USGS finds 2009 – 2010 storms caused unprecedented coastal erosion
By Summit Voice
SUMMIT COUNTY — Winter shoreline erosion at San Francisco’s Ocean Beach of more than 180 feet during the El Niño storms of 2009 – 2010 may be a harbinger of future climate change impacts, geologists said after an extensive West Coast assessment covering the shoreline between San Diego and Seattle. The researchs looked at up to 13 years of seasonal beach survey data along 148 miles of coastline to track shoreline changes through a range of wave conditions.
“The stormy conditions of the 2009–10 El Niño winter eroded the beaches to often unprecedented levels at sites throughout California and vulnerable sites in the Pacific Northwest,” said Patrick Barnard, a coastal geologist with the United States Geological Survey in Santa Cruz, Calif.
In California, for example, winter wave energy was 20 percent above average for the years dating back to 1997, resulting in shoreline erosion that exceeded the average by 36 percent, Barnard and his colleagues found.
Getting a better understanding of how the 2009–10 conditions tore away and reshaped shorelines will help coastal experts better predict future changes that may be in store for the Pacific coast, the researchers said.
Barnard’s team published their findings in the July 9 issue of Geophysical Research Letters, a journal of the American Geophysical Union.
The Ocean Beach erosion resulted in the collapse of one lane of a major roadway and led to a $5 million emergency remediation project. In the Pacific Northwest, the regional impacts were moderate, but the southerly shift in storm tracks, typical of El Niño winters, resulted in severe local wave impacts to the north-of-harbor mouths and tidal inlets. For example, north of the entrance to Willapa Bay along the Washington coast, 345 ft of shoreline erosion during 2009 – 2010 destroyed a road.
The beach erosion observed throughout the U.S. West Coast during the 2009–10 El Niño is linked to the El Niño Modoki (‘pseudo’ El Niño) phenomenon, where the warmer sea surface temperature is focused in the central equatorial Pacific (as opposed to the eastern Pacific during a classic El Niño).
As a result of these conditions, the winter of 2009 -2010 was characterized by above-average wave energy and ocean water levels along much of the West Coast, conditions not seen since the previous major El Niño in 1997 -1998, which contributed to the observed patterns of beach and inlet erosion.
Many climate change models predict ever-warmer waters in the central Pacific, so El Niño Modoki is projected to become a more dominant climate signal. When combined with still higher sea levels expected due to global warming, and potentially even stronger winter storms, these factors are likely to contribute to increased rates of beach and bluff erosion along much of the U.S. West Coast, producing regional, large-scale coastal changes.