Tsunami hazard presentation reveals Oak Bay’s vulnerability – Saanich News


A presentation on tsunami hazard in Oak Bay didn’t rock the boat much as the council considered the local impact of the scenarios presented.

David Forde of Associated Engineering presented to the board, meeting in committee of the whole on May 16, a summary of the CRD’s 2020 tsunami and flood risk assessment, which analyzed 11 scenarios and data from the Washington Geological Survey and from the Oregon Department of Geology and Minerals. Industry.

Emphasis was placed on three tsunami scenarios: the Cascadia L1 subduction zone (every 2,500 years), the northern segment of the Cascadia subduction zone (every 500 to 600 years), and the Devil’s Fault Mountain (every 2,000 years).

Mayor Kevin Murdoch, who said the Devil’s Mountain Fault has the best name of the three, asked how long it would take to reach Oak Bay. Forde said this scenario would only take five to 10 minutes to reach Oak Bay from across the Strait of Juan de Fuca, while the Cascadia subduction zone scenarios would take more than an hour to arrive from their sources along the Washington coast.

“The Cascadia subduction zone is a much better understood seismic hazard, as well as a tsunami source, compared to the Devil’s Mountain fault,” Forde noted.

Murdoch pointed out that the Devil’s Mountain scenario is only expected once every 2,000 years, “just to put that into perspective.”

In the case of flooding, Forde said it helps that Oak Bay is a relatively high municipality, above the six-meter contour.

The area most susceptible to flooding is what Forde called the McNeill Avenue Corridor, which runs approximately 1.25 km between McNeill Bay and the Oak Bay Marina.

“The long-standing (regional) plan was based on a four-meter safety elevation,” said Saanich Deputy Fire Chief Frank Macdonald, adding that it is now the district’s responsibility to educate the public about the risks. of flooding.

Macdonald said a digital advisory letter will be sent to residents living in what the presentation revealed to be tsunami and flood risk areas.

An educational brochure and an interactive CRD risk map are also being developed.

Eileen Grant, Oak Bay Emergency Program Manager, explained the nature of tsunamis and the local protocol for them.

“They’re quite unique and they’re usually related to earthquakes,” she said. “It doesn’t just happen because the ocean moves in a unique way.”

Grant said an earthquake capable of causing a tsunami could shake the area enough to knock people down. In this case, an evacuation order would already be announced and residents would want to move to safe areas, which include most of Oak Bay, in addition to the McNeill Avenue corridor. Residents of beachfront properties should likely head to higher ground, she added.

“The most important thing is that we don’t want people moving unless they have to,” Grant said, noting the traffic and chaos it would cause.

In her 10 years as program manager, she said the only protocol change was that residents now had to plan for a seven-day evacuation period, rather than the previous three-day plan.

“We need people to understand what could happen and what to do in these circumstances,” Grant said, adding that it’s important for those living in high-risk areas to have a kit to hand. take out ready at their doorstep.

“We hope to educate them so they know exactly what to do and if they are in a yellow or green zone.”

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