Making Of The Tehri Myth

The dam only delayed flooding, that too because it was early storage season

Tehelka, 5 July, 2013

Following the calamitous deluge in Uttarakhand, as criticism mounted that too many hydel projects were destabilising the hills, Chief Minister Vijay Bahuguna claimed that but for the Tehri dam, Rishikesh and Haridwar would have been washed away. Over the past fortnight, it has become a popular justification for multi-purpose dams.

We know the Tehri dam sits on an active faultline and the shifting load of reservoir water affects local seismicity. It has made the site landslide prone right from the days of its construction when 28 workers were buried alive. The reservoir is filling up rapidly with silt and debris and the productivity and longevity of the power plant itself is in question. But did the dam really save millions?

The Bhagirathi, on which the dam is built, and the Alaknanda come together at Devprayag to become the Ganga. Massive discharge in the Alaknanda and its tributary Mandakini caused havoc in the Garhwal Himalayas on 17 June. Had the dam not checked the excess flow of the Bhagirathi, the Tehri story goes, the combined impact of the two rivers in spate would have devastated the areas downstream of Devprayag.

But the peak flow in the Bhagirathi was recorded on 16 June. At the Tehri site, the discharge in the morning was 18,600 cusecs. It went up to 1,05,000 cusecs by evening and further to 2,44,000 cusecs in the early hours of 17 June. The Alaknanda started peaking on 17 June and the impact of its peak discharge of 2,45,000 cusecs hit Haridwar on 18 June when the holy town recorded its peak water level of 295.1 metres.

But for the Tehri dam, the excess waters of Bhagirathi would have shot up the water level at Haridwar on 17 June itself. But by the time the Alaknanda’s discharge reached Haridwar the next day, the Bhagirathi’s excess waters would have already moved further downstream. “It is not rational to add up the two peaks happening at two different points of time,” pointed out Himanshu Thakkar of South Asian Network of Dams, Rivers and People, an NGO focussing on water resources development. “If the dam was not there, there could have been floods downstream a day earlier, but the mean peak level would not have been any higher.”

Apparently, the Tehri Hydro Development Corporation moderated the peak inflow of 2,44,000 cusecs to an outflow of 14,000 cusecs. The data maintained by the Central Electricity Authority, however, appears incongruous. In its daily report on the reservoir levels, Tehri’s water stood static at 749 metres during 15-17 June when the Bhagirathi’s discharge peaked. Then, as the flow ebbed, the reservoir level suddenly recorded a jump to 777 metres on 18 June. This fits the claim that the dam held Bhagirathi waters the day the Alaknanda peaked.

But how could the Bhagirathi’s peak discharge be moderated during 16-17 June without any corresponding rise in the reservoir level? “It’s plausible that they achieved this moderation on 16 June when Bhagirathi was experiencing peak flow. The Tehri Hydro Development Corporation should make public hourly figures of flow in Bhagirathi on 15-19 June, outflow from Tehri in each of those hours, and the water level in the Ganga at Devprayag and Haridwar,” demanded Thakkar.

The dam probably saved the 30-km stretch between Tehri and Devprayag from floods during 16-17 June. But last year, this very stretch suffered a flood-like situation when the dam released water in August after its reservoir level reached within 10 metres of the capacity mark. Almost all our hydel projects fill their reservoirs for higher productivity very early in the monsoon, forfeiting their capacity to control floods.

Had this heavy bout of mid- June rains not hit the hills so early in the monsoon, the Tehri reservoir, like last August, might simply not have had the capacity to store the additional discharge it claimed to have held back. Few remember that the Ganga scaled the highest-ever recorded flood level at Haridwar three years ago. On 20 September 2010, the river swelled to 296.30 metres because the full-to-capacity Tehri reservoir was releasing water.