Low Impact Development

What is Low Impact Development (LID)?

Many cities have established zoning (land use) and construction (building) code regulations that facilitate sustainable building and development practices. One major approach, known as "Low Impact Development" (LID), focuses on rainwater once it lands on a surface. LID seeks to mimic natural hydrology and slow, evaporate or transpire, and filter rainwater, before it reaches a stream or Lake Washington.

Without development, rainfall naturally evaporates, absorbs into the ground, or is taken up by the roots of plants and trees. Today, with the influx of impervious roofs and buildings, other infrastructure (e.g. parking lots), and lawns, rainfall is becoming fast-moving "stormwater runoff" that often carries pollutants to streams, rivers, and lakes.

LID contrasts with traditional drainage techniques that collect and transport water to streams quickly; these traditional techniques can damage stream channels and degrade water quality. LID uses various land planning and design practices to conserve and protect natural resources and reduce infrastructure costs.

What are some LID techniques?

Minimize/eliminate impervious surfaces
Retain site vegetation
Amend soils with compost to improve water retention
Construct bio-retention swales or cells (natural areas that have specifically-chosen plans and engineered soils that slow, filter, and absorb water)
Use of permeable pavement or pavers for roadways, driveways, and walkways
Installation of green roofs and/or rooftop gardens
Installation of cisterns or rain barrels to hold and reuse rain water

When combined, such techniques can greatly reduce the amount of stormwater runoff from developed sites- which can improve water quality and reduce flooding downstream!

How can residents and businesses implement LID?

LID is not just for developers- there are many ways residents and businesses can implement LID! Some common and effective ways are to use Natural Yard Care techniques in your landscaping, replace your lawn with native plants, and use rain barrels to capture runoff from your roof. Click here for specific WA State rules on rain barrels.

Do I live in an area with good stormwater infiltration potential? Click here for a map that shows infiltration potential on Mercer Island.