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Low Impact Development (L.I.D.)

Low impact development (LID) is a new approach and set of tools to help communities better protect Puget Sound’s water quality, habitat and biological resources from the harmful effects of land development and stormwater runoff.

What is LID?

The low impact development approach to developing land and managing stormwater is to imitate the natural hydrology (or movement of water) of the site. In a mature Pacific Northwest forest, for instance, almost all the rainfall (or snowmelt) disperses along the forest floor, where it ‘infiltrates‘ into the ground, is taken up by the roots of plants and trees or ‘evaporates‘. Researchers estimate that about less than 1% becomes surface runoff.

But, when forests and natural open spaces are cleared, and buildings, roads, parking areas, and lawns dominate the landscape, rainfall becomes stormwater runoff, carrying pollutants to nearby waters. Much less, water infiltrates and is taken up by plants, less evaporates back to the atmosphere, and much more (about 20-30% in a suburban neighborhood), becomes surface runoff or stormwater runoff.

What are the benefits of LID?

When combined with other key elements of a comprehensive local stormwater program, effective land-use planning under the ‘Growth Management Act‘ and watershed or basin planning, LID can help communities more efficiency and effectively manage stormwater, and protect their water resources.

Below is a list of benefits:

  • LID can help better protect the environment
  • LID can help reduce flooding and protect property
  • LID helps protect human health
  • LID protects drinking water supplies
  • LID is good for the economy
  • LID provides cost-effective alternatives to systems upgrades
  • LID can increase the appearance and aesthetics of communities
  • LID can increase public safety
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    Here are some key LID strategies:

  • Conservation measure..
    -maximize retention of native forest cover or re-vegetate if already cleared
    -protect native soils that drain well, and restore the draining capacity of soils compacted during construction
    -protect topographic site features that slow, store and infiltrate stormwater
    -protect natural drainage patterns and features
  • Site planning..
    -use a multi-disciplinary approach that includes planners, engineers, architects, and landscape architects
    -place buildings and roads away from critical areas and well-draining soils
    -minimize impervious surfaces and completely disconnect them (zero effective impervious surface area)
  • Distributed management practices..
    -manage stormwater as close to it’s origin as possible by using many, small scale LID techniques
    -create a site design that slows surface flows and increases the amount of time stormwater flows over the site
    -increase the reliability of the stormwater system by using multiple, redundant stormwater controls
    -integrate stormwater controls into the design of the site and use the controls as site amenities
    -reduce the reliance on traditional collection and conveyance stormwater practices
  • Maintenance and education..
    -develop reliable, long-term maintenance programs with clear and enforceable guidelines
    -educate homeowners, building owner/operators, local government staff and others as needed on proper operation and maintenance of practices, and protection of all surface waters
  • Below is a little list of the most common LID practices:

  • Bioretention cells or swales (also known as rain gardens)
  • Pervious pavement
  • Amending soil with compost
  • Vegetated roofs (also known as green roofs or eco-roofs)
  • Minimal excavation foundations
  • Rooftop rainwater harvesting
  • Dispersion
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    What do LID projects look like?

    You may see examples of LID practices everyday and not even know it.

    Sometimes, an LID technique can be subtle as a swath of vegetation (bioretention) in a parking lot to capture and filter stormwater runoff.

    You may drive by a new development where houses have smaller footprints and are clustered closer together, share driveways with neighboring homes and much of the native vegetation has been preserved.

    You may walk down on a sidewalk that doesn’t look quite like a typical concrete sidewalk. Or you may park in a parking lot that isn’t asphalt. Instead of impervious materials, the surfaces are permeable pavement, which allows water to infiltrate to the ground beneath.

    In many cases, LID techniques are completely invisible. Soil amending is an important function of LID. Adding compost to soils disturbed in construction restores the soils health and it’s ability to infiltrate rainwater.

    Another invisible LID technique uses alternative building foundations composed of driven piles and a connector at or above grade. This practice eliminates the need for extensive excavation and reduces soil compaction.

    Sometimes, LID practices can be more obvious, such as a large cylindrical container next to a house acting as a rooftop rainwater catchment system. Or a rooftop covered with plants, instead of shingles. Or a beautifully redesigned neighborhood street with lush gardens.

    LID is gaining popularity in Puget Sound

    LID is gaining popularity in the Puget Sound basin as local communities, developers and builders, engineers and regulators look for cost-effective and more environmentally sound ways to develop land and manage stormwater.

    LID has numerous uses and applications for:

  • Individual sites
  • Large-scale subdivision sites
  • Residential, commercial or industrial projects
  • New developments
  • Redevelopment of existing sites
  • Rural, suburban and urban settings