Bengaluru’s SWDs need an upgrade. And now.

The pipe-and-chamber system promises to deliver what the box drain hasn’t, and the expertise is available.

Even before the monsoon has officially arrived, Bengaluru is reeling – 16 hours of pre-monsoon showers between May 18 and 19 brought the city to a standstill. Lives have been lost, infrastructure heavily damaged, roads vanished underwater, and low-lying areas turned into shallow lakes. This isn’t an anomaly. It is a warning; a warning that sounds annually in the city.

The reaction each year remains the same – temporary fixes that do not address the root cause. The real problem however lies underneath – the city’s stormwater infrastructure that is unscientifically designed, woefully outdated, and dangerously unfit for purpose. At the heart of it is an old design we have clung to for too long – the box drain.

Box drains are visible throughout the city – rectangular concrete trenches running alongside property edges, covered with loose slabs to allow for a makeshift pavement. These drains were perhaps fit for a different era, but we cannot fix 21st-century floods with 20th-century thinking. The reality is that Bengaluru’s stormwater drains were never designed to handle the 105 mm of rainfall it received within 16 hours this May. As rainfall becomes more intense and erratic, we need infrastructure built to withstand at least a 1-in-100-year flood event.

Solutions exist – pipe-and-chamber drainage systems are one of them. A pipe-and-chamber system carries stormwater through a network of underground pipes, connected to chambers that collect runoff from roads, and channel it downstream through the pipes. They’re not a cure-all, but they are fundamental to designing flood-resilient infrastructure.

There are compelling, fundamental reasons why the pipe-and-chamber system should be adopted as the gold standard for stormwater drains in Bengaluru.

It enables faster drainage. The pipe-and-chamber system is placed at the road edge. It collects water swiftly from the road surface through grated openings that lead into chambers, placed at intervals of 20 to 30 metres. This modular arrangement – connecting prefabricated pipes to regularly spaced chambers – helps maintain a consistent gradient and ensures efficient stormwater flow. Box drains, by design, are not capable of delivering this. Box drains are typically cast in place directly over uneven soil, which makes it difficult to maintain precise gradients. Backflow of water, or stagnation, is thus a common problem in such systems.

The pipe-and-chamber system is silt- and garbage-resistant. The grated openings in the system that channel stormwater into the underground pipes are carefully spaced to allow the water through while blocking solid waste and larger debris. Contrary to this, solid waste easily finds its way into box drains through loose covers. Siltation (accumulation of fine sand, clay and debris) is also a major concern in box drains – the rectangular section of these drains is particularly susceptible to silt deposits. Removal of silt requires cleaning the entire network of drains. The pipe-and-chamber system naturally reduces siltation owing to the circular pipe design which promotes a steady water flow and helps carry silt away, instead of letting it settle. Any sediment that does enter the drains settles in the chambers, which are easier to access and maintain.

The system also eliminates public health risks such as contamination of stormwater with grey and black water. Box drains are placed adjacent to properties that, in some cases, discharge not just stormwater but also grey water from kitchens and black water from toilets onto the drain. The pipe-and-chamber system prevents contamination by design – it is placed away from the property edges and does not allow any water (storm, grey, or blackwater) from private properties to enter into the drains.

It allows for groundwater recharge to a degree. In the Tender S.U.R.E. model, the chambers have the provision of in-situ recharge through percolation pipes that release a portion of stormwater into the ground. This feature is completely absent in box drains which are simplistically designed to channel all water downstream without any provision for recharge.

Finally, the pipe-and-chamber system creates safer streets and better footpaths. The stormwater pipe is enclosed and tucked beneath the footpaths, enabling continuous, level pedestrian networks. In contrast, the loose and uneven slabs covering box drains often become serious safety hazards for pedestrians.

Results are out

The pipe-and-chamber system isn’t a theoretical concept – it’s a proven solution. Over 100 km of Tender S.U.R.E. roads in Bengaluru already use this system, and they consistently show faster stormwater drainage and fewer flooding issues compared to roads with traditional box drains. The pipe-and-chamber drains are engineered to handle a 1-in-100-year flood event and flush out stormwater within 5 to 10 minutes of rainfall, keeping roads clear and cities moving. The system also has clear financial benefits. Indicative estimates suggest that it may cost about 30% more upfront – but this is more than offset by long-term savings on desilting, maintenance, and pothole repairs.

Bengaluru's stormwater crisis calls for a range of coordinated interventions – from increasing the city’s permeable surfaces through nature-based solutions to restoring the interconnectivity of its natural drainage networks and removing encroachments from ecologically sensitive areas. Many of these solutions require long-term planning and investments. However, upgrading the stormwater drains is vital and achievable in the short- to medium-term. BBMP’s engineers are already trained to implement the pipe-and-chamber system, and with the right commitment, this city-wide transformation can be completed within the next 5 to 10 years. What it needs now is not expertise – but the political will to act.

It is time for Bengaluru to break away from the box drain. The city deserves infrastructure that is functional and resilient. And our future demands systems that are built for the climate we live in now – not one that we had 50 years ago.

(The writer is an advanced associate, urban design, at the Jana Urban Space Foundation)