Is age catching up with India’s dams?

“At Independence, the new Government of India … made the building of big dams a central part of its strategy for transforming India, a commitment to which it adhered for decades,” historian Daniel Klingensmith wrote in his 2007 book ‘One Valley and a Thousand’.

The Damodar Valley Corporation, the Bhakra Nangal, and the Hirakud in the 1940s were followed by dams on the Rihand, Koyna, Tungabhadra, Chambal, and Krishna rivers in the decade after. In fact, in the two decades from 1951, India had started work on 418 large dams and by 2000 had completed around 4,000. In Klingensmith’s telling, building dams had become “a way by which the modernity and worth of the nation could be enhanced, tested, and displayed.”

Today, however, India faces the challenge of large parts of its hydrological infrastructure ageing en masse. According to the National Register of Large (Specified) Dams, some 1,065 were 50-100 years old and 224 were more than a century old in 2023. Many major dams of the post-1950 period are now in the last stages of their originally intended lifespan, raising safety and performance concerns that transcend problems of engineering alone.

In practice, India’s dam projects have typically assumed a useful life on the order of a few decades. The Bhakra Dam completed in 1963 was expected to serve for at least 100 years as a reservoir but its builders underestimated sedimentation rates, so much so that the reservoir’s capacity had dropped by nearly 25% in the first 35 years of its use. Likewise, the Lower Bhavani Dam in Tamil Nadu had lost 28% of its capacity between 1956 and 2005 and the Nizam Sagar Dam had lost roughly half its capacity just in the first three decades of use since 1931.

These examples illustrate one fact clearly: the initial design life of many dams isn’t equal to the actual life. The cost of running a dam at its original performance levels can shoot up as it ages — and this is before the additional ‘climate load’ is factored in. Dams more than 50 years old today have outdated spillway capacities and structural safety factors and require urgent attention to ensure they can continue to function safely.

Modes of failure

Dams’ multiple failure modes can be split into three types: structural, hydraulic, and geotechnical. These modes are hard to pry apart in practice but it’s useful to treat them separately if only to identify specific ways to surmount them.

A structural failure is when a dam ruptures or collapses due to weaknesses implicit to its structure. Common causes include poor design and/or construction, material degradation, and structural components being forced to withstand forces they weren’t equipped to. For example, progressive concrete deterioration can weaken a concrete dam over time. One way this happens is when silica in rocky aggregates in the structure reacts with alkali compounds in the cement to form a water-absorbing substance. As the substance expands, the concrete starts to crack from within. This category also includes structural cracks, slope instability in earth embankments, and gate and sluice failures.

Worldwide, about 42% of concrete dam failures have been attributed to foundational and structural issues. Structural failures in Indian dams have been traced to seepage, corroded piping, and/or weak foundations.

A hydraulic failure occurs when the dam can no longer safely store water. The best known cause of this mode, especially in the era of climate change, is overtopping: when flood waters pass over the dam’s pinnacle, potentially breaching the structure en route. When inflow exceeds the dam’s capacity, insufficient spillway capacity or blocked spillways can also lead to overtopping. Similarly, when a dam’s outflow is very fast, it can erode the structure’s downstream face, also resulting in hydraulic failure.

In earth and rock-filled dam failures worldwide, overtopping has been the single most common cause (about a third of the time). India’s first recorded dam failure, of the Tigra Dam in 1917, was also due to overtopping, and overall this cause has been the main one in most of the 36 recorded dam failures in the country.

Finally, a geotechnical failure occurs when the dam’s foundations, abutments or the materials within the dam are unstable. Internal erosion in the foundation has accounted for about 29% of masonry dam failures worldwide. Earth-fill dams are particularly susceptible to flawed piping in the dam’s body, where water can seep through the dam or its foundation and eventually cause a breach.

Earthquakes and landslides can also trigger structural as well as geotechnical failures. Dams in seismically active zones are particularly vulnerable to quake-induced cracking or slope failures. When the magnitude-6.6 Koynanagar earthquake in Maharashtra shook the Koyna Dam in 1967, the structure developed cracks and began to accumulate hydrostatic pressure, raising fears of a breach.

Real-world failures are a combination of these modes. An initial structural deficiency could lead to excessive leaks (geotechnical failure) that weaken the dam. Thus when the part of the river upstream of the dam receives heavy rainfall or when there’s a glacial lake outburst flood (like the one that roiled Sikkim in 2023), the waters overtop the dam and results in a catastrophic breach.

The world’s history of dams indicates more than 70% of failures occur in the first decade of operations as this is when flaws in the design or construction are most likely to become evident. But as dams age, delayed maintenance, material ageing, and unanticipated flooding or seismic events can dramatically increase failure risk. After all, as climate change intensifies, it increases the risk of natural disasters of unprecedented magnitude — and to not have precedent means to lose history as a guide.

Caring for older dams

India’s Central and State governments have developed an evolving framework of policies, laws, and projects to ensure dam safety, led by the safety regime established by the Dam Safety Act 2021. The instrument provides a framework to surveil, inspect, operate, and maintain all specified large dams, and requires institutional mechanisms at both the Central and the State levels to uphold it.

At the Act’s heart is the National Committee on Dam Safety, the apex body with the responsibility of evolving dam safety policies and reviewing the work of State-level agencies. The Committee is joined by the National Dam Safety Authority (NDSA), a regulatory body under the Union Jal Shakti Ministry tasked with enforcing policy and resolving interstate disputes.

In this scenario, every State with large dams is required to establish a State Dam Safety Organisation (SDSO) headed by qualified engineers to oversee dams in its jurisdiction. (If a dam is located in one State but operated by another, the NDSA supplants the relevant SDSO.)

The 2021 Act also specifies regular inspection schedules. Dam owners — often a State’s irrigation department or power utility — are required to conduct pre-monsoon and post-monsoon checks every year, among others. The law also requires each dam to have an emergency action plan and an alarm system, and provides for remedial actions that SDSOs can order if a dam is found to be falling short.

Before the Act, the Central Water Commission (CWC) had set guidelines for dam owners on regular maintenance and safety reviews. To this end, many States have had Dam Safety Review Panels: expert groups typically populated by experienced dam engineers, hydrologists, and geologists and which audit ageing dams and recommend rehabilitation measures. The Dam Safety Organisation within the CWC also maintains a database of dam incidents and assists States in investigative studies. After any major natural disaster, a dam is also subjected to special inspections.

In 2012, the Indian government mooted the flagship Dam Rehabilitation and Improvement Project (DRIP) to upgrade ageing dams. DRIP places particular emphasis on capacity building, including training State dam engineers in contemporary safety practices and developing au courant emergency action plans. Upgraded dams as a result have piezometers, inclinometers, and seismic monitors on site watching for signs of distress. These in turn also require dam health monitoring software to be integrated with dams’ operations and for each dam to maintain a log, like its report card.

From 2012 to 2021, DRIP I rehabilitated 198 dams in Jharkhand, Karnataka, Kerala, Madhya Pradesh, Odisha, Tamil Nadu, and Uttarakhand. Work included grouting cracks, strengthening spillway piers, improving drainage and filtration systems in earth dams, replacing gates and valves, installing modern sensors and instruments, and improving operational processes. The government approved DRIP phases II and III in 2020 to cover 736 dams in 19 States, with financial assistance from the World Bank and the Asian Infrastructure Investment Bank for physical rehabilitation and to undertake comprehensive safety evaluations. As of early 2024, reviews for more than 400 dams had reportedly been completed.

Dovetailing on DRIP are guidelines to deal with the consequences of natural events rendered more intense and/or frequent by climate change. This includes rechecking the probable maximum flood for spillway designs, improving spillway capacity, and adding auxiliary channels. Older masonry and concrete dams are also evaluated against current earthquake codes and strengthened if required by anchoring, buttressing or adding reinforced concrete overlays. The National Hydrology Project and flood forecasting initiatives have also been working to improve flood management upstream.

On the flip side, DRIP doesn’t make room for dams to be decommissioned; instead it focuses on extending the lifespan of dams at all costs. India in fact lacks an official dam decommissioning policy. The Dam Safety Act empowers authorities to declare a dam unsafe and potentially stop its operation, but there’s no procedure to decommission it altogether. Experts have recommended India develop a risk-based framework, i.e. when a dam’s failure risk exceeds acceptable limits and it’s no longer feasible to strengthen it.

Calls by experts to decommission specific dams, such as the Mullaperiyar, have thus far only been dealt with in courts.

Economics of ageing

As a dam ages, the cost of its upkeep rises. Older dams often require structural strengthening, e.g. by retrofitting their spillways or reinforcing concrete; upgrading gates and mechanical equipment; and continuously dredging and managing sediment.

Second, the loss of reservoir capacity thanks to siltation diminishes water supply, irrigation potential, and hydroelectric power generation capacity. Addressing sedimentation by dredging and restoring catchment areas, among other measures, is also expensive. At one point, the Government of India had deemed the Bhakra reservoir’s large-scale dredging to be “cost-prohibitive”.

To evaluate the potential cost of a complete failure, analysts use risk assessment models that consider the probability of failure together with its consequences. In practice, a dam’s hazard classification (low, significant or high) is based on the worst consequences should it fail. Consequence analysis frameworks, such as the one the US’s Department of Homeland Security uses to assess dam safety, enumerate the consequences in three categories: human (populations at risk, potential loss of life), economic (property damage, infrastructure loss, cost of replacement and remediation), and critical services (loss of water supply, power, irrigation).

Thus, a comprehensive failure scenario analysis might estimate the asset replacement cost of the dam and its associated structures, the remediation cost for downstream cleanup, and the lost power generation or water supply as part of business losses. Depending on the relevant rules, the analysis may also include intangible costs like environmental damage and long-term economic setback to the region.

India currently makes limited formal demands of economic analyses of dam failures. Before the government approves a dam, the project proponent is required to submit an environmental impact assessment (EIA) that includes a dam failure analysis. Since 2021, the Dam Safety Act has required certain dams to have emergency action plans and inundation maps on file. But the government has also been progressively weakening EIA governance, including approving projects sans EIAs and allowing defaulters to pay a fine and continue offending ones.

Perhaps the worst failure in India’s history was the collapse of the Machchu-II Dam in Morbi in Gujarat in 1979. This earthen dam was built in the 1970s and was breached after extreme rainfall. Water spilled from the dam in a flash flood that killed more than 2,000 people (although some estimates go up to 20,000). The failure also demolished most of Morbi town. More recently, the Tiware Dam in Ratnagiri district of Maharashtra failed in 2019, wiping out entire villages and killing 19 people.

Following tropical cyclone Daniel, the Derna and the Abu Mansour Dams in Libya collapsed in September 2023 and killed more than 3,800. The incident prompted countries worldwide to double-check their own dams — and thus the Himachal Pradesh government found 21 dams in the State had violated their safety norms, including possessing inadequate spillways. The discovery drew calls for older dams to have their safety margins reviewed by independent experts.

Dam failures also impose long-term costs as local governments have to restore damaged transport links, compensate and rehabilitate the affected families, and reverse losses in agricultural productivity. Even near-miss events can exact high costs. While the 2018 floods strained but didn’t breach several dams in Kerala, the State’s economy was hit by the emergency reservoir drawdowns and controlled downstream spilling it had to effect.

This said, economic evaluations of dam safety are now moving towards risk-based decision-making, which means vouchsafing investments for dams that pose the highest risk, which in turn is a function of the likelihood of failure and the magnitude of downstream consequences. Such an approach helps ensure limited funds are directed to averting the most severe potential disasters, even if the limitedness is arguably artificial and not inevitable.

Three talismans

Perhaps the best way to contextualise these measures and policies is to read them in the context of three of India’s great old dams (subjectively speaking): the Mullaperiyar, the Hirakud, and the Bhakra Nangal. They’re not the only high-risk dams, of course, but they rank among the most prominent for their age, size, and importance.

The Mullaperiyar Dam on the Periyar River was completed in 1895 as a 53.6-m high masonry gravity dam. The British colonial administration built it with lime surkhi (powdered burnt clay) mortar. Its intended lifespan was around six decades. It’s located in Kerala but Tamil Nadu owns and operates it to support agriculture downstream, and this shared nature has precipitated a long-standing dispute over the structure’s integrity.

Mullaperiyar lies in a seismically active region at the edge of the Western Ghats and has developed leaks and cracks over time. The structure was bolstered in the 1970s and the quantity of water flowing through the dam was mitigated for a time, but many experts still consider Mullaperiyar to be vulnerable. The dam’s spillway capacity is limited relative to current probable maximum flood estimates and thus faces a higher overtopping risk.

A UN University report published in 2021 estimated that if the dam were to collapse, around 35 lakh people would be at risk and the financial costs may be tens of thousands of crores (in rupees).

In 2014, the Supreme Court put together an Empowered Committee that found the dam to be generally safer at lower water levels but which nevertheless recommended ongoing oversight. (The NDSA hadn’t taken shape by 2022 so at the time the Centre had made the Chief Secretaries of the two States ultimately responsible for implementing the Supreme Court’s conditions.) Kerala has since stepped up demands to build a new dam to replace Mullaperiyar while Tamil Nadu has insisted it can be operated safely with continuous maintenance.

Commissioned in 1957, the Hirakud Dam in Odisha is among the first post-Independence river valley projects as well as one of the longest earthen dams in the world, stretching 25.8 km (including dykes). It forms a colossal reservoir on the Mahanadi River and has been crucial for flood control, coastal irrigation, and generating hydroelectric power. But almost seven decades on, Hirakud also typifies the challenges posed by large, ageing earth-fill dams.

Its safety depends on its vast embankments, masonry spillway, sedimentation rates, and its ability to handle floods. Even by the 1980s, Hirakud’s reservoir had lost roughly a quarter of its storage to silt while deforestation upstream of the facility continued to send down heavy sediment loads. In a close call in 1982, extreme inflow almost overtopped the dam, forcing operators to cut open an auxiliary spillway. With high-rainfall events proliferating in the region, a 2016 case study on the dam’s climate resilience published by the CWC highlighted a need to update flood routing and enhance spillway capacity.

As for geotechnical safety: Hirakud’s prodigious length means continuously maintaining its earthen sections, including to prevent slope failures and control seepage, is vital. The Government of Odisha and the CWC have of late undertaken extensive evaluations, including analysing its sluice gates for stress and seismic safety. Densely populated areas, including Cuttack city, lie downstream of the dam. A failure event is expected to inundate more than 11,000 sq. km of land and affect millions of people.

While the authorities haven’t reported any immediate structural red flags, the fact remains that the dam is 63 years old. In 2023, the National Human Rights Commission even responded to public anxiety and inquired into Hirakud’s safety status after heavy monsoon rains. The government’s approach has been to strengthen Hirakud by repairing its spillways and adding monitoring systems. Decommissioning has been out of the question given its economic value. The dam is thus an ageing but critical one that must be diligently managed to prevent any failure, especially as natural stresses accumulate.

Finally, let’s consider the 62-year-old Bhakra Nangal Dam, a 226-m high structure, creator of the Gobindsagar reservoir, and a veritable linchpin of North India’s water supply landscape. Jawaharlal Nehru famously called it a structure “worthy of worship” for having “been built with the unrelenting toil of man for the benefit of mankind”. Bhakra is a robust concrete gravity dam, which matters because India has yet to record a concrete dam failure to date — but this doesn’t mean the dam can never fail.

It faces significant age-related concerns, chiefly (and by this point familiarly), reservoir sedimentation and outdated design standards. The Sutlej River it straddles carries a high silt mass thanks to real-estate development and landslides in the Himalaya. By 2020 or so, investigations by the Bhakra Beas Management Board (BBMB) had also revealed sediment deposits had shaved off 23% of the reservoir’s gross capacity.

The dam was expected to be effective for a hundred years but officials have warned that the reservoir’s dropping capacity could considerably shorten that. In structural terms, Bhakra is considered well-designed but it also needs seismic reanalyses to ensure its stability under larger earthquakes and periodic checks of its spillway gates and powerhouse. (The spillways were designed for flood estimates drafted in the mid-20th century.)

Downstream of the dam, Bhakra serves Punjab’s agricultural heartland and several major cities. A hypothetical failure — which experts currently deem unlikely — would be catastrophic and so Bhakra remains a high-consequence structure. To its credit, the BBMB has also undertaken extensive catchment reforestation programmes to curb silt inflow and is exploring options to divert sediment elsewhere.

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Taken together, India’s ageing dams present a complex challenge at the intersection of engineering, economics, and public policy. More than 4,200 large dams in India will cross the 50-year mark by 2050 and dam safety will loom larger than it does today — yet each ageing dam has unique risk factors that need to be addressed individually. With climate change progressively intensifying hydrological extremes, India’s dam safety efforts must also incorporate forward-looking climate resilience.

Focusing on dams that pose the greatest risk and addressing their issues with state-of-the-art solutions and, crucially, in consultation with downstream communities should thus be a national priority.

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