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Of floods and fortifications

Whenever a major flood occurs, with accompanying loss of life, livelihoods and property, it generates a strong feeling...

Written by Ramaswamyriyer |
September 19, 2008 12:22:45 am

Whenever a major flood occurs, with accompanying loss of life, livelihoods and property, it generates a strong feeling that something should be done about this problem. Starting from the proposition that the problem, i.e., floods, should not be allowed to happen again, administrators and engineers decide that the river needs to be controlled, and come up with proposals for embankments and dams. This was what happened in the 1950s when Bihar was laid low by exceptionally heavy floods, and Nehru, appalled at the destruction and human misery, wanted something to be done urgently. Once again, in 2008, when Bihar is reeling under floods, we hear demands for a high dam on the Kosi in Nepal as a flood-control measure. Prima facie, that seems reasonable. Where is the fallacy in this?

First, we must distinguish between avoidable and unavoidable floods. When Delhi or Mumbai get heavily flooded with the first monsoon showers, the cause is inadequate or badly designed or poorly maintained or carelessly blocked drainage systems, or the ill-considered diversion of natural drainage channels. These are floods caused by human error or negligence. Floods are also sometimes caused by bad dam management, and these too are man-made. Periodical river-floods are different— they are natural phenomena — and could be seasonal floods because of heavy monsoon rains; flash floods from cloud-bursts; floods resulting from the sudden release of waters held up by mountain landslides; and so on. These cannot be prevented. They can be of varying intensities, and the regular floods, i.e., those other than freak events, are classified by probability of recurrence (once in 20, 100, 1000 or10000 years). When the flood waters come, the river needs space to spread and accommodate them. That space is known as the natural flood-plain of the river. If we occupy the flood-plain or build structures on it, or try to jacket the river within narrow confines, we are asking for trouble.

Against that background, let us consider the idea of flood-control. Embankments try to protect areas on either side of a river by confining the river within limits. This might work in some cases, but not with Himalayan rivers, where embankments fail and have to be re-built repeatedly. That could be a very costly affair. Secondly, assuming that the embankment is properly maintained — a questionable assumption — it might still give way in an exceptionally heavy flood. That is the nature of embankments. Thirdly, even if they do not break down, they might cause various problems: an increase in the velocity of the waters; possible attacks by the river further downstream; a rise in the level of the river-bed, with the river flowing above the level of the ground on either side; the blocking of drainage from either side into the river leading to waterlogging and even flooding in ‘protected’ areas, and so on. While it might be possible to cite some instances where embankments have worked, they are in many cases remedies worse than the disease.

It might appear that these objections do not apply to dams. The argument is that a dam will create a reservoir which will provide space for the temporary storage and gradual release of floods, thus moderating them. However, this is not necessarily always the case. Theoretically, a dam could be built exclusively for flood-control and operated strictly for that purpose. However, a dam-and-reservoir project is generally built for multiple purposes (irrigation, power-generation, flood-control, etc), and there is an inbuilt conflict. Flood-control would require the intended space in the reservoir to be kept vacant to accommodate flood-waters, whereas irrigation or power-generation would require the reservoir to be as full as possible; and the latter, being gainful economic activities, are apt to prevail over flood-control. If the space meant for accommodating floods is not available when the flood comes, the gates will have to be opened in the interest of the safety of the dam, and the downstream area might experience a greater flood than it would have done if the dam had never been built. This would be a manmade disaster; and has happened more than once.

Even if a multi-purpose dam is operated with due regard for flood control, and the flood cushion is maintained, the moderation that this can offer is very limited. The contingency of heavy floods posing a danger to the dam and compelling the opening of the gates is always present. The question is whether a limited protection under normal circumstances is worth the risk involved in non-normal circumstances. This is an inherent danger in all dams, and all the greater in the case of Himalayan rivers.

It is hoped that the expression ‘fallacy of flood control’ stands justified, though one is open to correction. What then must we do? We can learn to cope with floods, and perhaps even benefit from the silt that they bring. They could be anticipated and prepared for; there could be timely information, a state of readiness for an emergency, the minimisation of damage and prompt response by way of relief. That is what we try to do in the case of earthquakes or tsunamis: floods call for exactly the same approach.

The writer is an honorary research professor at the Centre for Policy Research

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