Low Impact Development (LID)

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 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-effe ctive 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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