New study predicts more retreat of barrier islands

By Linda Cicoira

A new study predicts a 50-percent increase in the retreat rate for Eastern Shore barrier islands within a century, with or without sea level rise. The move towards the mainland will lessen the islands protection of the coast from storm surge, waves, and flooding.

“These findings can be applied all over the world, but are particularly significant in the U.S., where houses are being built extremely close to the beach,” says lead author Dr. Giulio Mariotti, of Louisiana State University.

Study co-author, Dr. Christopher Hein of William & Mary’s Virginia Institute of Marine Science, wanted to know why “retreat has lagged behind the dramatic acceleration in global sea-level rise observed during the past five decades.”

Mariotti developed a model using data collected by Hein and others from the Virginia barrier islands. It shows the modern rate of barrier-island retreat isn’t controlled by sea-level rise, but by baseline rates of sea-level rise across the past few millennia.

“One reason previous models didn’t see the lag was because they assumed the geometry of the whole coastal tract—from the lower continental shelf to the upland boundary, including subaerial barriers, inlets and tidal channels—was frozen. However, the geometry can change and that’s what’s enabling this lag effect,” the scientists found.

The model predicts that retreat of the Virginia barrier islands will increase from its current rate of ~ 5 meters per year to almost 7 meters per year by 2100. If the rate of sea-level rise increases, barrier-island retreat may increase even more. It’s important to note these predictions do not account for any increase in the frequency or strength of coastal storms, which can also exacerbate barrier-island retreat.

Cedar Island’s annual rate of retreat is already rapid at 6.6 meters per year.

Hein noted that “because the Virginia Barrier Islands are almost entirely undeveloped, they are among the most dynamic in the world. This study shows what is likely in store for developed islands globally in the absence of ever-accelerating beach nourishment and hardening.”

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