Low Impact Development Concepts

 

What is Low Impact Development?

LID is a new, cost effective alternative to stormwater control technology that is being used by developers across the nation.  Unlike traditional stormwater control techniques, LID strategies prioritizes resource conservation and increasing green space, while simultaneously controlling runoff discharge, volume and quality to reach levels of preconstruction stormwater control.  One of the primary goals of LID design is to reduce runoff volume by infiltrating rainfall water to groundwater, evaporating rain water back to the atmosphere after a storm, and finding beneficial uses for water rather than exporting it as a waste product down storm sewers.

Basic LID Principles

LID is a blend of measures that include conservation, minimization of impacts, maintaining historic, pre-developed runoff rates, integrated management practices, and pollution prevention techniques. Together, these form a holistic approach to site design and stormwater management.

Conserve natural areas

Conserving natural drainages, trees and other vegetation, and soils is the first step in low impact development. Trees and natural forest cover in New England are terrific “sponges” for storing and slowly releasing stormwater. Comprehensive land use planning, watershed or basin planning, habitat conservation plans, and stream and wetland buffers are good tools to identify and set aside natural areas within a community and on an individual site.

Once conservation areas are established for each site, the designer can then work within the developable area envelope and evaluate the effects of design options on these areas. A significant portion of trees and other vegetation should be left in a natural state and not developed.

Minimize development impacts

LID design requires the planner and designer to carefully evaluate the physical and ecological characteristics of the site and consider how to minimize development impacts. The goal is to work with the site characteristics to maintain hydrologic functions and processes rather than attempt to mitigate impacts. For example, avoiding the disturbance and grading of vegetated areas can significantly reduce the need for stormwater controls and will help to recharge groundwater. Reducing impervious surfaces by reducing road widths, clustering buildings and using permeable surfaces for parking reduces surface runoff and improves infiltration.

The major points to remember are:

  • Reduce storm pipes, curbs and gutters
  • Cluster buildings and reduce building footprint
  • Reduce road widths
  • Minimize grading
  • Limit lot disturbance
  • Reduce impervious surfaces
  • Preserve sensitive soils

Maintain site runoff rate

Maintaining the natural runoff rate from a site protects receiving waters, such as streams and wetlands, stream channels, and fish and wildlife habitat. The goal is to maintain the historic, pre-developed volume, rate, frequency and duration of storm water discharges so that discharges are not excessively high during wet, winter months or excessively low during dry, summer months. A number of techniques are available to achieve this. In this example, runoff is directed to this vegetated swale, which slows down flows and allows for infiltration.

Remember to:

  • Maintain natural flow paths
  • Use open drainage
  • Flatten slopes
  • Disperse drainage
  • Lengthen flow paths
  • Save headwater areas
  • Maximize sheet flow

Use integrated management practices

Integrated Management Practices, or IMPs, are small-scale stormwater management controls that are strategically distributed throughout the site.  The job of IMPs is to maintain natural flow patterns, filter pollutants and recreate or maintain the hydrology of a site. The use of these controls, in combination with conservation practices, minimizing development impacts and maintaining site runoff rates, creates a customized stormwater management design that helps maintain overall watershed integrity and functions. Click here for a list of the EPA’s Best Practices regarding IMPs.

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. Stay informed about stormwater pollution prevention by clicking on the brochures below:

After The Storm

Water Efficient Landscaping

EPA CleanWater Bookmark

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