Stormwater services and information
King County, Washington
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.
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
King County precipitation map (5.1 Mb Acrobat pdf)
- 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.
2016 Stormwater Pollution Prevention Manual
Drainage maintenance resources
- Improving ditch maintenance for water quality
- Erosion and sediment control for construction sites
- Drainage maintenance standards - self assessment handbook (2005)
- Drainage system maintenance contractor list
- Drainage system design engineer list
Stormwater infrastructure
What are stormwater facilities?
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.
- 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
Background information
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 
Annual reports to Ecology for the NPDES Municipal Stormwater Permit
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.