An earthquake that caused a dangerous tsunami that could inundate Bainbridge Island hasn’t happened in 16,000 years.

But BI residents who feel an earthquake are encouraged to drop, cover and hold on and then head to high ground immediately after the shaking stops, said Ethan Weller, tsunami program coordinator at Washington Emergency Management Division.

The division recently completed a Tsunami Maritime Response and Mitigation Strategy for BI’s Eagle Harbor.

It’s the first strategy that includes potential impacts from the nearby Seattle earthquake fault and is geared to help the region understand the tsunami risk, build resilience and figure out protective actions to take to enhance life safety and protect property.

Tsunamis are the result of a sudden, large-scale displacement of water. They can be caused by landslides under or into water, large submarine earthquakes, eruptions of coastal volcanoes, meteor impacts into a body of water, and some weather systems. While dangerous for all, such events are especially hazardous for those on boats.

“Although rare — only one such event has been recorded in the geologic record over the past 16,000 years — a large earthquake on the Seattle Fault has a high potential to generate a tsunami,” the report notes. “A tsunami could reach Eagle Harbor in less than 10 minutes, bringing strong currents and large-scale inundation along the shoreline and low-lying areas.”

The strategy also looks at potential impacts from a tsunami that could originate from the Cascadia Subduction Zone, noting tsunami waves could enter the Strait of Juan de Fuca and reach Eagle Harbor about 2 hours and 20 minutes later.

Developed in partnership with Washington Geological Survey, the city of BI and key stakeholders, the strategy offers a comprehensive framework to understand, mitigate and respond to the tsunami risks around Eagle Harbor. The strategy included engaging local expertise, facilitating workshops and fostering dialogue with stakeholders.

Anne LeSage, BI’s emergency management coordinator, said Bainbridge Prepares played a big role. “Emergency management is truly a community effort and we couldn’t achieve this milestone without the help and collaboration of everyone involved.”

Among its key efforts, the Bainbridge Prepares Flotilla mobilizes private vessels to support the community during emergencies, particularly when conventional transportation routes are disrupted. Work has already been done to improve its maritime infrastructure on the City Dock, especially when it comes to sea level rise, which will also help mitigate for tsunami damage.

“The work Bainbridge Island and its residents have already done in preparing for disasters is admirable – something other communities should look to and replicate,” Weller said.

It’s recommended BI continue its public education about the tsunami report so people understand the risks. For instance, the existing wildfire response and evacuation plans could serve as a template to address the evacuation challenges the community could face from a tsunami.

The strategy also calls for the city to shut down harbor infrastructure before a tsunami arrives. The City Dock was upgraded five years ago with electrical systems that automatically shut down the flow of electricity upon detection of a stray current or faulty wiring.

The lead marine officer for BI’s Police Department, Jonathan Bingham, outlined a potential idea for constructing a dock that may house maritime response assets for the city. Such an earthquake and tsunami-resistant structure would protect city assets, allowing for faster response times and better coordination with surrounding communities.

“Going through this process, we realized our marine assets, like all the marine infrastructure in Puget Sound, are vulnerable to a tsunami,” Bingham said. “It became clear how self-reliant we as a city would have to become in any circumstance where the city of Bainbridge Island could be cut off from all assistance. The idea would be to protect essential marine assets that will be critical in a post-earthquake/tsunami response.”

The report also lists potential funding sources, along with evacuation zones on BI, contact numbers regarding notification and various charts, such as the danger of various wave speeds.

Other recommendations call for the city to secure moorings of city-owned vessels, restrict traffic entering the marina by land and aid in traffic evacuation, pre-stage emergency equipment outside affected areas, install more tsunami evacuation route signs and more. Leaders rated how likely it was for those recommendations to happen.

Response

Feasible: Evacuate public, vehicles from waterfronts; personal flotation devices, vests offer a better chance of survival if you can’t get away; establish notification process with boat owners, liveaboards; activate incident commands at evacuation sites to reduce confusion, organize and calm evacuees; activate mutual aid system; coordinate with first-responders; pre-identify personnel to assist in rescue, survey and salvage efforts; and secure moorings of vessels.

Needs review: Remove or secure hazardous materials, stage emergency equipment outside affected area, Aid in traffic evacuation and restrict traffic entering waterfronts, move vessels out of port, and shut down port infrastructure, such as power and supply valves, before tsumani arrives.

Not feasible: Reposition boats within port, remove small vessels from water, remove buoyant assets out of and away from the water, and restrict boats from moving or entering port during tsumani.

Mitigation actions

Complete: Improve floatation portions of docks; incrase size and stability of dock piles; strengthen cleats and single-point moorings; movement along of docks along pilings; and increase flexibility of interconnected docks.

Feasible: Install tsunami signs and debris collection booms to project docks.

Needs review: reduce exposure to chemical facilities and storage; and acquire equipment to assist in response.

Not feasible: Move docks away from hazardous zones; widen harbor entrance to prevent jetting; construct floodgates; construct breakwaters farther away from harbor; fortify breakwaters; and deepen channels near hazardous zones.

This graphic represents the maximum current speeds above normal for a Seattle Fault Zone earthquake and tsunami at the mouth of Eagle Harbor on Bainbridge Island. The darker purple colors represent speeds of 9 knots and more above background current speeds.

Local contact numbers

Local evacuation zones