New Delhi: The National Thermal Power Corporation (NTPC) has said that a 12-kilometre-long tunnel connected to Tapovan Vishnugad hydroelectric project is not responsible for land subsidence in Joshimath town. The response comes after the Union Power Ministry summoned NTPC officials to review the subsidence incident in Joshimath on January 10.
The country’s largest electricity-generating company explained to the ministry that the tunnel is 1 kilometre away from the sinking town and at least a kilometre below the ground. Further, the head trace tunnel (HRT), which connects water intake at the dam site to the powerhouse for the generation of the Tapovan Vishnugad hydro electricity project is not passing under Joshimath town.
According to a report by news agency PTI, the NTPC has written in its letter, “The tunnel is at a horizontal distance of around 1.1 km away from the outer boundary of Joshimath town and vertically around 1.1 km below the ground level. Construction of the tunnel in this stretch has been done through Tunnel Boring Machine (TBM) which causes no disturbance to the surrounding rock mass.”
Citing findings from a 1976 report by the government-appointed M C Mishra Committee, the NTPC has said that "hill wash, the natural angle of repose, cultivation area because of seepage and soil erosion" for the subsidence/cracks and that land subsidence in Joshimath is an old issue.
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The construction work of the 4x130 MW Tapovan Vishnugad project started in November 2006. The project includes the construction of a concrete barrage at Tapovan (15 km upstream of Joshimath town).
The hydroelectric project was to be completed in March 2013 but it is still under construction and has also undergone a major cost escalation from the initial investment of Rs 2,978.5 crore to now an anticipated Rs 7,103 crore.
At the time locals had raised concerns that the construction of tunnels will cause drying of the water table in the Selong area, which is about 6 km away from Joshimath Town.
An expert committee was constituted by DM Chamoli which in August 2010 concluded that "there is no ground evidence of any instability induced by HRT excavation using TBM."
Due to continuing subsidence in Joshimath town, another committee was constituted by DM (Chamoli) in August 2022. As per NPTC, the panel stated that power sewerage, rain and household wastewater seeping below ground, erosion due to floods and subsurface seepage were possible causes of subsidence in Joshimath town and the surrounding area.
(With agency inputs)