Joshimath sinking: What is the NTPC project and why are geologists blaming it?  

Joshimath disaster: Geologists are blaming an under-construction hydroelectric power project for land subsidence in Joshimath, a holy town in the Chamoli district of Uttarakhand. So far, over 700 houses and roads have developed cracks due to the sinking of the land underneath the town.   

While experts from seven different organisations including the Geological Survey of India, IIT Roorkee, and Wadia Institute of Himalayan Geology are studying the cause of the sinking, many geologists have blamed NTPC's Tapovan-Vishnugad hydroelectric power project for the current disaster. 

The power project, currently under construction, is on the Dhauliganga River in the Chamoli district - about 12-15 kms away from Joshimath. 

Atul Sati, a local environmental activist, says several geologists believe the sinking is happening due to the tunnel of the Tapovan-Vishnugad hydroelectric power project, being carried out by the state-run NTPC (National Thermal Power Corporation). 

This is the same tunnel where a disaster struck due to a glacier burst two years ago in which nearly 200 people died, Sati told India Today Group's The Lallontop.  

On 7 February 2021, a portion of the Nanda Devi glacier broke off in Chamoli, triggering an avalanche and deluge in the Alaknanda river system that washed away hydroelectric stations. The sudden flash flood also washed away a 90-meter span RCC bridge on Joshimath-Malari road located just downstream of the Rishi Ganga Hydel project and about two kilometers upstream of the Tapovan project.  

"The project's tunnel is passing through Joshimath," Sati said, adding that the tunnel got punctured in December 2009 and about 600 liters of water started overflowing per second. He said for the last 12 years, this water has been flowing. 

That means, Sati said, a reservoir beneath the town had gone burst, and water kept flowing. According to Sati, now the reservoir is empty due to which the land is now sinking.

This also found a mention in a paper titled 'Disaster looms large over Joshimath', authored by geologist Dr MPS Bisht and Piyoosh Rautela, now Executive Director at Uttarakhand State Disaster Management Authority. Published in May 2010 in the peer-reviewed journal Current Science, the paper expressed concerns about the power project by NTPC. 

The paper says despite being fully aware of the geological vulnerability of the area, a number of hydroelectric schemes have been sanctioned around Joshimath and Tapovan. The Vishnugad HE Project is one such scheme, it says. "The head race tunnel of the project traverses all through the geologically fragile area below Joshimath."

The authors further wrote a tunnel boring machine (TBM) was employed for excavating the head race tunnel. On 24 December 2009, it punctured water-bearing strata some 3 km inward of the left bank of Alaknanda near Shelong village. The site was more than a kilometer below the surface, somewhere below Auli.

"The water discharge was reportedly between 700 and 800 litres per second," the paper says, adding that the aquifer discharge was about 60–70 million litres daily, enough to sustain 2–3 million people. Even after a month, the aquifer had not dried out.

Bisht and Rautela had warned about the consequences of this accident and said this sudden and large-scale dewatering of the strata had the potential of "initiating ground subsidence in the region".

Harsh Vats, a geologist and PhD candidate at the Indian Institute of Remote Sensing-Dehradun, has also pointed to this punctured aquifer as one of the reasons causing the sinking now. Speaking to The Print, Vats said during the construction of a tunnel for the Tapovan Vishnugad hydropower plant, an aquifer was punctured in 2019, which led to considerable groundwater loss. "We don't know if that aquifer was ever recharged." 

Land subsidence occurs when large amounts of groundwater are withdrawn from certain types of rocks, as per US Geological Survey. 

Also Read: Why is Joshimath sinking? Big projects, rampant construction, extreme weather worsened situation