Sediment is being removed from the rivers like the Mekong faster than it can be naturally replenished, increasing the risk of riverbank collapse. This photo was taken in Cái Bè, Vietnam. [Credit: Corryn Wetzel | CC BY-SA 4.0]
Good sand is surprisingly hard to find, and some of the best — the kind used to make glass, concrete and even iPhones — is usually found only in riverbeds and along coasts. Now researchers are discovering that a global boom in sand mining is damaging some of the world’s great rivers, putting millions of people at risk from flooding and riverbank collapse.
A recent study of Southeast Asia’s Mekong River dramatically illustrates the problem: It concludes that sand mining is lowering the Mekong’s riverbed, destabilizing its banks and altering the way it flows, threatening communities and wildlife along the nearly 3,000-mile river.
“What we found was that the lowering that’s going on is effectively making the riverbanks more unstable,” says Chris Hackney, a sedimentologist at the University of Hull in England and lead author of the study published in January in Nature Sustainability. This means that “it’s more likely that they’ll collapse, and with that, wash infrastructure, or houses, or villages, farmland, people’s livelihoods, away into the river,” he says.
In addition to water, rivers carry sand, clay and even boulders as they flow. As sediment swept downstream is replenished by new deposits from upstream, there’s a balance of erosion — a hallmark of a healthy river. But when sand and other river sediment is dredged-out in huge quantities, the incoming sediment can’t keep up. Removing too much sand can destabilize river banks and cause the river to shift, potentially causing floods.
“We showed that there was about a 44-million-ton deficit every year in terms of the amount of sand that’s been taken out of the river and what the river naturally provides,” Hackney explains. The research team found that the Mekong riverbed is dropping an average of 10 centimeters a year, but the sonar images also revealed giant dug-out holes, which Hackney says can “completely change the shape of the river.” Some of these pits were up to 26 feet deep and 252 feet wide, slightly broader than the wingspan of a Boeing 747 airliner. They found that gouges in the riverbed as deep as 2 meters (roughly 6 and a half feet) could destabilize the banks during the rainy season, but most holes they found were far deeper.
In the case of Mekong, 60 million people live in and rely on the drainage basin of the lower river in Myanmar, China, Laos, Thailand, Cambodia and Vietnam. Because they all share the Mekong, one country’s actions — like sand mining — have direct impacts on the countries downstream. And the problem isn’t unique to the Mekong: Sand is being extracted from ecosystems around the globe.
An analysis of the Kangsabati River in India, for example, found that mining activity is changing how the river flows. Mining of Suriname’s beaches has shrunk Braamspunt beach, an important habitat for nesting sea turtles. And sand removal from the coasts of Mozambique led to unprecedented flash flooding. No continent, save Antarctica, has been able to escape the consequences of the sand mining frenzy.
The exploitation of river sand is driven primarily by booming urban infrastructure development. Sand and gravel are fundamental building blocks for concrete and are frequently used to fill in land or expand the footprint of port cities. Billions of tons of sand are extracted from sensitive ecosystems each year, making it the second most-consumed resource on Earth, only after water.
“It’s almost hidden in plain sight,” says Hackney. “Everyone knows what sand looks like but when you look around the city, you don’t see piles of sand––you see concrete, glass, roads, infrastructure. It’s there but it’s not.”
Global sand and gravel use is around 50 billion metric tons per year––enough to build a 90-foot-tall, 90-foot-wide wall around the equator, says Pascal Peduzzi of the United Nations Environment Programme in Geneva, who was not involved in the work. The demand for sand is so extreme, he says, that it works out to about 40 pounds of sand per person every day. Sand is used so ubiquitously in urban environments that Peduzzi calls it the “unrecognized hero of development.”
“The speed at which we are using it far exceeds the renewable capacity of producing sand,” adds Peduzzi, “and you cannot extract 50 billion tons of any material without a large impact on the environment.”
While most people think of sand as nearly ubiquitous, only some of it is usable for construction. Unfortunately, the most desirable sand is located on river beds, coasts and the seafloor — all places where sand plays a crucial ecological role. Because this sand is eroded by water rather than wind, its irregular shape makes it well-suited for concrete, while grains of desert sand are too smooth. This, Peduzzi says, is “the worst-case scenario.”
Lack of regulation and oversight is to blame for the rampant sand mining, according to Aurora Torres, an ecologist at Université Catholique de Louvain in Belgium who was not involved in the Mekong study. There is a thriving underground market for sand in part because anyone with a shovel can access it and it’s relatively easy to transport, Torres explains. Even where regulations exist, she says, they are challenging to enforce.
Two ways to lower the risks are to reduce demand for sand by recycling concrete and to mine in the center of rivers, away from riverbanks, according to Torres and Hackney.
To further their research, Hackney and his team hope to use high-resolution satellite imagery to spot mining boats and track where extractions––legal or illegal––are taking place on the Mekong.
“Unfortunately, sand is one of the resources that we’re always going to need,” says Hackney. “I think the important thing to recognize is that, although we’re going to need it, we need to extract it in a way that doesn’t detrimentally harm the environment it’s being extracted from.”