Slowly but surely, the world’s reservoirs are filling up with sediment. In unblocked rivers, flowing water carries sediment pieces, picking them up from the banks or washing them into the river with the rain. But a river whose flow is interrupted by a dam will deposit some of its sediment in a reservoir just behind the dam itself.” [over] Duminda Perera, a researcher at the United Nations University Institute for Water, Environment and Health in Hamilton, Ontario, told Ars.
Increased sedimentation in these reservoirs and the consequent decrease in volume are largely not considered, according to Perera. However, he and some of his fellow researchers recently wrote a new study that states that at more than 15 meters in height or 5 meters in height he is defined as blocking more than 3 million cubic meters of water. suggests that nearly 50,000 large dams have been robbed. their ability.
This slowly accumulating sediment occupies the volume of the reservoir, or cubic meters that would otherwise be filled with water that would eventually flow through hydroelectric turbines or be diverted to agriculture. “When you put soil in it… you lose water,” he said.
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To determine the scale of the problem, the team used 150 or 150 dams collected by the International Commission on Large Dams from a database (the dataset contains information on approximately 59,000 dams). We applied previously established storage loss rates to the country’s large dams. For the calculations, the team also looked at the dam’s initial storage capacity and age in operation. This data was available for only 47,403 dams.
Using these parameters, the team estimates that trapped sediment has robbed these large dams of between 13-19% of the reservoir’s original storage capacity. That total could reach 23-28% he by 2050, according to the paper. This reduction will reduce the capacity of these reservoirs from 6.3 trillion cubic meters to 4.7 trillion cubic meters. This is equivalent to the combined annual water use of Canada, China, France, India and Indonesia, according to the report.
Storage loss varies by country. Land-use change, such as deforestation (often associated with erosion), can also increase the amount of material entering rivers. The UK, Panama, Japan and others are expected to lose 35-50% of their storage capacity by 2050. By contrast, Cambodia, Ethiopia and Bhutan are expected to lose less than 15%.
No “hard and quick” fixes
This loss of storage can have a negative impact on humans in several ways. For dams that also house hydroelectric generators, the deposits can act as an abrasive and damage turbines and other parts of the facility, “reducing efficiency and increasing maintenance costs,” he said. the paper points out. Fully sedimented reservoirs have less space to hold floodwaters and less water to divert to agriculture. “Sometimes we can’t do what we’re supposed to do because we don’t have enough storage,” he says.
There are several things you can do to address this issue. One option is dredging, which uses machinery such as excavators and suction systems to remove silt. Another option is flushing, or flowing the sediment through a dam. However, the paper points out that dredging is costly and usually only a temporary solution, whereas flushing has unpredictable consequences as a deluge of soil and other material flows downstream. Additionally, some types of flushing, such as “empty flushing,” involve emptying entire reservoirs, temporarily shutting off the generating capacity of hydroelectric dams.
Another option, Perera thinks, is to bypass or use tunnels to divert the sediment steadily under the dam. However, all those options are likely to be case-specific, he said. “There are no hard and fast rules that say, ‘This is the only way to avoid subsidence,'” he said.
MDPI, 2023. DOI: doi.org/10.3390/su15010219
