GUWAHATI, July 26 � A group of engineers here claim that a local technology has been developed to narrow down the ever-widening Brahmaputra and to make it follow a desired and deep course with steeper flow gradient.
The Brahmaputra has greatly widened almost all through its course in the State, except at places like Pandu. Many factors are contributing to this phenomenon.
The present around 20-km wide Brahmaputra at downstream of Palasbari was only 4.6 km wide in 1828 as per the record of the survey conducted by the Britishers, say these engineers.
The river is eroding up more land, surpassing the previous record of seven per cent loss, just because no adequate care could be taken due to lack of fund and availability of a cheap method. Such a method was not known all over the world, they say.
Now, they claim, Assam has a cheap and successful method and no international method can match it in matters of success.
Explaining the science behind their technology, they say, a recent study revealed that Brahmaputra has as many as 21 hard points on each of its banks. Hard points guide courses of the rivers.
Two hard points at opposite banks in a cross-section of a river, gives rise to a rigid section called Nodal Point. If the gap between the two such hard points is less than the average width of the river in the corresponding reach of the river, it constitutes a constriction point.
The action of such a constriction point in a silt-laden river plays a very important role in determining the shape, size and location of sand bars (chars or chaporis) within the influence area of the said constriction point.
This consequently creates a tendency in the river to continuously increase its width within the said zone of influence with the other factors like silt load, flow velocity etc, supporting it.
Useable land on the banks of river Brahmaputra is not much in Assam. There is the need to reclaim the lost land. Reclamation of this lost land is quite possible and it can be done by a cheap method. If one looks at the land area covered by the chaporis and compare it with the area of the land lost due to riverbank erosion, no big difference is found between the two figures.
Moreover, the discharge of the Brahmaputra has also not increased. So, the river can have an width equal to what it had a hundred or hundred and fifty years back or prior to that.
From the 1828 survey map, it is found that in general, the river was then less than one-fourth in width compared to what it is today.
Scientifically, it is best to push the river�s deep channel to its mid-stream channel. Devices have been developed in Assam for this purpose and a few years work is sure to show results. There may be some specific problem areas where other measures may become necessary as supportive ones, say the engineers.
Explaining their devices, they say that these devices are pro-siltation devices. These structures produce reinforced bank of permanent nature. As these structures are made of concrete, thorny in nature and too heavy for the flow, the river current coming from any direction or disturbed by the forces of earthquake etc, cannot wash them away.
They reclaim land in a river having silt load. Moreover, they are easy to be constructed with small quantities of local eco-friendly materials and they could be handled easily using manual labour or a simple crane.
��A comparative study of cost of construction per kilometer shows that spurs cost nearly Rs. 7 to 8 crore, revetment about Rs. 15 crore and pro-siltation measures Rs. 0.5 crore.
And when their efficacies are taken into consideration, it is found that unlike the conventional structures, the pro-siltation measures create sustainable wide reinforced bank with natural transverse slope.
They gradually push the flow to the mid-stream without disturbing the river�s environment drastically, reduce chapori formation, drive the lighter sediment away and thus expand reclaimed banks with zero danger, claim the engineers.