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Reducing opacity

The proposed construction of a strategic rail-cum-highway underwater tunnel across the river Brahmaputra in Assam


Sentinel Digital DeskBy : Sentinel Digital Desk

  |  16 July 2020 4:39 AM GMT

The proposed construction of a strategic rail-cum-highway underwater tunnel across the river Brahmaputra in Assam has given rise to several questions which have no easy answers. The underwater tunnel including approach roads will connect Pachigaon in Jamuguri on the northern bank with Kaliabor tea estate in Silghat on the southern bank of the river. The Project corridor will be between the existing Kaliabhomora Bridge across the river and up to a distance of approximate 12-14 km upstream of the bridge. The strategic tunnel will provide all-weather connectivity and facilitate quick movement of army troops across the river to respond to emergency situation along the India-China border areas in Arunachal Pradesh. The recent face-off between two Asian giants along Galwan sector and the 1962 war call for India strengthening its preparedness for any kind engagement all along the Line of Actual Control. A strategic connectivity project, therefore, deserves desired national response and attention. The challenge, however, lies in balancing the environment protection and strategic requirement. This gives rise to a question as to which should get the preference between the two if the situation leaves out the option of balancing the two requirements. The challenge becomes monumental when it involves a mighty river like the Brahmaputra. The Request for Proposal issued by the Border Roads Organization for consultancy services for preparation of feasibility study and detailed project report (DPR) states that "Once the geophysical investigations and sub-surface investigation results have been interpreted, the consultant would be required to interpret and analyse the site and establish the feasibility of underwater tunnel option and bored tunnel option." It further adds that the underwater tube tunnels will lay on river-bed surface which needs to have the requisite bearing capacity for static loading. The bored tunnel design will be based on the final configuration of the tunnel tubes and the geotechnical environment. Either option will require in-depth understanding of the Brahmaputra riverbed and the characteristics of the river. The Brahmaputra is the third largest river in the world in terms of its annual discharge and carries highest silt load amongst rivers of its size, states the Annual Report 2018-19 of the Brahmaputra Board. "Due to heavy deposition of silt, the river frequently changes its course on its way. Excessive silt deposition has also given rise to braiding and meandering pattern in the alignment of the river system," it says. Recurring annual floods and erosion devastate the state every year which leave a cascading impact on its economy. Assessment of the impact of the proposed tunnel, therefore, cannot be area specific and will need to be more elaborate and should consider the cumulative impact of floods and erosion for the entire state. It will therefore require wide consultations with the experts on the river as to what could be the consequences of any disturbance of the bed by a project of such scale. The experts of the executing departments and agencies associated with the proposed tunnel as well as the experts not directly associated with it, in turn, need to explain it to the general public about the utilities and consequences of the project. The State government can play a critical role in this regard. It is not clear if the construction of the proposed tunnel will have any ramification on the proposed corrective dredging of the river Brahmaputra initiated by the Assam Government to improve its navigability and better management of floods and riverbank erosion. The State Water Resources Department floated a global tender to purchase a dredger after getting administrative approval for Rs. 18 crore. The Department claims that dredging of the river would dig out sediment from the riverbed and increase water carrying capacity which will help reducing pressure on the bank and minimise the chances of flood and erosion. An Expert Committee constituted by the State Government to go into the issue, however, cautioned that a massive dredging exercise in the entire Indian reach of the Brahmaputra would change the overall water quality status of the river with significantly increased turbidity level and changes in several other parameters that may have harmful impact on aquatic ecology and affect the riparian population whose livelihood depends on the river and floodplain ecosystems. The committee suggested to the State Government to go for corrective dredging at selective locations only for removal of silt to prevent erosion without disrupting the flow. This recommendation by the experts is a pointer towards consequences of any large project on the river Brahmaputra and should sound a word of caution to all stakeholders to undertake an exhaustive study before pushing the proposed tunnel project. The search for alternative solutions and strategy must continue. This can be possible only if transparency on the feasibility studies, DPR, environment impact assessments are ensured before rushing to execute the underwater tunnel project.

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