THE ISSUE OF THE  DAM ON THE SUBANSIRI – TWO WELL-KNOWN EXPERTS’ PERSONAL VIEWS

I have been perturbed over the media news that the youth of Assam are opposing the construction of the DAM for Hydel power by the NHPC on the Subansiri in Arunachal, because it would cause adverse calamities to life and livelihood of the people in Assam, living in the down stream areas. The fear was genuine, especially when it is known that the North Eastern Indian area was earthquake prone. However, in my humble opinion the issue of building a Dam in a seimically potent area and the likely scenario of the flooding the down stream area can be certainly tackled with modern technologies available, if and only if, the likely issues are factored into the design and construction of the dam and control parameters are stringently enforced. However, to some degree people living in the down stream areas will have to be rehabilitated and their lives and livelihood guarranteed. The crying need for power in Arunachal and Assam and adjoining areas, can not be underestimated, if we wanted economic progress.

However, I am a layman trying to understand the agitation by the youth and the media unduly  making it more sensitive. Therefore, I contacted two dear friends of mine, who are truly well recognised experts in this field for their views. First, I reproduce below the response from Dr.Sarada Kanta Sarma, who had been advising various governments in the world on building Dams in earthquake prone areas. He was a Researcher and Reader in this very speciality, for nearly 40 years at the Imperial College of Science & Technology, London

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Dear Pulin,

Thank you for your mail. The issue of big dams in seismic areas is huge. There is no unique answer. There are two aspects. One, can we design a dam to withstand an earthquake? The answer to this question is yes. The second question is - do we know enough about earthquakes to rightly say that a bigger earthquake than the design one will not occur and the answer is no. There is ofcourse another question and that is about trying to save money in the design and construction process and here, I am not talking about corruption but about compromise between the known and the unknown. I, as a dam design engineer, has no problem about designing the dam and to satisfy myself that the dam will resist the earthquake forces for which it is designed. But, as a seismologist, I cannot say that a lrger force than the design one will not occur, be that with a very very small probability. So, the design philosophy is to be prepared for a very very small probability of failure, which may not occur in the life time of the dam and  keep the down stream of the dam everready for that failure. The problem in India and for that matter, in any country, I do not think that the government has any power to force the dam builders to look after the down stream side forever (within the life of the structure which is forever).

As regards the environmental issues, there has to be a compromise between the desire for ever increasing power and the safeguard of the environment. If we think about the source of power, burning of fossil fuel is no good since it creates problems of its own, nuclear fuel is dangerous since any failure is catastrophic.  Hydropower is clean but has environmental problem such as drowning vast areas. Renewable source of power (such as sun and wind) is very good but the technology is still in its infancy but at the end this is the way we shall have to go.

Some minister (or a spokes person) of Assam (or may be of  India) has recently said that he has not known of any incidence of concrete dam failure in an earthquake but that person is wrong. In the recent past ( I do not remember the date but can be found easily by internet search), in the Chi-Chi earthquake in Taiwan, a concrete dam failed because the earthquake fault passed through the dam breaking the dam into two. There was no downstream flooding due to other reasons. But the point I am making is that we do not know enough about earthquakes. There are faults which are not exposed to the surface and these may become active in a future earthquake. This is another hazard of earthquakes that is not clear.

So, over all, if we can persuade the governments and the dam builders and the owners to look after the down stream of the dam forever, the dams can be built. Otherwise, we will always live with a risk. In India, we cannot even persuade the owners of the dams not to release excess water willy-nilly, how can we trust the same people to look after something for always. I am being cynical of course but that is how I feel.

We are all ok here and hope you are ok as well.

The summer has opened up for one week now but will not last long, I suppose. The cricket has gone the way of England. Good cricket though.

With best wishes’

Sarada Sarma

Unquote.

Now, I reproduce the response from Professor Nayan Sarma, Head of  Water Resource Management & Engineering at the IIT, Roorkee.

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Dear Pulin da,

There is no problem if you  write on the issues stated by me. I have gone through the Experts' Committee Report of GU, DU & IIT-G, which I have found to contain some erroneous and misleading technical results ( such as dam break analysis for rigid bed condition of the river even though Subansiri is an alluvial river, non-continuous time series meteorological data analysis etc.).

 The technical issues indicated by me can be analysed and incorporated appropriately , without opposing the dam construction. The stand of AASU & KMSS for small / micro dams is not technically sound , as because such small dams will get silted up very rapidly as their dead storage capacity will be quite less to absorb the incoming sediment inflows ; and also the project  cost vs-a-vis benefit will not be viable due to economics of scale.

 Furthermore, the China have been building a large dam ZANGMU on the Yarlung Tsangpo   (Brahmaputra ) in Tibet which is at a elevation of 3.2 KM above Assam valley and can pose serious threat to Assam in the event of major earthquake , and if Tsangpo is diverted there will be serious repercussions in assam. I have written several news report in The Assam Tribune & Amar Asom, but there was no response & Assam people seems to be oblivious of the hazard.

Regards,

Nayan  Sarma, IIT, Roorkee

Unquote.