Low impact development (LID) is an environmentally-sensitive approach to managing development and stormwater runoff. It can protect aquatic resources, water quality, and the natural hydrology of a watershed as development takes place.
Prior to development, most rainfall was slowed down by tree needles and leaves in Kirkland’s forests. The water then spread out over the forest floor, where it is absorbed into the ground, taken up by the roots of trees and other plants, or evaporated. LID elements work to mimic these processes and the natural movement of water through a site.
New Tools & Requirements for Surface Water Development
The City of Kirkland requires the use of low impact development (LID) techniques as feasible on new development and redevelopment projects.
- The PW Pre-Approved Plans include a section related to LID Storm facilities. The section includes policies, design criteria, and details for LID techniques. Please use this information when designing LID elements for development projects.
In 2016, the City of Kirkland adopted the 2016 King County Surface Water Design Manual (KCSWDM). As required by this manual, development projects that create more than 2,000 sf of new and/or replaced impervious surface must evaluate LID facilities to the maximum extent feasible and include amended soil in all landscaped areas.
LID Code Review Summary
Along with other jurisdictions in Western Washington, the City of Kirkland was required to review all development codes and standards to make stormwater LID the preferred and commonly-used approach to site development. This required Kirkland to incorporate stormwater LID principles and BMPs (measures to minimize impervious surface, loss of vegetation, and stormwater runoff) into enforceable documents, like zoning and municipal codes, city policies, and pre-approved standard plans and details. Kirkland completed this review and adopted new codes and standards on December 13, 2016. View project summary.
Benefits of Low Impact Development
- Homeowners can reduce water usage for irrigation by installing LID features. These systems often cost less to maintain.
- Developers can reduce the size of traditional stormwater facilities, reduce costs, and meet the City’s landscape requirements by incorporating LID elements into new development.
- Wetlands, lakes, and streams will receive less pollutants and cooler water as more LID techniques are used. This improves habitat and water quality for recreational uses.
Low Impact Development Elements
- Pervious pavement can be used for walkways, parking areas, driveways, and patios. The pervious pavement reduces the amount of storm runoff by allowing rain to infiltrate through the surface and into the ground. Examples are pervious concrete, pervious asphalt, permeable pavers, and grass pavers.
- Green roofs can be used on residential or commercial development. The thin layer of soil and installation of plants can reduce the amount of storm runoff by absorbing the rain.
- Disconnecting downspouts reduces the amount of storm runoff into the public surface water system. Runoff can be routed to a grass or gravel area and infiltrated. This replenishes groundwater and helps reduce the increase flow to small creeks during rain events. Be careful not to route runoff directly onto a neighbor’s property, or in a place that could cause drainage problems.
- Rain barrels and cisterns capture roof runoff to be used later for irrigation. This reduces the increase in summer water usage.
- Rain gardens and bioretention areas can be used to collect runoff from hard surfaces. Pollutants are removed by the plants and a large portion of the runoff is infiltrated.
- Amending soils with compost will increase infiltration and absorption. Nutrients in the composted soils work to break down and remove pollutants from the runoff.
Low Impact Development (LID) Guidance
2016 King County Surface Water Design Manual
Low Impact Development Technical Guidance Manual for Puget Sound (PDF)
LID Design Information:
For specific information on Residential Rain Gardens, look at this handbook
(PDF 19.22 MB).
LID Elements for Residential Stormwater Management
(PDF 4.0 MB) - Information on LID projects in Kirkland.
12,000 Rain Gardens
- A campaign to install 12,000 rain gardens in the Puget Sound region by 2016.
For questions regarding LID in Kirkland, contact Stormwater staff