Citizens map Bengaluru’s stormwater drain crisis

A coalition of urban researchers, hydrologists and citizen volunteers produced a granular public assessment of the Bengaluru's stormwater drain (SWD) network, finding systemic links between deteriorating drainage infrastructure and a cascade of urban problems — from localised flooding and rising heat to contaminated drinking water and public health risks in informal settlements.

The findings emerged from a day-long datajam held at BLR Design Centre on Church Street, organised by OpenCity, an initiative of Bengaluru-based Oorvani Foundation, in collaboration with Mod Foundation, WELL Labs, Biome Trust and Sponge Collaborative, supported by the Bengaluru Sustainability Forum's Small Grants Programme.

The datajam was a part of a wider initiative called Building a Resilient Bengaluru, which has combined online masterclasses, a series of guided citizen audits across the city.

A press statement said that the participants worked with audit data collected on the ground and cross-referenced it with official SWD maps, lake maps, topographical data and land use patterns.

One team examined the relationship between stormwater drains and urban heat, finding that open drains function as heat sinks while closed drains tend to become hotspots. Concretised surroundings intensified heat retention, whereas green buffers around drains helped moderate temperatures.

Another team focused on Shivajinagar constituency, analysing how built-up density around drains affects water permeability and quality, and whether BBMP work orders were meaningfully addressing the problems identified.

A third group looked at how natural drainage systems — lakes and tanks — historically absorbed flooding, and how land use change and the loss and encroachment of water bodies have altered drainage patterns and worsened current flood points. A striking finding was that many of the city's worst flooding locations today correspond to sites where lakes once stood.

One more team mapped the intersection of stormwater drains with sewage and water supply lines, identifying points where proximity creates a tangible risk of drinking water contamination for nearby residents.

A separate group examined how flooding and sewage interact in informal settlements and noted the relative absence of health facilities in the most vulnerable zones.

On land use and water quality, participants analysed whether proximity to industrial clusters was degrading drain quality, and whether residential areas were also contributing to inflows that compromise the network.

Participants noted that encroachment on drain margins, combined with large-scale concretisation, was steadily reducing the city's capacity to manage rainfall events.