AI-powered reefs may help beaches rebuild as erosion worsens

At one Maldives resort, the MIT-born system added 90 feet of beach without imported sand as storm erosion threatens the Outer Banks and Southern California.

An AI-guided field of underwater reef structures helped the ocean build about 90 feet of new beach in six months at a Maldives resort, offering an unusual possible weapon against coastal erosion.

Coastal Assembly, an MIT-born company, says it placed 54 marine-concrete structures near the JW Marriott Maldives Hotel in a hexagonal pattern about 30 meters long. The new beach was built with sand already moving through the water, the company said. No sand was dredged, pumped or trucked in.

A late-September nor’easter worsened erosion around homes in Rodanthe and Buxton and caused significant impacts across Hatteras Island, according to Cape Hatteras National Seashore.

In Southern California, swells from former Hurricane Marie stripped beaches, damaged seawalls and exposed infrastructure. A Kelvin wave could temporarily elevate coastal water levels by about a foot, increasing the risk when high tides and winter storms arrive.

“Beaches are our primary natural defense to backshore erosion and coastal flooding,” coastal geomorphologist Adam Young told AccuWeather. "Without that sand buffer, waves have less distance to lose energy before reaching roads, homes and bluffs. The first storm may strip all the sand off a beach, and without the natural sand buffer, the next storm can deliver a stronger punch.”

The conventional fixes are expensive: pump new sand onto the beach, armor the shoreline with rock or concrete or build structures meant to trap sediment. In Dare County, North Carolina, officials are pursuing more beach nourishment and repairs to a terminal groin at Buxton. In Carlsbad, California, officials declared a local emergency to speed work on a protective rock barrier.

Coastal Assembly is trying to work with the ocean rather than hold it back. The company grew from MIT’s Self-Assembly Lab, where researchers made waves in tanks and tested how different underwater shapes changed the way water and sand moved.

Its software combines years of satellite imagery with wave and current records, tide and swell data, and the shape of the seafloor. It identifies where erosion is happening the fastest, projects how a shoreline may change and determines the size, spacing and angle of submerged engineered reef structures for that particular beach. Essentially, the AI helps decide where to put the structures.

Once the structures are on the seabed, waves hit them and create churning water that moves sand differently. The reeflike arrangement is designed to break up erosive wave energy while allowing currents to keep flowing through it. In the right configuration, sand that might have kept moving away from shore instead accumulates near the beach. The structures need no pumps, pipes or power once installed, and Coastal Assembly says coral and fish have begun colonizing the Maldives installation.

The technology is different from a traditional groin — a rock or concrete wall that juts out from the beach into the ocean to stop sand from drifting along the shore. Groins can build up sand on one side of the wall, but they can also leave beaches farther down the coast with less sand and more erosion. A recent USGS study documented that pattern at several Southern California beaches.

Any U.S. installation of the new underwater reef structures would need years of monitoring to show it can rebuild one beach without accelerating erosion nearby. If it can, the technology could give coastal communities another option besides repeatedly hauling in sand or building harder barriers to protect homes, roads and ecosystems.

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