Study: Sediments reduce the storage capacity of dams

Study: Sediments reduce the storage capacity of dams

Sediments reduce the storage capacity of dams

Large dams are in danger of losing around a quarter of their storage capacity by 2050 due to the ingress of sediment.  Photo: Yu

Large dams are in danger of losing around a quarter of their storage capacity by 2050 due to the ingress of sediment. photo

© Julian Stratenschulte/dpa

Rivers fill reservoirs with water. But they also bring material with them that gradually fills up the tanks. Researchers at the United Nations have calculated the extent to which global storage capacity is shrinking.

According to a UN study, large dams around the world are at risk of losing around a quarter of their original storage capacity by 2050 due to the ingress of sediment. The estimated loss from the original capacity adds up to 1.65 trillion cubic meters for the approximately 50,000 plants considered, which roughly corresponds to the annual water consumption of India, China, Indonesia, France and Canada together, the United Nations University said on Wednesday with. The scale of the losses is worrying, especially as the world is already facing a number of other water supply problems.

Dams restrict the natural transport of sediment rivers a. Due to the deposited sediments, many reservoirs are gradually silting up, and there is also a risk of increased flooding upstream and increased erosion downstream. The entry into the reservoirs has become one of the most important challenges for the global water storage infrastructure, reports the team led by Duminda Perera from the Institute for Water, Environment and Health at the United Nations University (UNU-INWEH) in Hamilton (Canada).

A creeping global water problem

“The decline in available storage capacity by 2050 in all countries and regions will challenge many aspects of economies, including irrigation, power generation and water supply,” Perera said. “The new dams currently being built or planned will not compensate for the storage losses caused by sedimentation.” A creeping global water problem with potentially significant impacts is looming.

In Asia, for example, where 60 percent of the world’s population lives, water storage is critical to maintaining water and food security, the UN analysis says. The situation becomes more difficult when there are around 23 percent of the water storage in large dams lost due to sedimentation.

Sedimentation also has positive aspects

The deposition of sediments in reservoirs, for example, does not only cause problems in the water and energy supply, reported Theresa Schiller, officer for international water resources at the environmental foundation WWF Germany. Accordingly, sediments play a central role in determining the shape of a river on its way from the source to the sea. In addition, sediments acted as fertilizer when banks were naturally flooded. “If there is no sediment transport, this can lead to rivers digging deeper into their beds and riparian regions suffering more from drought,” says Schiller. In addition, important nutrients for many ecosystems and agriculture were then missing.

According to the study presented in the journal “Sustainability”, Germany ranks 6th among the 42 European countries considered. Reservoirs in this country have already lost around 24 percent of their original capacity. By 2050, the loss could rise to nearly 35 percent. According to the analysis, in Ireland the loss due to stored sediment is already almost 30 percent, and in 2050 it could be almost 40 percent. In Denmark, on the other hand, the storage loss is currently around 10 percent, and by 2050 it will be around 20 percent.

According to the researchers working with Perera, Great Britain, Panama, Ireland, Japan and the Seychelles will have the highest losses in water storage worldwide by 2050: between 35 and 50 percent of their original capacity. Reservoirs in countries such as Bhutan, Cambodia, Mongolia, Ethiopia, Guinea and Niger, on the other hand, are hardly affected for the time being because the dams there are usually relatively young. Japan’s dams, for example, are more than 100 years old on average, and Mongolia’s 12 years on average.

Bypass tunnels could reduce the sediments

Perera’s researchers had calculated the probable loss of storage capacity for more than 47,400 large reservoirs in 150 countries for the years 2022, 2030 and 2050 from estimates of the silting rates. A good 28,000 of the structures are in the Asia-Pacific region, around 2,300 in Africa, around 6,700 in Europe and 10,400 in America. Dams that are more than 15 meters high or that have a capacity of more than 3 million cubic meters at a height of 5 to 15 meters were defined as “large”.

The original global storage capacity of around 6,300 billion cubic meters of the structures considered will therefore fall to around 4,670 billion cubic meters by 2050. Among the possible countermeasures, the UN researchers include so-called bypasses. These are separate channels through which water is channeled directly downstream, especially during flood events – which often result in particularly high levels of sediment input. When operated optimally, bypass tunnels could reduce sedimentation by up to 90 percent, previous studies have shown.

The scientists explain that an alternative is to raise the dam to compensate for the storage loss. However, this would increase the area of ​​the reservoir, which could have consequences for adjacent habitats. Expensive dredging or sediment flushing is also possible, but could have a significant negative impact on downstream areas.


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