stormwater infrastructure. Even more intimidating is the additional challenge of restoring satisfactory water quality conditions to local creeks and rivers. These are economic realities we cannot ignore.

LID is a comprehensive method designed to prevent stormwater run off problems in developing areas, and help communities balance the need to both address economic growth and protect the local environment. The goal is to address stormwater concerns in advance and at their source. Conventional techniques are geared toward structural enhancements such as pipes. The LID approach exchanges these constructed fixes for the strategic and uniform use of stormwater control techniques throughout the landscape. The LID approach has a strong bias toward preventative measures: systems are modeled after nature and consider all landscape features, including both natural and built components of the development site.

LID's primary goal is to ensure that the post-development stormwater runoff is no greater than the pre-development runoff. The LID approach begins with the identification and conservation of sensitive natural areas, critical to successful LID projects. While conventional stormwater practices plan for rapid and efficient drainage from the development site, the LID approach recognizes that water movement into and through natural areas is evenly distributed. Understanding how water moves through the site and mapping this pattern before development occurs is crucial to the ability to mimic this pattern in developments after the site is developed.

Development plans that seek to control stormwater at the source will be the most successful in reducing the amount of water running off developed sites. The first step in implementing LID techniques begins at the planning phase with an analysis of how water moves into and across the development site. This information helps planners, focused on making full use of the development site, understand how essential natural functions can be preserved and integrated into the site plan. The completed site blueprint recognizes natural resource values and integrates these important save areas into the layout design. site blueprint recognizes natural resource values and integrates these important save areas into the layout design.

Conservation of existing resources is critical to success, but can't do the job alone. Other targets include a close look at proposed impervious surfaces, the major contributor to excessive stormwater runoff. For example, about 50% of the land in an average townhouse community is covered with impervious surfaces. LID seeks to minimize and disconnect impervious surfaces using a combination of techniques. Keeping in mind that water movement in natural areas is evenly distributed through the site, LID integrates many small, simple solutions throughout the development site. These techniques use natural systems as a model and include the use of vegetated buffers, bioretention and woodland conservation areas throughout the development site. Integration of these natural systems can also improve the visual appearance of the completed development.

Techniques in this area also can include reductions in road widths, on-the-street parking and sidewalks. Alternative construction materials that allow some water to filter through their surface are also available. Rooftops are another important contributor to the total impervious surface in the developed site. Even if the number of rooftops in the plan cannot be reduced, contributions to stormwater run off can be reduced by considering house types, shapes and sizes. reduced by considering house types, shapes and sizes.

The LID approach recognizes, considers and takes advantage of the natural features of the landscape. The blueprint for a LID development integrates natural resources protection into a comprehensive site design process. LID offers communities a realistic approach that can help reduce the amount of stormwater run off after a site is developed. The result is a development that minimizes negative impacts to creeks, rivers and other natural resource areas.

The LID combination of natural resource conservation, directed runoff through natural areas, small stormwater controls distributed through the site, customized site design and adequate maintenance can result in considerable advantages to communities. LID has been incorporated into many local government stormwater management programs in the Chesapeake Bay region. The Virginia Dept. of Conservation and the Chesapeake Bay Local Assistance Dept. are promoting LID as an alternative and supplement to existing stormwater programs. LID has been most often used in coastal plain areas. Most of Prince William lies in the Piedmont, where application and benefits of LID techniques is largely unknown.

Conservation of sensitive natural features is a primary ingredient of LID. Sites with significant amounts of sensitive natural features are valuable community assets. Conservation opportunities, including the purchase of development rights and other strategies, should be available to Prince William landowners. Choices in the types and amounts of practices used in LID designs are up to the local community. The LID approach offers Prince William an exciting opportunity for our community to make educated choices together.

Prince William Conservation Alliance