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'Widening Ramar Sethu can amplify tsunamis'

June 22, 2007 20:24 IST

Ramar Setu, or the Sethusamudram Project coming up in the Gulf of Mannar separating India and Sri Lanka, has evoked strong reactions both from those opposing the project as well as those in support of it. While the former – primarily led by the Sangh Parivar outfits – claim the project will destroy a pre-historic land link between the two nations that was erected by Lord Ram and his Vanara Sena, the latter, led by Shipping Minister T R Baalu, say the project will cut down shipping time drastically, leading to major savings in fuel etc.

As the controversy refuses to die down, Contributing Editor Shobha Warrier spoke to oceanographer Prof Tad S Murty of the Department of Civil Engineering, University of Ottawa in Canada, who is a world renowned expert on tsunamis. In an email interview, Prof Murty talks about the Sethu Samudram canal project and whether it poses a danger to the Kerala coast if another tsunami strikes.

In 2005 when I interviewed you, you said you were not against the Sethu Samudram project. Two years have passed. You must have been following the debate on the viability of the project. Now, are you for or against the project?

No, I have not been following the debate on this. The only time I get to read Indian newspapers is when I visit India. The hotels usually deliver a complimentary copy of a newspaper each morning and occasionally I find some news about the Sethu Samudram project. This is my only source of information. According to what I read, it sounds like a good project from an economic point of view. I do not know the full scope and all aspects of this project, and in any case my opinion is irrelevant. I have no official connection with this project.

In January 2005, following a question to me from a reporter, I said that  widening and deepening the  Sethu Channel will provide a route for some of the tsunami energy to travel and impact South Kerala. My position on this is still the same. However, on the overall project, my opinion is not useful to anyone. Please note that I am a meteorologist and physical oceanographer. I am not an economist, ecologist, archaeologist, and in those aspects I am a lay man.

I assume that the Government of India does not make hasty decisions without taking into account all aspects of the project, and I believe that whatever final decisions are made  will be in the overall interests of the nation.

It is reported at various places that if not for the Ramar Sethu, the 2004 tsunami would have created widespread destruction in Kerala. Is it true?

I have not seen any of these reports. It is quite possible that the Ramar Sethu might have had some impact. However, until and unless I do a very detailed numerical (computer) model on this aspect, I cannot say with any certainty the influence of these on tsunami travel. Of course I can do a numerical model if someone will provide me funds to do it. Other scientists might have done this already, but I have not seen those results.

If so, in what way did Ramar Sethu reduce the impact on the coasts of Kerala and Tamil Nadu?

I cannot comment on this until I do a numerical model specifically on this aspect.

Do you feel the canal project was designed without following any tsunami assessments?

I do not know, as I have no access to the project reports. However, I assume that they must have considered the possible threat from  tsunamis, and indeed from all other natural hazards, such as cyclones, storm surges and wind waves.

You said in 2005 to rediff.com that there was a real threat to southern Kerala from future tsunamis in South East Asia. Do you still feel if such a tsunami happens next, it would be a real threat to Kerala?

Yes, my position has not changed. In the December 2004 tsunami, the very southern part of Kerala was not significantly impacted by the tsunami mainly for the following reason.  Some of the tsunami energy propagated south of Sri Lanka and a part of it diffracted north and affected the middle part of Kerala.

Tsunami, being a long gravity wave, somewhat similar to tides and storm surges, can only take a wide turn, and in this process, missed the very southern part of Kerala. An analogy is  like a car making a turn, a long car can only take a wide turn, while a short car can make a narrow turn.

The middle and northern parts of Kerala were also impacted to a certain degree by tsunami waves reflected from the Lakshadweep-Maldives Ridge as well as from the east coast of Africa.

Whatever may be the reason,  significant tsunami energy did not propagate through the waters separating India and Sri Lanka during  the December 2004 event and did not impact  much the southern part of Kerala.  Deepening and widening the Sethu canal, will provide a more direct route for some of the tsunami energy to travel and impact southern Kerala.

I will draw an analogy with what happened in the Alberni Canal (also called Alberni Inlet) on Vancouver Island, in the province of British Columbia, Canada, during the Alaska earthquake tsunami of March 28, 1964. Outside of the generation area (Alaska) the biggest tsunami amplitude of some 5.2 metres anywhere else in the entire pacific ocean, occurred, not at the open coast, but at Port Alberni located at the landward end of the Alberni Canal. This came as a surprise to all the scientists at that time, because the traditional wisdom at that time was the tsunami energy will dissipate as the tsunami moves away from the coast. This is generally true, for tsunamis propagating on land and inundating it. However, this need not be correct when the tsunami propagates inland through a water body, such as a channel, river or estuary.

In this sense, tsunamis are quite similar to storm surges, the largest amplitudes could occur some distance upstream in the water body. The reason for this is the so-called quarter wave resonance amplification. If the linear dimension of a water body roughly matches one-fourth of the wavelength of the  incoming tsunami, then the tsunami amplitude  inside the water body can increase through  resonance.

In the 1964 event, the tsunami amplitude at the ocean end of the Alberni Canal (which is connected to the wider Barkley Sound) was about half a metre, but as the tsunami was propagating through the Alberni Canal, the amplitude increased to 5.2 metres through resonance. While no two water bodies are identical, there are certain similarities for me to feel that the Sethu Canal could amplify tsunamis during propagation. However,  only a detailed numerical model  can provide definitive and quantitative data on this process.

As a tsunami expert, would you advice the government of India to go ahead with the Sethu Samudram canal project?

So far the only official from the Government of India that approached me on this is Mr Raghupathy of the Tuticorin Port Trust. He invited me to meet him over lunch at some restaurant in Chennai. I do not remember the exact date, but I believe that it was in late 2005. We had a very cordial meeting and a pleasant discussion. Mr Raghupathy told me that he noted my concern and will look into it. When a Senior IAS Officer such as Mr Raghupathy tells me something, I believe him.

If the government goes ahead with the project, what tsunami protections it should take?

This is what  I suggested to Mr Raghupathy, to slightly re-orient the Bay of Bengal side entrance of the channel, so that the entrance is not facing south-east or east. Entrance facing any other direction will minimise the probability of tsunami energy from future events to be funnelled significantly into the Sethu Channel. The solution I am suggesting is  a very small part of the whole project. Again to draw an analogy, if we are building a house with a few thousand bricks, all I am suggesting is to change a few bricks.

Is the Gulf of Mannar area tsunami prone?

Any water body can be tsunami prone from two sources, one from local sources and the second from distant sources, such as the 2004 event. I am not aware of any tsunami event in historical time from local sources.  One of the recommendations I make (not just for the SSP)  for general  tsunami research in India, is to extend the tsunami database  through paleo-tsunami studies on the coastlines of India. I understand that some research groups in India are already undertaking such studies.

Many archaeologists and environmentalist are against the project because they feel it will destroy the precious environment and also a centuries old structure like Ramar Sethu. The other day the World Monuments Fund, a US-based international preservation body that brings out the annual world monument watch list of endangered sites, has also come out in an open support of Ramar Sethu. What is your opinion on this?

In the ultimate analysis, it is really a political decision, taking into account all aspects (pros and cons). I am sure the archaeologists and environmentalists have studied the problem. As a physical oceanographer, it is beyond my expertise to comment on this, but I am satisfied that  whatever decision the Government of India makes on this important project, will be the right one for the country.

The Mudaliar Committee report of 1956 suggested land-based canals. As a tsunami expert, do you think a land-based canal would be better for the coastline?

As for land-based canals (somewhat similar to the Suez and Panama canals), they may be better from the point of view of  environmental, archaeological  and natural hazards aspects, but may be more expensive to build. I am really not an expert on this.

Shobha Warrier