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
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.
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
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
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.
Key LID strategies
Key LID strategies include:
- Conservation measures
- Maximize retention of native forest cover or revegetate if already
- 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
- 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
- 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.
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
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)
LID is gaining
popularity in Puget Sound
LID is gaining popularity in the
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
. The Puget Sound Partnership continues to be a leader
in coordinating guidance, training and technical and financial assistance
on LID. The
region is considered
a national leader in LID guidance, education, state assistance, and implementation.
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.
- 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.
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 www.ecy.wa.gov/programs/wq/funding/lidprojects.html
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.
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.
Development Technical Guidance Manual for
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 publication—the LID brochure—has
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
SEA (Street Edge Alternatives) Project. Researchers from
have been monitoring this
street redesign on
2nd Ave. NW
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).
is continuing this highly successful and award-winning program (“Natural
Drainage Systems”) in additional neighborhoods around
- The Kitsap Homebuilders Foundation is using state grants to develop
site, develop countywide LID standards, retrofit their building site
with LID techniques, and more. See their Web site for more information: www.kitsaphba.org/LID/index.php?action=viewpage&page=0
- 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
>> What you can
more / get resouces about low impact development and stormwater
>> 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.