Panel flags unrealistic Hebbal SWD diversion in Tunnel Road DPR

BENGALURU: An expert committee appointed by the state government to review the Detailed Project Report (DPR) of the proposed Tunnel Road project has found the planned diversion of the Hebbal nala stormwater drain (SWD) - unrealistic. Experts also raised concerns over the committees findings, noting the absence of hydraulic design calculations and cross-drainage drawings for the downstream section near the Hebbal tank weir. The committee observed that the existing nala downstream of the Hebbal tank weir is proposed to be diverted through a U-turn with a long detour towards the airport an alignment it deemed unfeasible. It also noted that crucial hydraulic design calculations and drawings for the cross-drainage structure near the Hebbal Tank embankment were missing. The committee recommended that detailed hydraulic calculations be carried out, considering a 100-year return flood period. Environmental experts expressed further concern over the proposed design. Speaking to TNIE, environmentalist AN Yellappa Reddy said diverting natural drains could have lasting ecological and geological impacts. When you impose changes on nature, you alter the land surface, use heavy machinery, and risk infiltration that contaminates groundwater. The existing nala already filters and recharges aquifers naturally, he said. Reddy added that in a new soil profile, you lose the living organismsthe biotathat help filter and recharge groundwater. It takes years for the biota to rebuild. Moving a nala disrupts this balance and can cause untreated sewage to leak vertically or laterally, he cautioned. So, before any diversion, they must study the soilits porosity, texture, and structure. It varies every few hundred metres, he added. Diversion of natural drains violates the Karnataka Town and Country Planning Act, municipal bye-laws, NGT/HC orders protecting rajakaluves (SWDs), said Sandeep Anirudhan, convenor of Bengaluru Townhall. He added, Apart from violating operative laws, the step could lead to various negative outcomes such as backflow and flooding, erosion, pollution and contamination of lakes downstream, loss of habitat for flora and fauna, infiltration into aquifers, etc.