The result was a system of dunes that averaged 0.3 meter (1 foot) in height over the entire area, with elevations as high as 1 meter (3 feet) along the sides and the ocean-facing foredune ridge.
But while the new dunes looked promising, Emery said, “there had not really been a good opportunity to assess how well these dunes perform under some sort of disturbance event.”
That was until late December 2023, when storms battered the California coastline with waves as high as 10-20 feet in the Los Angeles area for several days, prompting coastal flood warnings and evacuations across the state. The waves on Dec. 31, 2023, according to Emery, were in the top 15 wave height days over the last 24 years.
Shortly after the storm passed, the research team conducted a survey to assess the new dunes’ response. The result? Waves that weren’t held back by the dune system — the ones that crashed on the flattened, groomed sections of the beach — ran an average of 13.6 meters (roughly 45 feet) farther up the beach toward the Pacific Coast Highway than waves that were intercepted by the restored foredune. The key, according to the scientists, was the added elevation, and the sandy mounds created by the foredune ridge.
“The young foredune acted as a natural barrier to this wave energy,” Emery explained, “by facilitating the seaward progression of higher elevations on the beach. That higher sand elevation prevented the wave runup from extending as far up the beach as it did in the groomed beach outside of the restoration project.” While more intense storms and wave action are anticipated as the world’s climate continues to warm, observing the effects of storms like the one in December 2023 is also “a good proxy” for the slower-onset effects of sea level rise, he added. Southern California in particular is predicted by some models to lose up to 24-75% of its sandy beaches by 2100 to sea level rise without intervention.