When the Ballard dam, spillway and locks were built, the future water levels were established, forever. Full in the Summer, lower in the Winter. The exact pattern is "written in stone".
Available, in paper form, at the Ballard Lock office.

The lower level minimizes shore erosion during heavier Winter weather, and allows better inspections and repairs.

Note the "bathtub rings" on the concrete posts under the arboretum interchange.

The present bridges are designed to handle the water level variations. Bridges shift laterally as well as vertically.

Rail design will include sliding switch points to accommodate variations in level and alignment.

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The Hood Canal bridge is "much more exciting". Tide plus weather plus salt. They wear out. I believe that the third edition is under construction.

Maybe, eventually, WSDOT may build two pair of approaches. This will allow bridge replacement without shutting down traffic.