The ageing of dams emerges as a development issue faced by many countries with many of the large dams worldwide reaching or almost near the lower bound (50 years) of their anticipated life span.
At 50 years, a concrete dam would probably show signs of ageing. Most of the 58,700 large dams were constructed between 1930 and 1970 with a life span of 50 to 100 years, said a study of the Unite Nations University.
The study “Ageing Water Infrastructure : An Emerging Global Rick” notes that Asia and North America has 16,000 large dams in the 50-100 year old range. It says the region has 2,300 large dams over 100 years old. The average age of 90,580 dams in the US is 56 years and 85 per cent of them reached life expectancy in 2020.
When over 30,000 dams are ageing in China, over 1,115 large dams will be at 50 years mark by 2025 in India.
More than 4,250 large dams will pass life expectancy of 50 years, with 64 large dams almost 150 years in 2050, the study said.
The UN University study said that well designed and maintained dams can “easily” reach 100 years. However, economic and practical limitations prevent ageing dams from being upgraded, the study added.
UNU-INWEH Director Vladimir Smakhtin, who is co-author of the study, said that the report aimed at attracting global attention to the issue of ageing water storage infrastructure. It also aims at garnering international efforts to deal with the emerging, rising water risk.
93 per cent of the large dams are concentrated in just 25 countries.
Smakhtin says that the frequency and severity of floods was on a rise. Moreover, the worlds witnessed extreme environmental issues and climate change. All these can overwhelm the design limit of a dam and accelerate its ageing process. As such, the study stresses that decision with respect to decommissioning need to be taken in the context of a changing climate. 
Signs of ageing
Increasing cases of dam failures,
Increasing costs of dam repair and maintenance
Increasing reservoir sedimentation
Loss of a dam’s functionality and effectiveness
Trends of larger dams
The construction of large dams was most in the mid 20th century. This peaked in the 1960s and 70s, especially in Europe, Asia and North America. However, Africa saw the peak of construction only in the 1980s.
China has the largest number of large dams (23,841).
Africa
Africa saw a surge in dam construction in the 1980s and 1990s. This means that ageing is still not a concern. Africa has less number of large dams than other continents. The continent has about 2000 lareg dams, including Akosombo Dam in Ghana, Aswan Dam in Egypt and Kariba Dam in Zambia and Zimbabwe.
Asia
India, China, South Korea and Japan are the countries that have the most most number of large dams. China alone has about 40 per cent of the world’s large dams. Many of them are reaching the life span of 50 years. China continues to build large dams with the Three Gorges Dam on the Yangtze River. The construction rate dams in India is among the world’s highest.
Australia
Half of the more than 650 large dams in Australia have reached the 50 years mark. The dams that are more than 50 years of age are in operation for more than a century, the study said. Australia has the largest number of water supply dams.
Europe
An interesting thing is that the dams for irrigation in the continent are young, whereas in other parts of the globe, they are the oldest. The United Kingdom has most of the older dams with an age of over 100-years.
About 10 per cent of large dams in Europe are over 100 years old.
The study says that construction of dams have stopped in Europe, mainly because a few waterways remain unimpeded. However, the construction rate in Eastern Europe and Turkey for hydropower dams is highest.
North America
The United States of America, Canada and Mexico are among the leaders in large dam. Among them, the US has the largest number of ageing dams. Almost 80 per cent of the dams here are over 50 years.
South America
The large dams in South America do not have a life span issue as in other continents. Brazil has the largest number of dams
