HYDERABAD: Chief Minister A Revanth Reddy and Irrigation Minister N Uttam Kumar Reddy will monitor from Monday the helicopter-borne VTEM Plus Magnetic Geophysical Survey of the Srisailam Left Bank Canal (SLBC), conducted by the National Geophysical Research Institute (NGRI).
On February 22, a collapse flooded 2.5 km of the SLBC tunnel, burying a 130-m TBM and killing eight trapped workers.
A high-level committee recommended advanced tunnelling with observational techniques and monitoring for safety. On October 23, the Cabinet approved the proposal to complete the tunnel by mid-2028 within the original budget.
Experts advised a heli-borne electromagnetic survey, leading to the sanctioned VTEM Plus by NGRI. It involves flying more than 200 km with a 24-m underslung transmitter loop over the alignment, sending signals to detect geology 800-1,000 m deep, identifying shear zones or water bodies for safe excavation adaptation.
Committee of top engineers formed
As the longest tunnel without intermediate access, the government formed a committee of top engineers (six meetings held), appointed Lt Gen Harpal Singh (ex-Army Engineer-in-Chief) as advisor, and deputed Col Parikshit Mehra for one year.
Completion will mark a global engineering feat for India and Telangana.
The government aims to complete stalled irrigation projects for public benefit. Initiated in 1983, Alimineti Madhava Reddy Project (AMRP) was designed to irrigate 3 lakh acres in drought-prone Nalgonda and supply drinking water to fluoride-affected villages using 3 tmcft Krishna water.
Tunnel 1, part of the SLBC, is a 43.93 km-long tunnel originating from the left bank of the Srisailam reservoir.
Currently, approximately 13.94 km of the tunnel has been excavated from the Srisailam (inlet) side and 20.4 km from the Devarkonda (outlet) side. Around 9.8 km of tunnel is yet to be excavated.
Once completed, it will be the world’s longest without intermediate access, passing under reserve forest through quartzitic/granitic rocks and 15 nalas (four perennial).
No side shafts are possible due to forest/technical constraints; excavation from the two ends only. Without the tunnel, a lift scheme costs more than `500 crore annually in electricity bills; gravity flow on completion will yield immediate savings.
