Opinion (Spotlight Weekly)

Kosi Dam: Highest In The World

By A.B. THAPA

Finding a satisfactory solution to the Kosi flood problem stands out as one of the most serious challenges we face today. Hundreds of thousands of people could be killed and millions more made homeless in our region if timely action is not taken to prevent this disaster. On the other hand, our region stands to benefit enormously, on top of protection against flood damage, if works are carried out in time to resolve the Kosi flood problem.

Solution to the problem of keeping at bay the Kosi flood disaster had been found a long time ago. Dr. A.N. Khosla, a prominent scientist in the field of hydraulic engineering and then-Director-General of Irrigation, Power, Flood Control and Navigation in the Government of India, had opined in the 1940s that storage dams would be needed to control the Kosi river to avert the flood disaster. Under his leadership, field survey works started immediately after the Second World War in 1946, while India was still under British rule.

The study recommended that a 269-meter high dam would be needed to control the Kosi floods. In the 1950s, the idea of building the Kosi high dam was abandoned and, in its place, embankments were built on both sides of the river. It is not difficult to perceive that the embankments were built to confine the Kosi river within a fixed perimeter. This was only a temporary solution. Anyone with the slightest knowledge of hydraulic engineering would know that storage dams would ultimately be needed.

Why was not the Kosi high dam built right away? Why it was decided to build embankments instead of a storage dam? Many people are still debating the correctness of the decision. The decision of the Indian government was not only justifiable but also absolutely necessary at that point in time. An effort is made here to explain why.

Enormity of Kosi Dam Problem

Recent studies of the Himalayan region provide a plethora information very useful for planning high dams. Such information was extensively used for detailed planning of the Karnali high dam. The Karnali studies, carried out at an enormous cost by a consortium of renowned consulting firms of several countries under the aegis of the World Bank in close consultation with the governments of Nepal and India, have greatly helped to realize that, compared to the earlier perceptions, the magnitude of the problems to be actually encountered in dam planning in the Himalayan belt would be far more serious and complicated. This has been amply reflected in the finalization of the design of the Karnali high dam.

As stated above, the height of the Kosi dam proposed by India in 1940s was 269 meters. At that time, the world's highest dam was the 221-meter Hoover dam on the river Colorado built in 1936 in the United States. Thus, the proposed Kosi dam exceeded the height of the Hoover dam by a huge margin of almost 50 meters. This suggests that even at that time India had felt that the height of the Kosi dam should be raised to a maximum possible extent to be constrained only by technical limitations.

Gravity-type concrete dam had been selected for the Kosi river. The dam height had been stretched to an extreme limit for this type of dam even based on the most recent global experience. There are only two concrete dams in the world slightly exceeding the proposed Kosi dam in height. They are the 285-meter Grande Dixene gravity dam built in Switzerland in 1961, and the 272-meter Inguri arch dam built in the former Soviet Union in 1980.

By comparison with the recalculated height of the Kosi dam based on the recent Karnali project study, the originally proposed Kosi dam height would still be very much on the lower side. It is quite possible that India might have realized even at that time that the height of proposed Kosi dam must be further raised for effective flood control but it would have been very risky to do so. It was already a very bold decision go up to a height of 269 meters. The technology of embankment type dam better suited to fragile geological conditions was not well developed then to be applied to dams of this height. Therefore, it could be the reason in taking the decision not to build the Kosi dam project in immediate future. Under such circumstances, the construction of the embankments on both sides of the Kosi river would have been at that time the only best option for the Kosi flood control, though such measures to protect against floods would not be lasting long.

New Height of Kosi Dam

The feasibility study of the Karnali high dam project can provide very useful information for the planning of the Kosi high dam. The Kosi and the Karnali rivers located close to one another in the Himalayan belt differ only moderately in size. The physical condition of the dam sites of both these projects is also quite similar. Therefore, the end results of the Karnali storage reservoir study could be safely applied to conceptualize the scope of the Kosi high dam.

According to the Karnali project feasibility study the total volume of the Karnali reservoir would be 39 billion cubic meters. Out of it, the dead storage volume, effective storage volume, and the flood regulation volume would be 12 billion cubic meters, 16 billion cubic meters and 11 billion cubic meters respectively. If we applied the Karnali design criteria, the Kosi project would require a storage reservoir even greater than the proposed Karnali reservoir in volume because the Kosi is a bigger river than the Karnali. The total drainage area of the Kosi is about 60,000 sq. km., whereas such area of the Karnali is only 44,000 sq. km. Similarly the total volume of annual flow of the Kosi is about 52 billion cubic meters, whereas such volume of the Karnali is only 44 billion cubic meters. The silt problem of the Kosi river is by no means less severe than that of the Karnali. However, for further review, it is presumed that the volume of the Kosi reservoir would be only equal to the Karnali reservoir volume, although the actually calculated volume of the Kosi reservoir based on Karnali data would have been much greater.

The total volume of the Kosi storage reservoir, according to Indian study, was only 13.45 billion cubic meters. Such volume is too small by comparison with the volume of the Kosi reservoir based on the Karnali study. The useful life of the storage reservoir originally proposed by India would have been very small. It would not be able to regulate satisfactorily the Kosi floods. This could be the reason why India abandoned in 1950s the Kosi storage dam project and decided to build the embankments to control temporarily the Kosi floods.

The 1997 Indo-Nepal Agreement

For a storage reservoir identical to the Karnali reservoir in volume, the height of the Kosi dam would be about 340 meters. At present, the 335-meter-high Rogun dam still under construction in the former Soviet Union is the highest in the world. Thus, the Kosi dam would be the highest in the world. Implementation of this project is certainly a very big challenge.

The scope of the Kosi high dam project has been further enlarged after the 1997 agreement between Nepal and India to carry out the feasibility study of this project alongside the feasibility studies of the Sunkosi high dam and the navigation canal from Nepal to the Ganges leading to a seaport outlet for Nepal. The 1997 study agreement is specially significant because the new Kosi planning perception developed within the Water and Energy Commission Secretariat without the involvement of the foreign expertise had been fully endorsed by the Indian government. It is now becoming increasingly clear even to those people virtually knowing nothing about dam engineering that the Sunkosi dam project should be the forerunner of the Kosi high dam project, and it should be implemented at the earliest to save the life and property of millions in Nepal and India. Until now, our effort for Kosi development is on the right track. It is up to the new management in our government and also the concerned body of the Indian government to ensure that this process will not be derailed to the detriment of the interest of our both countries and more particularly the interest of millions in our region threatened by the devastating Kosi floods feared to hit anytime in future.

Research and Development

In conducting the detailed study of an enormously big project like the Kosi high dam project research & development would be very important. A small panel of world-renowned experts should be constituted if necessary even from our side at the very early stage to examine the scope of the investigation works and to propose modifications if necessary.

The R&D works should proceed as soon as possible. Institutions like the International Center for Integrated Mountain Development could also play an important role. We should encourage involvement of our academic institutions in such research works. In 1998, Water and Energy Commission had even entered into an agreement with the Kathmandu University to use the external financial resources then available to the commission for training on the job engineers within the ministry under a special program. The recruited engineers were to be assigned to conduct research works under the supervision of external experts in those fields that concern the Kosi projects the most and at the same time on successful completion of the research works they would have been entitled to get M.Sc. or Ph.D. degrees. Unfortunately this work did not proceed further. There is an urgent need to take up this matter.

We should realize that Kosi development is an enormously big challenge before our country. The government, various academic and other institutions, and the donor community taking part in socio-economic development of Nepal should take special interest in the forthcoming studies of Kosi projects.

(The writer is water resource expert)