February 25, 2021

Aging prey becomes a growing threat


In the year 2050, most of the Earth’s inhabitants will live downstream of tens of thousands of large dams, more than 15 meters high from foundation to top or between 5 and 15 meters with more than three million dams. m3 dammed, built throughout the 20th century. According to a new report from the United Nations University (UNU-INWEH), many of these infrastructures are already obsolete in terms of their design and exceed their useful life, located between 50 and 100 years.

“The construction of large dams emerged in the mid-20th century and reached its peak in the 1960s and 1970s, especially in Asia, Europe and North America, while in Africa the peak occurred in the 1980s. number of large dams after that declined steadily and progressively, “explains co-author Vladimir Smakhtin, director of the Institute of Water, Environment and Health of the UNU-INWEH.

Most of the more than 58,700 large reservoirs built between 1930 and 1970. 60% of the largest dams are located in Asia, where four countries – China, India, Japan and South Korea – top the list along with EE. USA and Brazil.

Only in Spain, were built 1,064 large dams, out of a total of more than 1,200, who have an average age of 56 years, being the European country with the largest number of reservoirs, and tenth in the world.

Starting at 50 years of age, these concrete structures will probably begin to show signs of aging, such as increased bankruptcies or breakages that involve increasing maintenance and repair costs, increased reservoir sedimentation, and loss of functionality and effectiveness. All of these causes are “strongly interconnected,” the document says.

Main risks of old dams

These infrastructures, which serve as storage for the supply of water, irrigation, flood control, hydroelectric energy or even for entertainment, contain an enormous volume of water that is estimated to be between 7,000 and 8,300 km3, the equivalent of covering close to 80% of Canada’s land mass under one meter of water. Due to their age, what risks do these aging structures face?

The main danger, according to the team of scientists, would be a breakdown of the structure. “The worst case scenario is the collapse of the dam, which would cause a large number of victims and economic losses worth millions of dollars,” the lead author of the report Duminda Perera, a researcher at UNU-INWEH, told SINC.

Added to this is sedimentation that can reduce the storage capacity of the dam. “If they are not eliminated, the structure becomes obsolete,” he acknowledges. High maintenance and repair costs also increase as reservoirs age.

Risks also appear to be increasing due to climate change, the report notes. Dams built in the last century were based on “stationary” hydrological data, meaning they do not change over time. “Due to climate change, river flow records do vary,” the authors warn.

In addition, more frequent and intense rains can cause changes in the flood pattern with a greater impact on the structure of the dam. “Thus, more extreme rainfall can promote upstream erosion leading to accelerated sedimentation of the reserve,” continues the scientist. Increased temperatures also promote evaporation from the reservoir surface and make water storage less efficient.

According to the report, given this, only well-designed, built and maintained dams can reach 100 years of service, so the authors suggest that there will be an increase in “decommissioning”, a phenomenon that is accelerating in the US. ” Regular inspections and timely maintenance can significantly increase the life of a dam, “says Perera.

In the case of Europe, avoiding aging will depend on economic and practical constraints or on maintaining the original use of the structure. “Elimination or dismantling is an option when it is too risky to maintain a dam for longer or when the dam no longer fulfills its function,” Perera tells SINC.

According to the authors, if a dam is to be removed, partially or totally, dismantling is much less expensive than repair or reconstruction. “In general, the dismantling of dams should be considered as important as the construction in the planning process,” they collect in the work.

The European ones, the oldest

As in Spain, where the peak of construction occurred in the 1960s, the average age of European dams is around 50 years. The United Kingdom is the European country that concentrates the oldest dams with an average age of 106 years.

Like these, about 10% of European dams reach that age on a continent where activity to build them has practically ceased and few rivers and waterways remain free of obstacles, although in Spain the construction of dams has remained in the 70s, 80s, 90s to the present day, but to a lesser extent.

There are also other exceptions: “In Eastern Europe and Turkey, the rate of construction, especially of hydroelectric dams, is among the highest in the world,” Perera emphasizes.

According to scientists, in general, the trend in Europe is to remove and dismantle dams and protect waterways and keep them clear of obstacles. But “this is not due to a concern for public safety, but for environmental reasons, since various groups urge the restoration of migratory routes for fish,” the authors conclude to SINC.

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