Calcutta Notebook


Floods have once again engulfed Assam. In the coming months one may expect more floods across the country. In truth a number of states including Gujarat, Rajasthan and West Bengal have been ravaged by floods. The immediate cause of these floods is heavy rains. However, heavy rains are a routine event. The "normal" rains have been converted into damaging floods because of the artificial obstructions made in the path of the rivers. The Himalayan Rivers carry large amounts of sediments from the hills to the plains. Part of this sediment is carried to the sea and part is deposited in the riverbed. The level of the riverbed rises gradually. Then floods come after four or five years. The sediments deposited on the riverbed during these years is flushed into the sea in one go. This is as if the dust deposited in the home for four or five days is cleaned up on the weekend.

Efforts to "control" the floods have eliminated these flood flows. Floodwater is held back in dams like Bhakra and Tehri. These dams have two contrary impacts on the floods. On the one hand, they trap some sediments and reduce the deposition of sediments in the riverbed in the pains. On the other hand, these dams trap large quantities of water, reduce the velocity of the river during the monsoons, and the river is no longer able to flush the sediments to the sea. The intensity of the floods has become worse. This means that these dams are making a small reduction in the deposition of the sediments in the plains; but making a large reduction in flushing the sediments to the sea. It can be said that these dams have intensified the floods.

The increased net-deposition of sediments in the plains is leading to a rise in the level of the riverbed. The waters now flow on top of the raised riverbed during the monsoons. Thus, water spreads in the surrounding areas and creates much more damage. The riverbed would be lower if these dams were not made; floods were recurrent and had carried the sediment to the sea. Now efforts to control the floods have prevented the flushing of the sediments to the sea and actually made the floods more damaging.

Barrages too have contributed similarly to the making of the floods. The Farakka Barrage has created an obstruction to the natural flow of the Ganga. A shallow pond has been created behind the barrage. This pond extends many hundreds of kilometers into Bihar. The velocity of flow in the pond is less. As a result, the sediments are deposited in the pond. The gradient of the pond has reduced and the level has risen by about 30 feet near the barrage. As a result, the Ganga flows on flatlands and her capacity to carry the sediments to the sea has been reduced. Indeed, the gates of the barrage are fully opened during the floods. That does not help, however, because the slope of the riverbed upstream has been flattened and the waters do not flow speedily.

The increasing intensity of floods is then sought to be managed by making embankments. 5000 kilometers of embankments have been made in Assam. Previously the river flowed in a wide area and deposited the sediments on the fields. Now the river flows between the embankments and deposits the sediments here. The riverbed between the embankments rises gradually. The embankments are then raised. After a few years, the river starts to flow at a higher elevation than the surrounding land. However, there is a limit to how high an embankment can be made. Eventually the river breaks the embankment, the water gushes out like in a waterfall, and hell breaks loose all around. The large numbers of embankments made on the Kosi River in Bihar are a fine example of such manmade technological disaster.

The problem has been compounded by widespread constructions on the lakes and drainage channels. The lakes held back large amounts of water and helped them percolate into the groundwater. The lust for urban land has led construction on these. The Satliyabama University in Chennai, for example, was constructed in a water body on the Old Mahabalipuram Road. This has been a major reason for the floods in Chennai and Bengaluru.

The latest entrant into the man's tyranny towards the river is dredging. The Assam Government wants to control floods on the Brahmaputra by dredging. Sediments are removed from a deep channel in the riverbed and placed on the shallow sides. The cross section area of the river remains unchanged. It is like cutting a piece of paper from one side of the sheet and pasting into the other side. Dredging only changes the profile of the riverbed without increasing its capacity to carry water. The Assam Chief Minister Sarbananda Sonowal said after the floods last year that the State Government has decided to start dredging of the Brahmaputra River to deal with flooding. It appears to be a ploy to dredge the river for the plying of large ships. It will not help reduce the floods one bit.

The ferocity of the floods has increased over the years because of dams, barrages, and embankments. Engineers drive the irrigation departments of the states. They like to make big structures. They are aware but not willing to consider these long-term consequences because it hits at their incomes. More floods, more disasters, more calamities are doubly beneficial for the bureaucracy. First, they make money in making the dams, barrages, embankments and dredging. Then they make money in distributing flood relief. The people of the country are being made to suffer from floods because it is good for the irrigation bureaucracy.
The correct way to manage the floods is to live with them.

Vol. 50, No.7, Aug 20 - 26, 2017