WSG News Blog

King Tides Provide a Window into the Future of Washington Shorelines

From the autumn 2019 Sea Star print newsletter

By Andrew Chin, WSG Science Communications Fellow

On a quiet day in Oak Harbor last January, the surface of Puget Sound was as smooth as glass. The water gently reflected the winter sun as 45 pairs of eyes watched the tide slowly overtake the shoreline, reaching the line of driftwood that had been thrown ashore in storms past and the grass lawn of Flinstone Park. This encroachment was a king tide: the edge of the sea was at about the highest point it would reach all year. It was a natural, innocuous event—but as the group watched the water, they grappled with the fact that, as the seas rise, these high-water levels will become more and more common, raising the risk of floods that could damage nearby property.

The gathering was organized by Bridget Trosin, coastal policy specialist at Washington Sea Grant. Trosin heads the Washington King Tides Project, which monitors the extent of king tide flooding around coastal Washington. She also leads king tide viewing parties like the one in Oak Harbor to help people get a first-hand look at what sea-level rise might mean for their coastal Washington communities. “We invite the public down to the waterfront to talk about king tides and sea-level projections,” Trosin says. The projections come from the Washington Coastal Resilience Project (WCRP)’s sea-level rise report, the result of a collaboration between several groups, including Washington Sea Grant and the UW Climate Impacts Group. The projection for Oak Harbor is a 50 percent chance that seas will rise by nearly a foot by 2050. This means that today’s king tides could one day become the everyday tides across our region.

The ebb and flow of the ocean are a familiar phenomenon to those living in coastal communities, but the extent of both high and low tides varies throughout the year. The term king tide, Trosin explains, describes the most extreme high tides in any given year. Caused by the alignment of the sun, moon and Earth (called syzygy) or when the sun is closest to the Earth (a point called perihelion), these series of unusual tides occur regularly four to five times a year, usually in the winter.

While king tides are a natural phenomenon, the unusually high water levels they bring help scientists, planners and decision-makers visualize how sea-level rise will affect communities. The WCRP sea-level rise projections account for local variability within coastal Washington’s complex landscape. This variability can be due to tectonic plate movement, the shape of the seafloor, tides, weather, and human modifications to the shoreline. However, these projections can be challenging to translate to the local infrastructure and ecosystems.

Meredith Penny, a long-range county planner with Island County, is one of the people using these projections in local communities. She explained that Island County is especially vulnerable because of the high proportion of shoreline property across its two major islands, Camano and Whidbey. “We have a lot of private owners, historic beach communities, canal communities and a lot of coastal bluffs,” she explained. “Many of these properties are already being flooded by regular king tides. So, people are coming to the county and asking, ‘What can the county do? What can we do?’”

Island County hopes to use WCRP sea-level rise projections to inform future development. “We expect to use these projections as guidance and information for property owners during the shoreline permitting process by combining the projections with the expected lifetimes on other property investments, such as septic tanks or shoreline armoring,” says Penny. “This allows property owners to make their own decisions about risk tolerance.”

The long-term vision for sea-level rise adaptation for Island County includes developing best management practices, assessing risk and reaching out to the most vulnerable communities. It also includes monitoring sea-level rise thresholds in order to initiate discussions about further actions. “Some projects work better on a community-wide scale versus property-by-property, so we’re also hoping to develop a framework for community hazard planning—each community can outline flooding tolerance thresholds for themselves, and the county can help provide guidance for different projects, such as community septic systems, dyke repair, beach nourishment or restoration,” says Penny.

Trosin is looking forward to more viewing parties around coastal Washington in the winter. Tracking the impacts on every shoreline in Washington during a king tide is a tall order. To assist with this goal, Trosin and collaborators from the Washington Department of Natural Resources, U.S. Geologic Survey, Snohomish County and others have developed a tool for the public: The MyCoast app, which enables people to upload and share photos of king tides that they witness. The images help scientists identify the effects of sea-level rise around coastal Washington. Within only a few months of the new tool’s launch in November 2018, there were 56 reports with over 110 photos uploaded from all regions of Washington.

This year’s king tides will be the perfect opportunity to snap photos that contribute to the MyCoast database.

Share your king tide photos by downloading the iPhone/Android MyCoast app.