Damaging coastal storm conditions have become twice as frequent at a New Jersey Beach since 1979 — Phys.org

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Add as preferred source Storm conditions capable of causing major coastal erosion at New Jersey's North Beach on Sandy Hook are occurring about twice as often as they did in 1979, according to Rutgers researchers. The finding offers new evidence that storm impacts are becoming more frequent along the Mid-Atlantic coast.

The study, published in the journal Earth's Future , combined images of sediment beneath the beach with water-level measurements, wave records and computer modeling. Researchers used what they described as buried layers to identify the conditions associated with severe erosion and determine how often they have occurred over more than four decades.

"Most people think of beaches as constantly changing landscapes where evidence of past storms quickly disappears," said Kenneth Miller, a Board of Governors Professor in the Department of Earth and Planetary Sciences at the Rutgers School of Arts and Sciences and a co-author of the study. "What we've shown is that under the right conditions, beaches actually preserve a detailed geological memory of past storms. Those buried surfaces allow us to reconstruct how coastal storm impacts have changed through time."

The research began in 2019 when study co-authors W. John Schmelz and J.N. Stanley were graduate students working with Miller. Given access to older ground-penetrating radar equipment donated to the department, they chose North Beach because it had been building outward into the Atlantic Ocean for about 15 to 20 years.

The site also had been monitored since 2008 through work led by Norbert Psuty, a Rutgers professor emeritus and coastal geomorphologist. Its location within Gateway National Recreation Area helped protect it from construction and beach maintenance.

The researchers initially set out to image layers beneath the beach. What they found raised a larger question about whether North Beach had preserved evidence of past storms.

"Even initially, the data we collected were spectacular," said Schmelz, now an assistant research professor in the Department of Earth and Planetary Sciences. "The ground-penetrating radar clearly showed both the growth of the beach and the sedimentary structures left by erosion events that periodically interrupted that growth."

The team pushed ground-penetrating radar equipment along the sand to create images beneath the beach. The device sends electromagnetic pulses into the ground and records signals reflected by changes between sediment layers.

Unlike most beaches along the Jersey Shore and the broader Mid-Atlantic coast, North Beach has been expanding, Schmelz said. Sand traveling northward accumulates where the shoreline curves around Sandy Hook. During the past two decades, the beach has expanded seaward by about 1,300 feet, or 400 meters, averaging roughly 66 feet, or about 20 meters, a year.

That unusual growth made North Beach well suited for the study. As new sand accumulated, it buried surfaces created by earlier erosion, preserving evidence of tropical cyclones and nor'easters.

Researchers identified 20 buried surfaces associated with major erosion events between 2009 and 2019. Using highly accurate GPS measurements, they compared the locations of those surfaces with the beach-monitoring surveys led by Psuty to estimate when each one formed. They then dug trenches and collected sediment samples to confirm the radar images represented storm deposits.

Although the beach generally grew wider over months and years, storms temporarily reversed that trend, sometimes eroding dozens of feet, or tens of meters, of beach in just hours or days. Over time, however, expansion outpaced those losses.

The erosion surfaces were often marked by coarse sand topped by thin layers of dark, heavy minerals. One especially thick layer associated with 2012's Superstorm Sandy contained coarse sand, shells and pebbles, evidence of the storm's energy.

To identify the conditions that produced this erosion, the team used XBeach, computer software that models how waves and water levels affect coastlines. Researchers ran more than 1,000 simulations and compared the results with measurements from a Sandy Hook tide gauge, offshore wave data and observed changes in the beach.

The analysis established the approximate combination of wave height and water level linked to significant erosion at North Beach. When water levels are high, powerful waves can reach farther up the beach and remove more sand. Using records dating to 1979, the researchers calculated how often storms crossed that threshold.

"Our results suggest that storms capable of causing significant coastal erosion at this site are occurring about twice as frequently now as they did in 1979," Schmelz said.

The finding does not mean the total number of storms has doubled, he said. It means the combination of high water and large waves capable of causing major erosion at North Beach now occurs about twice as often.

The precise threshold applies only to North Beach because every coastline has its own shape, sediment supply and exposure to waves. Still, Miller said, the study has broader regional significance. Most of the major events recorded at North Beach were nor'easters and tropical cyclones that affected wide sections of the Mid-Atlantic coast. The site therefore reflects a regional storm climate, even though the amount of erosion may vary from one beach to another.

On Jan. 10, 2024, the researchers had an opportunity to test their findings during a storm forecast to produce waves and water levels above the threshold.

The storm lowered the beach elevation by about 8 inches, or 21 centimeters, and caused the beach face, the sloping front of the beach, to retreat roughly 6–8 feet, or about 2–2.5 meters. A trench...

Damaging coastal storm conditions have become twice as frequent at a New Jersey Beach since 1979 — Phys.org | AIPROPX