Stormwater services and information
King County, Washington
Learn about stormwater and how to reduce pollution
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.
- Stormwater runoff pollution and how to reduce it
- Stormwater science
- Stormwater educational videos
- Stormwater glossary of terms and abbreviations
- Homeowner requirements in unincorporated King County
- Clean carwash options (external link) - help reduce water pollution in streams, lakes and Puget Sound.
- Rain barrel information and sources for the Pacific Northwest
- How to build a rain garden
Rain gardens filter pollution from stormwater and support unusual native plants:
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.
- the Integrated Pond - architectural design tips for building beautiful and usable stormwater facilities
- Design Manual training
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.
Drainage maintenance resources
- Erosion and sediment control for construction sites
- Drainage maintenance standards - self assessment handbook (2005)
- Drainage system maintenance contractor list
- Drainage system design engineer list
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.
- Combined sewer overflow real-time map- Seattle area
- Combined Sewer Overflow Control - Wastewater Treatment Division
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.
- Green River Stormwater Retrofit Planning Project
- Model Low Impact Development Strategies for Big Box Retail Stores
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 , 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.
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.
Feb 12, 2019
External article, Seattle P-I
As snow turns to rain, flood warning issued in Seattle and other urban areas
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
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.
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)
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