New research reveals Cascadia tsunami would flood Navy piers, highways
BANGOR?— A powerful and incessant tsunami generated by?the next?Cascadia megaquake would crest Navy piers and wharves, flood critical state highways in Kitsap County and inundate other lowland areas of Puget Sound,?according to?new modeling released Tuesday by the state's Department of Natural Resources.?
In Hood Canal, the?9.0?quake in the Cascadia Subduction Zone?off Washington's coast would slosh water back and forth like in?a bathtub, topping the Navy's submarine piers?and pushing waves as high as 14 feet?onto the shore at Belfair.
In Sinclair Inlet, the waves would be smaller, the state says, but would still inundate the Puget Sound Naval Shipyard with about a foot of water and likely push more than 3 1/2 feet of water through Gorst, closing the highway. Other lowland areas of Puget Sound, particularly near the mouths of streams including Clear Creek in Silverdale and within Eagle Harbor on Bainbridge Island, would flood as well.?
"As we look at it, this is the most likely worst-case scenario," according to Corina Allen, the state's chief hazards geologist and a co-author of the study,?mapping and modeling project.?
New research at odds with prior analysis
The?new research by the state's Department of Natural Resources, in conjunction with federal agencies and the University of Washington,?is the most complete analysis of a?Cascadia subduction zone-caused tsunami?ever undertaken for the Puget Sound region.?It?also is at odds with prior research of the risk to?Kitsap's waterfront areas, including?its naval installations in Bremerton and at Bangor. For instance, a?2018?analysis conducted by the Navy at the completion of construction of a missile-loading?wharf concluded tsunamis from a Cascadia quake would have little consequence.????
"...?an earthquake outside of the Puget Sound fault system, e.g., one that occurs in the Cascadia Subduction Zone, is not expected to have an impact on (the wharf) as the tsunami will be largely attenuated by the time it reaches the facility," according to the safety assessment report completed for what's formally known as the Explosives Handling Wharf-2.?
That?report was released to activist Glen Milner of the anti-nuclear weapons group?Ground Zero Center for Nonviolent Action, which had sued the Navy over safety concerns at the new wharf and its location. The?Navy built the?new?wharf in the past decade?because it said an existing?wharf couldn't keep up with the loading and unloading of?ballistic missiles on the Navy's?eight Bangor-based Trident submarines. But both wharves, along with the nearby piers for both the nation's ballistic missile and Seawolf-class submarines, would see waves in excess of 20 feet, the new research shows.?
"There would be water that goes over the?top of them," Allen said of the Navy's waterfront structures.?
Though bluffs along Hood Canal would likely prevent a tsunami from going upland, the wave's energy would mean it would batter the Bangor waterfront multiple times.?
In a statement to the Kitsap Sun, Navy leaders and emergency planners at Naval Base Kitsap acknowledged the risks of a tsunami?and that it "could have significant negative impacts on most if not all Navy facilities within the NW Region."
Navy officials said the base maintains an emergency management plan and "routinely" conducts training with local, state and federal agencies "to better prepare for responding to various natural and man-made disasters." They noted the annual "Citadel Rumble" earthquake exercise will be held around Navy installations in the Pacific Northwest in July.?
The Navy views response to earthquakes and tsunamis as a "no-warning, reactive situation." Every effort would be made to distribute information, from the "Giant Voice" loud speakers on bases to Facebook and social media channels. An emergency operations center would be activated to?order evacuations and work through the catastrophe.?
"It has been determined that in the event of a tsunami, with limited or no real-time warning, vertical/high ground evacuation is the appropriate strategy," the Navy said in its statement to the Kitsap Sun.?
State officials do say that a Cascadia Subduction Zone earthquake's tsunami would afford around two hours before the waves would arrive in Kitsap. Other quakes, like those at the Seattle Fault, could see almost immediate waves. And the waves would continue to bounce around Puget Sound for up to 24 hours.???
How well the base's infrastructure withstands a tsunami is unclear. The Navy noted that buildings must be up to state and federal codes but that "there are no current building codes for potential tsunami impacts at our Kitsap installations."
Shipyard, highways at risk?
Meanwhile, most?of the Puget Sound Naval Shipyard and Navy base in Bremerton would be swamped with just under 1 foot of water, the modeling shows.?
The wave would move further along Sinclair Inlet toward Gorst, where it would flood both Highway 3 and Highway 166 with around 3 1/2 feet of water, likely taking out of service a critical transportation?link on and off the Kitsap Peninsula. The idea of such flooding has served to galvanize local leaders in supporting a megaproject to elevate the highway through Gorst in what would be a $500 millon project.?
The Hood Canal Bridge could also be affected, and transportation officials plan to try to?open its drawbridge if there is time to do so, according to WSDOT spokesman Doug Adamson. However, Adamson said the department is more worried about waves during storms.
"Storm waves are like breaking waves at the beach. They are very powerful and come from several directions, Adamson said.?"A tsunami wave is like a giant rolling wave that lifts up and then lowers you back down. Tsunami waves are typically more powerful when they run on shore and release all their energy."?
The state also used modeling to map where tsunami wave action would create the highest currents, in places where tighter passages create a funnel effect. In Kitsap, Gamble Bay and Rich Passage are expected to have 12-knot currents, creating havoc for vessels, including the Seattle-Bremerton ferries or any other boaters.?
Ferries, which could prove invaluable in emergencies, particularly when roads and bridges become impassable, would move "to the deepest possible body of water," according to the Washington State Ferries plan for a Cascadia event. If docked, ferries would evacuate passengers?and then move to the deepest possible body of water.
'If it's strong, if it's long, get gone'
Scientists, digging into layers of sediment in tidal zones, have found the last "megathrust"?Cascadia Subduction Zone earthquake occurred in 1700. One is likely to happen again, and it's just a question of when.??
Allen uses a simple adage when advising about?finding higher ground after an earthquake:?"If it's strong, if it's long, get gone."
One of the next reports from the state's geological survey is?mapping the other potentially devastating quake —?one involving the Seattle Fault. It expects to present?those findings to the public later this year.
To see the state's research, go to?dnr.wa.gov/tsunami.
This article has been updated with Corina Allen's new last name.