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Low Impact Development

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Low Impact Development, or LID, has become the new development standard for surface water. It is a stormwater planning and Best Management Practice (BMP) technique that is designed to mimic natural hydraulic processes. Low impact development techniques often focus on preserving native vegetation/soils and utilizing infiltrative stormwater management practices. LID is used to manage stormwater, protect water quality, minimize flooding and erosion, protect habitat, and reduce greenhouse gas emissions. New techniques are popping up every year and some have been integrated into the 2016 King County Surface Water Design Manual. Many of the new techniques utilize an assortment of BMPs including rain gardens (top), green roofs (bottom), bioretention facilities, and permeable surfaces.

Rain GardensGreen Roof

LID technologies are typically integrated into the project design to use existing on-site natural hydrologic processes. The goal of LID is to prevent measurable physical, chemical, or biological degradation to streams, lakes, wetlands, and other natural aquatic systems from commercial, residential, or industrial development sites (2012 LID Manual).

LID Technology Integrated Management, LID Manual 2012:

  1. Bioretention: The concept that utilizes chemical, biological, and physical properties of pants, soil microbes, and the mineral aggregate and organic matter in soils to transform, remove, or retain pollutants from stormwater runoff. Bioretention cells, swales, and planters are examples of engineered bioretention facilities that have specific water quality and flow control standards.

  2. Permeable Pavement: Several types of permeable pavement can be used to increase the infiltrative capacity of streets and sidewalks, while keeping the structure functional for vehicles, pedestrians, and bicycles. Some examples include pavement with microscopic voids between the aggregate, interlocking pavers with permeable aggregate at the joints, and concrete or plastic grid systems with permeable bedding in the openings.

  3. Urban and Suburban Trees: Trees reduce surface flow from impervious area by intercepting and storing precipitation until evaporated and redirecting intercepted precipitation to the trunk or surrounding soil into an extensive root system.

  4. Vegetated (or Green) Roofs: Urban roofs with thin layers of engineered soil and vegetation designed to reduce stormwater volume and velocity. The water is filtered slowly through the vegetation and drains via roof drain to reenter the storm system on the ground.

"Grasscrete" is a type of permeable surface with an open grid system
"Grasscrete" is a type of permeable surface with an open grid system

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