Sea level and the seawall?

Given the proximity of Seattle to the Puget Sound and the known impacts of climate change on the rise of sea levels, the Elliott Bay Seawall Project fields many questions on this topic. It’s an issue that the City of Seattle takes seriously, whether on this project, or on others throughout the city. During design of the new Elliott Bay Seawall, SDOT has taken into account findings of localized scientific studies that project sea level over varying scenarios.

Sea level today and versus projected rise in 2100

What information is the City of Seattle relying on for sea level rise?
There is no universally agreed upon projection for sea level rise, but the City of Seattle is fortunate to have an internationally-recognized, interdisciplinary research resource in our backyard: the University of Washington. The City has adopted guidance on sea level rise from the University of Washington’s Climate Impacts Group as the standard for the city, and the Elliott Bay Seawall Project has been a pilot using this guidance tool. 

What are climate change experts projecting?
There are numerous factors to consider with sea level rise. Given the complexity of the issues, the Climate Impacts Group provided a range of sea level rise estimates, each with different likelihoods of occurrence. By the year 2100, the rise in sea levels predicted for Elliott Bay could be as little as six inches or as much as 50 inches*. Given the importance of the seawall, SDOT is using the highest predictions from the study.

What does sea level rise mean for designing and constructing a new seawall today?
If the highest predicted sea level rise were to occur, the current seawall elevation would be three feet above the new still water level (see graphic). Based on the projections taken into account by the City of Seattle, we do not anticipate it being necessary to build a higher structure to accommodate sea level rise over the next 100 years. With sea level in mind, the seawall is being designed to use drainage structures to reduce the risk of inundation by tidal backwater during extreme high water events, such as a storm surge at high tide.

*Source: Mote, Philip, Alexander Petersen, Spencer Reeder, Hugh Shipman, and Lara Whitely Binder. “Sea-level rise in the Coastal Waters of Washington State”, University of Washington Climate Impacts Group, January 2008. See: http://www.cses.washington.edu/db/pdf/moteetalslr579.pdf