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 example, 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 one percent 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 percent in a suburban neighborhood) becomes surface runoff or stormwater runoff.

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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 efficiently and effectively manage stormwater, and protect their water resources.

  • LID can help better protect the environment. LID techniques remove pollutants from stormwater, reduce the overall volume of stormwater, manage high storm flows, and —or replenish—streams and wetlands.
  • LID can help reduce flooding and protect property. Reducing impervious surfaces, increasing vegetation and dispersing and infiltrating stormwater results in less runoff. This reduces the likelihood of flooding from big storms.
  • LID helps protect human health by more effectively removing pollutants from stormwater. Untreated stormwater can be unsafe for people to drink or swim in.
  • LID protects drinking water supplies by ensuring that rainfall infiltrates where it can recharge aquifers, rather than being treated as a waste and discharged to marine waters.
  • LID is good for the economy. LID can help protect shellfish growing businesses, water quality and marine sediment quality. This ensures that our resources remain clean and Puget Sound remains a great place to operate a business and attract employees. Taxpayers don’t have to pay for expensive cleanup efforts for polluted waters and sediments. And because LID projects in many cases are less expensive to build, it means that developers and builders can often save money on overall development costs by using LID.
  • LID provides cost-effective alternatives to systems upgrades. Land developed prior to the 1990s usually provides little, if any, stormwater treatment. In many cases, LID systems, such as bioretention, are much less expensive to use than costly stormwater vaults or land-consuming stormwater ponds.
  • LID can increase the appearance and aesthetics of communities. LID projects leave more trees and plants and have less impervious surfaces, which makes for greener developments and communities.
  • LID can increase public safety. One of the hallmarks of LID is more narrow streets. Studies show that when vehicle traffic is slowed, there are fewer pedestrian accidents and fatalities.

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Key LID strategies

Key LID strategies include:
  • Conservation measures
    • Maximize retention of native forest cover or revegetate 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 its 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.

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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 as 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 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 soil’s health and its 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. (use SEA Streets shot)

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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.  

In 1995, no one was using LID. Today, dozens of LID projects are happening in almost every county throughout Puget Sound . The Puget Sound Partnership continues to be a leader in coordinating guidance, training and technical and financial assistance on LID. The Puget Sound region is considered a national leader in LID guidance, education, state assistance, and implementation. 

 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.

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What's being done now?

  • Free assistance to local governments to help them revise regulations and development standards. In 2005-2006, after a competitive application process, the Partnership helped 19 cities and counties change their local regulations to allow for, encourage or require LID. For the 2007-09 biennium, the Partnership has $500,000 for more LID local regulatory assistance and LID training.
  • Grants to local governments for LID practices. For the 2007-09 biennium, the Washington State Department of Ecology will be providing nearly $18 million in grants to local governments to demonstrate and monitor the effectiveness of various LID techniques; retrofit existing stormwater infrastructure; and address non-stormwater discharges into systems. In 2006, Ecology awarded $2.5 million for 10 local projects; the local governments are working on the projects and each project includes monitoring
    >> See
  •  Incorporating LID into stormwater permits. Ecology has incorporated LID into federally mandated stormwater permits (requirement S5 in the NPDES phase I and II permits). All permittees must adopt ordinances to allow for LID techniques. Ecology coordinates with Washington State University Extension, Partnership staff, and many other professionals to periodically revise the incentives in the Stormwater Management Manual for Western Washington to spur use of LID.
  • Managing stormwater runoff on highways. As part of its effort to manage stormwater runoff from state highways, Washington State Department of Transportation, added LID techniques to its Highway Runoff Manual and conducts research on the effectiveness and practicality of using LID techniques on state highways.
  •  Staff from local conservation districts provide landowners with free technical assistance on how they can improve runoff from their lands using LID techniques.
  • The University of Washington Professional Engineering Program  offers regular classroom trainings on LID. Specialists from WSU Pierce County Extension share teaching responsibilities and Partnership staff contribute their time as guest speakers for these courses.
  • Low Impact Development Technical Guidance Manual for Puget Sound Due to high demand, the Puget Sound Partnership has had to reprint this manual twice since its original printing in January 2005. The manual has become indispensable to planners, builders and developers who want to incorporate LID into their projects.
  • LID brochure. Another Partnership publicationthe LID brochurehas been reprinted several times. This full-color, illustrated brochure describes LID in greater detail.
    >> Brochure: Web-friendly version | PDF
    >> Brochure: Printable 11 x 17 version | PDF
  • Seattle’s SEA (Street Edge Alternatives) Project. Researchers from University of Washington have been monitoring this street redesign on 2nd Ave. NW between 117th and 120th streets NW. Three years of data show spectacular results: from 2000-03 the SEA Project prevented the discharge of all dry season storm flows (May-September) and 99 percent of wet season runoff (October-April).   Seattle is continuing this highly successful and award-winning program (“Natural Drainage Systems”) in additional neighborhoods around Seattle .
  • The Kitsap Homebuilders Foundation is using state grants to develop a Web site, develop countywide LID standards, retrofit their building site with LID techniques, and more. See their Web site for more information:
  •  At the Stratford Place residential project, the community of Sultan discovered how pervious concrete can eliminate puddles on their streets and sidewalks, be more environmentally sensitive, and save the developer $260,000 in construction costs.

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>> What you can do

>> Learn more / get resouces about low impact development and stormwater management.

>> For more information about the Puget Sound Partnership’s work with stormwater management and low impact development, contact Bruce Wulkan, Stormwater Program Manager, 360.725.5455.

Low Impact Development Brochure
Print version | PDF
Web-friendly version | PDF