In the week since the flash flood in Uttarakhand’s Chamoli district, two tunnels of an NTPC hydro-power project in Tapovan area have been at the centre of rescue operations. The initial target was to clean an 180-metre area of slush to rescue 34 workers feared trapped there. On Sunday, five bodies were recovered from one of the tunnels.

Revisiting the painstaking, day-to-day progress in the operation, the changing strategies:

February 8
The rescue operation inside the intake tunnel, started after the February 7 flash flood, was halted for a few hours following a rise in the Dhauli Ganga river. It resumed at 5 am on Monday. The slush was cleared up to only 90 metres after a day-long exercise.

February 9
After removal of slush with rudimentary equipment like excavators, an aerial survey was done by a helicopter-bound Laser with Electromagnetic Pulse Imager for analysis of the density inside the intake tunnel. A drone with cameras was also sent inside the tunnel up to 120 metres, but failed to show human presence in that stretch. This day, NDRF and ITBP personnel were able to only reach up to 90 metres— as they removed the slush, more muck kept coming out. Army men attempted to launch a search near the barrage in Dhauli Ganga—a site where more than a hundred people are feared missing—but called it off after finding the surface unsuitable for movement. The rescue appeared more organised when a joint operational centre was set up and layout of the tunnel was displayed in public.

February 10
Rescue teams changed strategy after discovering that workers may be trapped in another silt filtration tunnel (SFT), located 12 metres below the intake tunnel. It was decided to start drilling 72 metres from the opening of the first tunnel. This was done so that lights with cameras could be lowered into the SFT. Two more excavators were deployed to speed up removal of slush. A helpdesk was set up for relatives of those people feared trapped.

February 11
The operation was suspended following a rise in river water flow, but resumed after an hour. Around 80 metres of slush was cleared in the intake tunnel. Drilling into SFT started at 3 am but was stopped due to sludge at a depth of 6 metres.

February 12
A fresh attempt was made drill into the SFT at distance of 75 metres. Teams managed to achieved drilling to more than 10 metres by evening.

February 13
Drilling inside SFT was completed up to a depth of 12 metres. With little space for lowering a camera, another heavy machine was pressed into service to increase the diameter of drilled area up to 30 cm and develop a borewell. But the lowering of camera failaed again due to the pressure of slush. The borewell was plugged and removal of slush from the intake tunnel resumed again late night.