Tuesday, 8 November 2011

Low Impact Development

Low Impact Development (LID) is an innovative stormwater management approach that aims to replicate a site's predevelopment hydrology by using simple design techniques that impacts of runoff while having a low impact on the environment. LID are cost-effective, site-level BMPs that address runoff close to the source and improve human health, enhance habitat and save municipalities, contractors, developers and homeowners money. Some common examples include downspout disconnection, vegetation plantings and preservation, raingardens, cisterns and sidewalk storage (if you are not familiar with all of these tools, don’t worry, we’ll cover them in upcoming posts!). The LID concept came out of Prince George County, Maryland in the mid 1980’s as a way to address growing environmental and economic costs of urban stormwater runoff. The following objectives and principles come from Maryland’s Department of Environmental Resources Programs and Planning Division document Low-Impact Development Design Strategies: An Integrated Design Approach.
Green Roof at Dalhousie University
LID Runoff Control Objectives:
  • minimize disturbance
  • preserve and recreate natural landscape features
  • reduce effective impervious cover
  • increase hydrologic disconnects
  • increase drainage flow paths
  • enhance off-line storage
  • facilitate detention and infiltration opportunities

The Principles of LID are to:

  • integrate stormwater management early in site planning activities
  • use natural hydrologic functions as the integrating framework
  • focus on prevention rather than mitigation
  • emphasize simple, nonstructural, low-tech, and low cost methods
  • manage as close to the source as possible
  • distribute small-scale practices throughout the landscape
  • rely on natural features and processes
  • create a multifunctional landscape

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