The Coupeville ferry dock will be closed for a weekend next fall to make it safer in the event of the Big One.

Brian Mannion, communications manager for Washington State Ferries, said the exact date for the $1.9-million seismic retrofit project hasn’t been set, but it won’t be on a holiday or a high-volume weekend.

“We are upgrading the timber tower structure to better withstand earthquakes,” he said.

The project will create better support for the dock’s timber towers, also known as transfer span towers.

Workers will place four steel piles on each side to support the towers and concrete caps will be installed on top of the towers to support the head frame that houses the pulleys for the transfer span cables.

Once completed, the dock should be able to continue operating in the event of a 100-year seismic event. The work will make the structure safer for a 1,000-year event, Mannion said.

For the sake of comparison, the 2001 Nisqually earthquake is considered a 30-year event.

The weekend closure will allow workers to do the pile driving.

Mannion said no other disruption to the route is planned.

Because the work is in the water, the project was published in the Federal Register. The National Oceanic and Atmospheric Administration is requesting comments on the proposal. Noise from the project is identified as causing “level B” harassment of marine mammals.

The ferry runs between the terminal in Central Whidbey and Port Townsend and is especially popular with tourists. The ridership last year increased 8.9 percent to a total rider number of 787,391.

Of that number, 425,188 were passengers, according to the ferries division.