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.
Benefits of Low Impact Development
- The 2010 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 2010, the City of Kirkland adopted the 2009 King County Surface Water Design Manual (KCSWDM). As required by Section 5.2 of this manual, development projects must evaluate the feasibility of LID facilities and install at least one element for a portion of the site runoff. Policy L-1 explains this requirement and includes worksheets to be submitted with a development permit.
- Development sites one acre or larger are required to include amended soil in all landscaped areas.
- 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 bio-swales 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.
LID Design Information:2009 King County Surface Water Design Manual Low Impact Development Technical Guidance Manual for Puget Sound
(PDF 7.5 Mb)
For specific information on Rain Gardens, look at this handbook
(PDF 6.5 MB). Other Resources:
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 Stacey Rush