The impact of the 2009-10 El Niño on West Coast beaches
Abstract
Long-term monitoring programs at a series of beaches in California, Oregon and Washington were used to evaluate beach evolution associated with the El Niño winter of 2009-10, and to relate the observed coastal change to past winters, including the last major El Niño in 1997-98. At the California study sites, analysis of Lidar (1997-98) and semi-annual or greater high-resolution beach and nearshore surveys (2004-10) shows that coastal change during the winter of 2009-10 broadly rivals that in 1997-98, and that the 2009-10 winter storms collectively forced the most beach erosion since high-resolution monitoring began in 2004. Along the Oregon and Washington coasts, many beaches exhibited classic El Niño shoreline responses, with significant shoreline retreat occurring immediately north of jetties and tidal inlets as well as the southern ends of pocket beaches and littoral cells. In Washington in particular, these areas eroded rapidly during the winter of 2009-10, comparable to the response seen in the El Niño winter of 1997-98. Wave buoy data from buoys in California and Washington that captured both the 1997-98 and 2009-10 El Niño show that the two events were comparable in wave energy as measured by the mean wave year (1 July- 30 June) energy flux (Fig. 1). The increased wave energy in 2009-10 had significant impacts on coastal infrastructure throughout the region; for example, in San Francisco the Great Highway was severely undercut by wave action, resulting in a $5 million emergency remediation project. In Washington, approximately 195 m of road was eroded along the entrance to Willapa Bay and southern Grayland Plains. While the impacts of the 2009-10 winter were substantial, impacts on the coast were moderated by an unusually mild wave climate in 2008-9 (Fig. 1), which left beaches more accreted prior to the severe wave season of 2009-10. As climate change accelerates sea level rise and potentially increases the magnitude and frequency of storms in mid-latitudes, the beach erosion seen in 2009-10 will become less unusual, making it critical that we continue to monitor beach morphology to provide data for coastal managers and to improve our understanding of beach dynamics. Figure 1. Yearly mean wave energy flux relative to the mean since each buoy’s deployment offshore of Washington (Grays Harbor), San Francisco (Point Reyes), and Santa Barbara (Harvest, Anacapa Passage).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMEP21D..05B
- Keywords:
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- 3020 MARINE GEOLOGY AND GEOPHYSICS / Littoral processes;
- 4215 OCEANOGRAPHY: GENERAL / Climate and interannual variability;
- 4217 OCEANOGRAPHY: GENERAL / Coastal processes;
- 4522 OCEANOGRAPHY: PHYSICAL / ENSO