Environmentalists emphasises to dredge wetlands to minimise flood problems

Wetlands, tributaries and low lying lands filled up with sand, silt and sediment must be dredged to control flood problems in Assam. 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. Chandan Kumar Duarah, a conservation activist and science writer suggests to dredge wetlands which became less deeper with silt and sediment carried by flood water. A K Mitra, the former Secretary of Water Resource Department of government of Assam, says that dredging Brahmaputra is just an idea proposed about. It is still in theoretical state which would be difficult to implement without a total plan. Flood in Assam needs multi measures to minimise it, Mitra said. China had success story of dredging Huawang Ho on account of its multi-measures, he recalled with his field experience in China. In Assam it can’t be succeeded unless and until some measures are taken in advance before dredging. The Assam government is taking seriously dredging of the Brahmaputra river as 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 Hydrabad based organisation for water-conservation in Asia, a number of engineers, conservation activists and experts discussed about dredging. Most of the scientists and experts in hydrology do 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, if other pre-measures are not taken. Rather it will be a waste of money , energy and time. He emphasized on checking siltation in upstream of rivers . Multi-purpose hydro electric project with special function can check silt at upper level and help to minimise both flood and siltation problem in down stream. He suggests 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, he said.
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 will not help to minimise 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. Bharat Saikia, a former superintendent engineer in the department of water resources and expert on erosion said earlier for dredging to be effective, it is first 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 had 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. But I don’t think so. 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.
According to Pradip Pujari, 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. would minimise the sediment and silt deposited in the riverbed of Brahmaputra.
Wetlands in Assam have a great role to minimise flood. Because 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 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, said Duarah.



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