Wednesday, January 11, 2012


River Periyar originates from the Western Ghats in ‘Sundara Malai’ in the Sivagiri group of hills 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 Mullaperiyar reservoir was conceived in 1886 with an FRL of 144ft (Please See 'History of Periyar Project by A.T. Mackenzie, 1899). But in 1908 after 13 years after completion of the project, the FRL was raised from 144ft to 152ft without the concurrence of Travancore. This FRL was reduced to 150ft in 1964 and then to 145 ft in 1978 and further to 136ft in 1979 due to safety concerns. The gross and live storages of the Mullaperiyar reservoir at various levels are given below for a quick glance:

Full Reservoir Level in feet
Gross Storage in TMC
Live Storage in TMC

The average inflow data for the last 50 years (1960-2009) shows that 23.5 TMC while the 50% dependable flow is 22.2 TMC. While the 75% and 90% dependable inflows for the same period is 18.5 TMC and 14.1 TMC respectively (1 TMC, ie, Thousand Million Cubic Feet = 28.317 Million Cubic Meter). [Source: Tamil Nadu Public Works Department Records]

The diversion data shows that Tamil Nadu had diverted 20.67 TMC on an average basis (1963-2010) and the 75% dependable diversion for the same period was 17.76 TMC. (Source: Tamil Nadu Public Works Department Records)

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 height 12ft and length of 5887 ft with a sectional area of 150 sq. ft and is now capable of discharging 2100 cusecs. But normal operation conditions only 1600 cusecs are drawn through this tunnel.
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).

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