3-billion-year-old Lalbagh rock at risk from proposed Hebbal tunnel, warns GSI

The Geological Survey of India (GSI) has cautioned the Karnataka High Court that the planned 16.7-km-long Hebbal underground tunnel could endanger the 3 billion-year-old Peninsular Gneiss rock formation situated within Bengaluru's Lalbagh Botanical Garden. This alarm was raised in a report submitted to the High Court in response to a Public Interest Litigation (PIL) brought forth by actor-activist Prakash Belawadi.

The GSI explained that the construction of the tunnel would necessitate the excavation of shafts close to the ancient rock formation. Subsequently, the GSI cautioned that the vibrations and modifications in stress distribution caused by the tunnel-building process could trigger new fractures or enlarge existing ones in the ancient rock mass.

The GSI's 27-page report also highlighted that the construction could potentially lower the groundwater level or change its flow paths, which might impact Lalbagh Lake and fracture-controlled aquifers in the vicinity. This could, in turn, affect the ground stability near the tunnel's ramp zones. The matter arose after the state government had initially approved an amendment to the Karnataka Government Parks (Preservation) Act, 1975, permitting the use of 5% of government park land for public utility construction.

However, the Karnataka cabinet swiftly rescinded the amendment following protests at Lalbagh. Bengaluru is home to approximately 1,353 parks, including the 240-acre Lalbagh Botanical Garden and the 197-acre Cubbon Park.