Water crisis: World to lose 26% storage by 2050 to trapped sediment, says new UN report

Subject: Geography

Context:

About 50,000 large dams across the world will lose 24-28 per cent water storage capacity by 2050 due to sediment trapped in them, a report by the United Nations Institute for Water, Environment and Health showed.

Details:

These water reservoirs have already lost about 13-19 per cent capacity to sedimentation.
The United Kingdom, Panama, Ireland, Japan and Seychelles will experience the highest water storage losses by 2050 from 35-50 per cent of their original capacities. By contrast, Bhutan, Cambodia, Ethiopia, Guinea and Niger will be the five least-affected countries, losing less than 15 per cent by mid-century.
India’s 3,700 large dams will have lost on average 26 per cent of their initial total storage by 2050.
Japan is the most vulnerable country with an estimated loss of nearly 50% of water storage capacity by 2050.
The loss will challenge many aspects of national economies, including irrigation, power generation and water supply.

Estimated storage loss by 2050

Estimated storage loss at present (2022)

Sedimentation and its impact:

Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier.
Sedimentation is caused when a river carrying eroded soil is blocked by a dam at its watershed.
The sudden drop in water velocity leads to the deposition of large volumes of particles in the calm waters of the reservoirs.
While sediment helps maintain the aquatic ecosystem, poor management can lead to nutritional disbalances causing eutrophication and other disruptions in the water pool of the dam, as well as damages in habitations downstream.
Loss of capacity occurs due to infilling of dams by trapped sediments.
Sediments can also damage dam structures and turbines.
Shallow water also reduces the recreational value of the reservoirs.
Unsustainable land-use practices may make sedimentation more aggressive by loosening up soil upstream.