A seawall (also written as sea wall) is a form of hard and strong coastal defense constructed on the inland part of a coast to reduce the effects of strong waves.
Seawalls may be constructed from a variety of materials: most commonly, reinforced concrete, boulders, steel, or gabions. Additional seawall construction materials may include vinyl, wood, aluminum and fiberglass composite.
The Alaskan Way Seawall is a seawall which runs for 7,000 feet along the Elliott Bay waterfront southwest of downtown Seattle from Bay Street to S. Washington Street. It was built to provide level access to Seattle’s piers and supports the Alaskan Way Viaduct and Alaskan Way itself, which is a surface street. Completed in 1934, the seawall was built on top of wood piling which has significantly deteriorated due to wood eating gribbles. In addition, everything behind the seawall from Alaskan Way to Western Avenue is built on top of fill, making for a very dangerous situation should a large earthquake occur. The viaduct itself is particularly at risk; experts give a 1-in-20 chance that it could be shut down by an earthquake within the next decade, and so plans are underway to replace both seawall and viaduct. The seawall replacement is estimated to cost $800 million US dollars.