Bengaluru: The Karnataka government’s ambitious Rs 17,698-crore tunnel road project for Bengaluru has sparked concern among geologists and environmentalists, as it threatens to impact Lalbagh — the city’s iconic 250-acre botanical garden — and the 3.5-billion-year-old Lalbagh Rock, a globally significant geological formation. Experts warn that underground drilling could compromise the stability of the ancient rock, which is part of the Dharwar Craton, one of the oldest rock structures on Earth.
Project details and alignment
According to the Detailed Project Report (DPR), the 16.7-km north-south tunnel road will connect Esteem Mall Junction in Hebbal to Silk Board KSRP Junction, with multiple entry and exit points at Mehkri Circle, Chalukya Circle, Lalbagh, and Silk Board. The tunnel’s alignment passes through the Lalbagh bedrock, which falls within its transition zone, raising red flags about its geological and environmental impact.
The DPR further indicates that a 1.1-km stretch between Ashoka Pillar and Marigowda Junction will cut through the garden, resulting in the loss of around six acres of Lalbagh land. Ventilation shafts for the tunnel are also planned to be constructed within the garden premises, requiring additional space.
Geological and environmental concerns
Lalbagh Rock is part of the ancient Dharwar Craton, a stable continental crust extending from Kolar to Mangaluru and up to Ballari in the north. The Geological Survey of India (GSI) has designated it as a heritage geological monument due to its immense scientific and educational value. Cratons like the Dharwar formation form the core of continents and provide seismic stability to large regions, including the Deccan Plateau on which Bengaluru rests.
Geologists caution that any tunnelling or drilling beneath Lalbagh Rock could cause fractures in the underlying bedrock, potentially altering groundwater movement and triggering instability. “Although the rock is extremely hard, even small cracks or fractures under it can inflict major damage,” said a senior GSI official.
Risk to water bodies and heritage trees
Environmentalists have expressed particular concern about the risk of water seepage from Lalbagh Lake into nearby areas, including the NIMHANS complex, if the rock’s structure is disturbed. “A rupture in Lalbagh Rock can lead to water from Lalbagh Lake entering the NIMHANS complex. Tall buildings with deep foundations along the tunnel alignment could also be affected,” warned noted environmentalist Dr AN Yellappa Reddy.
He added that the government must consult the National Institute of Rock Mechanics and conduct a comprehensive geotechnical investigation before proceeding. “Investigations must focus on fault lines, cracks, and joints in the rock to assess the real risks,” he said.
Permissions and conservation issues
KV Krishnamurthy, Secretary of the Geological Society of India, noted that since Lalbagh Rock is a declared protected site, any tunnelling activity would require explicit permission from the GSI. “The Metro alignment itself was planned at a safe distance from the rock to avoid any damage,” he said.
A senior horticulture department official confirmed that no approval has been granted yet for land acquisition or construction within Lalbagh. “Lalbagh was established in 1760 and houses over 2,200 species of plants, 680 genera, and 150 species. The impact on underground aquifers that sustain this biodiversity, including 250-year-old mango trees, is still unknown,” the official said.
Call for scientific review and public consultation
Experts are urging the state government to re-evaluate the alignment and conduct a detailed environmental and geological impact assessment before moving forward. “The tunnel project cannot compromise Bengaluru’s heritage and ecology,” said Dr Reddy, adding that alternative routes must be considered to protect the geological landmark.
For now, the horticulture department and the GSI have stated that they have not received any formal proposal for the project’s execution in the Lalbagh zone. Until a comprehensive scientific review is undertaken, the future of Bengaluru’s oldest green space — and one of Earth’s oldest rock formations — remains uncertain.