Rising sea levels are a direct result of climate change, due primarily to water expansion from warmer ocean temperatures and increased melting of glaciers and ice sheets. Local factors, including changes in land elevation, also affect how much sea level rises in a specific location.
Throughout King County, higher King Tides and storm surge are already impacting shoreline homes, businesses, infrastructure, and habitat. Preparing for and adapting to sea level rise is necessary to minimize the negative economic and environmental impacts of sea level rise, support the natural processes needed to maintain shoreline habitat, and reduce risks to public health and safety.
What's at stake
Sea level in King County is projected to rise approximately one foot by the 2050s and two to three feet by 2100, relative to water levels in 2000, unless greenhouse gas emissions drastically decrease.14 Both lower and higher amounts of sea level rise are possible, depending on different GHG emissions scenarios, with up to five feet of sea level rise considered a plausible upper estimate for 2100.
Rising sea levels can permanently flood low-lying areas, cause more frequent coastal flooding in places that rarely experience it today, increase shoreline and bluff erosion, impact habitat, contaminate coastal aquifers, corrode materials exposed to more saltwater, and increase damage to shoreline infrastructure. The severity of these impacts will vary by location depending on how quickly land rises as you move away from the shoreline, exposure to waves, and proximity of infrastructure to the water, for example. Hard armoring of the shoreline (i.e., use of bulkheads and sea walls) is making it difficult to maintain natural processes like erosion (especially from feeder bluffs) that provide the sediment needed for local beaches and shoreline habitat to keep pace with sea level rise.
A better outcome
King County envisions a climate-resilient marine shoreline where people can live and work safely in proximity to the marine shoreline; where risks associated with sea level rise decrease over time; where public and private shoreline infrastructure is built in the right places and designed to account for sea level rise; and where beach and marine shoreline habitats can adapt and move naturally in response to sea level rise, ensuring that tribes can meaningfully exercise treaty rights to harvest species that depend on healthy marine shorelines.
What we've done to get here
- Protected the vital functions of the Georgetown Wet Weather Treatment station in the Duwamish Valley by building the facility for two feet of sea level rise, launched a study looking at the impacts of sea level rise on groundwater in the Valley, and deepened local partnerships to coordinate planning for sea level rise in the lower Duwamish.
- Established areas on Vashon-Maury Island where construction must account for sea level rise.
- Worked with State Parks to redesign Saltwater State Park amenities associated with the McSorley Creek Shoreline and Estuary Restoration project to account for sea level rise.
- Identified sea level rise risks and adaptation actions for King County-owned infrastructure.
- Partnered with the U.S. Geological Survey to model sea level rise impacts on coastal flooding.
- Initiated a coastal hazard vulnerability study for Vashon-Maury Island to look at risks associated with both sea level rise and shoreline landslides.