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A view of the Subansiri project site
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Guwahati, March 17: The two-member technical expert committee constituted by the Planning Commission to review the Subansiri Lower Project has found serious flaws in the dam’s design.
The Central Water Commission had also pointed out flaws right during the technical examination.
“The weak foundation rock is the most important and critical aspect of the dam design and not the seismological aspects of the project location. The background to the project planning is replete with references to the weak foundation,” the committee said in its report, which has still not been made public, though it was submitted to the commission last year.
The report was prepared by C.D. Thatte and M.S. Reddy.
It said the CWC had made explicit comments on the foundation and its suitability to support the proposed concrete dam.
It said the sandstone on which the dam is founded has been deemed very weak.
“Its adequacy and competence to support the concrete gravity dam is not established satisfactorily. The geology of the foundation rock and its engineering properties reveal that innovations are required to enable it to support the concrete dam, especially in view of the seismic environment. It is a prerequisite that the foundation rock should be as good, if not better than that of the concrete in the dam. It is therefore axiomatic that gravity dams should have hard rock as foundation,” it said.
It has been a general practice, since long, to set up an independent panel of experts to review dam design in all respects, including hydrology and hydraulic design, and has been a practice prevalent earlier in the NHPC.
“The seismology and foundation problems that a large dam at Gerukamukh has to encounter and negotiate were well known right from the project concept stage. The NHPC was not possibly unaware of the problems, including those of landslides. Therefore, it should not have sidestepped the simple prerequisite of forming a dam design review panel, which could have obviated the present impasse to a great extent. In fact, it should be made mandatory for the Subansiri middle and upper projects to have similar panels,” the report said.
The panel and the CWC should, after comprehensive review, recommend necessary design and engineering features to ensure satisfactory performance of the dam.
“The review needs to be completed soon so that project completion may not be delayed,” it recommended.
It says that in the context of the apprehensions of the downstream inhabitants, it is more important to have dam distress monitoring mechanism or a dam safety review panel, apart from the dam design review panel already proposed, to periodically inspect the dam in operation for signs of distress.
“There is even a Dam Safety Act currently under consideration by Parliament, though it is meant for a review to be undertaken once in 10 years. In an environment that is traumatised by floods and is pervaded by forebodings of earthquakes, a dam distress monitoring mechanism will go a long way in instilling confidence in the inhabitants,” it said.
The committee has made it clear that there should not be any apprehension of the project having any impact on Majuli.
“During floods, with Subansiri’s contribution limited to 10 per cent, the project will have only a ripple effect. The small fluctuations created on account of peaking may hardly be noticeable and therefore there should not be any apprehension of the project having any adverse effect on Majuli. It is not fair to put the responsibility of managing bank erosion along Majuli on the project. Erosion and flood management will continue to be the responsibility of the Assam government,” it said.
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