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Diver Down!

The Ballard Bridge Seismic Retrofit project reached a major milestone this month with the start of work in the water.  Although the contractor began construction in July, until now it’s all been on land or over the water rather than in Lake Washington Ship Canal itself. 

Portions of the Ballard Bridge structure, namely the bottom of the bridge columns and the base­s on which they rest, extend below the water level.   To encircle the columns with a concrete and steel jacket – and improve connections between each column and its base – the water next to the structure must be temporarily lowered.  That’s done by installing around each base a sealed box that extends from a few feet below the water level to slightly above the water then pumping the water out. 

Divers help to install those water-tight boxes, which is why you may see a red buoy on the water’s surface identifying the worker below.

Crews will work from the north shore to the south, using a customized barge as a working platform.  The Department of Ecology only allows this in-water work to take place between October 1st and April 15th when it will not interfere with fish migration between Puget Sound and Lake Washington. 

As in-water work takes place the contractor will also continue jacketing columns, reinforcing deck joints, adding steel diaphragms, and making other seismic retrofits.  The work is all being done from below, with no lane closures anticipated as of yet for vehicles crossing the bridge.  Meanwhile, with the recent completion of bridge lighting replacement work, commuters should find Ballard Bridge traffic more fluid than it’s been for some time.