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Stormwater & Low Impact Development (LID)

Improving management of stormwater so that water quality, habitat and aquatic resources are protected is one of eight key objectives established in law for the Puget Sound Partnership’s 2020 Action Agenda.


 2012 LID Technical Guidance Manual for Puget Sound
The final 2012 LID guidance manual is now available. 

LID Local Regulation Assistance
The final July 2012 version of “Integrating LID into Local Codes: A Guidebook for Local Governments” is now available

The Partnership’s survey of the 36 local governments that received assistance under the LID Local Regulation Assistance Project is now available.

Learn more about the Partnership's local regulation assistance project during 2005-09

What’s the problem with Stormwater?

Rain is a part of life in the Pacific Northwest . Stormwater runoff is rain (or snowmelt) that flows off developed land—such as roads, parking areas, rooftops and lawns—into nearby streams, rivers and Puget Sound . Runoff enters these waterbodies either directly or through drainage systems.

Stormwater runoff poses a high risk to the health of Puget Sound by causing two major problems.

First, stormwater transports a mixture of pollutants such as petroleum products, heavy metals, animal waste and sediments from construction sites, roads, highways, parking lots, lawns and other developed lands, with the following results:

  • Stormwater pollution has harmed virtually all urban creeks, streams and rivers in Washington State.
  • Stormwater is the leading contributor to water quality pollution of urban waterways in the state.
  • Two species of salmon and bull tout are threatened with extinction under the federal Endangered Species Act. Loss of habitat due to stormwater and development is one of the causes.
  • Shellfish harvest at many beaches is restricted or prohibited due to pollution. Stormwater runoff is often one of the causes.
  • Stormwater likely contributes to the killing of high percentages of healthy coho salmon in Seattle creeks within hours of the fish entering the creeks, before the fish are able to spawn.
  • English sole are more likely to develop cancerous lesions on their livers in more urban areas. Stormwater likely plays a role.

Second, during the wet, winter months, high stormwater flows, especially long-lasting high flows, can:

  • Cause flooding.
  • Damage property.
  • Harm and render unusable fish and wildlife habitat by eroding stream banks, widening stream channels, depositing excessive sediment and altering natural streams and wetlands.

In addition, more impervious surface area means less water soaks into the ground. As a result, drinking water supplies are not replenished and streams and wetlands are not recharged. This can lead to water shortages for people and inadequate stream flows and wetland water levels for fish and other wildlife.

>> Learn more about Stormwater Management in Puget Sound

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.

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.

>> Learn more about Low Impact Development in Puget Sound

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