Tunnel road plan puts Hebbal lake’s flood shield at risk

Bengaluru's ambitious tunnel road project, aimed at decongesting the city's northern corridor, has run into fresh controversy. Officials and urban planners warn that the proposed alignment could compromise Hebbal lake's flood defence mechanisms, potentially exposing surrounding neighbourhoods to waterlogging during heavy rains.

The lake, spread across roughly 150 acres, has historically acted as a natural sponge for stormwater runoff from the Hebbal flyover region and nearby residential layouts. Recent rejuvenation works had strengthened its bunds and increased storage capacity, offering a buffer against flash floods. But the tunnel road's planned route, which skirts the lake's eastern edge, may require deep excavation and piling works close to the embankment.

Structural concerns and flood risk

According to documents reviewed by Bangalore Mirror, the tunnel's cut-and-cover section runs within 30 metres of the lake's bund in places. Geotechnical experts say such proximity could destabilise the soil, leading to seepage or even slope failure during monsoon months. The lake's role as a flood moderator would be severely diminished if its bund integrity is compromised.

"The lake is not just a water body; it's a critical piece of grey-green infrastructure," said a senior engineer from the Karnataka State Natural Disaster Monitoring Centre, speaking on condition of anonymity. "Any interference with its catchment or embankment could trigger a cascading effect on downstream stormwater drains."

The Bruhat Bengaluru Mahanagara Palike (BBMP) and the Bengaluru Tunnel Road Project Limited (BTRPL) have yet to release a detailed environmental impact assessment for the stretch. Citizens' groups have filed multiple RTI queries seeking clarity on the tunnel's depth, piling methodology, and contingency plans for dewatering during construction.

Residents demand transparency

Residents of Hebbal, Amruthahalli, and Jakkur have begun mobilising against the project, citing the 2022 and 2024 flooding episodes that inundated low-lying areas near the lake. "We are not against infrastructure, but we cannot let a road undermine a lake that protects thousands of homes," said Meera Krishnan, a resident of Hebbal Kempapura and a member of the local lake protection committee.

Local corporators have raised the issue in the BBMP council, demanding that the project be re-routed or redesigned. Some have suggested an elevated corridor instead of a tunnel in the sensitive stretch, though officials argue that would defeat the purpose of the underground network.

Officials remain non-committal

BTRPL officials have stated, in brief responses, that they are "conscious of the ecological sensitivities" and are "working with expert agencies to finalise the design." However, they have not confirmed whether the tunnel's alignment will be shifted or if additional protective measures, such as diaphragm walls or grouting, will be deployed.

Environmental activists point out that Bengaluru has lost over 70 per cent of its water bodies in the past four decades, and Hebbal lake is one of the few remaining functional ones. "Every engineering project must now be judged by its impact on the city's resilience, not just its traffic benefits," said an urban ecology researcher at a leading think tank.

The tunnel road is part of a larger plan to create a 60-km underground network across the city, with the first phase covering the Hebbal-Mehkri Circle corridor. The project is expected to cost upwards of Rs 15,000 crore and is being financed through a mix of state funds and multilateral loans.

As the monsoon sets in, the lake's water levels will rise, and any construction activity near the bund could become riskier. The state government has not yet indicated whether it will order an independent hydrogeological study before giving the final go-ahead.

The coming weeks will be crucial, as public consultations and expert reviews are scheduled. The question remains whether Bengaluru can build its way out of congestion without breaking its natural flood defence.