Low Impact Development

What is it?

Low Impact Development (LID) is a stormwater management approach that works with nature to manage rainwater as close to where it falls as possible.

Low Impact Development focuses on slowing rainwater down, soaking it up, and using soil and plants to clean it before it gets to our waterways.

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What is Stormwater runoff?

Stormwater runoff is rain or snowmelt when it flows over land or paved surfaces and is not absorbed into the ground. 

The Problem with Runoff

As water runoff flows across the ground's surfaces, it picks up what it touches and becomes polluted. Unless something is done, the runoff filled with dirt, chemicals, and other pollutants contaminates our streams and waterways. Runoff can also cause flooding damage in lowland areas.

All land on earth is a watershed (the land area down which all water flows). Water flows down over land until it is absorbed into the soil or caught in a low spot like a lake or the sea. 

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The Solution

Slowing the flow of water, so it can be soaked into and filtered through the soil to clean it before it gets to our waterways. That is the focus of Low Impact Development. 

The 5 core requirements for LID.

  • Conserve natural areas wherever possible (don’t pave over the whole site if you don’t need to).

  • Minimize the development impact on hydrology.

  • Maintain runoff rate and duration from the site (don’t let the water leave the site).

  • Scatter integrated management practices (IMPs) throughout your site that infiltrate, store, evaporate, and/or detain runoff close to the source.

  • Implement pollution prevention and proper maintenance.

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Is LID required?
LID is the preferred approach to stormwater management countywide.

Inside the NPDES Permit Area and the Special Flood Hazard Area, LID techniques are required unless not feasible. When required, applicants must use the techniques in the Low Impact Development Technical Guidance Manual for Puget Sound (Puget Sound Partnership and WSU Extension, 2012) unless the Administrative Official determines the techniques as not feasible.

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