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Lower Subansiri dam being built on �brittle rocks�

By Ajit Patowary
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GUWAHATI, Dec 18 - The layers of rock lying underneath the underconstruction dam of the Lower Subansiri Hydel Power Project (LSHEP) are splintered under the pressure of tectonic activities for the past several centuries. During an investigation carried out by the Brahmaputra Board for finalisation of the Subansiri dam�s location, it was found that the bed rocks, 18 metres in thickness, below the Subansiri river bed, were cracked by tectonic forces and reduced to fragile layers like that of the fried papads. Without removing these layers, the dam could not be erected on a stable and safe rock bed.

But, under pressure from vested interest circles, the Brahmaputra Board was not allowed to build the multipurpose dam projects on the Subansiri and other potential rivers of the Northeast, and the reports of the thorough investigations it carried out on these rivers were taken away from it and handed over to the Power Ministry for developing power projects on all these rivers. The Brahmaputra Board was constituted for permanently solving the problem of floods caused by the Brahmaputra and the Barak and their tributaries in the respective valleys. The Board proposed several multipurpose dams on these rivers as the solution to Assam�s flood-related woes. But, since the mid-1980s, the issue of bringing Assam�s floods under control was relegated to a low status by the Union Government.

This is the statement made by Bharat Saikia, a former senior engineer of the State�s Water Resources Department Bharat Saikia. He was working with the Brahmaputra Board when the aforesaid investigations on these rivers were being conducted.

The septuagenarian, while talking to this correspondent, said now it is learnt that the fragile rocks of only an eight-metre thickness below the Subansiri river bed have been removed. And, the rest 10 metres of the fragile rocks are reportedly �solidified� using some �cement grouting processes� and building curtain walls in the front and hind side of the dam. This gives rise to the apprehensions that in the event of major earthquakes or cloudbursts, the dam would not be able to withstand its assigned load and would collapse. Under such a situation, a tsunami-like situation is inevitable in the downstream areas, he warned.

Reasoning, he said there is no information as to whether any care had been taken to remove the moss or algae that were there in the cracks of the fractured rocks. If the moss or algae are not removed, no grouting process can be expected to be effective and hence the rock bed, on which the dam is standing, can, in no way, behave like a non-pervious monolith.

He pleaded for an out-and-out transparent and thorough investigation by experts on the bearing capacity of the rocks on which the dams are being built over the NE rivers, as the region is in the highly active seismic zone-V and the earthquakes occurring in the region have already rendered the rock layers below the river beds highly fragile. There should also be a clear picture as to how the phenomenon of climate change, which has amplified the incidents of cloudburst in the region, is sought to be taken care of. Any compromise on the dam safety issue, will prove to be an antinational act by putting the lives and property of lakhs of the riparian people at stake, he asserted.

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Lower Subansiri dam being built on �brittle rocks�

GUWAHATI, Dec 18 - The layers of rock lying underneath the underconstruction dam of the Lower Subansiri Hydel Power Project (LSHEP) are splintered under the pressure of tectonic activities for the past several centuries. During an investigation carried out by the Brahmaputra Board for finalisation of the Subansiri dam�s location, it was found that the bed rocks, 18 metres in thickness, below the Subansiri river bed, were cracked by tectonic forces and reduced to fragile layers like that of the fried papads. Without removing these layers, the dam could not be erected on a stable and safe rock bed.

But, under pressure from vested interest circles, the Brahmaputra Board was not allowed to build the multipurpose dam projects on the Subansiri and other potential rivers of the Northeast, and the reports of the thorough investigations it carried out on these rivers were taken away from it and handed over to the Power Ministry for developing power projects on all these rivers. The Brahmaputra Board was constituted for permanently solving the problem of floods caused by the Brahmaputra and the Barak and their tributaries in the respective valleys. The Board proposed several multipurpose dams on these rivers as the solution to Assam�s flood-related woes. But, since the mid-1980s, the issue of bringing Assam�s floods under control was relegated to a low status by the Union Government.

This is the statement made by Bharat Saikia, a former senior engineer of the State�s Water Resources Department Bharat Saikia. He was working with the Brahmaputra Board when the aforesaid investigations on these rivers were being conducted.

The septuagenarian, while talking to this correspondent, said now it is learnt that the fragile rocks of only an eight-metre thickness below the Subansiri river bed have been removed. And, the rest 10 metres of the fragile rocks are reportedly �solidified� using some �cement grouting processes� and building curtain walls in the front and hind side of the dam. This gives rise to the apprehensions that in the event of major earthquakes or cloudbursts, the dam would not be able to withstand its assigned load and would collapse. Under such a situation, a tsunami-like situation is inevitable in the downstream areas, he warned.

Reasoning, he said there is no information as to whether any care had been taken to remove the moss or algae that were there in the cracks of the fractured rocks. If the moss or algae are not removed, no grouting process can be expected to be effective and hence the rock bed, on which the dam is standing, can, in no way, behave like a non-pervious monolith.

He pleaded for an out-and-out transparent and thorough investigation by experts on the bearing capacity of the rocks on which the dams are being built over the NE rivers, as the region is in the highly active seismic zone-V and the earthquakes occurring in the region have already rendered the rock layers below the river beds highly fragile. There should also be a clear picture as to how the phenomenon of climate change, which has amplified the incidents of cloudburst in the region, is sought to be taken care of. Any compromise on the dam safety issue, will prove to be an antinational act by putting the lives and property of lakhs of the riparian people at stake, he asserted.

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