China’s Sanmenxia Reservoir is regularly flushed of accumulated sediment.
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By 2060, more than half of the world’s freshwater reservoirs are predicted to be “functionally dead” due to sediment accumulation, according to a comprehensive study.
Dams obstruct the flow of silt, sand, and gravel downstream, leading to the gradual buildup of these materials in reservoirs, which reduces available water space. Excessive sediment capture poses safety risks to dams and adversely affects downstream ecosystems.
Kai Liu and researchers from the Chinese Academy of Sciences in Nanjing utilized satellite imagery, sediment data, and machine learning to assess over 550,000 reservoirs globally.
They revealed a staggering loss of over 36 cubic kilometers of water annually from sedimentation, a volume comparable to that of China’s monumental Three Gorges Dam.
A reservoir is deemed “functionally dead” when more than half of its capacity is filled with sediment.
Countries like Australia and Spain are anticipated to experience the most severe impacts, with nearly 85% of Australia’s reservoirs and three-quarters of Spain’s projected to reach their operational limits by 2060.
In arid regions, nearly 75% of reservoirs may become functionally dead by the same year, whereas half of the reservoirs in wetlands could cease to function. Alarmingly, over 99% of dams in Namibia and nearly 96% along Australia’s west coast are at significant risk.
Liu et al. estimate that the world loses over 7% of its freshwater storage capacity every decade, threatening over 25% of the world’s irrigated lands and water supplies for over 2 billion people.
To combat this pressing issue, the research team advocates for strategies such as upstream tree planting, land stabilization, and erosion control to mitigate sediment input into reservoirs. They also highlight the necessity for engineering interventions like dredging and bypass tunnels, with an estimated cost of up to $100 billion.
Ian Wright, a professor at Western Sydney University who was not involved in this study, noted some “highly contradictory” findings, particularly since climate change is likely to elevate sediment deposition rates due to increased rainfall. He emphasizes the challenge presented by the growing global water demands.
“Sedimentation acts like a cancer that gradually diminishes reservoir capacity,” Wright warns, highlighting Australia’s vulnerability to this issue. He explains, “Our soils are fragile. Removing catchment vegetation exposes them to heightened erosion, leading to continuous sediment flow into storage dams.”
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Source: www.newscientist.com
