Who will control the erosion of Assam?
Neelim Akash Kashyap
The Brahmaputra River has wiped out nearly 4,000 square kilometers of area at a rate of 80 square kilometers per year, destroying more than 2500 villages and affecting more than five million people in Assam. Assam’s Water Resources Department has identified 25 vulnerable and very severe erosion-prone sites and estimated that the Assam valley portion of the Brahmaputra has lost approximately 7.4 per cent of its land area due to river bank erosion and channel migration.
Experts from Assam and the USA, who have formed a joint committee, christened ‘The Committee for Developing Mitigation Strategies for Brahmaputra River Basin Flood and Erosion Problem’, have come forward with a set of short and long term measures to address the problem and develop cost-effective solutions.
The experts have pointed out that the key factors in causing the river extremely unstable at many reaches are ‘aggradation’ (rising of the river bed due to sediment deposition), intense ‘braiding’ and large water discharge. They pointed out that till now both short and long term measures to tackle the erosion problem had been done only on a piecemeal basis during emergency situations depending on availability of funds. Experts in the committee are: Retired professor of civil engineering, University of Alaska, Dr Arvind Phukan, senior project manager at Wool pert, Virginia, Deva Borah, chairman of the Surface Water Hydrology Committee of the American Society of Civil Engineers Ananta Nath, Assam Water Resources Department’s senior engineer Rajib Goswami and professor of civil engineering in IIT, Guwahati, Chandan Mahanta. They have recommended phase-wise solution for the mitigation of erosion by including a combination of measures including strategic dredging, protection of erodible bank materials with anchored bulkhead or tie back sheet piles, spurs, toe and bank revetments.
Improvement of data quality and quantity by extending rain, flow and sediment monitoring network using state-of-the-art equipment and consider physical modeling to study severe and potential scour sites and their control have also been suggested by the experts. The experts further recommended development of advanced and efficient computational tools capable of utilizing the detailed hydro-meteorological data and predicting real-time flooding and hydraulic characteristics of the river for planning and designing effective flood and erosion control measures. The committee has suggested taking advantage of modern technology such as satellite image-based morphological study, studying of successful erosion control measures in major rivers of the world and feedback from international experts among steps to stem the erosion in the Brahmaputra at the earliest. It also suggested strengthening and monitoring of anti-erosion measures already taken up at Majuli Island and severely eroded towns along the river and armoring existing embankments located at urban and other strategic locations.
Lohit and Dibang Rivers called Brahmaputra was flowing along the northern side of Saikhowa Reserve forest. Since the year 1992, a part of this combined flow, followed a course along the southern side of Saikhowa Reserve forest, with increasing magnitude in successive years and joined the existing river channels of Dhola, Dangri and Dibru in the downstreram. The offtaking flow is called Anantanalla offtake, or only Anantanalla. With passage of time, Anantanalla went on increasing in magnitude. The problem of bypassing of discharge through Anantnalla, became very acute during 1997. By that time, the entire flow of Lohit River and the major part of Dibang River was observed flowing through Anantnalla. The high floods of 1997, caused wide spread floods devastation in Tinsukia and Dibrugarh districts, affecting 49 villages, due to submergence. The combined flow of Anantnalla continued and met river Brahmaputra, through Dibru River outfall and caused intense erosion at Rohmoria upstream of Dibrugarh. Acute erosion was observed in the year 1997 in about a 9 kilometer stretch on the southern bank of the Brahmaputra covering Bali Jan Tea Estate in the upstream upto Oakland Tea Estate affecting lives, property and fertile land of Litting and Gorapara village. The erosion was caused mainly due to the combined flow of the river Lohit and Dibang and the joined existing river channels river channels of Dhola, Dangri and Dibru in the downstream. The off taking flow is called the Anantalla and the joining of Anantanalla with Brahmaputra increased the intensity of erosion at Rohmaria.
A delegation of the Asam Jatiyatabadi Yuba Chatra Parishad, Majuli unit after their visit to the worst-hit areas of the river island alleged that the departments concerned did not take necessary action in time to stop the erosion.
On the other hand, a study on a selected stretch of the Brahmaputra river channel revealed that the mechanisms involved and responsible for riverbank erosion were basically related to aqueous flow of sediments (liquefaction) enhanced by the in homogeneity in the bank materials in question, over steepening and associated sub-aerial processes of weathering and weakening in relation to soil moisture content. The study revealed that the extent of erosion and deposition in not the same for the period 1914–75 and 1975–98. Different scale and nature and sheer failure are considered to be mainly responsible for bank erosion processes.
The Assam government has roped in a group of German experts to find a long-term solution to the decades old problem of floods and erosion caused by the Brahmaputra and its tributaries and a preliminary report has been prepared and submitted to the State Government by the group. The state is also looking at channeling the Brahmaputra with the help of the European Commission, and an integrated water resources management project called Brahma Winn is already underway to address this issue. Named after the Brahmaputra basin and the Twinning basin (in Europe), this project has developed a Decision Information Support Tool mechanism for dissemination of information on the Brahmaputra basin, official sources said. Recently, Assam Chief Minister Tarun Gogoi had complained that all measures taken to tackle floods and river-bank erosion have been ad hoc, with specific projects taken in isolation. “We must put an end to ad holism and adopt a holistic approach to tackle the mighty river,” Gogoi added. A pilot project has been taken up with financial support from OIL India Ltd for anti – erosion measures. The project may cost `2 to `3 Crores. In the meantime OIL has released `5.Lakhs. Work on construction of steel pipe dampner at the erosion site has already been started and two dampeners completed. During recent visit of Prime Minister Dr. Manmohan Singh of India to Dibrugarh on the 21st of April, Chief Minister Tarun Gogoi of Assam has submitted a memorandum highlighting the financial scenario of the state and the need for an economic package for the all round development of the state.
The question here is, when will the erosion problem in Assam be solved permanently?