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.

... contd.