The Sunday Deep Dive

Rain, rain; no drain

CHENNAI : 13/11/2021 : FOR CITY : A view ofthe Mambalam Canal for Sunday Story. Photo : PICHUMANI K / THE HINDU

CHENNAI : 13/11/2021 : FOR CITY : A view ofthe Mambalam Canal for Sunday Story. Photo : PICHUMANI K / THE HINDU

When Chennai was preparing for a rainy, lazy Sunday last week, many residents woke up to relentless downpour in the early hours. Within a few hours, several parts of the city had sunk under water. For a week now, as a depression off the Bay of Bengal pounded the city, Chennai is still picking up the pieces. Some parts remain submerged.

Even localities in the core areas remain waterlogged, with the ground floor of several houses still under sheets of water. Some subways and roads are still closed. Power supply that was cut to avoid casualties due to the wind and stagnation was being restored in most parts. But some areas are yet to be plugged back into the grid. In some parts, residents suffered without power for five days, they said.

There has been no respite from waterlogging for many parts of north and south Chennai, including Pulianthope, Pattalam, Jawahar Nagar, Mylapore, Saligramam and Velachery, that are traditionally prone to inundation. T. Nagar, which underwent area-based development under the National Smart Cities Mission, and its neighbourhoods are one of the worst-affected localities.

On Friday, S.V. Ramakrishnan, a resident of North Crescent Road, T. Nagar, had called helpline 1913, requesting the Greater Chennai Corporation to bring tractors fitted with heavy duty pumps to drain water. “Both the sewer network and the storm-water drain are blocked. Water is knee-deep in houses,” he said.

For many residents like V.S. Jayaraman of Motilal Street, T. Nagar, it was a return to the 2015 floods as water has not receded even after five days. “Many people have vacated apartments as there is no power supply or drinking water. An overwhelmed drainage system has led to the stubborn problem. Speed-humps laid on the street as part of the National Smart Cities Mission blocked the rainwater from draining,” he said.

Even according to official estimates, more than 1.5 lakh residents in T. Nagar alone have been affected by the localised floods. The depression that crossed the coast close to Chennai on Thursday had brought more water into the Adyar, slowing down the draining of the floodwater carried by the Mambalam canal into the river. It is this canal that carries water from T. Nagar and Valluvar Kottam to the Adyar.

Residents of various areas, particularly T. Nagar, blamed the lack of drains or a poor storm-water drain network for the inundation, and also the shoddy work carried out as part of the ₹105-crore Smart Cities Mission. Chief Minister M.K. Stalin alleged corruption in the Smart Cities project and called for a probe into the work carried out by the previous government. He said action would be taken against the contractors.

Pumping of water into drains leading to the canal, too, was a tough task. T. Nagar MLA J. Karunanidhi said pumping of water was taken up at 40 locations on Friday. Water was pumped near the railway track towards the drains leading to the Mambalam canal. But the water did not drain as quickly as expected.

Dumping of waste, including construction debris, in the drains in the area — a hub of commercial activity — was also cited as a reason for inundation. Omani Palani, a conservancy worker, said, “The water was four feet near the Mambalam canal on Vijayaraghava Road on Thursday. A huge quantity of waste clogging the culverts was removed then.”

In T. Nagar, there are just three culverts near Mambalam to drain water from the western part of the rail line to the eastern part. These culverts are inadequate to drain water, especially the volumes that are likely during intense spells, or during a depression or cyclone. As the culverts were clogged beneath the bridges, the Corporation demolished the retaining walls of such bridges along roads, like Vijayaraghava Road, to facilitate flow of water.

Local efforts

Corporation Commissioner Gagandeep Singh Bedi said many initiatives were taken at the local level to mitigate flooding in areas like T. Nagar. “For example, we found that the bund had caved in at a number of places along the Mambalam canal during midnight and we cleared it to ensure flow of water. Wherever solutions were required, local-level decisions were taken. We have used over 100 horsepower motors for the first time. These motors are used only for draining out water during dam construction. We have started using 620 motors, over and above our capacity. We identified vulnerable places and put the motors there before the November 10 rain,” said Mr. Bedi.

Corporation officials are planning to redesign the mouth of the Mambalam canal near the Adyar. Urban planners feel that the new work along the canal under the National Smart Cities Mission should be redesigned by increasing the width to 20 metres, according to the old maps prepared by the Chennai Metropolitan Development Authority.

The extremely heavy rain of 21.5 cm recorded on a single day till the morning of November 7 and the depression near Chennai on Thursday were mainly blamed for the waterlogging in the city. However, weather experts and bloggers noted it was not one single rainfall episode that had led to flooding.

Not record rainfall

Senior meteorologist Y.E.A. Raj said that while the rainfall was very intense, it was not by any means a “record rainfall”. “We had a torrential downpour on November 25, 1976, when it rained 45 cm. The Adyar then was in spate though the floodgates of Chembarambakkam were not opened. But what happened last week was more localised floods because of unabated urbanisation without planning or adequate infrastructure.”

According to weather blogger K. Srikanth, consistent rainfall over many months this year has increased the soil moisture, resulting in higher surface run-offs. “We have recorded rain, except in March this year. Weather stations in the city, be it Nungambakkam, Meenambakkam or the DGP office, have received rain of at least 2.5 mm on every other day since the onset of the northeast monsoon on October 26. As most waterbodies are filling up, groundwater recharge would be good. This could be a reason for water not receding in the city,” he said.

The India Meteorological Department drew flak for its radar under repair, said to be the reason for the absence of severe rain alert. S. Balachandran, Deputy Director-General of Meteorology, Chennai, said the radar network was in working condition and the Chennai radar was used with limitations because of its age. “Radars are part of an integrated observation system monitored for weather forecasts. The intense rain on November 7 can be compared to a cloudburst, which is usually 10 cm of rain received in one hour. The intensity of Sunday’s rain was 6 cm in one hour. Forecasting such a sudden phenomenon is challenging,” he said.

Environmental experts, however, noted that the real issue was a change in mindset as Chennai was more of a drought-prone city than one vulnerable to floods. Krishna Mohan, chief resilience officer, Chennai Resilience Centre, said, “We must advocate a redesigned storm-water drain network that also recharges aquifers. We now have an opportunity to address issues of rampant urbanisation in the Third Master Plan. All stakeholders must be involved in ensuring land use laws are adhered to. Residents must think before buying property in marshland or lake bed.”

The storm-water drain network needs to be studied holistically for its bottlenecks. Balaji Narasimhan, professor, Department of Civil Engineering, IIT-Madras, who is spearheading the ‘Report a Flood’ data collection initiative, said the city’s storm drainage was not equipped to handle such volume. The drainage network must be checked during execution for its gradient and invert level. Sewage and solid waste management also needs to be addressed to tackle localised floods. Such initiatives may be resource-intensive and need better public participation.

Given the city’s flat topography, he also suggested pumping as an engineering solution. He said the government must consider stopping further land development near waterways and declare them wetlands. For example, the government may buy land at places like Mudichur and have dedicated floodplains. These could be preserved to buffer the floods.


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