Tunnel road project a threat to Lalbagh Rock, surroundings

BENGALURU: The state governments ambitious Rs 17,698-crore tunnel road project for Bengaluru will shrink the size of Karnatakas oldest lung space, Lalbagh, and the underground drilling will impact the famed Lalbagh Rock, part of the 3.2-3.5 billion-year-old Dharwar Craton, among the oldest rock structures in the world that extends from Kolar to Mangaluru and up to Ballari in the north. The projects 16.7-km north-south corridor connecting Esteem Mall Junction in Hebbal to Silk Board KSRP Junction will have multiple entry and exit points at Mehkri Circle, Chalukya Circle, Lalbagh and Silk Board. Its Detailed Project Report (DPR) shows that Lalbagh bedrock falls under the tunnel roads transition zone. The alignment is set to cross a prominent lineament with Lalbagh lake in the vicinity. The DPR said one intermediate ramp will exit on Marigowda Road at Wilson Garden and the other on Siddapura Road. Around six acres of Lalbagh land will be lost for the 1.1-km stretch between Ashoka Pillar and Marigowda Junction. The DPR also stated that the creation of vents for the tunnel road passes through Lalbagh, and will also need land. The impact of the project is feared because it is planned to snake below and through the botanical garden, and the Geological Survey of India (GSI) has declared Lalbagh Rock as a heritage site, as it is a visible part of the Dharwar Craton. Cratons are ancient, thick, rigid, stable and undeformed portions of the continental lithosphere, forming the core of continents. Lalbagh Rock is valuable as it is the Dharwar Craton jutting out of a layer of subsequent and younger sedimentary rocks that form the surface. These ancient crystalline basement rocks have deep roots reaching down into the Earths mantle, and provide stability and seismic safety. Dharwar Craton provides that stability to the Deccan Plateau, on which Bengaluru is located. Geologists said although Lalbagh Rock is extremely hard, cracks or fractures under it, where tunnelling is proposed, can inflict major damage. Noted environmentalist Dr AN Yellappa Reddy said a rupture in Lalbagh Rock can lead to water from Lalbagh Lake entering the Nimhans complex. Tall buildings along the alignment with deep foundations will also be impacted. He said the government should consult the National Institute of Rock Mechanics before proceeding with the project. A senior GSI official also pointed out that a thorough geotechnical investigation of the rock is needed on fault lines, weathering, cracks and joints. KV Krishnamurthy, secretary, Geological Society of India, said since the rock is declared a protected site, tunnelling will require permission. But a senior horticulture department official said: So far, no permission has been given for construction and land acquisition. Lalbagh (botanical garden) was created in 1760 and has over 2,200 species of plants belonging to around 680 genera and 150 species. The impact on the aquifers, which is the lifeline of varied species, including 250-year-old mango trees, is yet to be known. A senior GSI official said although protection of the rock and its surroundings is managed by the horticulture department, permission from the GSI head office is also required fo any work around or under the rock. This is why the Metro is far from the rock site. So far, no proposal has come (for the tunnel road project).