NEW DAM 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.
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.
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