Science Spotlight: Beach Erosion

by Ula Chrobak

The popular Seabright Beach in Santa Cruz attracts ocean lovers every summer with its sandy 600-foot-wide shore. But in winter, this broad playground withers to half its summer size.

This waxing and waning occurs all along the California coast. Beaches initially form where waves and currents move sand deposited by coastal streams. The shape of a shoreline and human structures like harbors and jetties influence where sand piles up. Strong winter waves eat up sediment and move it underwater, shrinking beaches. During the summer, the beaches grow back. About every four years, more vigorous El Niño storms scour away even more beach sand, but it returns in calmer years.

However, people also influence beach erosion. “We’ve trapped about one-fourth of all sand that would have come down in coastal California streams behind dams,” says coastal geologist Gary Griggs of UC Santa Cruz. Removing dams, an expensive process, can help restore beaches near the mouths of streams.

Sand mining, where machines remove sand for uses like sandblasting, can accelerate erosion. There’s just one such mine on U.S. shores: the Cemex Plant in Marina, Monterey County. This number may soon be zero: In March 2016, the California Coastal Commission called for the plant’s closure.

The gradual rise of the oceans, caused by climate change, may permanently erode our beaches. As sea level rises, beaches would naturally move inland. But coastal barriers like seawalls and roads now prevent this in many places. With nowhere to go, these trapped beaches may disappear.

“As it gets warmer, beach erosion may be like the El Niño years,” Griggs says. Over time, higher waters and hungrier waves will thin our beloved beaches.

Note from the editors: Science Spotlights are a joint project of the UCSC Science Communication Program and Hilltromper. This article was published in May 2017.