Recent floods in the Krishna basin have left hundreds of people dead and lakhs homeless. Countless livestock have been destroyed and the total monetary loss ran into thousands of crores of rupees. As a hydrogeologist with 4 decades of experience, these are my observations on this disaster.
1. There are several major dams across the Krishna river and its tributaries and these dams were supposed to prevent such disasters. So the dams have failed in one of their primary purposes. Not just that, it now appears that these dams themselves were a major cause of this great tragedy.
2. The backwater of these dams has submerged some of the richest black soils in the country and rendered them worthless.
3. This soil is silting up the dams and is continuously reducing their designed water holding capacity. This capacity has already gone down by as much as 30%.
4. The land which is intended to be cultivated with the water stored in these dams is mostly barren rocky land with poor soil cover. Even if this land is supplied with plenty of water, there is little scope for highly productive cultivation. The increase in agricultural output due to the dams may not be even enough to cover the interest charged on the huge loans taken from international organizations to finance these dams.
5. It is quite likely that the enormous additional pressure exerted by the water reservoirs on the basaltic rock bed of the river valley has been responsible for a large number of earthquakes in and around Koyna (Maharashtra). Additional reservoirs may cause bigger earthquakes in times to come.
6. The loss of fertile lands and the submergence of hundreds of villages and towns by the dams and inadequate compensation has made the rehabilitation of the countless displaced people a major continuing humanitarian problem.
In light of these major problems posed by big dams, it is time we start looking at effective alternatives to big dams in managing river waters. Building a system of small and medium barrages across the rivers in the valley and canals to carry the waters stored in the barrages seems a much superior scheme. In the ghat section in which Krishna and its tributaries originate, they have cut deep ravines in the hill areas and deep gullies in the plains with banks 8-10 m high on either side. These natural structures can be put to optimum use by constructing a series of barrages starting from the source all the way to the plains with an accompanying canal system. The advantages of this system are:
1. There would not be any overflow of water over the banks.
2. The fertile lands on either side of the rivers would remain intact and available for intensive agriculture.
3. The usage of water would be optimum.
4. There is no need for resettlement of people and the consequent heartburn, corruption and huge expenditure.
5. Since each barrage weakens the force of flood water, damage to life and property will be minimized even in the case of intense rainfall.
6. The cost of each barrage will not exceed a crore of rupees and could be as small as a few lakhs of rupees. The total expenditure for a series of barrages will be much less than the cost of a major dam and would eliminate the need for foreign assistance and loans. The construction time for barrages is also very short and so benefits start accruing within a few months.
7. Since the irrigation is seasonal, soil quality and fertility are not damaged.
8. Since submergence by the backwater is kept to a minimum, soil erosion and loss of water storage due to silting are very small.
9. Since the water is stored in several reservoirs, the pressure on the river bed is distributed and so the barrages will not cause an increased incidence of earthquakes.
10. The canal network from this series of barrages will be spread over the entire river basin and will immensely help the building up of ground water which, if used in conjunction with the surface water, will greatly enhance the area and scope of irrigation. Since ground water is being recharged continuously, there will be no shortage of drinking water in the entire river basin.
11. The water distribution is more equitable.
So it is clear that the construction of many barrages is preferable to the construction of a big dam in more than one way. The arguments given above for the Krishna river basin apply by and large to other river basins also. Recently published studies of the Bhakra Nangal dam have shown that the return on the investment in the dam is far below what was claimed. So it is high time we come out of the straightjacket of major dam construction and consider alternative approaches to irrigation which may be more effective.
V. Mahesh, Mysore Grahakara Parishat