Kottayam: Geologist Dr A. V. George feels the Mullaperiyar water level should stay below 136 feet. He fears ‘dam-induced earthquakes’ similar to Koyna dam in Maharashtra if it goes beyond that level. He says the pressure may induce slight movement along the fractures zones (the heavy fractures extending from the surface to deeper zones of the earth’s crust) within the catchment or surrounding areas causing an earthquake.
There are ‘fracture zones’ at the catchment area of the Mullaperiyar dam which will be weakened due to the pressure when the water level is increased, he said.
The earthquake occurred at the Koyna in 1967 in its catchment area claiming many lives.
“The same kind of earthquake may also happen here. The satellite pictures confirm this,” he said.
There are 12 serious fracture zones in Kerala. Out of this 12 most important zone is Idamalayar – (northwest-southeast), and Periyar (southeast – northwest).
Both these are joining in the nearby areas of Mullaperiyar and Idukki dams. Also, Kumily – Kambam – Bodinayakanur – Theni extending into Kerala (Kambam fracture zone) is also a threat to them.
However, he said that the Idukki dam is constructed using the ‘spring technology’ which has the earthquake deterrent capacity up to 8 on the Richter scale. If the water from Mullaperiyar reaches Idukki dam all of a sudden due to its failure within 45 minutes; it may topple due to the overflow.
“In the case of the Idukki arch dam, even if the water pressure is increased, the spring erection will control an earthquake. The dam has its disadvantage that if the water level comes above the full reservoir level, there is a possibility of toppling,” he said.
The studies conducted by the National Centre for Earth Science Studies (NCESS) and the Indian Institute of Technology (IIT) Roorkee say that the Mullaperiyar dam cannot withstand an earthquake of more than 5.5 on the Richter scale even if the water level is 136 feet.
The earthquake occurred at Adukkam near Erattupetta in 2000 December and 2001 January recording 5.2 and 4.8 due to natural reasons.
Fortunately, the water level was only 110 feet.
If the same earthquake occurs now when the water level is above 141, the scenario would be different, Dr George said.The International Dam Safety Authority (IDSA) gives a lifespan of 70 years for a dam, and the water level should be brought down periodically after that.
The Mullaperiyar dam has completed 122 years.
