Low Impact Development

What is Low Impact Development?
LID Manuals and Other Resources
Presentations from the 2006 LID Conference 
Web Resources

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 Development 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.

Low Impact Development Design Manuals and Other Resources

Presentations from the 2006 Low Impact Development Conference

From Larry Coffman and Friends:

Introduction to Low Impact Development An overview of the philosophy behind LID and the key elements of LID technology. Discusses the importance of maintaining ecological integrity of sites and why traditional stormwater management practices are not working.

Planning, Site Design, and Cost A primer on site planning principles and design techniques. How to match development practices with soils and site conditions as well as LID objectives. Includes smart design techniques that don't add cost to the price of development, as well as cost comparisons for conventional development vs. LID.

Hydologic and Hydraulic Methods Techniques for modeling stormwater runoff curve numbers and determining BMP sizing for LID projects. Shows various models that contain LID analysis elements.

Redevelopment and Urban Retrofit  Highlights case studies where LID techniques have been used in developed areas to retrofit and improve stormwater facilities, reducing runoff and restoring urbanized watersheds.

Bioretention the only limit to the number of LID practices is your imagination! This presentation defines bioretention (uptake of pollutants by plants) and talks about pollutant removal mechanisms from the plant/soil/microbe complex, and shows lots of examples of bioretention in action.

LID Issues and Lessons Learned The seasoned pros share their knowledge.

Using Low Impact Development Stormwater Controls at Long Lake, Littleton, Massachusetts A stormwater retrofit project to reduce nutrient and sediment loading to a recreational lake.

Perspectives on Implementing Low Impact Developments Bielinski Custom Homes embraces new concepts of conservation and Low Impact Development. See the 18 general planning guidelines and the guiding principles used by this company and learn how they discovered that nature sells.

From Friends of the Mississippi River and partners:

Low Impact Development: Having Your Cake and Eating it Too! A about a study that compared the Crossroads Development (Lakeville, MN) under three development scenarios, including traditional design and Low Impact Development (LID). Compares stormwater quality, stormwater volumes and rates, development cost, development yield, and 30-year maintenance costs. See a presentation on the topic and get detailed information on development/ maintenance costs and stormwater performance of LID practices.

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