Extreme coastal total water levels (TWLs) that result in flooding are the result of the complex interactions between multiple oceanographic, hydrological, geological, and meteorological forcings that act over a wide range of scales (i.e., astronomical tide, wave set-up, wind set-up, large-scale storm surge, precipitation, fluvial discharges, monthly mean sea level, vertical land motions, etc.). Coastal flooding that occurs during extreme TWLs can significantly impact communities and infrastructure resulting in substantial economic losses, even threatening human lives. Climate change may cause an increase in extreme coastal water level events driven by rising sea levels and changing patterns of storminess. An improved understanding of the physical processes during extreme coastal water level events will ultimately lead to an improved ability to predict the present day and future hazards faced by coastal communities. This information, in turn, provides the foundation for building more resilient coastal communities.
The primary objectives of this project were to 1) assess the relative contributions of the various processes that drive extreme coastal TWLs; 2) quantify the impact of a range of climate change scenarios on each of the drivers and on the resulting combined TWLs; and 3) assess the impact of present-day and forecasted future coastal flooding events on infrastructure in several communities within the Treaty of Olympia area.
This report is organized as follows: Sections 1, 2, and 3 highlight the primary results of each project objective listed above. Section 3 ends with a specific discussion of climate change impacts and some possible recommendations for adaptation. The details of the original modeling approaches specifically developed for this study have been published in the peer-reviewed literature and are given in Appendices A and B. Finally, the overarching results of a completed outer coast vulnerability assessment (Chapter 5 of Dalton et al., 2016) are reproduced in Appendix C.