Sand mining from rivers is depriving many low-lying Asian deltas of the sediment they need to maintain themselves.
Researchers said the activity would raise the risk of worsening land loss to sea level rise.
Combined with losses of soil-holding mangroves and accelerating groundwater extraction, which can lead to land sinking, the mining is increasing climate-related threats for those living in low-lying coastal areas, they said.
“We have created a recipe for climate disaster,” said Marc Goichot of the World Wildlife Fund (WWF).
Deltas dependent on the Ganges-Brahmaputra-Meghna, Mekong and Yangtze rivers are now sinking and shrinking, according to research carried out by WWF – a situation worsened by climate-related warming and rising sea level.
That is a problem not only because the deltas are home to millions of people but because they produce a significant share of the region’s food.
The Mekong delta, for instance, home to 17 million people, is a major source of rice for the region and underpins a quarter of Vietnam’s GDP, Goichot said.
“It is 40,000 square kilometers – larger than many countries – and most of it is sinking,” he said.
More floods, more salt
At the heart of the problem, Goichot said, is a lack of enough sediment moving down the rivers – and much of that is the result of mining of sand as a construction material and for other uses, he said.
In some major rivers in Asia, such as the Mekong, Yangtze and Ganges-Brahmaputra-Meghna, as much as 90 percent of the sediment that once traveled down the system is now collecting in reservoirs or being mined, WWF’s research showed.
That means much less material is arriving in delta areas to replace soil lost to coastal erosion and other natural processes.
For those living in the deltas, it can mean growing risk of floods, inundation from coastal storm surges and worsening salt contamination in drinking water.
Kusum Athukorala, former chair of the Sri Lanka Water Partnership, said the loss of sand also means less water-storage capacity in rivers, and less water flowing in to restore aquifers.
That is a particular problem as climate change brings longer and hotter dry season and growing water stress, he said.
Worldwide, over half a billion people live in delta areas, WWF said.
According to the U.N. Environment Programme, though record keeping is poor, global consumption of sand and gravel likely exceeded 40 billion tonnes in 2012, up from 9 billion tonnes in the 1970s, making it one of the world’s most extracted resources by volume.
“To give a sense of its use, for every bucket of cement, five to seven buckets of sand are used in concrete. For every kilometer of road built, 30,000 tonnes of sand is used as its base,” Goichot said.
But sand is just as important in the river systems it is harvested from, he said.
“Keeping sand in the rivers is the best adaptation to climate change. If a river delta receives enough sediment, it builds itself above sea level in a natural reaction,” Goichot, told the Thomson Reuters Foundation in an interview in Stockholm.
But sand mining also feeds Asia’s rapidly growing cities. New buildings and roads require it and urban land is often expanded by pouring sand into wetlands or rice paddies.
The island state of Singapore has expanded its land area 20 percent in the last 50 years, using sand dredged from the seabed but also imported by Vietnam, Malaysia and Cambodia, said Goichot.
Sand mining remains unregulated in many areas, however, and illegal sand mining operations operate in as many as 70 countries worldwide, Goichot said.
“In India unregulated sand mining is really an (escalating) menace,” said Himanshu Thakkar, coordinator of the South Asia Network on Dams, Rivers and People (SANDRP).
India issues sand mining licenses, he said, which limit the quantities of sand that can be taken and the locations where mining is allowed. But with limited monitoring, “the actual mining may be very different,” he said.
River sand is preferred for construction in many cases because desert sand is too rounded to bind concrete well, while seabed sand contains salt that can corrode metal and dredging it can be costly.
But too much harvesting of river sand is now taking a toll on those living downstream, Goichot said, with the Mekong delta, for instance, losing 12 meters of land along its coast each year, the equivalent of a football field and a half of land every day.
In India, insufficient effort is being put into finding alternative sources of sand, including from construction waste or de-silting of reservoirs, Thakkar said. That means “the rivers and everyone dependent on them are sufferers.”