The Karnataka High Court has asked the Karnataka government to clarify how a proposed 2.2-km tunnel near Bengaluru’s Hebbal Lake will affect the water system around it. The tunnel, planned from Hebbal Junction towards the GKVK campus, is intended to ease traffic through one of north Bengaluru’s busiest corridors. The government maintains that the project will not use the lake bed, but will pass beneath its buffer zone, involving about 3.45 acres. Petitioners have raised concerns over whether construction in this area could interfere with the lake’s inflow and outflow, stormwater drainage and groundwater recharge. At the centre of the dispute is a larger infrastructure question: how do you build through a dense city without compromising the environmental systems that already occupy the same space?
A Water System Under Pressure
Hebbal Lake is not an isolated water body. It sits within Bengaluru’s interconnected network of lakes and stormwater drains, where water moves from one lake to another through channels known as rajakaluve. In the Hebbal-Nagavara valley, Hebbal receives water from upstream lakes before passing it downstream towards Nagavara and Kalkere. But this network has already been weakened by urbanisation and encroachment. The DPR identifies Hebbal Junction and its surrounding areas as prone to urban flooding, citing inadequate stormwater capacity and backflow from Hebbal Lake. It also states that the existing stormwater drains are insufficient to carry peak monsoon discharge. It is in this hydrologically sensitive setting that the proposed tunnel is being planned. The DPR outlines measures to manage water both during construction and after completion, including the temporary diversion of stormwater drains and dewatering during excavation. Once completed, the tunnel is designed as a permanent watertight structure to prevent groundwater from entering it.
Engineering Around Water
Building the tunnel will require the ground to be opened to a depth of about 18.5 metres. The project’s DPR proposes the cut and cover method for this excavation. Because the work will take place in an area where stormwater and groundwater are present, the construction plan includes measures to keep water away from the excavation. Stormwater drains along the alignment may be temporarily diverted, while cofferdams can be used to prevent water from entering the work area during the monsoon. Groundwater that enters the excavation may also have to be removed through dewatering. The water-management measures continue once the tunnel is built. The structure is planned to be watertight, with drainage systems to collect seepage and rainwater and sump pumps to move the collected water into municipal drains. Flood barriers are proposed at the tunnel entrances, while the ramps will have canopies, side drains and sumps for rainwater management.
The Groundwater Question
The measures in the DPR address how water will be managed around the tunnel. But the area’s groundwater conditions add another dimension to the project. Groundwater supplies about half of Bengaluru’s water needs, making recharge an important part of the city’s water system. The issue is particularly relevant around Hebbal. The 2025 Central Ground Water Board assessment classifies Yelahanka taluk, which includes Hebbal, as overexploited. WELL Labs has reported average borewell depths of 700–800 feet in the area, with its deepest surveyed well reaching about 1,200 feet. The geology beneath the city is also significant. Bengaluru’s hard-rock terrain contains fractures and joints that act as pathways for groundwater. Rainwater first moves through the soil and weathered-rock layers before reaching these deeper pathways. This puts the tunnel in an area where groundwater is already heavily used and where the underlying geology plays a key role in how that water moves and is replenished.
Under the Court’s Scrutiny
The government has maintained that the tunnel will not take any land from the lake bed. Advocate General Shashi Kiran Shetty told the Karnataka High Court that the project will instead use 3.45 acres of land within the lake’s buffer zone. He also assured the court that the project would not restrict the use of the lake.The Bengaluru Development Authority has said that it conducted hydrological studies as part of the project. A geotechnical report submitted before the court also states that the tunnel will not affect the lake’s inflow and outflow. The High Court, however, has sought further clarification on how the project will ensure that the lake’s natural inflow and outflow, as well as underground water movement, remain unaffected. The government was asked to provide this clarification by September 10. The court’s scrutiny therefore centres on whether the studies and engineering measures are sufficient to support the government’s assurances.
Managing a Constrained Site
The project brings multiple agencies and interests into the same construction plan. The Greater Bengaluru Authority and Bengaluru Development Authority are responsible for implementation, while the work also involves land and infrastructure under other public authorities.This makes coordination central to execution. Decisions on construction, land use, drainage and the surrounding road network have to work together rather than being handled as separate interventions.For an infrastructure project in a constrained urban setting, coordination is as important as the engineering itself.
The Hebbal tunnel therefore is a case of infrastructure being fitted into a space where the available room is already limited by roads, a lake, drainage networks and the ground conditions below them. That makes the project's success dependent on more than completing the tunnel itself. Its design has to respond to the conditions of the site, while its construction has to work around the systems that already exist there. For infrastructure projects in dense cities, this is becoming an increasingly important part of the brief: not simply finding space to build, but understanding the space before deciding how to build in it.
Sources: Karnataka High court proceedings, Bengaluru development Authority (BDA), Central Ground water board ( CGWB ), WELL Labs, Bengaluru urban water balance report, The Indian Express
