Stormwater services and information

Learn about stormwater and how to reduce pollution

Download infographic: How does stormwater impact us? — 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.

King County precipitation map - rainfall, snow and other precip

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

Commercial property requirements

Drainage maintenance resources

Stormwater infrastructure

What are stormwater facilities?

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

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

The Restore and Protect Project
Project to identify habitat stressors and recommend restoration and protection actions to improve freshwater quality and aquatic habitat in lowland Puget Sound streams.

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.