Extreme Waves and Coastal Erosion in the Pacific Northwest

The extreme wave climate of a Pacific Northwest littoral cell has been characterized by examining four long-term databases of measured wave parameters. Winter waves in the region average 3.0 m in significant wave height and 12 s in period, while summer waves average 1.5 m and 8 s, respectively. There is a distinct seasonality in monthly mean wave direction, with winter storm waves arriving from the southwest and the milder summer waves arriving from the northwest. Projections of the 50-year design wave height vary greatly, depending on the data source, ranging from 8.5 m to 12.2 m. A probabilistic model, combining these long-term measurements of waves with measurements of tides and local beach morphology, has been applied to a sub-region of the littoral cell. The model quantifies the susceptibility of coastal properties to erosion by predicting the frequency with which wave runup impacts either sea cliffs or sand dunes. The coastal erosion model is based on wave runup measurements obtained on high-energy dissipative beaches typical of the Pacific Northwest. Statistics o