Mullapperiyar

The Mullapperiyar dam is more than 100 years old whereas the useful life of a well-designed and well-built dam is generally considered to be about 50 to 60 years. Thus the dam has already exceeded its normal lifetime by 40 to 50 years. So, the concern about its safety is not misplaced. All structures deteriorate over time and become vulnerable to breakage. So has Mullapperiyar.

Hence, it is imperative that measures are taken to replace the dam. In 1979, Kerala, Tamil Nadu and the Central Water Commission came to an agreement that the maximum reservoir level should be kept low at 136 feet and additional spillways should be constructed to avoid the risk of water level rising in the reservoir. It is notable that Tamil Nadu has not completed the construction of spillways even after 17 years. The spillway capacity is very important from the point of dam safety for as many as 50 per cent of dam failures in the World1 had resulted from inadequate capacity of the spillways. Tamil Nadu not only neglected this aspect, but also took certain measures that further jeopardised the dam’s safety. (I am not forgetting that it took some measures to strengthen the foundation of the dam.). It allowed excavated materials to be dumped upstream of the spillways, that too to the level of the spillways.

The expert committee appointed by the Government has reported that the loose earth dumped on the upstream side of the spillway crust would flow over the crust and ogee and might damage the concrete surface. This report was made some time ago. Now plants have started growing over the dumped material. While this may reduce the amount of loose earth that may overflow, it creates the additional risk of debris getting trapped on them and finally blocking the spillway at least partially. In any case, the presence of the dump above the spillway is bound to affect spillway efficiency, which would be crucial in case of a heavy monsoon. If the spillways, including the additional ones proposed, are not fully functional, that would increase the risk to the dam.