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Revisiting a controversy
Arun Bapat

The Stockholm conference of 1971 and the subsequent UN resolutions on thepreservation of atmosphere and prevention of pollution saw a large number of groups emerging. They saw themselves as environmentalists and found an easy target in the irrigation projects of the period like the Narmada and Tehri dams. Yet, despite 20 years and more of activism of this kind, a proper assessment of dams has still not emerged.

There is no getting away from the fact that a large number of dams, such as the Bhakra, Hirakud, Nagarjunasagar, and so on, has generated electric power for the industrial sector and ensured water for irrigation. This may not, in itself, have removed poverty but it has definitely paid the desired dividends in the form of a rise in living standards, as well as agricultural and industrial production. So the pro-dam lobby is quite right in emphasising this. However, the aspects highlighted by the anti-dam lobbyists, such as water logging, salt-water ingress, the adverse effect on biological and zoological species, reservoir-induced seismicity, submergence of forests, and so on, require a considered scientific response and not a flat authoritarian refusal to listen. What makes things worse is that the debate between the pro-dam and anti-dam lobbies has deteriorated into a slanging match with vital issues being all but forgotten in the process.

As far as submergence of forests and the effect on biodiversity is concerned, undeniably there will be some losses. However, this will certainly not result in the total extinction of the biodiversity of the region. In fact, the rise in population and urbanisation pose a greater threat to the biodiversity than do the dams. The disproportional expansion in urban limits have affected a large number of rivers, lakes, estuarine areas, agricultural lands, forests, and so on and requires the urgent attention of conservationists. Yet hardly any voices of concern have been raised regarding this danger.

Let us now come to the crucial question of Reservoir Induced Seismicity (RIS). This aspect first came into play when an earthquake of 6.5 magnitude visited the vicinity of the Koyna Dam in Maharashtra on December 10, 1967. At that time, it was thought that the landmass of peninsular India was free from any earthquake and the area was considered aseismic. As the epicentre of the earthquake happened to be in the proximity of the dam, an ad-hoc hypothesis propounded that the combined effect of the load of the water body on the rocky environment and the trickling of water down the rocks had resulted in the earthquake. In absence of any proper scientific explanation, a large number of people and a few seismologists came to accept this catchy hypothesis.

In order to verify the RIS hypothesis, some computer studies were conductedat least three decades ago and it was found that the load on the rock due to the water body comes to about 3 kg/sq cm. As this was too small a load to break any rock, this point was repudiated. The other aspect concerned the trickling of water to some depth, a process that weakens the rock and subsequently triggers off an earthquake. In the early seventies, lack of experimental proof meant that this concern remained unaddressed. Early this year, the Koyna authorities performed a novel experiment of lake tapping, which involved among other things the puncturing of the bottom of the lake.

The experiment proved beyond any measure of the doubt that the RIS thesis was untenable. It is only to be hoped that it will soon come to be regarded as one of the great historical blunders of the past. Anti-dam activists should desist from raising this bogey in their future campaigns.

There has also been widespread concern expressed over the long-term viability of dams, given the fact that siltation is an acknowledged problem. It is a fact that the rate of silting assumed by experts, based on the past records of the Central Water Commission (CWC), are definitely subject to correction and require some element of modification. But the sediment data for the last two decades are sufficiently reliable. The lives of the dams could be re-estimated on the basis of sediment data garnered over the last 20 to 25 years.

To overcome the so-called problem of reservoir life estimation, an example is available from the Khadakwasla dam, near Pune. This dam was conceived, designed and built by the famous engineer M. Visveshwariah, about a hundred years back. Conventional wisdom has it that the estimated life of a reservoir is about a hundred years. By this token, the Khandakwasla reservoir should have been silted up totally by now. But at present the dam is supplying drinking water to the Pune municipal area and the canal from this dam is supplying water to a length of about 90 km. The very existence of the Khadakwasla dam is evidence that a dam need not necessarily silt up very quickly. Of course, it also needs to be remembered that this dam is situated in the region of the rocky Sahyadris. The process of sedimentation of the alluvial rivers of the Himalaya may well have some other pattern.

Last, but not the least, if the construction of new dams such as Narmada and Tehri is so much harmful and detrimental to the environment, then the anti-dam activists should not limit their activities to the two said dams alone. They should organise a nation-wide campaign and demand the total and full dismantling of the existing dams to save the environment. If the campaign is limited to few dams, it is likely to give the impression that it is inspired by vested interests.

Whenever there is any construction, there is an element of risk. Risk is an unavoidable part of construction. Therefore, every effort must be made to address every possible risk while designing the dam and allied structures. It is felt that although anti-dam activists have raised some very pertinent issues, the benefits to be derived from dams are so many that instead of dismissing them outright, it would make more sense for scientists and engineers to try and address the concerns. It would help, of course, if anti-dam activists exercise some restrain and not indulge in propagating disinformation.

The writer is a research seismologist and was formerly head, Earthquake Engineering Research Division at the Central Water Power Research Station (CWPRS), Pune

It is to be hoped that the Reservoir Induced Seismicity thesis will sooncome to be regarded as one of the great historical blunders of the past

Copyright © 2000 Indian Express Newspapers (Bombay) Ltd.


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