Photo by MIT Self-Assembly Lab
Over the past 100 years, sea levels have risen between 6 and 8 eight inches globally, with half of the increase occurring over the last three decades, according to NASA. And with about 40 percent of the world’s population living in coastal areas, those rising tides will continually threaten peoples’ homes, say researchers at the Massachusetts Institute of Technology's Self-Assembly Lab.
Static physical barriers and ongoing coastal dredging simply won't solve the problem, the scientists say. So instead, their goal is to “work with the forces of nature, harnessing them to build rather than destroy.”
Along with the sustainability firm Invena, the scientists have come up with a system of underwater structures that harness the energy of ocean waves to redistribute sand. Eventually, they hope these mounds will grow into new islands or help rebuild coastlines as sea levels continue to rise.
Since 2017, the researchers have tested out their theory in the lab. They built two wave tanks to see how their concept would hold up in a variety of wave conditions, sand behaviors, and geometries. In the larger tank, a robot pumps waves at various frequencies and intensities to see how each will impact the dispersion of sand. In the smaller tank, the researchers test out different sand formations, ripples, dunes, and other structures.
Within minutes, but sometimes in mere seconds, the scientists can generate sand patterns that align with real-world conditions. In this case, they wanted to match up the tanks to two predominant seasons in the Maldives so they could begin deploying their structures in the real world. They eventually used their best test setups in real-world experiments in February and November 2019.
In the first field experiment, the team installed two bladders underwater. These bags are about 3 meters wide, sewn with heavy duty canvas, and filled with sand. The researchers folded them up and shipped them to the Maldives in suitcases, where they were placed in the water as artificial reefs. When a wave passes over the bladders, they create an adjacent lump of sand in front of them (on the side closer to the beach), which becomes larger over time.
About 6 months later, on a second trip to the Maldives, the researchers installed their second field experiment. Through satellite imagery, they’ve been collecting data on the impact of their work, surveying how the bladders have helped to build up new sections of sand. Since that installation, the scientists have seen about 0.5 meters of new sand accumulation over a 20-by-30 meter area since November.
“These are early, yet promising, results and are part of a much longer term project where we aim to continue to test these approaches in the Maldives and various other locations around the world,” the scientists say. “Our goal is to create a system of submersible structures that can adapt to the dynamic weather conditions to naturally grow and rebuild our coastlines.”
Eventually, with more tests, the scientists would like to scale their approach to other locations around the world and rebuild heavily populated coastlines, like New York City, as well as the most vulnerable island nations. The work may very well keep the world afloat.