Solutions to help replenish beach sand

MIT and Invena are testing submerged structures to collect sand, protect the islands of the Maldives, and even create new islands.

The third field experiment from the MIT and Invena Self-Assembly Lab, taking place in late 2021, uses lightweight, low-cost structures that can be deployed quickly and easily customized. (Video: MIT/Invena Self-Assembly Lab).

Around the world, coastlines are under threat from rising sea levels and increasingly powerful storms. Many island nations and coastal cities are taking steps to save themselves, from building breakwaters to dredging sand from the seabed and pumping it onto beaches. But these interventions can be expensive, difficult to maintain, and harmful to ecosystems.

In the Maldives , a nation of about 1,200 islands that form a 900km-long chain in the Indian Ocean, the Massachusetts Institute of Technology (MIT) Self-Assembly Lab and Maldives-based Invena are working on a more natural solution. Using submerged structures , the team harnesses the forces of the ocean to cause sand to accumulate in carefully selected locations to protect the Maldives, potentially even creating new islands.

The team first tested the idea in MIT's wave tank in Cambridge, Massachusetts. To determine the ideal orientation and shape of the submerged structures, they studied information about ocean waves and currents from sensors in the Maldives, tide and weather data, thousands of computer simulations, and a machine learning model trained on satellite imagery to predict how sand would move.

Since 2019, MIT and Invena have been conducting field trials in the Maldives, where the coastlines of most of the islands are eroding. With an average elevation of just 1 meter above sea level, it is the lowest country in the world.

The tests, which took place mostly in a shallow area of ​​a reef south of the capital Malé, were varied. They included submerging a network of tightly tied ropes to collect sand and using a material that turns from fabric into hardened concrete when sprayed with water to create a barrier on the seabed that would help collect sand. In another test, the team set up a floating garden on a sandbar to see if plant roots could help stabilize the accumulated sand and collect more.

A naturally formed sandbar about 1 meter above sea level in the Maldives. (Video: MIT/Invena Self-Assembly Lab).

With each field trial, the team learned more about what materials, structures, and construction techniques could accumulate sand in a simple, cost-effective, sustainable, long-lasting, and easily scalable way. So far, the second field trial, launched in 2019, has shown the most promising results. It involved placing biodegradable fabric bags filled with sand in strategic locations to create a sand ridge.

In just four months, about half a meter of sand had accumulated over an area measuring 20 by 30 meters. Today, the sandbar is about 2 meters high, 20 meters wide, and 60 meters long. The material used is expected to last about 10 years, making it more durable and cost-effective than dredging and pumping sand, says Skylar Tibbits, founder and co-director of MIT's Self-Assembly Lab.

In the near future, Tibbits believes that what they have learned will help them reclaim beaches and islands more efficiently. The ultimate goal is to build new artificial islands.