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How mechanically placed sand on beaches moves and the impact

Torrey Pines State Beach

Torrey Pines State Beach in San Diego County, California. At Torrey Pines, where sand similar to the native grain size was used for a nourishment project in 2001, all the added sand washed offshore in just one storm, months after it was placed.

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A study by researchers at the Scripps Institution of Oceanography at the University of California, San Diego, is shedding light on how mechanically placed sand on San Diego County beaches moves, and its potential impacts. These findings could help planners develop beach nourishment projects that will reach their intended goals without causing unintended problems.

For the study, which is funded by the National Science Foundation (NSF) and the California Sea Grant program, researchers analyzed four beach nourishment projects in San Diego County to see how they fared in the years after the nourishment. The findings provide a better understanding of how nourishment sand moves in response to waves and currents and could provide insight for more effective beach nourishment projects in the future.

"There’s a lot that is not known about how sand moves," says Scripps postdoctorate Bonnie Ludka, who led the study. "If you put sand on a beach, it won’t just stay in one place. The question is, how long does it stay where you want it? And as it moves, where does it go?"

Among their findings, the researchers found that the size of the sand grains made a big difference in how far and fast the sand moved. At Torrey Pines beach, where sand similar to the native grain size was used for a nourishment project in 2001, all the added sand washed offshore in just one storm, months after it was placed. Coarser sand used at the other three projects in 2012 largely stayed on the upper beach, even through the El Niño winter of 2015-16, which brought exceptionally energetic waves to the coast.

Learn more about this research in the NSF News From the Field story To shore up California beaches, just add sand?. (Date image taken: December 2018; date originally posted to NSF Multimedia Gallery: July 20, 2018)

Credit: Katherine Leitzell, California Sea Grant
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