Regional Stormwater Facilities

The City is working hard to improve the quality of the water flowing from City streets into the Sammamish River, Lake Sammamish, and our streams. One of the major tools toward completing this overhaul of the City's stormwater infrastructure is the use of regional stormwater facilities.

To provide better protection for the environment and comply with federal and state laws, the City complies with a federal permit for discharge of stormwater. Conditions of this permit require the City to enhance efforts to clean the stormwater before it gets to the groundwater, river, lake, and streams.

These requirements have become more challenging with each passing year, and the cost of constructing and maintaining these facilities is rising rapidly. As such, the City is taking forward-thinking steps to build facilities that will treat this stormwater for years to come.

The City's Regional Stormwater Facilities Plan is an effort to use regional stormwater facilities to meet the City's water quality goals, support new development that is required by the Growth Management Act, and do so in a cost effective manner.

The City has worked closely with the Washington State Department of Ecology to develop a plan for constructing regional facilities that complies with the City's permit and the state's stormwater management guidance manual. The City is making rapid progress in the construction of these regional facilities, funded by the stormwater CIP with support from developers and state grants. Documentation of the City's program, Ecology support, and the progress of the various identified projects is below.

2024 Completed Facilities 

NE 40th Water Quality Facility

NE 40th Street Stormwater Bioscape

The 40th Street water quality facility collects rainwater (stormwater) from 19 acres of SR 520 and NE 40th Street and cleans the rainwater before draining to Villa Marina Creek and Lake Sammamish. Villa Marina Creek is home to salmon and trout. The project is part of the City’s effort to provide regional stormwater facilities that treat new or existing development to keep our local streams and creeks clean for local wildlife.

 The City has installed an educational sign along NE 40th Street explaining how the system works to protect our waterways. Please take a moment to check it out when you are in the area!

 The NE 40th Water Quality Facility was built with funds from the City, King County, Washington Department of Ecology, and Redmond Community Facilities District 2016-1.

See a PDF of the Stormwater Treatment Sign below

Stormwater Treatment sign

Past projects

In 2005, the City initiated work on the Overlake Neighborhood Plan (ONP) Update and Implementation Project. Citizens, property owners and interested parties participated throughout the planning process - sharing recommendations and ideas, including concepts for park, open space, and stormwater facilities.

Following the 2007 adoption of the ONP update, planning for the stormwater and parks facilities commenced. Following an 18-month consultant effort and public process that included briefings to the Parks and Trails Commission, Planning Commission, and three Community meetings, the City Council adopted the Implementation Plan (see Related Documents) on July 20, 2010.

Overlake Village LID Retrofit2012 to 2013
  • Construction of rain gardens in existing streets that provide stormwater treatment and flow control to protect creeks downstream from urban runoff
Overlake Village South Detention Vault2013 to 2015
  • First large stormwater facility
  • A regional detention facility that detains stormwater that has been treated locally within public rights-of-way and private development areas. 
  • This vault became operational in 2015.
Overlake Village Station Infiltration Vault2016 to 2018
  • Second large stormwater facility
  • Regional infiltration facility that will provide retention of stormwater and treatment by infiltrating the stormwater into the ground.
  • This facility is proposed for construction in coordination with the Sound Transit East Link Light Rail, proposed to open in 2023.
  • This vault became operational in early 2018.

Upcoming Projects

Overlake Village Central Infiltration Vault

Estimated 2025

  • The third and final large stormwater facility will occur as redevelopment occurs in the future.
  • will complete the retrofit of the Overlake basin
  • A two-acre park will be constructed on top of the stormwater vault, surrounded by new streets, (NE 26th Street, NE 27th Street, 151st Avenue NE, and 152nd Avenue NE).

Urban Pathway

Estimated 2030

  • Connecting the three large stormwater sites is intended to be developed within dedicated easements adjacent to City rights-of-way
  • Would be designed to include low impact development (LID) components.
  • Will allow more efficient use of the large regional stormwater facilities and will help create much-improved flow conditions in the streams.
  1. Onsite vs Regional Facilities
  2. Downtown Regional Facilities

Onsite Stormwater Management (Traditional)Onsite Facillity

  • Using like vaults, ponds, and swales for each development is the traditional approach. 
  • The developer finances the design and construction of these controls. 
  • In commercial sites, property owners are responsible for maintaining the facilities. In residential neighborhoods, these may be turned over to the City to maintain.

Regional Stormwater ManagementRegional Facility

  • Are facilities designed to manage stormwater runoff from multiple projects and/or properties through a City-sponsored program, where the individual properties may assist in the financing of the facility, and the requirement for onsite controls is either eliminated or reduced. 
  • In Redmond, developers pay a fee, in lieu of constructing onsite facilities. This may be optional or mandatory depending on the location of the site. More information is available in the Stormwater Technical Notebook.

Onsite Stormwater Management (LID)

One way of reducing the size of traditional stormwater management facilities, is to use the concept of low impact development. The low impact development approach to developing land and managing stormwater is to imitate the natural movement of water through a site. Before development came to Redmond, almost all rainfall was dispersed along the forest floor, where it infiltrated into the ground, was taken up by the roots of plants and trees, or evaporated. Where forests and natural open spaces have been cleared, and buildings, roads, parking areas and lawns dominate the landscape, rainfall now becomes stormwater runoff, carrying pollutants to nearby waters. The city and state are moving toward requiring developers to use onsite, low impact development techniques to reduce the requirement for traditional onsite stormwater management or regional facilities. The developer finances the design and construction of these controls, and the property owner(s) are responsible for maintaining them following construction.

The City of Redmond uses all three techniques to manage stormwater, favoring regional stormwater facilities in highly urbanized areas, favoring low impact development techniques outside of wellhead protection zones and in less urban areas, and using traditional onsite facilities to finish the job of stormwater management as needed.

Advantages of Regional Stormwater Controls

  • Reduced construction costs.  Design and construction of a single regional stormwater control facility can be far more cost-effective than numerous individual onsite structural controls.
  • Reduced operation and maintenance costs.  Rather than multiple owners and associations being responsible for the maintenance of several stormwater facilities on their developments, it is simpler and more cost-effective to establish scheduled maintenance of a single regional facility.
  • Higher assurance of maintenance.  Regional stormwater facilities are far more likely to be adequately maintained as they are large and have a higher visibility, and are typically the responsibility of the City.
  • Maximum utilization of developable land.  Developers are able to maximize the utilization of the proposed development for the purpose intended by minimizing the land normally set aside for the construction of stormwater structural controls.
  • Retrofit potential.  Regional facilities can be used by a community to mitigate existing developed areas that have insufficient or no structural controls for water quality and/or quantity, as well as provide for future development. The City is doing this in the Downtown and Overlake neighborhoods.
  • Other benefits.  Well-sited regional stormwater facilities can serve as a recreational and aesthetic amenity for a community.

Disadvantages of Regional Stormwater Controls

  • Location and siting.  Regional stormwater facilities may be difficult to site, particularly for large facilities or in areas with existing development.
  • Capital costs.  The community must typically provide capital construction funds for a regional facility, including the costs of land acquisition.  However, if a downstream developer is the first to build, that person could be required to construct the facility and later be compensated by upstream developers for the capital construction costs and annual maintenance expenditures.  Conversely, an upstream developer may have to establish temporary control structures if the regional facility is not in place before construction.
  • Need for planning.  The implementation of regional stormwater controls requires substantial planning, financing, and permitting.  Land acquisition must be in place ahead of future projected growth.