Kerala - Thiruvananthapuram   

IIT study confirms State’s fears

THIRUVANANTHAPURAM: The Mullaperiyar dam could fail in the event of a ‘once in a hundred year flood’ even if it is assumed that the dam retains its strength on account of strengthening measures taken by Tamil Nadu.

More than that, this could happen even if the spillway gates are kept open (at a flood impinging level of 136 feet).

These are some of the conclusions that could be drawn from the results of a probable maximum flood estimation and flood routing study for the Mullaperiyar done by the Civil Engineering Department of the Indian Institute of Technology, Delhi.

The key finding of the study is that the water level would go up to 160.22 feet in the event of a maximum probable flood even if the impinging level is kept at 136 feet.

Tamil Nadu has been demanding that the water level be kept at 142 feet. This would result in a maximum water level of 160.43 feet.

The study has taken the contingency of at least two of the 13 vents not operating at the time of floods as per Indian standards that specify a contingency factor of ten per cent. (At least ten per cent of the gates could be inoperative considering mechanical and human failures).

However, even when 13 gates are operating, water could rise above 155 feet which is the maximum water level for the dam.

The study concludes that “the Mullaperiyar dam is hydrologically unsafe for passing the estimated probable maximum flood with the existing spillway capacity”.

This means that the dam could fail. Gravity dams or composite dams like Mullaperiyar stand mainly because of their weight. That is, the weight of the dam will counterbalance the pressure of water.

Theoretically, the water pressure will exceed the weight of the dam once the maximum water level is crossed and the dam will fall over.

The study shows that flood waters will flow over the parapet of the dam at 158 feet. This is a recipe for disaster. Even if sheer luck prevents collapse of the dam, the waters will exceed the carrying capacity of the channel to the Idukki dam and even the capacity of the spillways of the Cheruthoni (Idukki) dam. The waters will flood populated areas.

At full reservoir level, Idukki will also face the same fate as that of the Mullaperiyar dam. There is nothing to show that the 113-year-old Mullaperiyar dam could withstand such an onslaught of flood waters at 160 feet.

If the dam is strong enough, disaster could be averted by increasing its spillway capacity. This will require increasing the number of vents or lowering of the crest level of the spillways.

However, these are beset with problems. If the number of vents is to be increased, both the capacity of the channel and the spillways at the Idukki project would have to be increased.

Lowering of the crest level will also require considerable work that would take a lot of time. Such efforts would not be justified in the case of an old dam. So, Kerala is suggesting construction of a dam downstream.

The finding of the study will not only help the State to challenge Tamil Nadu’s demand for raising of the full water level in the reservoir not only from a safety point of view, but also from a legal point of view.

As per the Mullaperiyar agreement, the lease is only for an area up to the contour level of 155 feet. Tamil Nadu cannot have any structures that would cause the water to go above this level.

If water goes up above this level, Tamil Nadu would be breaching not only the agreement but also the Wildlife (Protection) Act as the area surrounding and enclosed by the reservoir is now a tiger reserve. However, the Kerala Irrigation and Water Conservation (Amendment) Act, which Tamil Nadu is challenging before the Supreme Court, gives it a legal loophole.

It specifies that water level in the reservoir could be maintained at 136 feet. Once the Supreme Court accepts the study, Kerala will have a case for its demand that the full reservoir level should be lowered further.

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