Sand Motors: A Revolutionary Solution for Coastal Erosion

This story originally appeared on Grist and is part of the Climate Desk collaboration.

Explore how sand motors are reshaping coastal protection strategies, inspired by the Netherlands’ innovative approach. Discover how these structures combat erosion and safeguard shorelines in a groundbreaking manner.

Governments typically use a rather straightforward approach to combating the problem posed by coastal erosion: if sand is being lost from a beach, additional sand is pumped in to replace it. Known as “beach nourishment,” this tactic complements hard structures like sea walls and has been a mainstay of coastal defenses worldwide. For example, during the last 30 years, North Carolina has spent more than $1 billion dumping more than 100 million tons of sand onto its beaches.

There is no denying the issue with beach nourishment. It’s simply a matter of time until newly added sand erodes on a beach that is already deteriorating. After that, you’ll have to start over.

Although beach nourishment programs are intended to last five years, they sometimes end sooner. Not only that, but a powerful coastal storm might destroy them in a single night. And the prices are exorbitant: renting and operating massive diesel dredge boats is necessary for dragging in additional sand. The wealthiest regions are the only ones who can afford to do it annually.

Currently, a new method of controlling erosion is emerging on beaches all around the world, following decades of reliance on recurring beach nourishment. The Netherlands, a low-lying country with decades of experience in coastline protection, is the origin of what is known as the “sand motor.”

A “sand motor” is a sculpted landscape that functions in harmony with nature rather than in opposition to it. It is not an actual motor. Engineers extend a portion of the shoreline at an angle out into the sea rather than reconstructing the beach with an even line of fresh sand. The sand from this outlying landmass is gradually pushed out along the remaining portion of the natural shoreline by the ocean’s wave action, which works as a “motor” and spreads the sand for miles.

Sand motors preserve more land and have a longer lifespan than typical beach nourishment, even though they often need a larger initial investment and more sand. Developed nations like the United Kingdom and the Netherlands are using these massive initiatives as a substitute for frequent feeding, and as part of a billion-dollar adaptation effort aimed at halting sea level rise, the World Bank is funding a sand motor in West Africa. But these massive projects only work in areas where erosion is not yet at a critical stage. This implies that they won’t likely be found in the US, where a large number of coastal regions are currently in danger of completely disappearing.

The concept was the brainchild of Marcel Stive, a professor in the Netherlands, who became frustrated seeing his nation’s government spend billions of dollars repeatedly rehabilitating the same coastal districts as sea levels rose. After Stive brought the proposal to the government’s attention, Boskalis, a sizable dredging company, was contracted to construct a prototype on the coast south of The Hague.

Even this experimental project—known as “de Zandmotor” in the Netherlands—was a first for its kind. Boskalis extracted almost 28 million cubic yards of sand from the ocean floor, which is more than the Netherlands utilizes in a single year for all of its national nourishment initiatives. Engineers then sculpted the sand into a hook that curved eastward along the shore, ensuring that waves would push the sand northeast toward beaches near The Hague. To avoid having to walk for nearly a mile to reach the water, they also made a lagoon in the center of the sand building. In the years since Boskalis finished construction on the $50 million project, the hook of sand has flattened out, almost the way a wave breaks as it reaches the shore.

According to Mark Klein, a senior morphological engineer at Boskalis who has experience with sand motor projects, “it’s cheaper to do one large nourishment rather than to return every two to three years by mobilizing your dredging equipment only once.” “If you make one large nourishment, it saves mobilization costs.”

Although most typical beach nourishment projects cost less than one million cubic yards, the South Holland sand engine came with hefty initial costs. However, both the money and the sand will go significantly further than if they had been utilized for regular replenishment. According to Klein, the sand motor is expected to beyond its 20-year planned life, which is an unprecedented result for an erosion control project.

Even with the project’s success, not many other nations have tried to imitate the Dutch approach. In 2018, Nigeria constructed a sculpted sandbar in a Lagos suburb, and the following year, the UK constructed a movable sand barrier to safeguard a natural gas station in the coastal town of Bacton. For example, the Bacton sand landscaping project required just 2 million cubic yards of sand, significantly less than the South Holland project.

The World Bank, the primary global donor for climate adaptation initiatives in developing countries, gave the idea a boost, nevertheless, about the time these programs were finished. The bank provided funding for the installation of a sizable sand engine in the tiny nation of Benin, which is also severely threatened by erosion, as part of an approximately $500 million adaptation package intended to save coastal communities in West Africa.

The Gulf of Guinea coast in West Africa is losing land faster than anywhere else in the world, which will have dire repercussions for the local population that lives close to the water. According to a recent study, almost two-thirds of the region’s coastal settlements face severe economic and health disruptions from sea-level rise—most notably in the Nigerian megacity of Lagos, which sits on a marshland just a few feet above sea level. According to estimates from the World Bank, the effects of erosion might eliminate up to 5% of the gross domestic product in the area.

Benin is in very bad shape: since the year 2000, miles of coastline have disappeared and portions of the nation’s shoreline have been losing up to 45 feet annually. Roads have been swept out, local fishermen’s livelihoods have been impacted, and beaches that are popular tourist destinations have been severely damaged by erosion. Prior attempts by the national government to slow down land loss through the construction of rock structures and concrete sea walls were ineffective.

Therefore, the Beninese government chose to construct a sand motor in a well-known beachside area where erosion has hampered fishing and tourism when the World Bank granted them $60 million in 2018 to investigate a variety of erosion remedies. Construction of the project began in May of last year, with the dredging company Boskalis vacuuming up around 8 million cubic yards of sand to construct a motor that is roughly one-third the size of the original one in the Netherlands.

According to Peter Kristensen, the World Bank’s environmental economist in charge of the West Africa erosion effort, most governments are unable to pursue sand motors without assistance from other nations due to their high cost, sand requirements, and dredging skills. Rather, they make do with shorter-lived concrete barriers, rock walls, and smaller-scale nourishment efforts. Sea walls can also accelerate erosion in the vicinity by deflecting wave energy into adjacent sand sections without defenses.

“They can afford to replenish often in the US and other countries,” Kristensen said. “The African countries find it more difficult to regularly afford that kind of replenishment.”

Additionally, West African nations have constructed mangrove forests, rock groins, and traditional nourishment projects with funds from the World Bank. In the upcoming years, the bank intends to keep an eye on all of these projects to determine which are best at halting erosion. It then plans to scale up those solutions for the entire region. Should the Beninese sand motor endure as long as the Dutch counterpart, the bank might attempt to duplicate its achievements through more mega-nourishment initiatives in other global regions.

Rob Young, a professor of geology at Western Carolina University and an authority on coastline erosion, says that this intervention, however effective, will only be successful if nations such as Benin likewise attempt to move their growth away from the water’s edge.

He stated, “The Dutch made two choices.” “We’re going to shield as much of the nation as we can from storm surge,” was one of them. The second was, “We’re not going to build new stuff in stupid places, and we’re going to remove infrastructure from the lowest lying areas.”

According to Kristensen, the new sand motor may make it challenging to leave the shoreline in the Benin region. The area’s residences and beach hotels are arranged in a tight strip along a river, making it impossible to reverse expansion.

“It’s not always the case that you have a place to put everything and all the people that you want to move when you want to do a managed retreat,” he stated. However, he added that if national governments in other parts of West Africa desired to implement so-called managed retreat strategies, the World Bank would be prepared to provide funding for them.

In the same vein, Young stated that it is doubtful the sand motor would be of much use in the US. States like Florida have millions of beach homes and high-rise condo buildings bordering their shorelines. Relocating this construction back from the water would present a number of political and practical difficulties, not the least of which is the fact that no one who already resides there wants to move.

Moreover, the beach in areas like Miami has degraded to the point where residents are only shielded from the oncoming ocean by a tiny strip of sand, making replenishment even more critical. Florida beach communities need annual injections of sand to prevent total erosion by the sea; they cannot wait for sand from sand motors to drift onto their beaches. Furthermore, there could not be enough sand in places like South Florida due to the advanced stages of erosion: prior dredging operations have removed high-quality offshore sand deposits, leaving behind low-quality material that is useless for replenishing beaches.

According to Young, these characteristics together suggest that the sand motor will only be beneficial for nations like the Netherlands who are able to move growth inland as part of a more holistic plan for climate adaptation.

“We’re scrambling to keep sand in front of them in a lot of coastal resort communities in the US where the houses are right now,” he said. “If you observe the sand motor’s down drift along the Dutch coast, you won’t see any buildings perched precariously on the edge.”

Conclusion

Sand motors represent a promising frontier in coastal protection, offering a sustainable alternative to traditional methods. As coastal communities worldwide grapple with rising sea levels, the adoption of innovative solutions like sand motors becomes increasingly imperative. With further research and implementation, these structures could redefine how we combat coastal erosion, ensuring a more resilient future for vulnerable shorelines.