We made a visit to the controversial Mullapperiyar site last week along with engineers from the CUSAT Civil department and made a careful observation of the site and the dam premises.


First let me draw you the technical aspects of the dam which were explained to us by Engineer Wilson at the site...

River Periyar originates from the Western Ghats in ‘Sundara Malai’ at an elevation of about 1830m above MSL. From its origin, it traverses through an immense cliff of rocks in a northerly direction receiving several rivulets in its course. About 48 Km downstream, the Mullayar joins the main River at an elevation of 845m above MSL and the River then flows westwards. About 11 Km downstream of the above confluence, the river passes through a narrow gorge. A dam was constructed at this gorge to intercept the flow and it got christened as ‘Mullaperiyar dam’, which received the above title from the rivers Mullayar and Periyar. The dam have a catchment area of 624 square kilometres, which lies completely inside Kerala territory.The Mullaperiyar dam is having a length of 1200 feet and a height of 155 feet from the river bed and the height from the deepest foundation is 176ft. The front and rear faces of the dam are of uncoursed rubble masonry in lime, surki and sand mortar. The hearting is of lime surkhi concrete with 3.125 parts of stone and 1 part of mortar.  The proportion of lime surkhi mortar is 2 parts of lime, 1 part of surkhi and 3 parts of sand.The central core constructed with lime surkhi concrete occupies about 60% of the total volume of the dam. As part of the strengthening measures suggested an RCC capping was added to the top of the dam. Also a 10 m concrete backing was provided to the downstream side, but the joint between the old dam and the new dam remain ungrouted even though shear keys were provided The main dam is having two saddles on the left and right banks. The left bank saddle of 483 feet length was closed by means of a masonry dam named ‘baby dam’ of length 240 feet and height of 47 feet and the remaining portion by an ‘earthen bund’. The baby dam is also designed as a solid gravity dam constructed in similar fashion as the main dam. The right bank saddle is converted as a surplus arrangement by providing 10 vents of 36ftx10ft and 3 additional new vents with 40ftx10ft with a crest level of 136 feet.The gross storage of the reservoir is at an FRL of 152 feet is 15.662 TMC and the live storage is 10.530 TMC. The 75% dependable inflow is around 21 TMC. (1 TMC, ie, Thousand Million Cubic Feet = 28.317 Million Cubic Meter)

The water from the Periyar Lake is taken through an open cutting having a length of 5342 ft and a bed width of 21 ft. Then the water is controlled through a tunnel, which is regulated by a head sluice at the entry of tunnel. The tunnel is of length 5887 ft with a sectional area of 150 sq. ft and is now capable of discharging 2100 cusecs. Then the water is collected after at a fore bay dam of capacity of just 3.2 Mcft and from there water is taken through a power tunnel of length 3992 feet with a discharge capacity of 1600 cusecs. This forebay dam is also provided with an irrigation sluice to discharge waters exclusively to Cumbum Valley. The power tunnel terminates at a surge shaft and from there the water is taken through 4 penstock pipes each with a discharge capacity of 400 cusecs to the Lower Camp Power House (4x35 MW) which generates 500 Million Units (MU) of electricity annually. After power generation, the tail waters are discharged into Vairavanar, a tributary of the Suriliyar River, which is a tributary of Vaigai River. The tailwaters thus released are then collected at the Vaigai Reservoir and then released for irrigation purpose. The gross command area envisaged for the Project is 90,000 acres for the first crop and 60,000 acres for the second crop (Ref – History of Periyar Project, A.T. Mackenzie, 1898).