Kerala - Thiruvananthapuram   

Mullaperiyar, Idukki dams facing risk

Thiruvananthapuram: Mullaperiyar and Idukki dams are facing a higher risk than ever this monsoon. Both the reservoirs are nearly full at the same time of the year.

The Idukki reservoir has never been full when waters flowed down spillways of Mullaperiyar (at 136 feet) in the past. But the situation is different this time as the water reaches 136 feet in the Periyar reservoir.

The increased risk arises from the fact that the spillway capacity at Idukki is inadequate to meet a probable maximum flood situation in the catchments of Mullaperiyar.

The Idukki reservoir had almost reached its full capacity during the South-West monsoon this year. Water level has since been brought down to 2397 feet above the mean sea level by increasing power generation.

The catchments of both the reservoirs have been experiencing heavy rain for the past few days. Tamil Nadu has reduced the intake from the Mullaperiyar owing to heavy rains in Madurai district. This can increase spillage, which flows down to the Idukki reservoir.

The probable maximum flood (that is likely to occur once in 100 years) in the Mullaperiyar basin is estimated to be of 6003 cumecs. However, higher peak flows have been observed in the past. According to the State government, the reservoir had recorded a peak flow of 8453 cumecs in 1943. However, the capacity of the spillways of Idukki project (at Cheruthoni dam) is only 5100 cumecs, which is inadequate to meet a higher discharge. The result would be overtopping of the dam, which could result in failure of the structure.

The full reservoir level of the Idukki project is 2403 feet (732.62 metres) above the mean sea level. The risk could be reduced by starting the release of water before it rises to the full reservoir level at Idukki and keeping the generation levels up. (The water level can safely go up to the maximum reservoir level of 2408.5 feet). However, problems compound when something unexpected like blockage of spillways or disruption of power generation occur. (Sudden stoppage of a generator, combined with old and rusted penstocks, had triggered the recent accident at Panniyar in Idukki district.)

The problem will be beyond management if the 110-year-old Mullaperiyar dam fails when the Idukki reservoir is full. Overtopping of Idukki dams will be a certainty in such an event. Theoretically, a concrete gravity dam like Cheruthoni will topple if water level exceeds the maximum reservoir level.

A population of about a lakh people between Mullaperiyar and Idukki and millions downstream are thus at risk.

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