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Stormwater services and information

King County, Washington

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Surface Water Management Fee

Contacts: Stormwater Services Section

Stormwater Pollution Prevention Manual

2016 King County Surface Water Design Manual

Learn about stormwater and how to reduce pollution


How does stormwater impact us?

1/3 of the pollution in Washington State's water is from stormwater runoff.

Using Weed and Feed?

  • 23 pesticides can be found in our streams during any given rainstorm.
  • 5 of those exceed the level that is considered safe for aquatic life.

After 1 inch of rain...

  • 748 gallons of stormwater runs off a 1,200 square foot roof
  • 27,000 gallons of stormwater runs off a 1-acre parking lot

Other stormwater impacts

50% of all salmon and steelhead runs in Puget Sound are considered unhealthy.

Washington State is the number 1 producer of oysters, clams and mussels in the U.S.

32% of the certified commercial shellfish growing areas in Puget Sound, or 140,000 total acres, have been partially or completely closed due to water pollution since 1980.

Download infographic: How does stormwater impact us?

Reduce stormwater and its pollution at home

Introduction to stormwater in King County
Learn about the science of stormwater, common problems related to stormwater including causes and solutions, homeowner tips, regulations, and how to get help from King County.

Neighborhood Drainage Assistance Program (NDAP)
Get technical assistance for questions about construction, permitting, and storm drainage and request capital improvements or repairs to address flooding, erosion and sedimentation problems affecting private property in unincorporated King County.

Drainage design resources for professionals

2016 Surface Water Design Manual 
Documents and software to help engineers design storm drainage systems that reduce problems for downstream neighbors and minimize damage to our natural environment.

KCRTS hydrologic and KCBW hydraulic modeling software

  • The King County Runoff Time Series (KCRTS) hydrologic model is a required methodology under the 1998 King County Surface Water Design Manual for sizing detention and infiltration flow control facilities.
  • The King County Backwater (KCBW) Program is a standard step backwater analysis program for pipe networks, culverts, and simple open channels.

2016 Stormwater Pollution Prevention Manual

Drainage maintenance resources

Stormwater infrastructure

What are stormwater facilities?

Interactive map of stormwater facilities (opens new window)
Stormwater facilities map

Wastewater system

Combined sewer overflow status map
Some old segments of our regional sewers were designed to drain stormwater too, but these combined systems occasionally flood in big downpours.  Combined sewers were designed to let diluted wastewater overflow untreated into rivers, lakes or Puget Sound to avoid sewage backups in homes and businesses.

Regional Inflow and Infiltration Control Program 
What King County is doing to reduce the unintended flow of surface water and groundwater into the sewer system.

Stormwater projects and plans

King County Stormwater Management Program (SWMP)
Describes King County's action plan to comply with the National Pollutant Discharge Elimination System (NPDES) phase I municipal stormwater permit issued by the Washington State Department of Ecology.

Green River stormwater retrofit planning project
Study modeling and comparing methods to manage stormwater and reduce pollution in developed areas, to establish best practices to manage stormwater.

Miller and Walker Creeks stormwater retrofit planning for improving streams
Project to reduce stormwater pollution in urban creeks that drain into Puget Sound.

King County climate change plan 
How King County seeks to reduce greenhouse gas emissions, adapt to projected climate change impacts, and embed mitigation and adaptation into county policy decisions. The plan incorporates issues, goals and actions related to stormwater.

Low impact development

Low impact development resources (external link)
The EPA offers Low Impact Development guides, fact sheets and other resources.

Background information

Driving rain - stormwater in King County, Washington

Rainfall washes pollutants from yards and pavement into our local streams, lakes and Puget Sound.

King County's surface water management fee
How your fees pay for these services in Unincorporated King County including Vashon Island.

Stormwater resources and references
Links to regulatory agencies, environmental organizations, King County stormwater staff directory, and other resources for information on stormwater and related water resource topics.

Interactive map - stormwater complaints, facilities, projects and studies
Note: this link will open a new browser window
View map layers related to stormwater by clicking the layers icon iMap layers icon, expand the "Stormwater Services" group of layers and check those layers you want to view and query including drainage complaints, stormwater facilities, neighborhood drainage projects, and stormwater studies among other things. Click a symbol or area to display the data about it.

Annual reports to Ecology for the NPDES Municipal Stormwater Permit

Facility and permit compliance - King County performance measures
These performance measures track King County's compliance with its surface water management permit among other things.

Stormwater treatment and flow controls map - Post 1990 (17.5 Mb)
This map shows parcels in King County that were developed after 1990, when stormwater treatment controls and substantially more effective stormwater flow controls started to be required for new development. Thus the map presents a general graphic illustration of where modern stormwater controls are presumed to have been implemented and where development has occurred with no treatment control and little or no flow control. Note, the map is based on the year of latest development and does not represent actual stormwater control. In addition, the area presumed to have modern stormwater controls is likely smaller than what is shown because not all incorporated areas began requiring such controls when unincorporated King County did in 1990.

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Feb 12, 2019
External article, Seattle P-I
As snow turns to rain, flood warning issued in Seattle and other urban areas 

4Culture
Call for Artists: Rain Gardens X Public Art
We're looking for an artist to lead the way as we take on green stormwater infrastructure and rain garden design.

Nov. 14, 2018
External report, KING5 News
King County budget calls for investments into healthier salmon habitats 

May 9, 2018
King County sues oil companies for climate impacts  

Puget Sound Climate Preparedness Collaborative
Spring Convening: Climate Change & Extreme Precipitation in Puget Sound
May 11, 2018, 10 a.m. - 2 p.m. at Sea-Tac

Apr. 6, 2018
External article, CITYLAB
Seattle Thinks It Knows Rain. Climate Change Begs to Differ. 

Mar. 1, 2018
A major King County infrastructure project will protect the Duwamish River from stormwater pollution for the next century

Feb. 12, 2018
External article, WSU Insider
Salmon face double whammy from toxic stormwater

Oct. 18, 2017
External article, Seattle Times
Stormwater pollution in Puget Sound streams killing coho before they can spawn

Register for Wastewater & Stormwater Education Summit (external link)
February 28, 2017 at Brightwater Center near Bothell

Jan. 23, 2017
External editorial, The News Tribune
Sound advice: Don’t drip and drive 

Nov. 2, 2016
External article, American Rivers
Tackling stormwater challenges on the Green-Duwamish 

Surface water management infographic (952 KB pdf)
Preventing pollution, protecting our water

2016 WSU Innovators: stormwater, toxins and salmon (external video) 

May 6, 2016
May is ‘Puget Sound Starts Here’ month, stresses stormwater pollution prevention

Apr. 12, 2016
External article, Seattle Times
Stormwater detox: Pollution solutions are within reach

Nov. 5, 2015
External opinion, Seattle Times
Puget Sound recovery hinges on blocking polluted runoff