Kerala is concerned about the refusal of the Tamil Nadu for joint verification of the seepage from the Mullaperiyar dam and lack of system to determine the real seepage.
The concerns have been communicated to the empowered committee of the Supreme Court on Mullaperiyar.
No visible damage such as cracks has appeared on the dam structure following the recent tremors in Idukki district. Any observed increase in seepage water from the dam after the tremours could be an indicator of damage. However, this could not be assessed correctly.
Chairman of Kerala’s Mullaperiyar Special Cell M. K. Parameswaran told The Hindu that the seepage being recorded by Tamil Nadu did not represent the actual seepage from the dam. Water could be seeping down the foundation and also through gap between the old dam and concrete backing. Though Kerala had suggested construction of toe drains to capture all the seepage on the down stream side, Tamil Nadu had not done so.
The Chairman noted the 116-year-old dam did not have observation galleries to measure seepage as in the case of modern dams. When Tamil Nadu undertook strengthening measures and built a concrete backing for the dam on the downstream side, two galleries were built. However, seepage would have to reach these galleries through the structure of the old dam.
The foundation of the old dam was not stabilised (with grout curtains and drainage holes) as is the practice now. Hence, water could be seeping down through the foundation and emerging on the down stream side. A gap could have developed between the old dam structure and the backing because of expansion and contraction of cement during setting, and water could be seeping down through that gap also. Tamil Nadu had not acted on Kerala’s suggestion that the gap should be grouted.
Mr. Nair said that the seepage being measured by Tamil Nadu from the galleries was very low because seepage water was collecting elsewhere. The quantity measured was even lower than those being recorded for Idukki dam (70 litres per minute against a water column of 550 feet in Idukki reservoir). That itself showed that full picture of seepage at Mullaperiyar dam was not being captured.