Q. What is the Global Scenario?
- Most of the 58,700 large dams worldwide were constructed between 1930 and 1970 with a design life of 50 to 100 years.
- By 2050, most people on Earth will live downstream of tens of thousands of large dams built in the 20th century, many of them already operating at or beyond their design life.
- At 50 years, a large concrete dam “would most probably begin to express signs of ageing.”
- Ageing signs 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 - “strongly interconnected” manifestations.
- 32,716 large dams (55% of the world's total) are found in just four Asian countries: China, India, Japan, and South Korea - a majority of which will reach the 50-year threshold relatively soon.
- The same is true of many large dams in Africa, South America, and Eastern Europe.
Q. What is Indian Scenario?
- 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 dangerous as their shelf life is even lower than that of large dams.
- Examples: Krishna Raja Sagar dam was built in 1931 and is now 90 years old. Similarly, Mettur dam was constructed in 1934 and is now 87 years old. Both these reservoirs are located in the water scarce Cauvery river basin.
Q. What are the problems as highlighted by report?
- Decreasing Storage Capacity:
- As dams age, soil replaces the water in the reservoirs. Therefore, the storage capacity cannot be claimed to be the same as it was in the 1900s and 1950s.
- The storage space in Indian reservoirs is receding at a rate faster than anticipated.
- Flawed Design:
- Studies show that the design of many of India’s reservoirs is flawed.
- Indian reservoirs are designed with a poor understanding of sedimentation science.
- The designs underestimate the rate of siltation and overestimate live storage capacity created.
- High Siltation Rates:
- It refers both to the increased concentration of suspended sediments and to the increased accumulation (temporary or permanent) of fine sediments on bottoms where they are undesirable.
Q. What might be the consequences for it ?
- Less Water:
- When soil replaces the water in reservoirs, supply gets choked. The cropped area begins receiving less and less water as time progresses.
- Impact on Groundwater:
- The net sown water area either shrinks in size or depends on rains or groundwater, which is overexploited.
- Affecting Farmers’ Income:
- 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.
- It is important to note that no plan on climate change adaptation will succeed with sediment packed dams.
- Frequent Flood:
- The designed flood cushions 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.
Q. What are some recent steps taken by the government ?
- Recently, the Cabinet Committee on Economic Affairs has approved the Dam Rehabilitation and Improvement Project (DRIP) Phase II and Phase III.
It envisages comprehensive rehabilitation of 736 existing dams located across the country and complements the Dam Safety Bill, 2019