Disaster in the making

The Hirakud dam, Asia’s longest earthen dam, has been causing man-made floods in Odisha

Ranjan K Panda Sambalpur

In 2005, Odisha Minister of Water Resources and Chief Minister Naveen Patnaik said at a dam safety workshop, “Dams are monsters. Even though these have been a lifeline for the people since civilisation, from the point of view of potential hazard, they are monsters if not monitored for their proper health. If there is an outburst, the entire geography and history of the area will be changed.”

More than a decade later, the Hirakud Dam, Asia’s longest earthen dam, built over India’s sixth largest river, may prove him right, especially if one analyses flood control operations in the current decade. Whenever floods occur in Odisha, the Hirakud dam spells disaster. The Comptroller and Auditor General of India (CAG) too has raised serious questions about the mismanagement of floods because of the dam in a new assessment. The National Human Rights Commission (NHRC), in a case pertaining to loss and damages due to the dam’s mismanagement during the 2011 floods, mentions the state’s water resources secretary saying it was essential to open the flood gates for the dam’s safety. All this points to the fact that the Hirakud dam has been causing man-made floods in the state.

Flood control

The Mahanadi drains an area of around 141,600 sq km and has a total course of 858 km. The river flows through the states of Chhattisgarh and Odisha, and the Hirakud dam is the only major flood control system on the river, as well as in Odisha. The Hirakud reservoir spread over 746 sq km – almost half the size of Delhi – is the largest dam in the country. Inaugurated in 1957, the dam was intended to control floods in the Mahanadi delta, with irrigation and power generation as incidental benefits.

Government engineers and supporters of the dam claim it successfully moderated 24 out of 30 potential floods. However, these claims are doubtful. Our ground observation tells us the dam has been unsuccessful in flood management. By its very design, the dam cannot control high floods as it has the capacity to intercept only 16% of the Mahanadi’s total flow at its location. Independent studies have indicated the dam’s failures in just two decades after it became functional; our observations further show that the issues have been compounded because of its faulty design, ineffective flood management operations, and other factors such as climate change-induced disturbed rainfall distribution in the river basin. 

A contributing paper to the World Commission on Dams noted, “India’s Hirakud Dam was first justified in the name of flood control, yet extreme floods in the Mahanadi Delta between 1960 and 1980 were three times more frequent than before Hirakud was built.” The flood impact in the region has increased post the dam construction, and from four flood-affected districts in the 1950s, almost all districts in the Mahanadi basin are now flood-prone. In the first decade of the 21st century, floods occurred in five years, and the dam can be blamed during on at least four instances. The dam has failed to control any floods since 2008.

In 2008, we—the Water Initiatives Odisha (WIO), a civil society network that works on water, environment and climate change issues in the state—warned the state government about the failure of Hirakud in managing floods. The media in the state took it up seriously and large-scale awareness about the issue could be generated. Hirakud’s flood management had continued almost unquestioned till then. 

As heavy floods lashed the Mahanadi and Hirakud again failed to control them, we focused on flood management practices primarily done through a “Rule Curve” which was devised in 1988 at a time when the state government changed its priorities of water management to accommodate industrial needs. The “Rule Curve” was a radical shift from earlier water management manuals which guided dam authorities to keep the reservoir empty for most parts of the monsoon and start filling the reservoir gradually from September onwards and fill it to the full reservoir level (FRL) of 630 feet above sea level by October 31. The Rule Curve of 1988 changed the latter date to September 30, with the CWC observing that the reservoir had failed to fill up most years as rainfall was inadequate in September and October, and the reservoir was under pressure to meet irrigation and other demands. The new rule ignored the reservoir’s flood protection priorities and gave more importance to filling it to its fullest.

But in order to fill the reservoir, the Rule Curve proposed such high water levels that there is virtually not much scope for dam authorities to retain flood water inflow at crucial times. The new rule prescribes an upper limit of 627 feet by September 1, 629 feet by September 11 and 630 feet by September 30. The rule ignored the fact that September is a peak monsoon month.

In 2008, the new rule’s flaws were exposed by our continuous advocacy. In fact, the 2004 State Water Plan (SWP) had already apprehended this, and had admitted the scope for flood control was very little. “The operation schedule (popularly referred to as the rule curve) approved by the CWC never allows the reservoir to be sufficiently at lower level to absorb the inflow from the U/s catchments of 83,400 sq km, especially if the flood hits late in the monsoon,” the SWP says.

Since 2008, there have been two severe floods, in 2011 and 2014. In each of these years, Hirakud has created man-made floods due to mismanagement of the Rule Curve. We contend that the Rule Curve is faulty for the dam’s design, and it would force the dam authorities to release excessive water to keep the dam safe every time there is an adverse situation such as excessive rainfall upstream in Chhattisgarh. 

Meanwhile, Odisha and Chhattisgarh are now entangled in an inter-state water dispute over Mahanadi water. Odisha is complaining about the high-handedness of the upper riparian state which has constructed a number of barrages upstream without Odisha’s consent. While most of these barrages are summer reservoirs and may not have much impact on flood control operations of Hirakud, the dams—some constructed prior to the inter-state conflict and some after (such as Minimata (Hasdeo) Bango, Kelo and so on)—need to be properly integrated with Hirakud’s Rule Curve, a rule that itself needs upgradation by taking into account factors such as climate change. 

An emerging danger

There’s also the fact that rainfall distribution patterns in the Mahanadi basin are deviating from the times when the dam was planned. Various reports suggest climate change is already causing heavy intensity rainfall within a short span of time, something the Mahanadi has been witnessing since 2001. In fact, the SWP had recognised this danger in its report: “Variability of monthly rainfall is also increasing, which means that rainfall is concentrated in a particular period. Volume of flood events are increasing, 2001 and 2003 floods are examples.” Unfortunately, the state government has not yet conducted any serious study of the impact of climate change deviations on flood management rules of the dam. 

Way ahead

The Odisha government has recently announced a real-time monitoring system of flood data in the Mahanadi. However, we cannot assess its effectiveness unless they coordinate with Chhattisgarh dams and review the Rule Curve. The state government first needs to admit that the floods are man-made; if for nothing else, then for the simple fact that the Hirakud dam can only intercept 16% of total inflow. Only then can it work out a solution in a transparent manner. Hirakud is an ageing dam that is heavily silted, which has reduced its capacity to intercept and store water by almost 40%. 

We have asked the government since 2008 to come up with a White Paper on Hirakud flood management and not limit the Dam Safety Committee meetings to just an ornamental event, but things have not improved. There is an urgent need for intervention by the CWC to establish a real-time dynamic data-sharing mechanism, to improve and restructure flow reading stations, and to synchronise rule curves of all the dams that are potential threats to Hirakud's flood control measures. Further, Hirakud’s rule curve also needs a relook to avoid future flood damage. Any delay would mean grave danger for more than half of Odisha.

This story is from the print issue of Hardnews: SEPTEMBER 2017