NEWS Dams and reservoirs are believed to secure our water needs for the future. However, data and studies show that they can threaten our water security.

DAMS IN INDIA 

• India is ranked third in the world in terms of building large dams. 
• Of the over 5,200 large dams built so far, about 1,100 large dams have already reached 50 years of age and some are older than 120 years.
• The number of such dams will increase to 4,400 by 2050. This means that 80% of the nation’s large dams face the prospect of becoming obsolete as they will be 50 years to over 150 years old.
• The situation with hundreds of thousands of medium and minor dams is even more precarious as their shelf life is even lower than that of large dams.

CHALLENGES WITH AGEING OF DAMS

• As dams age, soil replaces the water (technically known as silt or sediment) in the reservoirs. Therefore, the storage capacity cannot be claimed to be the same as it was in the 1900s and 1950s.
• Studies show that the design of many of our reservoirs is flawed. In a paper, ‘Supply­side Hydrology: Last gasp’, published in 2003 in Economic & Political Weekly, it is observed that the siltation rate in India’s iconic Bhakra dam is 139.86% higher than originally assumed. 
• At this rate, the Bhakra dam is now expected to function for merely 47 years, virtually halved from the original estimate of 88 years. Similarly, the actual siltation rate observed for the Hirakud, Maithan and Ghod dams are way higher at 141.67%, 808.64% and 426.59%, respectively. 
• Various studies show that Indian reservoirs are designed with a poor understanding of sedimentation science, thus underestimate the rate of siltation and overestimate live storage capacity created.

CONSEQUENCES

• When soil replaces the water in reservoirs, supply gets choked. 
• The cropped area begins receiving less and less water as time progresses.
• The net sown water area either shrinks in size or depends on rains or groundwater, which is over­exploited. 
• Crop yield gets affected severely and disrupts the farmer’s income. In fact, the farmer’s income may get reduced as water is one of the crucial factors for crop yield along with credit, crop insurance and investment. 
• No plan on climate change adaptation will succeed with sediment packed dams.
• The flawed siltation rates demonstrated by a number of scholarly studies reinforce the argument that the designed flood cushion within several reservoirs across many river basins may have already depleted substantially due to which floods have become more frequent downstream of dams. 
• The flooding of Bharuch in 2020, Kerala in 2018 and Chennai in 2015 are a few examples attributed to downstream releases from reservoirs. 
• The nation will eventually be unable to find sufficient water in the 21st century to feed the rising population by 2050, grow abundant crops, create sustainable cities, or ensure growth. 

Therefore, it is imperative for all stakeholders to come together to address this situation urgently. Water policymakers, planners, and water managers need to think of alternative plans for large storage structures with sustainable decommissioning of present dams and simultaneously building sustainable structures to recharge, store underground water. 

Reference:

1. https://www.thehindu.com/opinion/op-ed/the-problem-of-ageing-dams/article33711348.ece