Riverbed construction
Riverbeds hold some of the most high-quality sands for the construction industry. Credit: Ajdin Kamber/Shutterstock

Smartphone screens, wine bottles, and porcelain toilets share a surprising ingredient: sand. In fact, the ubiquitous material is the second most exploited natural resource on Earth, after water.

Most sand pours into the construction industry, which in turn pours much of it into concrete. “Sand is the most mined solid material on Earth, and we’re using more and more sand as we’re becoming more and more people,” said Mette Bendixen, a physical geographer at McGill University in Montreal.

“The use of sand is now faced with two major challenges,” said Xiaoyang Zhong, a doctoral student in environmental science at Leiden University in the Netherlands. “One is that it has caused enormous consequences in the environment,” he explained. “The second challenge is that easily usable sand resources are running out in many regions.”

“The crisis that exists around sand is mostly a crisis of sand sustainability, not of availability.”

Sand is extracted from the environment with irreversible impacts, the scale of which will be magnified as the world prepares for an additional 2 billion people within the next century. People will want—and need—homes, infrastructure, and livelihoods that directly or indirectly involve sand. To begin planning for this future, the United Nations Environment Programme (UNEP) issued a detailed report in April 2022 outlining 10 strategic recommendations (see the first table) for sand supply chain stakeholders (see the second table). Finding alternatives to naturally occurring sand and gravel is imperative, as are reuse and recycling-related solutions.

“The crisis that exists around sand is mostly a crisis of sand sustainability, not of availability,” said Daniel Franks, a report coauthor and professor at the University of Queensland in Australia.

Reining in Rivers

Although regional sand shortages are familiar phenomena, “we don’t know if there is a global sand scarcity,” said Aurora Torres, a report coauthor and Marie Skłodowska-Curie postdoctoral fellow at the Université catholique de Louvain (Belgium) and Michigan State University, because “we don’t know how many global sand resources exist.”

Local and regional sand shortages occur for a variety of reasons, Torres said. Sometimes, she explained, a sand shortage may occur because high-quality materials have already been extracted or never existed in that region because of unfavorable geology.

Sands of the Libyan desert, like those from many deserts around the world, are not usable for most construction purposes. Credit: giomodica/Wikimedia CC-BY-3.0

The UNEP report describes how officials and community members in Makueni County, Kenya, for example, worried that a river would run out of sand because of unsustainable mining, which would in turn decimate the water supply, thus collapsing the community’s resilience.

Accessibility presents a different type of sand scarcity, said Torres. For instance, sand reserves may lie beneath something of importance, like agricultural land or the economic and social infrastructure of a city, like London, which sits atop valuable sediment. In other cases, local residents oppose sand mining for environmental or health reasons.

Quantifying the characteristics of sand resources is key to understanding where they should be preserved or could be extracted, said Arnaud Vander Velpen, a report coauthor and the sand industry and data analytics officer at the UNEP’s Global Resource Information Database (GRID) network in Geneva. “Silica sand is not the same as construction sand is not the same as desert sand.”

Bendixen concurred. The sands of great deserts around the world, for example, cannot be used for construction because the grains are too rounded, she said. “It’s almost like building with marbles.”

Size matters, too. Differently sized angular grains adhere better to make stronger concrete. “And that’s exactly what you get from river sand,” Bendixen said.

“You tend to get very high quality aggregate [the industry term for sand and gravel]” from river sand, said Matt Kondolf, a geomorphologist at the University of California, Berkeley. This aggregate “needs minimal processing simply by taking it out of the riverbed.” This straightforward process is especially clear in river systems with seasonal flow patterns, which allow miners simply to dig up and sieve sand and gravel during the dry season to sell in nearby markets. In undammed systems, the next rainy season often brings new sediment that can help fill in the holes left by the excavators.

“In many regions, we have been extracting beyond the sediment budget.”

Mining in active river channel deposits—such as streambeds and sand bars—was standard practice until the 1980s, when the method’s devastating ecological impacts became apparent, said Kondolf. The gravel needed for aggregate, for example, is approximately the same size gravel that salmon need to spawn. Indeed, the features removed (or created) by mining provide critical habitat for a variety of aquatic organisms.

Regulations in the western United States and Europe began to limit extraction from rivers, but in many other regions it remains essentially uncontrolled, said Kondolf.

Vander Velpen likens this extraction process to trying to get money from a bank, a metaphor popularized by Maarten Kleinhans, a professor of geosciences at Utrecht University. “In order to [borrow] money, the bank will ask, ‘OK, what’s your income?’ If you go to a river to take out sand, you should check the budget,” Vander Velpen explained. “At the moment, we’re not doing that…in many regions we have been extracting beyond the sediment budget.”

Dam Complexities

Another place to find sand is in the reservoirs behind dams. Extracting sand from these spaces is more complicated than mining a riverbed. As sediment begins to fill a dammed reservoir, the coarsest material begins forming what’s called a reservoir delta where the river empties into the lake, upstream of the dam. “The finer sediment tends to spread out more downstream, through the reservoir,” said Kondolf. “You get a complicated stratigraphy, which is why it’s not as easy to mine.”

Size matters here, too: Smaller reservoirs trap gravel, larger ones hoard sand and silt, and the biggest amass even the finest sediment, said Kondolf.

Free-flowing rivers transport sediment continuously, typically from rapidly eroding mountainous areas all the way to the coasts, said Kondolf. This sediment supports deltas and beaches where a river meets the ocean. “By building a dam, you block that continuity of transport,” said Kondolf.

Downstream from dams, starving rivers yearn for their lost sediment load; the hungry water erodes the beds and banks, attempting to satiate its appetite.

With the proliferation of dams throughout river basins, sand supply to coastal deltas has been cut off at a decadal scale, Kondolf noted. Many of these deltas are already retreating because of sand mining.

One solution to maintaining a steady supply of sediment throughout the course of a dammed river is to find a way to pass sediment from the upstream side of the dam to the downstream side. But dredging—suctioning sand from, in this case, the lake floor into a boat—and hauling sediment via trucks are expensive and “a lot of [work] compared to what the river does by itself with gravity,” said Kondolf.

In the United States, Great Lakes Dredge & Dock Company has successfully dredged sand from reservoirs, said Bill Hanson, the company’s senior vice president of government relations and business development. However, he said, simply sending the sand downstream hasn’t been feasible because of permit requirements and other regulations.

In a few places, like Japan and Switzerland, large dams have been engineered with sediment bypass tunnels that use river flows to flush sediments through steep slopes, explained Vicente Tinoco, a doctoral student at the College of Environmental Design, University of California, Berkeley. Managers can also clear smaller reservoirs by completely draining them, he said. This returns the stockpiled sediment to the river system.

Bye-Bye Beaches

Sand indirectly influences sex determination in many sea turtle species. Credit: USFWS, CC-BY-2.0

Sand can also be mined from the seafloor. Beach nourishment, also known as coastal protection, typically takes sand from the seabed and pumps it onto shore, explained Hanson. In South Florida, for example, “before we started doing regular nourishment, there was concrete and debris on the beaches,” said Hanson. Beach nourishment buffers the shoreline against storms, waves, and sea level rise. Where offshore sand mining is prohibited, as is the case in South Florida, trucks bring in manufactured sand—crushed rock that’s sieved and sorted to exact specifications—from elsewhere.

Dredging is cheaper and has a smaller carbon footprint than the manufacture and transportation of sand, although with seafloor dredging, “you get what you get” in terms of sediment, said Hanson. However, a substantial amount of geotechnical work prior to dredging happens with the goal of matching seafloor sand to beach sediment, he said. This matching is more than just aesthetic.

The color of the sand, said Vander Velpen, in part dictates its temperature—the darker the sand is, the hotter it gets because it absorbs more of the Sun’s radiant energy. Certain animals like sea turtles, which lay their eggs in the sand, are subject to temperature-dependent sex determination. In other words, the temperature of the nest dictates whether an egg will hatch a male or female turtle. Darker, hotter sand can result in too many females relative to males, putting the population at risk.

Whether sand comes from the river itself or from people bringing it in, beaches and deltas—and the protection they offer—would disappear without regular nourishment. In Southeast Asia, “assuming no sediment management,” said Kondolf, “you would only get 4% of the natural sediment load arriving in the Mekong Delta due to upstream dams trapping sediment and sand mining, which basically means there’s no long-term future for the delta.”

A Golden Goose in Greenland?

Greenlandic fjords often expel plumes of fine, glacially derived suspended sediment. Credit: Anders Anker Bjørk

A potentially untapped source of sand is a curious consequence of climate change: the coastal sands around Greenland. As the world warms, Greenland’s ice sheets are melting. Both water and glacial sediment drain through coastal outlets into the sea, with a single outlet delivering a quarter of all material, said Bendixen. In 2019, she and her colleagues proposed that Greenland could potentially benefit economically from this sediment exodus.

Two years after the study’s release, the Geological Survey of Denmark and Greenland prepared a report on the subject. Bendixen said that it declared the recently deposited glacial sediments unsuitable for export to countries that need construction materials. “I’m a little skeptical about that report because they never went to investigate the material,” she said.

Similar sands are already being dredged from the bottom of the nearshore ocean environment for use in construction projects as the capital city of Nuuk expands. Thomas Lauridsen of Greenland’s Ministry of Mineral Resources and Justice explained that indeed, “a few Greenlandic companies are exploiting sand in the offshore environment for local use in Greenland.”

“The environmental impacts [are] one of the very biggest unknowns.”

“This is a country which wants to modernize and which wants to diversify [its] economy,” Bendixen said. The survey also found that respondents want local control over extraction and export, with most saying that environmental impacts need to be addressed by any proposed mining concern. “The environmental impacts [are] one of the very biggest unknowns,” she said.

Greenland sits between North America and Europe—regions that largely satisfy their sand demand from domestic sources, which include recycled demolition waste, according to a paper led by Torres. Future needs for sand are more likely to arise in places like Asia and sub-Saharan Africa. One of the challenges with mining Greenlandic sand for export, she said, “is the transportation cost and how this could significantly increase the price of sand.” Both the cost and the greenhouse gas emissions associated with transport may simply be too high.

Toxic Tailings, Stronger Circularity

“The vast majority of what we call sand or aggregate that’s used by humans is actually crushed stone,” said Franks. But another industry already crushes rocks and produces an annual waste stream of more than 13 billion metric tons.

That industry, of course, is mining, and mining companies may be able to offer a readily available source of sand. Vale, for instance, is a Brazilian multinational corporation that generates millions of metric tons of tailings each year. Tailings are waste materials left after the target mineral is extracted from ore. Large companies like Vale have significant challenges surrounding the safe storage of tailings, said Franks. “They’ve had the deep learning experience of causing a major tragedy.”

Vale experienced two disasters in the past decade: the Mariana dam collapse in 2015 and the Brumadinho dam failure in 2019. Hundreds of lives were lost, and hundreds of kilometers of rivers were polluted. “People in that organization are now motivated to change because they saw their work colleagues pass away from these failure incidents and also because investors and some governments have demanded reform,” Franks said.

The University of Queensland and the University of Geneva worked with Vale to investigate whether sand produced during mineral ore processing could be a sustainable aggregate source for industry, thus reducing the amount of sand demanded from the natural environment and reducing the amount of mining waste that needs to be stored. “We’re not talking about taking the tailings waste and finding a purpose for it,” said Franks. In other words, the proposed process does not deal with existing tailings but instead would ensure that volumes of future tailings would be reduced by adding another set of mineral processing steps in tandem with metal ore extraction. The ore-sands report detailed these steps and the feasibility of creating sand suitable for certain construction materials.

Franks said that the tests revealed very minor concentrations of potentially toxic elements, “much lower than the environmental thresholds and background concentrations that might appear in soil.”

To efficiently process ore minerals, the rocks are ground very finely, which means that any coproduct would also be very fine sand—useful for some construction purposes but not all. “It’s a solution that can currently contribute to the construction industry either as a blended product,” said Franks, “or also on its own…to make bricks or be used as road base.”

Many major ore-producing countries are also rapidly building infrastructure, and they cannot rely on construction and demolition waste the way economies with a mature infrastructure network (as in Europe and North America) do. Such recycling is an important component to a circular, no-waste economy, said Vander Velpen, who was also an ore-sands report coauthor. To that end, the report’s authors examined distances between potential ore-sand sites and urbanizing regions with a demand for sand, finding that the two correlated in most instances.

Built to Last

Across Africa and Asia, the demand for sand is driven by economic growth. Vander Velpen described talking to people in African countries like Mauritania and Nigeria who want modern-looking concrete homes.

Cement and concrete were first introduced during European colonization of Africa, said Doudou Deme, co-owner of Elementerre, a Senegalese company focused on using earthen materials, not concrete, to construct environmentally friendly buildings. These materials, he said, protect against tropical climate more effectively than concrete. Concrete and cinder blocks “convey heat very quickly,” whereas earthen materials provide “thermal comfort and humidity regulation.” Regardless, Doudou said, the majority of construction in Senegal uses relatively cheap and widely available reinforced concrete, which contributes to the erasure of local construction cultures that use components like clay, stone, and fiber (e.g., palm trees, straw, and bamboo).

China has erected cities of concrete over the course of years, instead of the decades or even centuries taken to build cities in North America and Europe. The statistics are staggering, with China having used more sand in 3 years than the United States did in the past century.

“If you want to build a city in 10 years, you’re [using] concrete, you’re using glass, you’re using steel.”

Materials made from sand are necessary for rapid development, explained Vander Velpen. “If you develop slowly, you use a huge variety of materials,” he said, whereas “if you want to build a city in 10 years, you’re [using] concrete, you’re using glass, you’re using steel.”

In a recently published study, Zhong and his colleagues including Paul Behrens, a professor of environmental change at Leiden University in the Netherlands, explored how to reduce sand needs through material efficiency strategies in building construction like increasing the lifetime of new and existing buildings, using different materials in new construction, and reusing building components.

The need for new buildings, Zhong explained, is driven by increasing populations and gross domestic products (GDP). In general, as GDP goes up, so does area per capita. By estimating how much concrete and glass are required per square meter based on building practices, he calculated how much sand the world would need to construct the majority of its buildings every year between 2020 and 2060.

Using these material efficiency strategies decreased projected sand demand by half. Zhong and the other researchers tested how the overall need for sand would change, for instance, by tweaking floor area per person or increasing the longevity of existing buildings. They found that using alternatives to concrete, such as timber, would help somewhat, and limiting floor space—specifically, not following current projections for future floor space per capita—could also decrease projected sand use. Most important, new buildings should have longer lifetimes than existing ones.

Studies like Zhong’s and businesses like Doudou’s highlight how individuals can help limit environmental impacts. “Value your local and traditional construction materials and encourage your local authorities to refurbish and restore buildings [instead of] demolishing and replacing them,” said Vander Velpen.

Sand as a Strategic Resource

“Sand is a strategic resource, not only economically but also for our environment,” said Vander Velpen. “There are sometimes reasons to excavate sand from a beach, but we call for sand from the beach system not to be used as a source of construction or industrial material.” Sands of the beach and nearshore environment provide long-term defense against storms and sea level rise while housing fish stocks, plants, and many endangered species.

Regionally tailored solutions to sand need to involve small-scale sand miners so they don’t bear the brunt of the transition, said Stephanie Chuah of UNEP/GRID and a coauthor of both the UNEP and ore-sands reports.

This table from the United Nations Environment Programme (UNEP) report offers 10 recommendations to avert a sand crisis.

Because most sand is a local resource, “price setting needs also to be done locally and not globally,” said Vander Velpen.

Sand mining also has a gender dimension that needs to be addressed, said Chuah. Women may not own or even have access to land, which can be a problem in parts of the developing world where women are responsible for providing food and water for their families, said Chuah. Sand mining can cause water quality to diminish such that women have to go much farther to obtain potable water. However, families may depend directly on sand mining for their livelihood, she explained. In some instances, men are miners, but in others, women are becoming directly involved in sand mining because traditional ways to support their families, for instance, by fishing, have become threatened.

The UNEP report describes a project in the southeastern coastal state of Andhra Pradesh, India, involving a decades-old government scheme called the Development of Women and Children in Rural Areas (DWCRA), which focuses on creating opportunities for women in rural communities to improve their lives. The state government gave DWCRA women’s groups mining rights in the mid-2010s. These groups were responsible for managing the purchase and delivery of sand, earning 25% of profits from sales and monthly salaries for employed women.

This table from the UNEP report lists relevant stakeholders in sand and sustainability.

The project was plagued with problems, however. For instance, women reported delays in receiving payment, as well as concerns over their own health and personal safety, and it is unclear whether DWCRA groups continue to participate in sand mining–related activities.

“A lot of people working within the artisanal small-scale mining industry often exist and work in poverty and [engage in] very informal governance when it comes to sand,” said Chuah. In addition to more sustainable business models, the authors of the sand mining reports are “also calling for better governance when it comes to managing sand resources,” she said. Moreover, she explained, “we will also need a just transition, where we take into consideration the voices of all people and avoid any deterioration in workers’ rights, increased hardship, or poverty.”

“There’s this need to extract this material for development—for livelihoods—and at the same time, the need to preserve the ecosystem and the natural services that the sand provides,” said Chuah.

“The gravel and the sand, that’s the architecture of the river channel,” said Kondolf. It’s also the architecture of the coastal seafloor and the architecture of thousands of local economies.

“You build a house literally out of sand to protect yourself,” said Vander Velpen. “In the same way, we need sand—nature—as a protection. We need such an enormous amount of sand in our environments…for resilience.”

—Alka Tripathy-Lang (@DrAlkaTrip), Science Writer

Citation: Tripathy-Lang, A. (2023), Grains of sand: too much and never enough, Eos, 104, https://doi.org/10.1029/2023EO230025. Published on 25 January 2023.
Text © 2023. The authors. CC BY-NC-ND 3.0
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