The dam is a composite structure with rubble masonry in lime surki mortar as facing upstream and downstream and a lime surki concrete inner core. Later in 1980s, a concrete backing of 10 Meter width was added to the downstream of the old dam. It makes use of its own weight both to stand straight and to resist the huge thrust of water in the reservoir. It is by achieving a balance between the following two huge forces that the dam remains stable. It lost much of its strength due to continuous leaching of lime from its core. This dam is situated in an active fault zone, which makes the dam vulnerable to failure in an earthquake of moderate intensity with an epicenter close to the dam.

World over masonry gravity dams have failed and a few examples are shown below:
Name Country Year of Failure Height in meters
Austin USA 1900 20.7 m
Tigra India 1917 26 m
Khadakwasla India 1961 40 m
Kantalai Sri Lanka 1986 27 m
The actual gross storage of water in Mullaperiyar and Idukki during the recent past is as follows:
1981 13-Nov 70.59 11.22 81.81
1992 18-Nov 70.20 7.78 77.98
1994 11-Nov  66.58 11.99 78.57
1998 15-Nov 67.35 10.79 78.14
2005 17-Sep 68.56 11.21 79.77
2007 28- Sep 69.45 10.23 79.68
Note:- The gross storage at FRL of Idukki is 70.5 TMC and at MWL is 74.4 TMC
The double standards adopted by the Central Water Commission to justify the 152 feet height can be understood from the following table showing their downsizing of the PMF (Probable Maximum flood) measurements:
Project Observed Maximum Peak Inflow PMF Value adopted as per CWC recommendation
Dantiwada dam, Gujarat 12770 cumecs 18122 cumecs
Machu – I dam, Gujarat 7277 cumecs   13224 cumecs
Machu-II dam, Gujarat 13421 cumecs 26420 cumecs
Mullaperiyar  8453 cumecs 6003 cumecs
(Ref: Workshops on Strengthening of Dams, CBIP, 1989)


The Western Ghats, one of the most bio-diverse areas of the world, contain many ‘hot spots’ of disappearing, endangered and endemic animal and plant life. Of the thousands of animals and plants found in the region many are endemic. 1500 of 4000 flowering plants, 37 of 330 butterflies, 116 of 218 fishes, 94 of 121 amphibians, 97 of 156 reptiles, 19 of 508 birds and 14 of 120 mammals are endemic to the Western Ghats. Amongst vertebrates, endemism is the highest in amphibians (78% species), followed by reptiles (62%), fish (53%), mammals (12%) and birds (4%).

Many of the endemic and endangered plant and animal life exist in the waters and along the shores of Periyar. One of the proposed World Heritage Sites is Periyar Sub-Cluster including Periyar National Park and nature reserve, spread over 777 square km. If the Mullaperiyar dam gives way and tumbles down, it will wash away this World Heritage and annihilate most of these rare forms of life once and for all. The murky waters carrying mud, rocks and trees will also destroy valuable animal and plant life on the plains and even in the backwaters near the sea. It will be the greatest environmental disaster in recent history.

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