NEW DELHI: The water levels in Tehri dam were low at the start of the monsoon. This proved a critical factor in the dam retaining waters of an engorged Bhagirathi and preventing a 10-12 feet rise in the Ganga at Rishikesh that could have been ruinous for the town and its ashrams.
A report said the fury of nature in Uttarakhand was such that waters rose as high as a four-storey building at Devprayag, where Alaknanda and Bhagirathi meet, in a 24-hour period after the June 16-17 cloud burst.
The rise at Devprayag, Rishikesh and Haridwar could have been much higher but for the Tehri dam.
On the morning of June 16, the discharge of water in Bhagirathi was 18,600 cusecs at the Tehri site, by evening, it went up to 1,05,000 cusecs and next morning it touched 2,44,000 cusecs. This led to a phenomenal rise in the river level at Devprayag by 11 meters. The inflow from Alaknanda was already 2,45,000 cusecs by then.
This rise was unprecedented - said officials of the Tehri Hydro Development Corporation (THDC) who made the first assessment of the flash floods -- and could have resulted in total destruction of Rishikesh town and much of Haridwar if flow of Bhagirathi was not contained by the Tehri reservoir.
Uttarakhand chief minister Vijay Bahuguna had in an interview told TOI that but for the Tehri dam, Rishkesh, Haridwar and parts of western UP would have been inundated.
As it was the start of the monsoon season and the Tehri reservoir was relatively empty, authorities retained 95% of Bhagirathi's fury and maintained a release of only 14,000 cusecs instead of 2,44,000 cusecs and prevented a rise in water level by at least 5 meters (more than 16 feet) in Devprayag and 10-12 feet at Rishikesh, about 60 km away as the river flows.
"All ashrams along the Ganges in Rishikesh would have been washed away and Ram Jhula would have been submerged if the river level had further gone up by even 3 meters," said D V Singh, director technical of THDC.
The strong currents of the river would have damaged the weak embankments and destroyed structures along the river bank, he said. Haridwar too would have witnessed largescale devastation with any further rise in water level even by 2 meters under such circumstances.
At Devprayag, the confluence of Bhagirathi and Alaknanda, the river level was 458.25 m at 11 am on June 16, the next day around the same time, the rise in water level was by 11 meters to 469.10 m.
"It would have been a catastrophe downstream of Devprayag, in Rishikesh and Haridwar, if instead of 14,000 cusecs, 2,44,000 cusecs was added from Bhagirathi," Singh said, adding that Tehri dam was effectively used to regulate water levels and avoid flooding downstream.
"In Haridwar, the river level would have risen from maximum level of 295.90 m (1.9 m above danger level mark) by around 3 meters creating a catastrophe. All low lying areas would have been completely submerged and eroded due to ferocity of flowing water," the official said.
Unlike Bhagirathi, there was no storage on Alaknanda, the reason why flood waters flew uninterrupted, creating a flood like situation after Devprayag. THDC officials rejected arguments that dams were causing floods.
Instead they advocated "a right blend of storage dams with ROR (run of the river) projects in each basin to mitigate flood fury".