People of Idukki, Kerala’s second largest district having several giant, large and medium-sized dams, now feel that they are perhaps sitting on a geological time bomb in the context of recurring tremors, soil piping among hills surrounding a huge reservoir and cracks and leaks that keep on appearing in a 115-year-old old-technology dam due to seismic activities.
In fact, the strange geological occurrences and their alarming effects on the dams of mountainous Idukki are spreading panic not just among the people of that district but also among those in at least two others, Kottayam and Ernakulam. Idukki comes in Zone 3 seismic category where quakes of magnitude up to 6.0 on the Richter scale cannot be ruled out.
What has caused fresh concerns among the people of the low-lying areas of Idukki district are the new cracks that have developed in the 115-year-old Mullaperiyar dam on the border between Kerala and Tamil Nadu. Fresh cracks appeared at least at three points in the dam and water seepage through cracks increased after two low-intensity tremors hit the region on Friday.
According to amateur geologists who accuse their professional counterparts of keeping facts subdued for understandable reasons, the large and medium-sized dams numbering over a dozen in Idukki district constitute a huge threat to millions of people, other fauna and flora and the geography itself of an entire region.
However, the biggest concern stems from the changes occurring around the biggest dam of the district itself, the Idukki arch dam, the largest of its kind in entire Asia, which normally keeps 1.5 billion cubic metres of water, used for generating 66 per cent of the total electricity the State consumes.
The Idukki reservoir system, constituted by three giant dams, is situated right in the downstream line from the Mullaperiyar reservoir, where the ancient-technology dam is said to have reached the last phase of its life. The worry is that the Idukki dam system would not be able to withstand the weight of additional water in the event of a breach in the Mullaperiyar dam.
“Every time there is a tremor — and tremors keep happening here — we run out to see what is happening,”says Thomachan, a tea garden employee in Vandiperiyar. “It is not for us alone we are worried. We don’t think the Mullaperiyar dam will be there for long. Any danger to it can cause an inconceivable catastrophe for Kerala,” he says.
Though no scientist suspects the strength of the Idukki arch dam, even geologists are not sure of the strength of the hills that surround the giant reservoir. “Geologically speaking, these hills are very young and may not have grown firm enough to withstand the pressure of so much water for several decades,” says a former official of the Kerala Department of Geology.
He says that the soil piping (tunnel erosion) phenomenon that had occurred in Udayagiri hills, bordering the Idukki reservoir, in September last year was indicative of how the pressure of water was acting on the soil around the reservoir. Piping occurs when water flows beneath the earth’s surface eroding loose soil and this can worsen with increasing water pressure.
The live water storage in Idukki reservoir is estimated as 1.5 billion cubic metres which can cause a downward and sideward thrust of up to 1.5 billion tonnes on the reservoir bed. “I don’t think we can allow these young hills to bear such huge weights,” said the former Geology Department official.
At present, the biggest concern in Idukki is tremors, though of low magnitude, which the Kerala Government is using to justify its demand for the construction of a new dam at Mullaperiyar. The Kerala Water Resources Department says that a minimum of three fresh cracks had appeared in the Mullaperiyar dam in Friday’s tremors and such occurrences were a matter of concern.
A minimum of 15 mild tremors have hit the Idukki district, sitting on a faultline, in the past five months. A 3.8-magnitude quake had hit the Idukki region in July last but the strongest tremor occurred in the area in the recent past was in December, 2000. It had measured 5.0 on the Richter.
During his visit to areas hit by Friday’s tremors, John Mathai, head of the Geology wing of the Centre for Earth Science Studies, Thiruvananthapuram said that more quakes were likely to occur and that the people of Idukki should learn to live with the phenomenon as the region came under Zone 3 seismic category
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