What is Low Impact Development?

Low Impact Development (LID) is an innovative, ecosystem-based approach to land development and stormwater management. The LID philosophy is modeled after nature: manage rainfall at the source. LID's goal is to mimic a site's natural hydrology by using design techniques that infiltrate, filter, store, evaporate, and detain runoff close to its source, resulting in a 'hydrologically functional' landscape and a protected watershed. Techniques are based on the premise that stormwater management should not be seen as stormwater disposal. LID is a versatile approach that can be applied equally well to new development, urban retrofits, and redevelopment / revitalization projects.

There are five basic principles of Low Impact Development:

1) Conserve natural areas
Planning is the first critical step in any LID project. Solid plans, based on natural resource inventories and assessments of the inventory data are important in identifying natural areas that should be conserved in the development process. These areas can be key for stormwater management, and their protection will help maintain the ecological integrity of the site. Regional, watershed, local, and site based plans, based on natural resource inventories and assessments are crucial for implementing LID strategies such as conservation subdivision design, stream and wetland buffers, and habitat conservation areas,

2) Minimize Dev elopement Impacts
There are many low- or no- cost LID strategies that can be implemented during subdivision design and building. Impervious surfaces can be reduced by minimizing road widths, shrinking parking lots, and building footprints, decreasing setbacks. Storm pipes, curbs, and gutters can also be reduced significantly (see #3 and #4). During development, preservation of sensitive soils, minimizing grading and lot disturbance help maintain the site's ecological integrity.

3) Maintain site runoff rate and control small storms
Maintaining the natural runoff rate from a site protects receiving waters, such as stream channels and wetlands, as well as the fish and wildlife habitat they provide. The goal is to maintain the historic, pre-developed volume, rate, frequency, and duration of stormwater discharges so that discharges are not excessively high during wet winter months or excessively low during dry summer months. Techniques include maintaining natural flow paths, using open drainage instead of closed (pipe) systems, flattening slopes, dispersing drainage, lengthening flow paths, maximizing sheet flows, and saving headwater areas.

4) Use integrated management practices (control volume and pollutant loads)
Instead of conveying stormwater and treating it in large, costly end-of-pipe facilities located at the bottom of drainage areas, LID addresses stormwater through small, cost-effective landscape features strategically distributed throughout the site. These landscape features, known as Integrated Management Practices (IMPs), are the building blocks of LID. Almost all components of the urban environment have the potential to serve as an IMP. This includes not only open space, but also rooftops (green roofs), streetscapes (rain gardens), parking lots (porous surfaces), sidewalks (tree filter boxes), and medians (vegetated swales). The use of these controls, in combination with the other LID principles listed here, creates a customized stormwater management strategy that helps maintain overall watershed integrity and functions.

5) Implement pollution prevention, proper maintenance, and public education programs
Pollution prevention and proper maintenance can help increase the efficiency and long-term success of integrated management practices and reduce the introduction of pollutants into the environment. Many practices are easier and less expensive to maintain than traditional stormwater facilities. For instance, many bioretention facilities need only to be cleared of any trash and then have mulch applied periodically. Individuals and groups that are responsible for maintaining LID facilities should receive educational brochures and other materials, and have access to workshops, so that they know their responsibilities and have the knowledge to carry them out.

What LID is NOT:
While LID can incorporate techniques of conservation subdivision design (or 'open space' design), it is not synonymous with conservation subdivision. Similarly, LID is not the same as smart growth or sustainable building. Each of these philosophies has overlapping goals and strategies, but the terms should not be used interchangeably.

Minnehaha Creek Watershed District is committed to promoting Low Impact Development within its communities and across the region. See the Fall 2005 issue of WaterPro, featuring LID, and the Winter 2006 Water Pro, highlighting the March Conference and the new Minnesota Stormwater Manual.

"THE LATEST IN LOW IMPACT DEVELOPMENT:
Engineering and Landscape Design"
   was Endorsed By:

• City Engineers Association of Minnesota
• Sensible Land Use Coalition
• Builders Association of the Twin Cities
• Association of Metro Municipalities
• League of Minnesota Cities
• Metropolitan Council
• Minnesota Erosion Control Association
• Northland NEMO
• Minnesota Board of Water and Soil Resources
• Minnesota Pollution Control Agency
• University of Minnesota Extension Service
• Minnesota Department of Natural Resources
• Minnesota Sea Grant
• Minnesota Association of Watershed Districts
• Minneapolis Blooms Programs of the Committee on Urban Environment

For More Information...
Contact Julie Westerlund, MCWD Communications and Education Coordinator via email or at 952.471.0590x209

Low Impact Development Design Manuals and Other Innovative Stormwater Management Resources

Presentations from the March 21 Conference