Thousands of coastal communities, from the low-lying islands of the Maldives to the crowded shoreline of Miami, are watching the sea steadily claim ground. Pounding waves eat away at beaches, while rising seas push water farther inland, causing chronic flooding in heavily populated areas and threatening communities built for a shoreline that is no longer staying put.
In places such as Plum Island, north of Boston, homes have been lost despite years of efforts to protect the shoreline. Farther south, Boston itself faces a growing threat from coastal flooding and sea level rise. More than 40% of the city’s residents live in areas at risk of coastal flooding, and without additional protection, cumulative losses could exceed $54 billion between 2040 and 2090, according to the city and the U.S. Army Corps of Engineers.
Now AI is entering the fight to reduce and even reverse erosion. Coastal Assembly, a Boston-based company spun out of research at the Massachusetts Institute of Technology’s Self-Assembly Lab, has developed a system that uses AI to study how waves, currents and sand interact, then designs underwater structures intended to harness those forces to rebuild disappearing shorelines. Rather than trying to overpower the ocean, the technology uses the movement of the water itself to push and deposit sand where it is needed.
The approach has already been put to work in the Maldives, an archipelago of nearly 1,200 islands in the Indian Ocean where coastal erosion and rising seas pose an enormous threat. At one site, Coastal Assembly says its system helped generate about 90 feet of new beach within six months, without pumping or trucking additional sand to the shoreline. The sand was already there, moving through the water. The challenge was figuring out how to make more of it stay.
Coastal Assembly is monitoring shoreline behavior at nearly 900 coastal sites. The company also has work planned in the Bahamas, Boston Harbor and Miami, locations that could show whether results from the Maldives can be replicated under different conditions. Boston’s colder waters, for example, bear little resemblance to those surrounding a tropical island resort, while Miami presents the added complexity of an intensely developed coastline where billions of dollars in real estate and infrastructure sit close to the water.
Miami Beach has spent hundreds of millions of dollars on pumps, larger drainage pipes, elevated roads and other infrastructure designed to keep water at bay. But the region remains vulnerable to king tides and intense rainfall, particularly when rain falls faster than the stormwater system can move it away. South Florida’s porous limestone and high groundwater make the job even more difficult.
Coastal Assembly’s approach would not stop sea-level rise or eliminate flooding caused by rising groundwater and overwhelmed drainage, but it could create a buffer to reduce erosion and lessen the impact of waves and storm surge.
Coastal Assembly analyzes years of satellite imagery along with information about waves, currents, tides and bathymetry, the underwater topography of the seafloor. AI helps process that information to build a picture of how a particular shoreline has changed, where erosion is occurring and how sand moves through the area.
That analysis guides the physical design. Coastal Assembly creates engineered reef structures for the conditions at a particular coastline. Their shape, spacing, location and angle relative to incoming waves can be adjusted according to the movement of water and sediment at the site. The structures can be fabricated locally, lowered onto the seabed and left there.
Once underwater, the structures change the way waves, currents and sediment interact. They reduce erosive wave energy while allowing currents carrying suspended sand to continue moving. The goal is to alter those forces just enough that more of the sand settles in targeted areas rather than being swept away. Over time, the accumulating sediment can expand the shoreline.
The concept grew out of about a decade of research at MIT, where researchers studied waves in tanks and used computer simulations to better understand how water transports sediment. Instead of concentrating solely on how to stop waves from reaching shore, researchers examined whether the energy already moving through coastal waters could be redirected to help build land.
The Maldives became an important testing ground. The nation’s islands are particularly vulnerable because much of the country sits only slightly above sea level, and communities and resorts have long relied on measures such as dredging, land reclamation and shoreline defenses to protect valuable land. MIT researchers began experimenting there through the Growing Islands project, studying whether structures placed underwater could influence currents and encourage sand to accumulate.
At the JW Marriott Maldives Resort & Spa, Coastal Assembly installed 54 structures in a hexagonal arrangement along roughly 30 meters of shoreline. The company says the installation helped extend the beach about 90 feet toward the ocean within six months without bringing in additional sand. Satellite observations later showed that sand continued to accumulate after the initial study period.
The structures also began changing what was happening beneath the water. Coral colonized portions of them, while fish and other marine life appeared around the installation. That raises the possibility that infrastructure designed to protect a shoreline could also provide habitat.
Traditional methods of combating erosion remain the go-to approaches, but they have limitations. Seawalls can protect property directly behind them but may alter wave behavior and sediment movement. Beach nourishment can quickly restore a disappearing beach, but the replacement sand can eventually wash away, as has occurred on Plum Island.
A 2018 study published in Scientific Reports that examined more than three decades of satellite imagery found that about 24% of the world’s sandy and gravel shorelines were eroding at rates greater than half a meter per year. Rising seas, changing wave patterns, disrupted sediment supplies and extensive coastal development are adding pressure to shorelines in many parts of the world.
