Brahmaputra upstream needs silt check, not hasty dredging

 

Assam Government declared dredging as an answer to solve the flood and erosion problem. Government declared that the World Bank had sanctioned Rs 980 crore to dredge the river. But, it is in doubt whether it will help to minimize flood and erosion problem anyway.

Assam chief minister Sarbananda Sonowal told media last month that dredging of the Brahmaputra would yield a plethora of benefits. It is possible that erosion would be reduced as the depth of the river bed would increase and the force of the water would be less on the banks . He added that the exercise could be carried out along all the affected spots including Majuli which he represents in the assembly.

Dredging the Brahmaputra is not a sole solution to minimise the flood and erosion problem of Assam. Scientists and experts say that the sole plan to dredge the riverbed will not help to solve the problem. Flood in Assam needs multi measures to minimise it. China has been an example to dredge the Brahmaputra by some enigineers. China had success story of dredging Huawang Ho on account of its multi-measures. In Assam it can’t be succeeded unless and until some major measures are not taken in advance before. The Assam government is taking seriously dredging of the Brahmaputra river is not an way to mitigate the flood and erosion problem. Some engineers and scientists suggests to dig the river bed as it can carry more water without causing flood problems.

In a seminar on ‘Policy Dialogue for Governance of the Brahmaputra River’ held in Itanagar, the capital city of Arunachal Pradesh was organised by SACIWATER, a Hyderabad based organisation for water-conservation in Asia, a number of engineers and experts discussed about dredging and I was also one of participants. Most of the scientists and experts in hydrology did not agree with the move of Brahmaputra dredging. Pradip Pujari, formerly with Brahmaputra Board and a consultant engineer, also said that dredging is not an answer to solve or mitigate the flood and erosion problem. I met A K Mitra, a retired Chief  Engineer of Water Resource Department, who said that dredging Brahmaputra to control flood problem is just an idea proposed about. It is still in theoretical state which would be difficult to implement without a total plan.Rather it will be a waste of money , energy and time.

I also emphasised on checking siltation in upstream of rivers . Multi-purpose hydro electric project with special function can check silt at upper level and help to minimize both flood and siltation problem in down stream. Mitra and Pujari also suggested a mechanism to check silt and remove the silt from the dam. If silt carried by rivers are not stopped all efforts would be futile and deep river-bed would be filled up with sand and silt again with the very next flood water.

t is said that if Brahmaputra is dredged the erosion would be reduced as the depth of the river bed would be increased and the force of the water would be less on the banks . The Chief Minister added that the exercise could be carried out along all the affected spots including Majuli which he represents in the assembly. Before the dredging,  first it is necessary to understand the nature and quantity of silt deposition. Silt gets deposited very fast and so it is doubtful if such schemes would be successful.

Considering the annual silt load of Brahmaputra, water carrying capacity of the river has been reduced to an extent causing floods in the state when there was incessant rains during summer. It is very common and simple idea that making deeper the river bed or dredging of the river bed will help to control flood and erosion problems in Assam. Because siltation and sedimentation are continuous process which occurs with the flow of water. Dredging can’t be a sole answer to the problem of flood and erosion that has been gobbling up hundreds of acres of land every year on both banks of the river. Engineers and experts must invent a mechanism which will check siltation in the upstream of rivers.

We should remember that wetlands in Assam have a great role to minimize flood. Wetlands store a large amount of excess water during flood. According to ENVIS center Assam 690 lakes and ponds recorded in Assam. These lakes /ponds cover an area of 15494.00 ha which constitutes 0.20 percent of the total geographical area of the state and 15.30 percent of the total area under wetlands. The smallest of them measures 2.50 ha while the largest one has 882.50 ha of areal coverage. But most of wetlands in the state have became shallow due to silt and sediment deposition. As they are becoming shallow the capacity of flood water storage also decreasing. So if these wetlands can be dredged and make deeper these will have more capacity to store more amount of flood water. Apart from flood and erosion mitigation, dredging wetlands will help farmers with irrigation and fishery for winter cultivation.

If silt and sediment carried by the Siang (Brahmaputra in Arunachal Pradesh) and its tributaries are not stopped, all efforts would be waste of money and energy. Sand and silt will fill the dredged river-bed again. So, in stead of dredging the Brahmaputra, dredging of wetlands and shallow river beds of tributaries of the Brahmaputra (Yarlung Zangbo) will be more effective. Dragging wetlands and rivers like Jiadhal, Gainadi etc. will minimize the sediment and silt deposited in the riverbed of Brahmaputra.

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