Bengaluru floods: Anatomy of a drainage system gone horribly wrong

Last week, Bengaluru was battered by rains that were unprecedented in scale and floods that were disastrous in impact. While the rains have abated, thousands living on the periphery of the Bellandur-Varthur lakes in east Bengaluru are still gripped by fear, worried that deliberately narrowed drains, encroachment of wetlands, and state apathy could trigger another round of devastation.

For years, the Karnataka government and the city corporation, the Bruhat Bengaluru Mahanagara Palike, has held out a long-term fix for the recurring floods – remodelling the city’s stormwater drains. But 16 years after its launch, the project is nowhere near completion and, worse still, has a glaring design flaw that ironically aggravated the flooding this year.

Faulty drain redesign

Flood management experts have dubbed this remodelling as a project to help the land mafia.

Why? After their redesign, the drains have shrunk from about 60 feet to 18 feet along several flood-prone stretches dotted by fancy apartment complexes. This, as experts point out, clearly violates the National Green Tribunal’s guideline to maintain the physical integrity and buffer of the SWDs.

The impact of this violation affected thousands last weekend. As rains pounded Marathahalli area barely a km away from the HAL Airport, the drain – or rajakaluve, a channel that connects water bodies – taking excess water from the upstream Doddanekundi lake to Bellandur and Varthur overflowed. In a flash, vast swathes of the locality and its surroundings were five feet underwater.

The locals knew exactly what the problem was.

“The rajakaluve here is 40 feet wide but, about 500 metres from here, has been narrowed down to just 10 feet by a big builder,” said Jagadish Reddy, who has lived in Marathahalli for decades. “They laid a slab over it for a road to their complex. We had complained several times and asked them to at least clear the silt under it, but they did not care even for the MLA.”

Only after chief minister Basavaraj Bommai visited the flood-affected areas and ordered removal of encroachments on SWD that the people managing the residential enclave, which is named Divyasree 77, reluctantly agreed, Reddy added.

On September 8, the BBMP’s earthmovers razed concrete slabs installed on the SWDs and demolished a wall. Many residents in flooded villas within the enclave were evacuated.

Expensive and delayed project

In the last 16 years, BBMP has remodelled only 428 km of the city’s 842-km network of SWDs. It spent a hefty sum to do so of Rs 1,658 crore and has estimated a cost of Rs 4,670 crore – three times the initial cost – to complete the remaining 414 km.

Yet this project, now costing a total of Rs 6,328 crore, has been found to be seriously wanting in design and utility, even as it’s touted to be a robust defence against future floods.

“If you look at the Bellandur-Agara lake side, the drains are narrowed and concretised in the name of remodelling,” said Dr TV Ramachandra, who heads the Centre for Ecological Sciences at the Indian Institute of Science. “If they had not concretised, 60 percent of the water would have seeped down to the underlying layer. Now, since it is a paved surface, all the water flows over land.”

This is seen even a week after heavy rains at Devarabeesanahalli, an area adjoining the Outer Ring Road. This area, with several big tech companies and a large super-speciality hospital, saw waist-high flooding. The drain, which is considerably narrowed here, is still filled to the brim with rainwater mixed with sewage.

“People say the corruption is 40 percent. It must be more than 150 percent,” Ramachandra said. “The chief minister announced Rs 1,100 crore for remodelling drains [as another instalment]. This tamasha happens every year. Not only do they make money through kickbacks but also earn more from builders by narrowing the drains.”

Ill-prepared pre-monsoon

Angry residents point out that it’s not rocket science for BBMP to desilt drains well before the onset of monsoons.

“Yes, the rajakaluves are narrowed and encroached. But why wait till the rains to clear the muck out?” said Anand Raj, who has lived in Yemalur for 35 years. “Even the shoulder drains flanking the houses are not cleared for years. When it rains, we have no peace of mind. We cannot sleep. It is mental torture.”

And everyone knows why the drains get clogged – through dumping of solid waste and construction debris. Additionally, the unregulated inflow of raw sewage continues unabated.

“When the drains overflow, our drinking water lines get contaminated,” said Glen Souza, a resident of Marathahalli. “The piped water stinks. We end up spending thousands on cleaning our storage tanks and sumps.”

The excuse of ‘record rains’

Thanks to both mainstream and social media, the recent floods cornered the state government. But its response was to deflect, blaming previous governments and the record rains.

It’s true the downpour was intense. The city received rain in excess of 1,450 mm this year, far higher than the annual average of 986 mm. But residents, who bore the brunt of it, are unimpressed.

“I have been in this area for 25 years,” said a local on condition of anonymity. “We have had heavy rains before but the water would drain out faster. Now, there is no place for it to go. Within no time, Balaji Layout, Manjunatha Layout, Kaverappa Layout and other adjacent localities were flooded.”

In its 2021 report, the Comptroller and Auditor General had pulled up the SWD department for serious lapses in stormwater management. There was not even a manual to standardise and specify drain design, construction and maintenance. The department did not factor in design tweaks and other strategies to address high-intensity rainfall, and the report also flagged lack of proper drain linkages and groundwater recharge structures.

Warnings unheeded

But even before the floods put a national spotlight on Bengaluru, scientists tracking rainfall patterns had told the government to speed up its mitigation efforts.

“The frequency of extreme events is increasing,” pointed out Dr GS Srinivasa Reddy, former director of the Karnataka State Natural Disaster Monitoring Centre. “The city has received continuous rainfall from July onwards. Heavy rains were recorded in the first and last weeks of August, and the first week of September.”

On August 30, the flooded Outer Ring Road led to thousands of tech workers being stranded for hours. According to the ORR Companies Association that represents major IT and banking firms, this caused a loss of Rs 225 crore to the industry. In a strongly worded letter to chief minister Basavaraj Bommai, the association sought immediate action.

Could this traffic mess have been avoided using a good warning mechanism? In 2020, the Karnataka State Natural Disaster Monitoring Centre, in collaboration with IISc, launched two dedicated mobile apps – Bengaluru Megha Sandesha and Varunamitra – for real-time alerts on weather and urban flooding.

But, as Reddy said, “Flood forecast depends on rainfall forecast. Accuracy matters. Due to the inconsistency of the rainfall patterns, even the forecast goes wrong.”

Forecasting boost, a non-starter

To boost accuracy and speed of forecasting, the Karnataka State Natural Disaster Monitoring Centre had applied in 2012 to acquire a Doppler radar exclusively for Bengaluru.

“The radar can clearly indicate the cloud thickness, density and moisture. Based on its data, you can easily predict the rainfall at least an hour in advance,” said Reddy. “But now I hear the project has been cancelled. The Indian meteorological department too had urgently written to the government urgently seeking the radar.” The proposal, it is learnt, has been kept on the backburner.

Accurate real-time data could feed the communication channels of the BBMP and Bangalore Water Supply and Sewerage Board, as well as equip the Bengaluru traffic police to take quick decisions on traffic diversions. Motorists, alerted in advance by their smartphone apps, could completely avoid flood-prone roads.

Reliable technology could also help residents in flood-prone areas in the long term. Unaware of the encroachment of lake beds, wetlands and SWDs, thousands have bought flats in buildings in close proximity to water bodies. “Geographic Information System, or GIS, spatial data should be made public so that buyers know where the lake boundary is,” Reddy said.

He alleged that this data is deliberately suppressed to benefit builders and vested interests in the government.

“We have a good database,” he said. “You can get the cadastral map. Even if some data is missing, the Karnataka State Remote Sensing Application Centre can get it. It is not difficult. But the bureaucrats and politicians deliberately keep the gaps in the system.”

Wetland encroachment, by design

These gaps have ensured that wetlands, which enrich and sustain a lake, are encroached with impunity by builders for tech parks and other fancy mega-realty projects. In the wetland zone attached to Bellandur lake, construction debris was dumped by mammoth trucks for over a decade. Today, there is no trace of the ecosystem that once fed the lake.

The modus operandi is the same across the city. Once levelled with debris, the wetland automatically qualifies to be a special economic zone and even gets approved by the Karnataka Industrial Area Development Board.

In 2016, the NGT had quashed the environmental clearance for one such project – a Rs 2,300 crore SEZ on the Bellandur lake wetland near the water body’s southern boundary. The construction was stayed and a hefty penalty imposed. The Supreme Court upheld the NGT’s order three years later. But the order to reclaim lake land and restore the rajakaluves destroyed for the project is yet to be implemented.

Poor road infrastructure

Intricately linked to the lake and drainage systems is mobility – a big, visible part of which is Outer Ring Road. As urbanist Ashwin Mahesh points out, the highly congested road is symptomatic of flawed planning. Simply put, very large communities of housing and offices were allowed to spring up with very minimal road connections. Even a short spell of rain could flood the road, and quickly escalate.

“Even to encourage public transport, walking and cycling, you need pathways,” Mahesh said. “If you see the satellite imagery of Bengaluru, the newly developing areas in the east and southeast don’t have the road infrastructure at all.” There are no alternative pathways either, leading to phenomenal congestion on ORR.

ORR has almost 40-50 giant software tech companies, all of which are destinations for daily road trips by people in thousands. “It creates a tremendously lopsided traffic pattern, which no system can tolerate,” said Nagesh Aras, an environmentalist from the eco-collective Friends of Lakes.

Cylindrical drains

Returning to drain design, Mahesh pointed out serious problems with both their location and shape.

“We build rectangular drains instead of cylindrical drains,” he explained. “We don’t have adequate soak pits to absorb water where the rain falls. We needlessly transport large amounts of water to low-lying areas, inevitably blocking drains and triggering overflows.”

Rising periods of intense rainfall warrant storage infrastructure beyond what Bengaluru currently has. Since the city’s lakes are filled with silt fed by sewage-carrying drains, the storage capacities have shrunk. “The storage infrastructure for any geography should be appropriate for the rainfall pattern of that geography. We need a rethink,” Mahesh said. “Chennai is finally doing it, Bengaluru should follow.”

Lakes and sluice gates

The whole ecosystem of road, drain networks and lakes demands a serious relook, said Nagesh Aras from Friends of Lakes. “The water system itself is designed wrong because we have not calculated how the lakes can play a part in buffering the water when it rains,” he said. “Most lakes do not have sluice gates and so, flood management cannot be done.”

So, what next?

Aras is clear: “Our disaster management cell has to come out with delineation of flood plains for each lake and each area, and it has to correlate the rain and flood that occur in that location. This information is available, but not shared publicly. If it is so co-relatable and predictable, then why are we forced to live with such floods?”

Ramachandra emphasised that the way forward is reestablishing the interconnectivity between lakes and canals, removing all blockages and encroachments, rethinking and scientifically designing the SWD network, and seamlessly integrating multiple projects handled by different agencies.

Water should then flow seamlessly from one lake to another, as the city’s founder Kempegowda planned. But for the average Bengaluru resident, precariously perched on the edge of flooded roads and encroached drains, that vision is getting hopelessly blurred.