Gaps in dealing with Bengaluru floods

Bengaluru: Bengaluru’s recent downpours have once again turned the city into a chaotic mess. From tech hubs to residential areas, roads transformed into rivers, leaving residents stranded and frustrated. The BBMP received over 18,000 distress calls in just four days. Power outages affected thousands, and tragic incidents, including the electrocution of a young woman, highlighted the city’s inability to deal with the rains.

As memes flood social media, mocking the city’s recurring woes, it’s clear that Bengaluru’s battle with floods is far from over. This isn’t the first time the city flooded like this: Previous floods have presented enough data on the areas where they flood, offering ample opportunities for the town to fix them. But the city flooded yet again, proving that no lessons were learnt.

‘Apathy is the biggest issue’

Ram Prasad, founder of the Friends of Lake group, pins the blame on citizens, the government, and their misplaced priorities. “Funds do not go where they should, to fix the lakes or drains. Instead, it is used for beautification and cosmetic changes. Citizen participation in governance is lacking. There is no unity or responsibility among them. The problems bother citizens only when they happen, and they forget about them later,” he adds.

“Everyone knows everything. Lakes have to be converted into flood mitigation zones. Nalas have to be fixed. Encroachments should be cleared. When the BBMP removes silt and deposits on the side, citizens should ensure it is taken away and disposed of properly. This is not happening. Officials are in a different zone: They hope for separate tenders to remove and transport the silt,” he says.

Climate change and more

“It’s not just Bengaluru; most regions worldwide have witnessed extreme weather patterns. Climate change impacts are omnipresent, from floods in arid regions to droughts in harvest bowls. It’s important to understand our hydrology or river systems to understand our upstream and downstream water flow and our urban vulnerabilities,” says Rajagopal, a citizen activist and founder of Bengaluru Coalition, a citizen group.

“The concept of cloudbursts was unheard of in this city until recently. Weather studies show how these mega thunderstorms are forming in concentrated patterns, leading to very heavy downpours 2x to 5x normal amounts, which perhaps need recalibrating, in one local area in a very short time window,” he observes.

According to Rajagopalan, rising urban temperatures, greenhouse gases (GHG), a loss of 80% or more green cover in the city, concrete jungle growth, heat islands, and rapid urbanisation are behind the problems we see today. These also lead to weather issues, including cloudbursts.

Unseasonal rains with no pattern are a big problem. “The weather forecasts are inaccurate, and civic agencies only react after things happen, which is usually too little, too late,” adds Rajagopal.

B S Prahlad, Bruhat Bengaluru Mahanagara Palike’s Chief Engineer, who has been in the eye of the storm due to the flak he drew recently from the chief minister, blames the lack of planning in how Bengaluru is designed. He says the erstwhile watershed canals used for irrigation are now used for water management, and the channels in Bengaluru can handle only upto 70 to 80mm of rain.

“Beyond this, our stormwater drains cannot handle the runoff. On May 18 and 19, the rain ranged between 72 and 132 mm. On average, we had 100 mm of rain, the second highest in the last 10 years. This is why the city flooded,” he explains, when asked why the city still floods, when everyone knows all the issues.

What’s BBMP doing?

“There was a time when stormwater drains handled only 40mm, and the network was below 300 kms. We added 212 kms in 2016-17. In 2020, we added 95 kms. Now we are adding 195 kms,” says Prahlad.

Prahlad explains an ‘out-of-the-box’ solution to increase the water flow. “We are constructing retaining walls along stormwater drains to increase water velocity. We can’t give more space in the drain, but we can improve the speed at which water flows by limiting the spread of water,” he adds.

He says the solution is derived from Manning’s Formula, a way to estimate how fast water flows through an open channel like a river, stream, or ditch, used in civil engineering and hydrology. “Water flow is directly proportional to the smoothness of the surface. Rough surfaces slow down water flow. Smooth surfaces can make the water gush out,” he explains.

“We have given an annual maintenance contract to remove the silt in stormwater drains,” he says, denying the existence of any blockage in the drain network.

“We have identified 137 waterlogging points. Shoulder drains adjacent to roads are clogged due to silt and other things. We are installing vertical gratings in these drains and improving velocity,” he explains when asked about waterlogging in roads. Vertical gratings trap leaf litter and other trash while letting water pass through.

“We have a road network of 1682 kms. We have addressed 40-50 % of these roads in the last two years, while the remaining 800 kms remain to be addressed. By March 2026, all the roadside drains in Bengaluru will have vertical gratings,” he explained.

Curious case of percolation pits

According to Rajagopalan, rapid, rampant, and unplanned urbanisation, plan violations, and unapproved layouts have led to concretisation and no water percolation, which are the root causes of urban flooding.

\When the water crisis hit the city last summer, the BBMP announced digging rainwater percolation pits inside the shoulder drains. According to Prahlad, this plan would contaminate the groundwater. “Our water expert is unhappy with this plan because the runoff contains sewage water and might contaminate the groundwater,” he adds.

“We have polluted surface water, now we should not pollute groundwater. It’s not scientifically correct. When there is no rain, sewage flows into the shoulder drains, which is called dry weather flow. During the rainy season, rainwater is mixed with sewage flows, which is a wet weather flow,” says Prahlad. He adds that he is waiting for the BWSSB to explain why there is dry weather flow when there should not be any water flowing in the shoulder drains during the dry season.

“The biggest problem with roads is that we design the roads to handle the runoff only in the carriageway - the water flowing on the actual road, not the flow from adjacent buildings,” explains Ratnakar Reddy K B, a consultant working in the field of highways, transportation engineering and urban infrastructure.

“The policy calls for rainwater harvesting for water, or water has to be percolated to the ground; it cannot come to roadside drains,” he adds.

Rainwater not harvested enough

The current RWH policy for Bengaluru covers only bigger plots, and the smaller plots are still a problem.

“Rainwater Harvesting (RWH) at scale has not been implemented nor enforced for existing homes or new housing communities. Large public buildings, office parks, commercial buildings, and apartments should especially comply with and maintain these systems,” says Rajagopalan.

Reddy highlights another issue: “Our roads are perennially under construction. Wherever there is construction, drainages get blocked. Water does not flow continuously. The various parastatals that handle such constructions should have coordination meetings to plan rainwater management, along with traffic and pedestrian management.

“Looking ahead, we may never be able to catch up to the density of such downpours and reverse this worsening trend. We have let urban decay go too far and may need to think about bare survival, as grim as it sounds. Most efforts in the face of nature’s fury could be mere band-aid steps that will easily peel off and not weather the storm,” cautions Rajagopalan.