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Insights into Editorial: The problem of ageing dams

 

Introduction:

Dams are critical infrastructure. They are important for the country’s development in various ways: water, power, irrigation, drinking etc.

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. Here is how.

It is not a secret anymore that India’s dams are now ageing and concomitantly, reservoir water is being replaced by soil, technically known as silt or sediment.

Their operational safety is extremely important as they impact lives as well as ecology.

 

Becoming obsolete with Indian Dams:

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.

Recently, a UN University report titled “Ageing water infrastructure: An emerging global risk“, held that by 2050, most people on Earth would live downstream of tens of thousands of large dams built in the 20th century, many of them including India’s already operating at or beyond their design life, putting lives and property at risk.

Ageing signs of dams 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.

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. 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.

 

293 big dams in country over 100-years old:

 

What will be happen when ageing of dam happens?

  1. 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.
  2. To make matters worse, studies show that the design of many of our reservoirs is flawed.
    1. Case Study: In a paper, Supply-side Hydrology: Last gasp, Rohan D’Souza writes that the observed siltation rate in India’s iconic Bhakra dam is 139.86% higher than originally assumed.
    2. At this rate, he wrote, “the Bhakra dam is now expected to function for merely 47 years, virtually halved from the original estimate of 88 years”.
  3. 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. Studies in later years showed similar findings.
  4. Almost every scholarly study on reservoir sedimentation shows that Indian reservoirs are designed with a poor understanding of sedimentation science.
  5. The designs underestimate the rate of siltation and overestimate live storage capacity created.
  6. Therefore, the storage space in Indian reservoirs is receding at a rate faster than anticipated.
  7. Reservoirs are poised to become extinct in less than a few decades with untold consequences already under way.

 

Disaster Consequences with over sedimentation:

  1. When soil replaces the water in reservoirs, supply gets choked. The cropped area begins receiving less and less water as time progresses.
  2. The net sown water area either shrinks in size or depends on rains or groundwater, which is over-exploited. Crop yield gets affected severely and disrupts the farmer’s income.
  3. 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.
  4. It is important to note that no plan on climate change adaptation will succeed with sediment-packed dams.
  5. 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.

 

Need of the hour: Dam Safety Act:

  1. A Bill seeking to set up an institutional mechanism for surveillance, inspection, operation and maintenance of specified dams across the country has been passed by the Lok Sabha.
  2. The provisions of the Bill are proposed to be applied to all dams in the country which have a height of more than 15 metres, or between 10 metres to 15 metres.
  3. Among other things, the Bill also seeks to resolve the inter-state issues concerning maintenance and safety of dams as around 92% of dams in the country are on inter-state river basins.
  4. The Bill also envisages setting up of a National Dam Safety Authority to be headed by an officer not below the rank of an Additional Secretary, to be appointed by the central government.
  5. The main task of the National Dam Safety Authority includes implementing the policies formulated by the National Committee on Dam Safety, resolving issues between State Dam Safety Organisations (SDSOs), or between an SDSO and any dam owner in that state, specifying regulations for inspection and investigation of dams.
  6. The NDSA will also provide accreditation to agencies working on construction, design, and alteration of dams.
  7. Since the dam safety is dependent on many external factors, the environmentalists, and the environmental angle in this, needs to be taken.
  8. There is a need to strengthen the state irrigation department and the Central Water Commission.
  9. It should be ensured that the inspection of dams is done by the respective state governments.

 

Conclusion:

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.

A preventive mechanism to avoid dam failures is necessary because if a dam fails, no amount of punishment can compensate for the loss of lives.

While considering uniformity across dams, local factors such as climate and catchment areas, need to be taken into consideration.

Therefore, it is imperative for all stakeholders to come together to address this situation urgently.