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Study: Coastal Erosion Makes Beach Sand

Erosion along the cliffs at Huntington Beach, Calif. is a never-ending problem for park space managers. Photo courtesy U.S. Army Corps of Engineers

Scientists have cracked one of the enduring geological mysteries of Southern California’s famed beaches: where the sand comes from.

Researchers had long assumed that coastal rivers washed the bulk of the naturally introduced sand to the beaches south of Los Angeles.

But two new research projects by scientists at the University of California, San Diego (UCSD) found that erosion of the area’s majestic sea cliffs is the primary source.

The results likely apply to other beaches around the world, at least to some degree.

“We were very surprised,” said UCSD engineering professor Scott Ashford, who used a portable laser imaging system to study coastal formations as part of one study.

“It’s telling us that we don’t understand the beach system as well as we think,” he said.

Ashford’s research, presented on Wednesday at a meeting of the American Shore and Beach Preservation Association, looked at six years worth of imaging data from the 50 miles of coast between Dana Point and La Jolla.

In the past, geologists had assumed that as much as 90 percent of beach sand in this sector had been introduced by deposits from coastal rivers.

But Ashford’s study showed that erosion of sea cliffs is responsible for an annual inflow of 80,000 to 100,000 cubic yards, or 67 percent, based on current estimates of total sediment input.

A separate UCSD graduate project using so-called “sand fingerprinting” techniques found similar results. Source: Reuters

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June 18, 2019, 6:38 pm PDT

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