The flood that devastated the Libyan city of Derna and caused the death of more than 11 thousand people occurred because with the intense rains of storm Daniel, two dams also built to protect the city from similar events collapsed, dispersing large quantities of water. waterfall. The two dams had been built in the Seventies, had not undergone modernization works since 2002 and according to a study published last year in a scientific journal of the University of Sebha they needed “immediate measures” because “in the event of a large flood the result will be disastrous for the people residing in the plain and in the city”.
In recent days, hydrology experts from around the world have commented on what happened, calling it a “human disaster” rather than a “natural disaster” and reiterated that there are many other dams in the world that were built decades ago and have become obsolete. , that is, inadequate for one reason or another to the current situation. Some should be modernized or rebuilt, others should even be demolished because the environmental changes that have occurred since their construction, for example drying out processes, have made them superfluous.
Like all human infrastructures, dams are not eternal, but have a sort of expiration date beyond which they are no longer as useful and safe as when they were built. Water erodes the concrete walls of which they are made and the ground on which they are built and it may be necessary to reinforce the structure or foundations. In some cases, there are problems with the siltation of the artificial basins formed by the dams because large quantities of sediment have accumulated there over time; when this is the case, dams can even become useless or harmful because they contain less water and do not allow hydroelectric energy to be produced as they should.
Depending on how they were built and the context in which they are located, the “life expectancy” of the dams can be different, but on average after about fifty years from construction some kind of interventions should be carried out. And a very large part of the almost 50 thousand large dams in the world, those that are at least 15 meters high and can contain more than 3 million cubic meters of water, were built in the 1970s or earlier to produce hydroelectric energy and guarantee reserves of water for agricultural irrigation: most are obsolete today, some are almost a hundred years old.
According to a United Nations report on the world’s old dams published in 2021, between North America and Asia there are about 16,000 large dams that are between 50 and 100 years old and about 2,300 that are more than a year old. century. In India, more than 1,115 dams will be around 50 years old in 2025; in China those considered obsolescent are more than 30 thousand. The problem also greatly concerns the United States: the average age of the more than 90 thousand dams in the country was 56 years in 2021. In Europe the number of large dams is much lower, but also in Italy, where there are 541, the their average age is high: it was 67 when the report was published.
The most problematic situations are in India and China. For example, the Mullaperiyar dam, located in the Indian state of Kerala, is more than a hundred years old, is visibly damaged and is located in a seismic risk area: it has been estimated that its collapse would harm 3.5 million people. In April, an Indian parliamentary committee expressed concern that 234 dams in the country are more than a hundred years old – they were built during British rule – and should be decommissioned.
In an intervention published by the New York Times Josh Klemm and Isabella Winkler, the directors of the environmental NGO International Rivers, which deals with the way in which rivers are exploited throughout the world, wrote that in the United States, the second largest country in the world in terms of the number of large dams, there are approximately 2,200 dams at risk of collapsing. President Joe Biden’s administration has allocated funds that should finance the modernization work for some of these, but many others do not fall under the jurisdiction of the federal government; they are managed by individual states, which often struggle to find the huge resources necessary for extraordinary maintenance.
In some cases, such as the numerous dams located along the Mississippi, the most important river in the country, it is not easy to establish who should pay the costs for the works because the infrastructure serves different states and different economic entities.
The problems could worsen due to climate change due to human activities, which is causing and will increasingly cause extreme precipitation in various parts of the planet. When the dams currently in use were built, the statistics on extreme events were different from those today: for this reason they were not made to repeatedly withstand particularly intense events that could more likely occur in the future.