Create protocols and decommission the ageing large dams speedily, recommends latest UNU-INWEH study

Create protocols and decommission the ageing large dams speedily, recommends latest UNU-INWEH study

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published Published on Jan 29, 2021   modified Modified on Jan 30, 2021

Large dams that cause environmental degradation and large-scale displacement, among other things, have been opposed in India by civil society organisations (CSOs), such as Narmada Bachao Andolan (NBA), National Alliance of People's Movement (NAPM) and People's Union for Civil Liberties (PUCL). A recently published study by the United Nations University's Canada-based Institute for Water, Environment and Health along with other partner organisations reveals that tens of thousands of existing large dams across the world have reached or exceeded an “alert” age threshold of 50 years, and many others will soon become 100 years old. As a result, on one hand maintenance needs and costs have arisen, while on the other hand effectiveness of these large structures have declined, posing potential threats to human safety and the environment.

Based on an extensive survey of literature, the UNU-INWEH report states that North America and Asia together accommodate nearly 16,000 large dams, which are 50-100 years old, and around 2,300 large dams, which are over 100 years old. Many large dams across the world have reached or are nearing the lower bound (i.e. 50 years) of their anticipated lifespan. For example, in India, over 1,115 large dams will reach the 50 years mark by 2025. Over 4,250 large dams in the country would pass 50-years of age, with 64 large dams being 150 years old at 2050.

Chart 1: Age of large dams by main geographical regions (Data Source: ICOLD WRD, 2020)

Source: Ageing Water Storage Infrastructure: An Emerging Global Risk, please click here to access

Titled Ageing Water Storage Infrastructure: An Emerging Global Risk, the report shows that the majority of the world's large dams are located in Asia. China, India, Japan, and the Republic of Korea together accommodate 55 percent of all large dams recorded, as per the database of World Register of Dams (WRD) of the International Commission on Large Dams (ICOLD), and of these, a majority will reach the 50-year threshold in the forthcoming years. In Asia, there are almost 9,894 large dams, which are 50-100 years old, and around 17,169 large dams, which are 10-50 years old. Please consult chart-1.

Table 1: Large dams by country (Data Source: ICOLD WRD, 2020)

Source: Ageing Water Storage Infrastructure: An Emerging Global Risk, please click here to access
Note: *The average dam capacity for Canada cannot be accurately estimated from ICOLD WRD.

The top 10 countries in the world with most number of large dams are China (23,841), the United States of America (9,263), India (4,407), Japan (3,130), Brazil (1,365), South Korea (1,338), South Africa (1,266), Canada (1,156), Mexico (1,079) and Spain (1,064). The average height of the 4,407 large dams in India is 24 meter. The average age and median age of large dams in the country are 42 years and 41 years, respectively. The average capacity of large dams is 80 million cubic meter. Please see table-1.  

Please note that “large dams” have been defined by the International Commission on Large Dams (ICOLD) as having a “height of 15 metres or more from lowest foundation to crest, or a dam between 5 metres and 15 metres impounding more than 3 million cubic metres.” ICOLD's current World Register of Dams (WRD) comprises more than 58,700 large dams that satisfy these criteria, although this list may not be comprehensive, mentions the UNU-INWEH study. It has been estimated that all these large dams can together hold nearly between 7,000 and 8,300 km³ (cubic km) of water i.e. almost 16 percent of all global annual river discharge.

Chart 2: Decadal large dam construction in main geopolitical regions since 1900 (Data source: ICOLD WRD, 2020)

Source: Ageing Water Storage Infrastructure: An Emerging Global Risk, please click here to access

Construction of large dams soared up in the mid-20th century and peaked in the 1960s and 1970s, especially in Asia, Europe, and North America, while in Africa, the peak happened much later in the 1980s. Most large dams in Asia were constructed during the decades 1951-1960, 1961-1970 and 1971-1980. Construction of large dams in Asia reached the peak in the decade 1971-1980. Around 9,578 large dams were built during the 1970s in Asia. However, the rate of construction of large dams globally has slowed down in the last four decades and continues to decline. Elsewhere in Asia, India's current dam construction rate is, however, considered to be among the world’s highest. Kindly check chart-2.

Dams are constructed to carry on functions like water supply, irrigation, flood control, hydropower, and recreation. Despite plans in some regions and countries to construct more water storage dams, especially for generating hydropower, the world is unlikely to witness another “dam revolution” to match the scale of high-intensity dam construction that was observed in the early to middle of 20th century, says the UNU-INWEH study. Many of the large dams, which were constructed during 1950s, 1960s and 1970s, are ageing. Hence, the world is witnessing “mass ageing” of water storage infrastructure.

Some studies indicate that an average life expectancy of a dam is 50 years, and that dams constructed between 1930 and 1970 (when most of the existing large dams were constructed) have a design life of nearly 50-100 years. However, some experts have suggested that the service life of well-designed, well-constructed, and well-maintained and monitored dams can easily reach 100 years, while some dam elements (like gates, motors) may need to be replaced after 30 to 50 years. However, all modern dams must meet safety regulations that typically model and examine scenarios of failure up to 100 years. In the present study, an arbitrary age of 50 years has been used as the point when “a human-built, large concrete structure such as a dam that controls water would most probably begin to express signs of ageing.”  

Some of the signs of ageing may include increasing cases of dam failures, progressively increasing costs of dam repair and maintenance, increasing reservoir sedimentation, and loss of a dam's functionality and effectiveness. Aged dams are more vulnerable to climate change on account of exposure to more frequent and extreme floods and/or increasing evaporation from the reservoir that can lead to accelerated loss of its function. Although the risks associated with large dams are “low probability and high consequence”, older dams combined with poor maintenance pose a higher risk to public safety, particularly for downstream areas.

Discussing the issue of decommissioning of dams, the report throws light on the tussle between Kerala and Tamil Nadu over the maintenance and management of Mullaperiyar dam. At the time of construction, the Mullaperiyar dam, which impounds the Periyaru River in Kerala, downstream to Tamil Nadu, had an intended lifespan of 50 years. Built in 1895 by the British government, the dam is located in a seismically active area and cracks in the dam have appeared over the years. Although the dam is maintained by Tamil Nadu (located upstream), people of Kerala are afraid of a dam collapse and argue that the reservoir level must be lowered until the dam is fixed. Nearly 3.5 million people are at risk if the Mullaperiyar dam collapses.

Decommissioning ageing dams means either removal or re-operation. Decommissioning dams is a relatively recent phenomenon, which is noticeable in the USA and Europe. Experience shows that small dams are likelier to be removed instead of the large ones. It is essential to develop protocols and policies that will guide and speed up dam removal. Removal of dams is generally a lengthy process, which requires regulatory approvals and consultation with the experts and the general public. There are several arguments in favour of decommissioning ageing dams, including protection of public safety, growing maintenance costs, progressing sedimentation of the reservoir, and environmental restoration, mentions the UNU-INWEH report. However, decommissioning can also have various positive and negative economic, social, and ecological consequences.

Decommissioning is the only option left to be considered if economic and practical limitations prevent a dam from being upgraded or if its original use has become obsolete. Decommissioning takes place when the cost of dam removal is less than that of repairing. The primary target audiences of the UNU-INWEH report are governments and their partners, who are responsible for planning and implementing water infrastructure development and management, emphasising adaptation to a changing climate and sustainable development.

There exists several global-scale databases on existing and planned dams. Although many features of these databases are overlapping, each has deficiencies with mixed levels of details. The UNU-INWEH report has suggested for merging these databases into one online portal, adopting one approach and thresholds for differentiating the data by dam characteristics, such as size and functions. It has also suggested for open and free access of the newly created database for low-income, developing regions. It should be mentioned here that accurate data helps to understand the factors and impacts of dam ageing in the local context.


Ageing Water Storage Infrastructure: An Emerging Global Risk –Duminda Perera, Vladimir Smakhtin, Spencer Williams, Taylor North, Allen Curry, United Nations University Institute for Water, Environment and Health (UNU-INWEH), UNU-INWEH Report Series-11, please click here to read more

Executive Summary: Ageing Water Storage Infrastructure: An Emerging Global Risk, please click here to access

Ageing dams in India, US, other nations pose growing threat: UN report, PTI/ The New Indian Express, 23 January, 2021, please click here to read more


Image Courtesy: Ageing Water Storage Infrastructure: An Emerging Global Risk, UNU-INWEH Report

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