Older dams pose a threat to growth – most of humanity can be at risk

Examples of reports include the Caribbean Dam in Africa, the world’s largest man-made reservoir, with a discharge of 181 km³. About $ 300 million was lent in 2014 to repair the warehouse, which is expected to be completed by 2023. The report says: “Dams such as the Caribbean will continue to operate for much longer with recurring investments in repairs, despite their advanced age, as they can be very old and risky. and removal is costly. ”Credit: Rhys Jones

By 2050, most of humanity will live in the lower part of the great dams built in the 20th century; Experts, who are increasingly expensive to use, predict a tendency to decommission dams.

By 2050, according to an analysis by the UN University, most people on Earth will live in the streams of tens of thousands of large dams built in the 20th century; many of these have a design life of one year or more.

According to a report by the UN Institute for Water, Environment and Health in Canada, “Aging Water Infrastructure: An Emerging Global Risk,” most of the world’s 58,700 major dams were built between 1930 and 1970 with a design period of 50 to 100 years. , A large concrete dam in 50 years “will probably begin to show signs of aging,” he said.

Signs of aging include increasing dam damage, increasing dam repair and maintenance costs, increasing reservoir sedimentation, and loss of dam operation and efficiency.

The report says that well-designed, constructed and maintained dams can “easily” reach 100 years of service, but predicts an increase in “decommissioning”, a rapidly growing phenomenon in the United States and Europe, as economic and practical constraints prevent aging dams. if the improved or original use is already obsolete.

Older dams by region

Today, the problem of aging of large dams is faced by a relatively small number of countries – 93% of all major dams in the world are located in only 25 countries, led by China and the United States. Credit: UNU-INWEH

Globally, the volume of large bodies of water stored behind large dams is 7,000 to 8,300 cubic kilometers – enough to submerge about 80 percent of Canada’s landmass by one meter.

The report provides an overview of the aging of dams around the world and its main functions – water supply, irrigation, flood control, hydropower and recreation.

It also explains the growing risk of old dams, increased repair costs, reduced functionality due to collapse, the benefits of restoring or redesigning the environment, and the impact of a society that evaluates what policymakers should decide – supporters and supporters. et. In particular, “the nature of these effects varies significantly between low- and high-income countries.”

The analysis also included cases of decommissioning or aging of dams in the United States, France, Canada, India, Japan and Zambia and Zimbabwe.

Climate change will accelerate the aging of the dam

UNU-INWEH Director co-author Vladimir Smakhtin said: “This report aims to draw global attention to the aging reservoir infrastructure and to stimulate international efforts to combat this emerging, increasing water risk.”

“The increasing frequency and severity of floods and other extreme environmental events are beyond the design boundaries of a dam and accelerating the aging of the dam,” he said. Decisions on decommissioning must be made in a changing climate. ”

Duminda Perera, lead author and senior researcher at UNU-INWEH, said: “Today, the problem of aging large reservoirs is faced by a relatively small number of countries – 93% of all large reservoirs in the world are located in only 25 countries.”

“The construction of large dams increased rapidly in the mid-20th century and peaked in the 1960s and ’70s,” he says, “especially in Asia, Europe and North America, and in Africa the peak occurred in the 1980s. continuously and gradually decreased. ”

Old Water Infrastructure

UNU-INWEH report cover. Credit: UNU-INWEH

According to the report, the world is unlikely to witness a revolution in the construction of a large dam, as in the middle of the 20th century, but then the dams will have to show their age.

China has 23,841 major dams (40% of the world’s total). The 32,716 major dams (55% of the world’s total) are in only four Asian countries: China, India, Japan and the Republic of Korea – most of which will reach the 50-year mark relatively soon. The same is true of many large dams in Africa, South America and Eastern Europe.

Over the past four decades, the pace of construction of large dams has declined sharply and continues to decline in part, as “about 50% of global river volume is already regulated by dams, and the best places for such dams in the world are declining.” the report says.

There are also serious concerns about the environmental and social impacts of dams, especially on large dams, as well as emerging ideas and practices regarding alternative reservoir types, nature-based solutions, and non-hydropower generation.

Damp decommissioning drivers

Public safety, rising operating costs, the collapse of the reservoir and the restoration of the natural river ecosystem are among the reasons for the dam’s closure.

However, most of the dams removed so far were small; decommissioning of large dams (defined by ICOLD as 15 or more meters from the lowest foundation to the top, or between 5 and 15 meters with more than 3 million cubic meters of water spilled) is still in its infancy, with some cases known in the last decade.

“Several studies of large dams that are aging and decommissioning show the complexity and length of the process that is often needed to safely organize the decommissioning of a dam,” adds R. Allen Curry, co-author and professor at UNU-INWEH. New Brunswick.

“Taking a small item requires continuous expert and public participation and long-term regulation over such years (often decades). Since the mass aging of dams is well started, it is important to develop a protocol framework that will guide and accelerate the process of dam removal. ”

The decommissioning will have various positive and negative economic, social and environmental impacts that will be considered in the local and regional social, economic and geographical context as “critical to the maintenance of broader, sustainable development goals for a region”.

“In general, the decommissioning of the dam should be considered as important as the construction of the dam in the overall planning process for the development of reservoir infrastructure.”

“As a result, value judgments will determine the fate of many of these large reservoirs. This is not an easy process, and thus the sharing and sharing of decommissioning practices should be a common global goal. The lack of such information and its reflection in relevant regional / national policies / practices can have a gradual and negative impact on the ability to properly manage reservoir infrastructure as we age. ”


In addition to the three UNU-INWEH experts, the report was prepared by Spencer Williams of the Alumni Institute for International and Development Studies in Geneva, Switzerland. and Taylor North, from McMaster University, Hamilton, Canada.

According to the numbers


  • 58,700: Large dams registered in the International Commission on Large Dams (ICOLD) database are defined as the largest dam at a height of 15+ meters measured from the lowest base to the top, or 5 to 15 meters at a height of more than 3 million cubic meters (0.003 km3). Of the 58,700 large dams, about one in eight has a capacity of 100 million cubic meters (0.1 km3).
  • 7000 – 8300 km3: The volume of water collected behind large dams worldwide – one-sixth of the world’s annual discharge – is enough to submerge about 80% of Canada’s landmass by one meter.
  • Between 50 and 100 years: the design period of dams built between 1930-1970 (when most of the existing large dams were built). Average life: 50 years
  • ~ 16,000: Large dams between the ages of 50 and 100 in North America and Asia
  • ~ 2,300: Large dams 100+ years old in North America and Asia

USA / Canada

  • 56: 90,580 Average age of US item (in any size)
  • 85%: Items operating in the length of the United States or longer in 2020
  • 75%: Accidents in a US warehouse after the age of 50
  • $ 64 billion: Estimated cost to restore U.S. dams
  • 1,275: dams have been lifted in 21 US states in the last 30 years; 80 was removed in 2017 alone
  • 50% +: Large items over 50 in Canada

Asia / Pacific


  • 56%: The proportion of the world’s largest dams located in China and the United States (more than the first 25 countries ~ 93%)
  • 23,841: Large dams in China (most of all countries and 40% of the world’s total)
  • 60%: the proportion of the world’s largest dams in Asia
  • 55%: The proportion of large dams around the world – China, India, Japan and the Republic of Korea – most will soon reach 50


  • 1.115+: Big dams in India that will be about 50 years old in 2025
  • 4.250+: Big dams in India that will be 50 years old in 2050
  • 64: Large dams in India by 2050 that will be 150+ years old
  • 3.5 million: The number of people at risk if India’s Mullaperiyar Dam, built 100+ years ago, fails. The seismically active dam shows significant structural flaws, and its management is a contentious issue between Kerala and Tamil Nadu.


  • 100+ years: The average age of large dams in Japan


  • 650: Large dams in Australia half-50 years old; Has been operating for 50+ 100 years. Part of Australia’s hydropower generation: 65%

England / Europe

  • 100+ years: The average age of large dams in the UK
  • ~ 10%: Large dams in Europe 100+ years old


  • 2,000: Large dams in Africa (including South Africa), at least from all continents; used for more irrigation

UNU-INWEH is supported by the Government of Canada through Global Affairs Canada and McMaster University, Hamilton, Canada.

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