UC Santa Cruz

El Niño events affect the wave climate in the eastern north Pacific which can have a significant impact on the behavior of west coast beaches. In California, El Niño winters are characterized by anomalously higher and more southerly winter wave energy. This study seeks to quantify beach changes during the 2009/2010 El Niño Modoki from Point Conception to the Los Angeles-Long Beach Harbor, a 265-km portion of the Southern California Bight. Two LiDAR datasets from September of 2009 and September of 2010 were used to measure the change in position of the mean high water (MHW) and mean sea level (MSL) shorelines at over 5,000 transects spaced 50 m apart, as well as determine beach volume changes. Over the entire study area, during this one-year period, the MHW shoreline accreted by an average of 0.51 m while the mean beach elevation dropped by 0.05 m, but local beach response within the region was highly variable. Distinct cells of erosion and accretion throughout the region suggest that the observed beach changes are a result of a combination of factors including geography, shoreline orientation, beach morphology, artificial structures, sediment supply, and alongshore variations in wave energy and direction. Predictions of the increasing frequency and/or intensity of El Niño events under global warming conditions underscore the importance of understanding how coastlines will respond to changes in wave climate and may help in future coastal management.