KOCHI: The 126-year-old Mullaperiyar dam, which is a composite gravity dam (combination of concrete and embankment), is in a deteriorating condition and should be decommissioned to enable the construction of a new dam, Kerala submitted before the Supreme Court in a written note on Thursday.
“The consequences of any failure of the dam could be extremely catastrophic and beyond human imagination. The apprehensions of the Kerala government regarding the life and safety of more than 30 lakh people in five districts residing downstream the dam have to be given due importance and consideration,” Kerala submitted.
The state has opposed the view of the SC-constituted supervisory committee that the dam would hold water up to the level of 142ft. The committee and Tamil Nadu maintain there is no danger or threat to the dam. The committee had recommended before the Supreme Court on Wednesday that there is no need to change the water level in the dam.
Kerala added the hearting (material used as fill) of the dam, which accounts for more than 60% of its volume, was constructed with lime surkhi concrete. Quite understandably, seismic forces were not considered in its design. In spite of the strengthening measures taken twice, the dam is in a deteriorating condition. There would be an exponential increase in water pressure and uplift pressure acting on the dam when the water level is raised from 136ft to 142ft.
The catchment area of Mullaperiyar reservoir is 624sqkm. The gross storage capacity is only 12.758 TMC ft at 142ft. Mullaperiyar, therefore, is exceptionally vulnerable because it has a large catchment area and limited storage capacity. Consequently, the water level in the dam increases rapidly compared to Idukki, which has a catchment area of 650sqkm and storage capacity of 70.5 TMC ft.
Kerala sought to keep the water level in Mullaperiyar at 139ft as the Idukki reservoir is nearing full reservoir level and any sudden large release from the upstream dam can worsen the situation, forcing to make large releases from Idukki, causing flood in downstream areas.
Kerala pointed out that Tamil Nadu was not utilising the full outflow capacity of the Mullaperiyar dam. At 137ft, the full outflow possible is 2,735 cusecs but Tamil Nadu was drawing only 2,200 cusecs, which was increased to 2,300 cusecs as the water level reached 137.8ft.
Kerala pointed out that Tamil Nadu can create additional storage facilities at appropriate places and enhance the capacity of Vaigai dam to store water drawn from Mullaperiyar. Capacity of the existing tunnel can be enhanced or an additional tunnel can be built to draw more water, which will help keep the reservoir level at a safer level without reducing water viability as suggested by an empowered committee constituted by Supreme Court in February 18, 2010.