Mullapperiyar: Issues of Dam Safety

The Mullapperiyar (Mulla Periyar) dam is one of the oldest dams in service in the World. We are talking of safety of the 105-year-old dam when the average life span of well designed and well built dams is generally considered to be about 50 to 60 years by International experts.

The safety issues relating to Mullapperiyar are heavily interlinked with the safety of the dams of the Idukki project downstream. The level of risk associated with a dam is a function of probability as well as consequences of dam failure.* The fact that the failure of the Mullapperiyar dam could lead to failure of the Idukki dam increases the magnitude of the risk associated with the continued use of the Mullapperiyar dam.

Given the size of the Idukki, the extent of the devastation that could result from failure of Idukki dam is unimaginable. Idukki's reservoir capacity is about 74400 million cubic feet of water with a weight of more than 2100 million tonnes. The expert committee set up by the State Government to study the Mullapperiyar issues has stated that failure of Idukki dams would lead to inundation of more than three districts of Kerala. This itself presents a frightening picture. The problem is compounded by the fact that hardly any up-to-date early warnings systems, emergency action plans including an evacuation plan exists in the case of both Idukki and Mullapperiyar. Evacuation of people in the event of a dam break from three highly populated districts is practically impossible. Moreover, no dependable dam break inundation study is available to determine the zones to be evacuated.

The probability of a dam failure depends on many factors such as spillway capacity, seismic resistance, nature of foundation, quality of design and construction, monitoring and maintenance and a host of human factors.* Idukki has some weak points in almost all these respects, which I shall discuss later in this paper.

In the case of Mullapperiyar the main risk factor arises from its age itself. As I pointed out earlier, not many dams of this age are in service in the World now. It is a dam built using old technology and naturally was not based on modern parameters for design of dams. Much of the binding material (lime) have leached out over the years. Though the Tamil Nadu Government has grouted the dam with concrete, the expert committee has concluded that this was neither sufficient nor highly efficient in making up for the loss of lime from the body of the dam. There is the possibility that hollow areas would remain inside the dam whatever be the efforts taken in this regard.

Apart from maintenance, monitoring is an important aspect of keeping a dam safe. The Central Water Commission had suggested installation of a definite pattern of instrumentation at Mullapperiyar to monitor the condition of the dam. Though Tamil Nadu did install some instruments, no measurements had been made available to Kerala. Though the Kerala Government suggested joint monitoring, Tamil Nadu has not agreed to this. In fact, Tamil Nadu engineers have told the technical committee of Kerala that it had not been successful in implementing the necessary instrumentation of the dam. There is apparently no instrumentation in the old portion of the dam. In the backing concrete portion, built as part of the strengthening works, uplift pressure cells, strain metres, joint metres and thermometres have been provided. These were said to have been installed in 1984. However, Tamil Nadu has either not done systematic monitoring of the dam so far or is hiding the data from Kerala. An old dam left without any monitoring itself is a serious matter. Moreover, no instrumentation like piezometres, inclinometres, extensometres and gauging weirs are in place to monitor the foundation.

There is monitoring failures in the case of Idukki dam also. Some of the instruments embedded in the dam were either not working or giving unreliable readings for several years. The Kerala State Electricity Board (KSEB) defaulted on taking regular readings and publishing the data. There is also no indication of sufficient preparedness from the part of the Board for emergency measures such as the opening of the spillways. According to the expert committee, the spillways at Idukki do not have the capacity to handle even the probable maximum flood (PMF) discharge from Mullapperiyar not to speak of a breach of the Mullapperiyar dam. The PMF of Mullapperiyar basin is 6003 cumecs while the maximum spillway and outlet capacity provided at Idukki reservoir is only 5100 cumecs. This mean that a big flood in the Mullapperiyar basin itself can endanger the Idukki dams if they are at or near full reservoir levels. All these should raise concerns even if the Mullapperiyar dam is strong enough.

There is a notion that we got the best of design and technology from Canada for the Idukki project. This is not entirely correct. We went for Canadian assistance mainly because we wanted funding. One of the conditions for assistance was that we would accept technical consultancy and equipment from Canada. Our own proposal for Idukki was to have concrete gravity dams for which our engineers had considerable expertise. The major modifications suggested by the Canadians to our plans were the arch dam at Idukki and underground power tunnel and the underground powerhouse at Moolamattom. The reason for preferring an underground tunnel and powerhouse was the occasional land slips in the district, which could damage pipelines, and saving of steel needed for the over the ground intake structures. The Canadians had considerable expertise in building tunnels.

However, the proposal for arch dam had its pluses and minuses. It reduced costs, but had some inherent problems. Canada had only built its multiple arch dam, Manic-5, at that time. Manic-5 subsequently became a heavy burden on Hydro Quebec which operates the project. The dam developed bulging cracks and problems with the foundation requiring costly maintenance. It is notable that two of the World's biggest dam disasters that occurred before Idukki was built-- Vaiont in Italy in 1963 and Malpaseet in France in 1959, involved arch dams. (In the case of Vaiont, it was a landslide and not the weakness of the arch dam that caused the accident. But it is to be remembered that Idukki is also prone to land slips). Two arch dams, El Atazar in Spain and Kolnbrein in Austria, which were completed around the same period as Idukki, are facing problems, mainly relating to their foundations, now. The repair cost of Kolnbrein is put at 190 million dollars.

To put the situation in the right perspective, it must be noted here that one of the oldest serving dams is the 75-miles arch dam of Australia constructed in 1880. However, such long serving dams are exceptions. There is a limit to the number of years one can keep dams in service through maintenance and strengthening measures. One day, it has to be rebuilt, or the dam will give way. Visionary leaders should anticipate this and act accordingly, though that may be difficult course of action for a popular Government in Tamil Nadu under the present circumstances. The problem with Mullapperiyar is that there is no alternate site for construction of a new dam (unless Tamil Nadu/Kerala is prepared to construct a wider dam downstream at a high cost). So, disruption of water supply is bound to occur if the existing dam is demolished and reconstructed. The leaders should prepare the people to go without water for irrigation for some years, if no other alternatives could be found. Kerala cannot be giving water to Tamil Nadu at grave risk to its own population.

Note: Mullapperiyar dam, located near Kumily in Idukki district of Kerala State in India, is 438.91 metres long and 48 metres high. The front and rear faces are of uncoursed rubble masonry in lime mortar. Concrete with sandstone and lime surkhi mortar forms the core. It was built for a gross storage of 443.23 M Cum.(15.6 TMCft). It is on the Mullapperiyar, one of the tributaries of Periyar (river), and the reservoir formed by it is often referred to as the Periyar reservoir.

The dam was constructed on the basis of a lease deed between the erstwhile Travancore State and Madras Governments (under British rule) in 1886. Now, there is a dispute between the Kerala and Tamil Nadu State Governments, formed after India became an independent country, over raising of the reservoir level at Mullapperiyar. The maximum water level at the reservoir had been lowered to 136 feet about 20 years ago, on the advice of the Central Water Commission, as the dam developed leaks. The Tamil Nadu Government demands that it should be raised to the original 152 feet as the State had strengthened the dam.