According to the United Nations (UN) report “Ageing water infrastructure: An emerging global risk”, there is a rising concern over approximately 1,000 large dams in India that will be almost 50 years old by 2025. The report has been compiled by the Canada-based Institute for Water, Environment and Health. It suggests that another dam-building revolution akin to the mid-20th century is improbable, but the dams built during that period are reaching their expiry dates.
Global Snapshot: Ageing Dams
The world is home to nearly 58,700 large dams, most of which were constructed between 1930 and 1970. Their design life typically spans 50 to 100 years. By 2050, most of the world’s population will reside downstream of these large, 20th-century dams, many of whom already operate beyond their intended lifespan. As many of these structures approach the 50-year mark, signs of ageing, such as dam failures, increasing maintenance costs, reservoir sedimentation, and loss of functionality, become apparent.
Notably, 55% of the world’s large dams are located in just four Asian countries: China, India, Japan, and South Korea. A significant majority of these are approaching the half-century mark. Similar trends are also observed in Africa, South America, and Eastern Europe.
India’s Ageing Dams: A Growing Concern
India ranks third globally in terms of large dam construction. Out of over 5,200 large dams, about 1,100 have surpassed their 50-year lifespan, with some even older than 120 years. It’s estimated that by 2050, this number will rise to 4,400, indicating that 80% of India’s large dams will be 50 to over 150 years old. The status of hundreds of thousands of medium and smaller dams, which typically have shorter lifespans than large dams, is alarming.
For instance, the Krishna Raja Sagar dam, constructed in 1931 and the Mettur dam, built in 1934, are both located in the water-deprived Cauvery river basin. Both are showing their age, being 90 and 87 years old respectively.
Impact of Ageing Dams on Water Storage
As dams get older, their storage capacity decreases with soil replacing water in the reservoirs. The storage volume in Indian reservoirs is declining more rapidly than predicted. Flawed designs that underestimate siltation rates and overestimate live storage capacity are widespread, leading to high siltation rates that contribute to sediment build-ups where they are undesirable.
Consequences of Dam Ageing
The consequence of soil replacing reservoir water is a diminishing water supply, causing the crop area to receive less water over time. This negatively impacts the groundwater and results in either shrinkage of net sown water area or increased dependency on rainfall or overexploited groundwater. Farmers’ incomes could potentially drop as water availability is a key determinant of crop yield. Moreover, climate change adaptation plans may fail if we continue to have sediment-packed dams.
Frequent floods downstream of dams are another issue due to the depleting flood cushions within many reservoirs across several river basins. Several recent flooding events in India, such as Bharuch’s in 2020, Kerala’s in 2018, and Chennai’s in 2015, can be attributed to downstream releases from reservoirs.
Interventions: Dam Rehabilitation Measures
To address this issue, the Cabinet Committee on Economic Affairs recently approved the Dam Rehabilitation and Improvement Project (DRIP) Phase II and III, which aims at the comprehensive rehabilitation of 736 existing dams across the country. This initiative complements the Dam Safety Bill of 2019.
Moving Forward
By 2050, without appropriate action, it is anticipated that the nation will struggle to find sufficient water to sustain population growth, ensure agricultural yield, develop sustainable cities, or ensure overall growth. This pressing situation calls for urgent collaboration from all stakeholders. Measures to prevent dam failure are crucial as the fallout can lead to devastating loss of life that cannot be compensated for by any punishment. Notably, dam decommissioning must be equally prioritized as dam construction in planning for water storage infrastructure. In light of climate change, careful and proactive consideration of water-related issues is increasingly becoming essential.