GUWAHATI, May 12 - Without the components of controlling flood and erosion, there is probably no point in dredging the Brahmaputra purely for providing navigation facilities and constructing expressways along its banks by utilising the excavated materials. This is the observation made by two senior engineers GK Bordoloi and Hareswar Talukdar. They were talking to this newspaper.They laid emphasis on evolving some innovative and cost effective methods for the purpose of tackling the above problems. For, they maintain accommodating the flood discharge of the Brahmaputra by providing hydraulically balanced cross sections along its length and constructing deflector bunds at vulnerable locations may emerge as the ultimate solution to the problems of flood and erosion.
Moreover, they say extensive comprehensive studies, including model studies, would be required to determine the vulnerable locations, lengths of the bunds, depth of dredging, hydraulically balanced section, etc., for the entire length of the river. And this study should preferably be done before preparing the project reports for implementation of the dredging scheme, as the expressways will have to be constructed on surplus space after incorporating the required width of balanced cross sections.
They maintain further that the traditional method of controlling the Brahmaputra flood by constructing embankments on its banks and raising and strengthening it after every few years and also plugging the breaches whenever they occur on these earthen structures, are no solutions to the problem.
For, they say raising and strengthening will be a continuous requirement to keep these structures effective due to the deposited silt raising its bed level every year. As per expert’s opinion, annual silt load of the Brahmaputra varies from about 402 to 710 million tonnes. To dredge the river and carrying the huge quantities of dredged materials to the bank or elsewhere will be of a gigantic exercise.
Some experts suggest that dredging should be taken up at isolated stretches and the excavated materials should be utilised in constructing bunds at banks to make artificial reservoirs on the river to contain the excess flood discharge. But the moot point is — where is the existing firm bank of the Brahmaputra as today’s bank becomes the river bed tomorrow, they say.
From the news paper reports it seems that the Centre is going to dredge only at isolated stretches just to maintain a navigable channel of about 45 metres on the river throughout its length from Sadiya to Chittagong. Hence this will not be able to control the Brahmaputra flood, say the senior engineers.
The flood discharge of the Brahmaputra varies from about 30,000 cubic metres per second (cumecs) near Sadiya to about 1,00,000 cumecs near Dhubri and average width of the river may be around 4,000 metres all along its length, except near Guwahati where the river is narrowest at about 1,300 m.