The Expert Committee formed in 1979 to inspect the ailing dam held a discussion on 25/11/79 at 11 AM in Thiruvananthapuram. In this, one of the long term measures suggested to this issue was as follows: "A joint team of engineers from Tamil Nadu and Kerala will explore the possibility of locating a new dam within reasonable distance from the existing dam, within a month's time, as an alternative to long term measures for strengthening the existing dam" (Annexure A). In the minutes drafted after the joint inspection of the team of engineers of Tamil Nadu and Kerala, it is stated that "the team feels after inspection of the site AA (1300 ft below the existing dam) and examination of other sites with reference to contour map, that site AA is the nearest possible alignment from geographical considerations without impairing the safety of the existing dam during construction of dam" (Annexure B). The same has been signed by the representative of Tamil Nadu Sri. A. Mohanakrishnan. But, surprisingly, in the memorandum on 'Strengthening Proposal of Mullaperiyar Dam' submitted by the Central Water Commission in 1986 it is stated that it was decided to strengthen the existing dam and the case of construction of new dam was not pursued (Annexure C). In the Expert Committee report (March 2001) filed before the Supreme Court, it is stated that "Although originally it was suggested that the engineers of Tamil Nadu and Kerala will explore the possibility of locating a new dam within a reasonable distance from the existing dam, subsequently this was not found feasible and the proposal was dropped" (Annexure D). It is not known what made them to say so. The measures taken in this direction are not known. The proposal to construct a new dam is the sustainable solution to assure water to Tamil Nadu and save the life of the downstream population. But from the above it is seen that this suggestion once put forward by the Central Water Commission, has been sidelined, on unknown grounds.
PROBABLE MAXIMUM FLOOD
The argument that Mullaperiyar reservoir is safe even for PMF (Probable Maximum flood) and the fear of overtopping of dam is baseless is actually wrong. It may be stated that for any dam and particularly for masonry or composite gravity dams, flow of water over the top of the dam is the most dangerous situation that a dam can be put in. It results in collapse of the dam as a result of sliding or overturning. Because this is such a crucial safety aspect of the dam, the pattern followed uniformly in all dams in the country is to identify the maximum observed flood that has occurred in the catchment area. Then this figure is significantly boosted up and the PMF identified from this boosted up figure. A table showing explicitly such an exercise done by CWC is given below.
Observed Maximum Peak inflow
PMF Value adopted as per CWC recommendation
Dantiwada dam, Gujarat
Machu - I dam, Gujarat
Machu - II dam, Gujarat
It may be seen from the above table that in the case of Mullaperiyar dam, the maximum flood that took place in the reservoir was in the year 1943 was 8453 cumsecs. However, curiously for the purpose of determining the PMF, Chairman, CWC recommended a figure lower than this maximum amount, namely, 7249 cumsecs. Copy of the Rehabilitation Memorandum dated 24/25 March, 1986 in this regard is enclosed. This recommended figure of Chairman, CWC was again lowered for reasons unknown to 6003 cumsecs. Even with this artificially lowered figure the water would flow over the top of the dam but for the parapets. Not only this but also the siltation in dam would further contribute to the rising of MWL so that water flows over the top of the dam.
It is felt that this has been an exercise in playing with figures to ensure that MWL (Maximum Water Level) comes to 157.7 ft so that FRL (Full Reservoir Level) will come to 152 ft. Just like PMF has a relationship with MWL, MWL has a relationship with FRL. The point that was stated emphatically in the meeting was that if the normal exercise of prudence was adhered to in the Mullaperiyar case in determining the PMF, then the FRL would have come far below 152 ft and possibly close to if not below 136 ft.
It is found that while assessing the safety of this dam the expert committee had taken the design horizontal seismic co-efficient as 0.12g instead of 0.18g, The value 0.18g is the least recommended value for zone III as per IS 1893-1984 where Kerala is situated. In this context it may be noted that the standing committee set up Government of India for advising the seismic coefficient for the river valley projects recommended a value of 0.24g (Ref: Workshop on Strengthening of dams, CBIP,
1989), the Expert Committee chaired by the Member (D&R) and another Chief Engineer of CWC has taken an extreme lower value of 0.12g instead of 0.24g. This extremely low value of 0.12g has incorrectly made the dam 'safe' for water level up to 142 ft. This action of the expert committee is against the guidelines published by the CWC in this regard.
It is evident that if the least seismic co-efficient for zone-III is taken for stability analysis, Mullaperiyar reservoir is not at all safe even to hold water up to the height of 136 ft.
OLD VICTORIA DAM
In the meeting the analogous situation of the Old Victoria Dam of Australia was also pointed out. The old Victoria Dam was constructed in 1891 with lime concrete, around the same time when the Mullaperiyar dam was constructed. In 1966 there was considerable seepage in the dam as had been and is being noticed in the Mullaperiyar dam. Certain safety measures like construction of a reinforced concrete slab attached to the upstream water face and a gallery in between the dam
and the slab were carried out. In Mullaperiyar dam, certain other types of strengthening measures including a concrete backing on the downstream face were carried out. However, in 1988 it was observed by the concerned authorities that the strengthening measures carried out in Victoria dam have not worked and the dam did not satisfy the safety standards. The dam was subsequently decommissioned in April 1990.
During the Chief Minister level discussion between the two States, Tamil Nadu has argued that there are 37 other dams, which are similar to Mullaperiyar dam. The details of these dams are at Annexure (E). It is pointed out here that out of 37 dams 30 are earthen dams. It is also evident from the list that out of the remaining 7 dams, all the six except Mullaperiyar are very small in its capacity, length and height. It is worth mentioning here that the Kadakvasala dam, in Maharashtra, which is second in capacity amongst these seven dams, collapsed in 1961. Its capacity was 86m and height 32.9m, while that of Mullaperiyar is 443.55 and 53.64M. Hence the concern of the State.
The argument of Tamil Nadu that due to the non-restoration of FRL from 136 ft to 142 ft, Tamil Nadu's irrigation benefits are suffering is not correct. It is clear that Tamil Nadu was able to irrigate more area with the Mullaperiyar water, even after lowering the water level to 136ft. During the year 1979-80 the gross area cultivated in Periyar command area was 171307 acres. Then, after the lowering of the level to 136ft, the gross irrigated area increased and in 1994-95 it reached 2,29,718 acres. The above fact is evident from the statements (Annexure F), which is published in the book 'History of the Periyar Dam with Century long Performance' by Prof. A. Mohanakrishnan. Also it is evident from Tamil Nadu PWD Water Resources Organisation website that Tami\ Nadu had added 22647 ha (55,962 acres) of new ayacut to the PeriyarVaigai Irrigation Project since 1980.
Due to the above said reasons and other similar incorrect decisions the report of Central Water Commission submitted to the Supreme Court cannot be said to be a correct assessment of things on ground. Unfortunately it so happened that the Supreme Court relied heavily on this report to pronounce its judgment in February 2006 in which Tamil Nadu was allowed to raise the water level of Mullaperiyar to 142 ft and then to 152 ft. We are therefore grateful that the Supreme Court ask both the States to sit together to find out an amicable solutions to the issue as it would save the lives of the people of Kerala from an impending danger due to the weakening of a century old dam.
||Dam Safety: Mullapperiyar and its Implications
||Mullapperiyar-- Issues of Dam Safety