UN’s study of Dams

In News

• Recently a study by the United Nations University Institute on Water, Environment and Health (UNU-INWEH), also known as the UN’s think tank on water was released.

Study highlights

• Global status:
  • Potential reduction in storage: 
    • The study shows that 6,316 billion cubic metre of initial global storage in 47,403 large dams in 150 countries will decline to 4,665 billion cubic metre, causing 26 percent storage loss by 2050.
    • The loss of 1,650 billion cubic metre storage capacity is roughly equal to the annual water use of India, China, Indonesia, France and Canada combined.
  • Reduced dam storage in Asia-Pacific:
    • In 2022, the Asia-Pacific region, the world’s most heavily dammed region, is estimated to have lost 13 per cent of its initial dam storage capacity. 
    • It will have lost nearly a quarter (23 per cent) of initial storage capacity by mid-century.
      • The region is home to 60 per cent of the world’s population and water storage is crucial for sustaining water and food security.
• India’s dams:
  • The study warns that around 3,700 dams in India will lose 26 percent of their total storage by 2050. 
  • Reason of loss:
    • This storage loss will be due to the accumulation of sediments which can undermine water security, irrigation and power generation in the future.
      • Trapped sediment has already robbed roughly 50,000 large dams worldwide of an estimated 13 to 19 percent of their combined original storage capacity.
• China’s dams:
  • China, meanwhile, the world’s most heavily dammed nation, has lost about 10 percent of its storage and will lose a further 10 percent by 2050 according to the report.

More about dams

• About:
  • Dam is a structure built across a stream, a river, or an estuary to retain water. 
  • India has 4,407 large dams, the third highest number in the world after China (23,841) and the USA (9,263).
  • Types:
    • Large: A dam is considered large if it is higher than 15 m or between 5 and 15 m high, but impounds over 3 million cubic metres.
    • Low: A low dam is less than 30 m high; 
    • Medium: A medium-height dam is between 30 and 100 m high, and 
    • High: A high dam is over 100 m high.
• Significance of dam construction:
  • Water storage infrastructure is critical for development. 
  • Large dams and reservoirs provide hydroelectricity, flood control, irrigation, and drinking water and often perform multiple functions simultaneously.
• Major threats to dams:
  • Ageing:
    • All over the world, many large dams built in the 20th century may start to show signs of ageing, and many may already be operating at or beyond their design life. 
    • For India, 2025 is set to be a big year as more than 1,000 dams would turn roughly 50 years or older.
  • Accumulation of sediments & siltation:
    • Accumulation of sediments decreases a reservoir’s capacity over the years and determines a reservoir’s life expectancy.
    • Siltation, which is the accumulation of silt and debris behind the reservoir, also leads to a reduction in the storage capacity of the dams.

• Structural issues:
  • India’s dams are more vulnerable to deterioration because a large proportion of them are earthen–built by compacting successive layers of earth, and not concrete–and are hence more prone to ageing.
• Flooding:
  • The country gets concentrated rainfall every year for a designated time period as opposed to distributed rainfall, which contributes to the dams’ vulnerability.
  • In India, the downstream areas are often exposed to flood disasters& flooding has caused 44% of dam failures in India.
• Seismic threat:
  • Some of the Himalayan dam systems, including the Tehri Dam, are in an active seismic area given that the Himalayan mountain system is constantly changing and growing giving rise to several tectonic movements.

Way ahead

• The Central Water Commission’s recent study on the Srisailam project on the Krishna river also found that the dam’s storage capacity was reduced as a result of siltation. 
  • There are several more studies that clearly show that the actual siltation rates are several times higher than what was estimated.
• Therefore, a timely assessment of the structure should be carried out with the removal of reservoir silt from dams.