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.
Minor and medium dam shelf-life is lower than large dams for example Krishna Raja Sagar dam built in 1931 is 90 years old and Mettur dam built in 1934 is 87 years old.
Implications of ageing dams:
In a paper ‘supply-side hydrology last gasp’ Rohan D’Souza writes the siltation rate of Bhakra dam is 130.86 % so at this rate it will function for merely 47 years as against the original estimate of 88 years.
When when the dams ages the soil replaces water, the supply of water decreases and this in turn leads to reduction in the cropped area as less water is received and which increases dependency on on the rain which is erratic in nature and groundwater is overexploited, the crop yield increases and farmers income thereby decreases.
By 2050 this will pose difficulties such as scarcity of water to feed the ever increasing population.
The flawed siltation rates reinforce the argument that designed flood cushions within several reservoirs across many river basins may have already depleted substantially due to which floods become more frequent downstream of dams. For example the flooding of Bharuch in 2020, Kerala in 2018 and Chennai 2015 a few examples attributed to downstream releases from reservoirs.
The way forward in the situation can be the building of medium or minor irrigation based small storage structures, identifying mechanisms to recharge aquifers and store water underground.
Hence, India will eventually feel difficulty in finding sufficient water in the 21st century to feed the rising population by 2050, grow abundant crops, create sustainable cities, or ensure growth. Therefore all stakeholders must come together to address this situation urgently.