Dams, in distress?

It is time water policies in India acknowledge that many large dams have aged and can no longer be looked upon as the only path to water security.
Hirakud, India's oldest dam (Image Source: India Water Portal on Flickr) Hirakud, India's oldest dam (Image Source: India Water Portal on Flickr)

India is reeling from a severe water crisis. Large parts of the country are experiencing water-stress worsened by the ever increasing demand for water due to population growth, rapid urbanisation, changing lifestyles and consumption patterns, inefficient use of water and climate change.

While current policies and plans continue to imagine dams as one of the important means to tackle this growing water crisis, the paper ‘Ageing large dams and future water crisis’ published in the Economic and Political Weekly argues that it is time to rethink our policies and plans that continue to place emphasis on large dams. This is because we seem to be oblivious to the fact that a number of large dams in India have aged over the years, undergoing structural deterioration that can negatively influence water availability in the future.

About 5,264 large dams exist as of now in India and about 437 are under construction. In  addition, there are several thousand smaller dams. These dams are said to be vital for ensuring the water security of the country.

 The EPW paper highlights the problems faced by large dams in India and their implications for future water availability. It also suggests some solutions.

Current challenges facing large dams

Space to build large dams is shrinking

While policies in India continue to place emphasis on building of large dams to solve the water crisis, they do not consider the fact that the scope for building large storage structures in India has a spatial limit. The per capita storage capacity in India is very low with its existing 5,000+ large dams in comparison with countries such as the United States, China, South Africa, and Australia.

For example, India’s per capita storage capacity, estimated on the basis of the 253 km3 storage capacity (as on 2012), is 209 m3, whereas the per capita storage created by the US is 2,192 m3 and that by South Africa is 609 m3. There is no space available in India to further build structures and increase storage capacity.

 Thus, any plan to tackle future crises with the assumption of higher per capita storage cannot be implemented realistically in India.

Many of India’s dams are very old

While the Central Water Comission states that the 5,000+ large dam projects are vital for ensuring India’s water security, a large number of these large dams were built half a century ago. They are thus highly vulnerable to wear and tear and decrease in water storage capacity.

Evidence shows that about 64 dams in India are more than 115 years old, 301 large dams are between age 65 years and 115 years, and 237 large dams are more than 55 years old. Thus, about 619 large dams have already crossed the age of 50 years as of 2015.

Many large dams in India are structurally vulnerable

Any large storage structure, be it concrete, masonry, or earth, can become structurally weak with time. Such is the case with a number of old dams in India. such large constructions become weak because construction materials such as concrete and steel deteriorate due to abrasion from waves, silt, sand and gravel. They also wear and tear due to thermal expansion and cavitation.

Large dams are made by assembling different components built with different construction materials. For example, spillways are built with concrete and steel reinforcement; the flanks of the dam are built with earth or rockfill; the earth dam core is built with impervious material like clay; while many of the other dam structures are built by using concrete. These different components of a dam are designed to withstand different levels of stresses depending on the projected load they undertake.

Thus dams can face varying problems with respect to settlement of foundation, clogging of filters, increase of uplift pressures, cracks in the dam core, loss of bond between the concrete structure and embankments, reduction in slope stability in earthen and rockfill dams, erosion of earthen slopes, and deformation of the dam body itself. This differential ageing and deterioration of different parts of the dam can greatly affect the efficiency, water storage capacity and the safety of a dam in the long run.

Design standards and construction practices vary widely among India’s large dams

Since India’s large dams were constructed during different periods of time, the design standards and construction practices differ widely amongst the country’s existing and ongoing 5,000 large dams.

During the British rule in the 19th century, dams in India were built with rubble masonry, adopting rather poor British standards of concrete technology. Add to this, the lack of skilled manpower and poor construction and maintenance mechanisms. After India’s independence, the Bureau of Indian Standard’s (BIS) design codes were designed and revised from time to time along with changes in technology.

Thus, large dams constructed over several years have different levels of technology requiring different design codes and standards. Aging dams are thus highly likely to not be remedied or fortified, raising serious concerns about their ability to withstand the impending water crisis.

Lack of information on dam ageing

The loss of storage capacity of large dams over time is part of the dam ageing process. However, this information continues to be sporadically documented in India and serves as a blind spot in terms of understanding the true gravity of the water crisis in the country.

India’s differently aged 5,000 large dams are located in different geomorphological and agroclimatic regions and have been exposed to changes in land use and land cover over many years. The sedimentation rates as well as storage capacity across dams varies both spatially as well as temporally within the lifespan of a dam. However, no information is available on the differential ageing of these large dams.

Lack of information masks the real water situation in the country

There is an overall lack of information on large dams, particularly with regard to ultimate storage capacity (USC) of India’s major and medium size dam projects, utilisable surface water (USW), and ultimate gross irrigation potential (UGIP). This is dangerous because our country’s current policies are devised to address future water challenges based on these indicators – of which there is very little concrete information.

India’s ever-constant figures of USC, USW, or UGIP in its water management discourse, do not consider the impact of differential age and generations of dams built, the varied designs and construction practices used for building different dams and their declining service life and storage capacity due to sedimentation.

The way forward

The paper argues that it is important that the impending water crisis is acknowledged at the policy level and urgent efforts made to estimate the true extent of this crisis and cope with this situation at the earliest. For this to happen:

    • India’s water organisations have to be more transparent with respect to dysfunctional and deteriorating large dams. Thus, real time information on the live storage capacity of large storage structures should be made available and a realistic estimate of the irrigation potential of the country needs to be made based on this for proper planning and management of available water.
    • Water policymakers, planners, and water managers need to think of alternative plans to large storage structures. Some alternatives include:
    • - Selecting sites for construction of water harvesting structures of varying capacities;

 

      - Building medium or minor irrigation based small storage structures;

 

      - Identifying mechanisms to recharge aquifers and store water underground;

 

    - Decommissioning large dams that have fulfilled their service life and restoring the flow path of these rivers or streams, researching the site and reconstructing fresh storage structures as per feasibility;
      - Developing an integrated and sustainable plan for water management, taking into consideration the hydrological units involving allied sectors or disciplines such as soil management, agriculture, land use, land cover, etc.

 

      - Undertaking long term research on dam decommissioning, river morphology, feasibility of rebuilding of storage structures.

 

A copy of the paper can be downloaded below.

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