Can the ‘sand motor’ save West Africa’s eroding coast?

When governments discover themselves combating the specter of coastal erosion, their default response tends to be fairly easy: If sand is disappearing from a seashore, they pump in additional sand to exchange it. This technique, referred to as “seashore nourishment,” has turn into a cornerstone of coastal defenses around the globe, complementing arduous constructions like sea partitions. North Carolina, as an illustration, has dumped greater than 100 million tons of sand onto its seashores over the previous 30 years, at a value of greater than $1 billion.

The issue with seashore nourishment is apparent. For those who dump sand on an eroding seashore, it’s solely a matter of time earlier than that new sand erodes. Then it’s important to do it once more.

Seaside nourishment initiatives are speculated to final for round 5 years, however they typically disappear quicker than anticipated. Furthermore, a giant coastal storm can wipe them out in a single evening. And the prices are staggering: Dragging in new sand requires leasing and working large diesel dredge boats. Solely the wealthiest areas can afford to do it yr after yr.

Now, after a long time of reliance on repeated seashore nourishment, a brand new technique for managing erosion is exhibiting up on coastlines around the globe. It’s referred to as the “sand motor,” and it comes from the Netherlands, a low-lying nation with centuries of expertise in coastal safety. 

A “sand motor” isn’t an precise motor — it’s a sculpted panorama that works with nature somewhat than towards it. As an alternative of rebuilding a seashore with an excellent line of recent sand, engineers lengthen one part of the shoreline out into the ocean at an angle.. Over time, the pure wave motion of the ocean acts as a “motor” that pushes the sand from this protruding landmass out alongside the remainder of the pure shoreline, spreading it down the shoreline for miles. 

Whereas sand motors require rather more upfront funding than regular seashore nourishment — and lots of occasions extra sand — additionally they defend extra land and final for much longer. Developed nations such because the Netherlands and the UK are turning to those megaprojects as an alternative choice to repeated nourishment, and the World Financial institution is financing a sand motor in West Africa as a part of a billion-dollar adaptation program meant to battle sea stage rise. However these large initiatives solely work in areas the place erosion just isn’t but at a essential stage. Meaning they’re unlikely to point out up in the USA, the place many coastal areas are already on the purpose of disappearing altogether.

The thought for the challenge got here from a Dutch professor named Marcel Stive, who had watched with frustration as his nation’s authorities spent billions to nourish the identical coastal areas again and again as sea ranges saved rising. Stive offered the thought to the federal government, which employed a big dredging firm referred to as Boskalis to construct a prototype on the shoreline south of The Hague.

Even this experimental challenge, which the Dutch name “de Zandmotor,” was an unprecedented enterprise. Boskalis dredged up round 28 million cubic yards of sand from the ocean ground — extra the Netherlands makes use of on nourishment initiatives nationwide in a given yr. Engineers then sculpted the sand right into a hook that curved eastward alongside the shore, guaranteeing that waves would push the sand northeast towards seashores close to The Hague. In addition they created a lagoon in the course of the sand construction in order that locals wouldn’t need to stroll for nearly a mile to get to the water. Within the years since Boskalis completed development on the $50 million challenge, the hook of sand has flattened out, virtually the best way a wave breaks because it reaches the shore.

“By mobilizing your dredging gear solely as soon as, it’s cheaper to do one massive nourishment somewhat than to return each two to a few years,” mentioned Mark Klein, a senior morphology engineer at Boskalis who has labored on sand motor initiatives. “It saves mobilization prices if you happen to make one large nourishment.”

The upfront prices of the South Holland sand motor had been appreciable — most conventional seashore nourishment initiatives clock in at beneath one million cubic yards — however the sand and the cash will go a lot farther than they might in the event that they’d been used for bizarre nourishment. The sand motor was designed to final for 20 years, however Klein says it’ll probably final even longer than anticipated — an unheard-of consequence for an erosion management challenge. 

Regardless of the challenge’s success, just a few nations have tried to repeat the Dutch mannequin. Nigeria created a sculpted sandbar in a suburb of Lagos in 2018, and the UK constructed a shifting sand barrier to guard a pure gasoline terminal within the coastal city of Bacton the next yr. Each had been far smaller than the South Holland challenge; the Bacton sand scaping challenge, as an illustration, used solely 2 million cubic yards of sand.

However across the time these initiatives had been accomplished the idea bought a lift from the World Financial institution, which is the world’s largest supply of funding for local weather adaptation initiatives in growing nations. As a part of an virtually $500 million adaptation bundle meant to guard coastal areas in West Africa, the financial institution funded the development of a big sand motor within the small nation of Benin, one other nation that faces an excessive erosion risk.

The shoreline of West Africa’s Gulf of Guinea is eroding quicker than virtually every other place on this planet, with extreme penalties for a inhabitants that’s clustered by the water. In response to a current research, virtually two-thirds of the area’s coastal settlements face extreme financial and well being disruptions from sea-level rise — most notably within the Nigerian megacity of Lagos, which sits on a marshland only a few ft above sea stage. The World Financial institution estimates that the impacts of abrasion might wipe out as a lot as 5 p.c of the area’s gross home product.

Benin is in notably dire form: Elements of the nation’s shoreline are eroding by as a lot as 45 ft yearly, and miles of seashore have vanished for the reason that flip of the century. The erosion has washed out roads, disrupted the livelihoods for native fishermen, and carved up seashores which can be main vacationer points of interest. The nationwide authorities’s earlier efforts to regulate land loss with concrete sea partitions and rock constructions didn’t do a lot to decelerate the speed of abrasion.

So when the World Financial institution gave the Beninese authorities $60 million in 2018 to pursue a raft of abrasion options, its leaders opted to construct a sand motor in a preferred beachfront space the place erosion has disrupted fishing and tourism. The dredging agency Boskalis constructed the challenge final Could, vacuuming up greater than 8 million cubic yards of sand to construct a motor about one-third the dimensions of the unique one within the Netherlands.

As a result of sand motors require a lot cash, sand, and dredging experience, most nations can’t pursue them with out worldwide assist, mentioned Peter Kristensen, an environmental economist on the World Financial institution who’s main the West Africa erosion initiative. As an alternative they accept concrete boundaries, rock partitions, and smaller nourishment initiatives, all of which have quick lifespans. Sea partitions may even pace up erosion in close by areas by redirecting wave power towards neighboring sand stretches that don’t have fortifications.

“Within the U.S. and different nations, they will afford to replenish typically,” mentioned Kristensen. “It’s more durable for the African nations to afford that sort of replenishment regularly.”

West African nations have additionally used cash from the World Financial institution to construct rock groins, mangrove forests, and conventional nourishment initiatives. The financial institution hopes to observe all these initiatives over the approaching years to see that are handiest at combating erosion, then scale these options for all the area. If the brand new sand motor in Benin survives for so long as the Dutch model has, the financial institution could attempt to replicate its success with extra mega-nourishment initiatives in different elements of the world.

However this intervention will solely work if nations like Benin additionally attempt to shift their growth away from the water’s edge, in keeping with Rob Younger, a professor of geology at Western Carolina College and a number one professional on shoreline erosion. 

“The Dutch made two selections,” he mentioned. “One was, ‘We’re going to guard as a lot of the nation from storm surge as we are able to.’ Quantity two was, ‘We’re going to get infrastructure out of the bottom mendacity areas, and we’re not going to construct new stuff in silly locations.’” 

Kristensen says that shifting again from the shoreline is perhaps troublesome within the area of Benin with the brand new sand motor. Properties and seashore accommodations within the space sit clustered on a slender strip of land with a river flowing behind it, so it’s not doable to shift growth backward. 

“It’s not all the time the case that once you need to do a managed retreat that you’ve a spot to place all the pieces and all of the folks that you simply need to transfer,” he mentioned. However he additionally mentioned that the World Financial institution could be prepared to fund so-called “managed retreat” insurance policies in different areas of West Africa if nationwide governments wished to pursue them.  

By the identical token, Younger mentioned, it’s unlikely that the sand motor could be a lot assist in the USA. There are tens of millions of seashore houses and high-rise condominium buildings lining the shorelines of states like Florida, and shifting this growth again from the water would elevate a bunch of political and logistical challenges, not the least being that nobody who lives there needs to maneuver. 

Moreover, the seashore in locations like Miami has eroded to this point that solely a skinny strip of sand protects folks from the encroaching ocean, which makes nourishment way more pressing. Seaside communities in Florida can’t wait years for the sand from a sand motor to float towards their seashores — they want fixed infusions of sand, yr after yr, or the water will wipe them out altogether. Plus, the method of abrasion is to this point superior in locations like South Florida that there will not be sufficient sand to construct a motor: Earlier dredging efforts have drained offshore deposits of high-quality sand, leaving solely low-quality materials that received’t work to replenish seashores.

Younger says that each one these components imply that the sand motor will solely be helpful for nations that may additionally shift growth inland as a part of a extra complete local weather adaptation plan, because the Dutch did.

“Within the U.S. we’ve numerous coastal resort communities the place the homes are on the sting of the ocean, proper now, and we’re scrambling to maintain sand in entrance of them,” he mentioned. “For those who take a look at what’s down drift of the sand motor on the coast of Holland, they don’t have buildings teetering on the sting.”