Managing the monsoon

The city of Chennai has always had an uneasy relationship with the northeast monsoon. While it depends on this monsoon for the majority of its water requirements, inundation, waterlogging and disruption of life are serious concerns, especially after the floods of December 2015

Published - November 01, 2020 03:17 am IST

An incomplete stromwater drain at Periamet; and below, An MTC bus stuck in an inundated street follwing heavy downpour.R. Ragu

An incomplete stromwater drain at Periamet; and below, An MTC bus stuck in an inundated street follwing heavy downpour.R. Ragu

The northeast monsoon this year set its foot into Tamil Nadu with formidable rains, especially over the coastal districts. The first spell of copious rain on October 29 brought with it the usual issue of inundation of Chennai’s vulnerable areas. While the city managed to bounce back, concerns over the recurrence of the monsoon woes among residents are inevitable.

With the meteorological department forecasting near normal rainfall this monsoon, a section of residents in vulnerable areas raises doubts about infrastructure needed to control urban flooding. People in some localities like Anna Nagar Western Extension were relieved that the desilted stormwater drains (SWD) and freshly added infrastructure helped to drain rainwater off the roads. S. Rajagopal, a resident, noted that people had to constantly press officials for completion of the work, a matter of challenge during the pandemic.

In contrast to this, residents of other areas such as Mylapore and Saligramam blamed poor stormwater drains for their localities covered with sheets of water long after the rain abated. People in Singaravelu Street and Gandhi Nagar, Saligramam said water pumped out of the Vadapalani bus depot added to stagnation on Kumaran Colony Main Road. C. Thomas of Saligramam said the stormwater drains need to be redesigned to prevent localised flooding. The lack of coordination between Greater Chennai Corporation (GCC) and the Highways Department was evident with water-logging on some key roads such as General Patters Road and Anna Salai.

However, the official word is that one need not fear a repeat of the December 2015 situation, since a lot of preparatory work has been done. Officials of government agencies engaged in monsoon preparedness noted that the long-term flood mitigation works implemented so far in Chennai and its neighbouring districts would help to reduce the severity of floods, experienced in 2015, by 65% to 70%. Commissioner of Revenue Administration K. Phanindra Reddy said many projects had been completed in phase I in the flood-prone areas to conserve floodwater with riverine reservoirs across the Adyar, eco-restoration of waterbodies and bridging of missing links to carry the rainwater between lakes.

The major issues of breaching of lakes and unplanned discharge of surplus water from lakes in the Tambaram region had been addressed, he said. Eight lakes, including Sembakkam, Narayanapuram and Selaiyur, have been provided with flood regulators for a systematic discharge and prevent inundation in foreshore areas. “We have also initiated an early warning system through text messages, irrespective of service providers in the city. On October 29, city residents received weather forecast messages. The project of the Centre for Development of Telematics and the State government will help people to be prepared about impending inundation,” he said.

Some of the highly vulnerable areas may be spared localised flooding, according to the Water Resources Department. While the COVID-19 pandemic and the lockdown have delayed the completion of significant projects, long-term flood mitigation works initiated since 2017 will help to reduce local flooding to a large extent.

What has been done

Of the ₹344 crore allotted, works worth ₹260 crore have been completed so far, besides six cut-and-cover drains in areas such as Chitlapakkam and West Tambaram and 31 tanks in southern parts of the city such as Manimangalam and Somangalam that drain surplus water into the Adyar river have been deepened. A total of 13 major drains are being improved, and the completion of some projects had helped to be monsoon-ready by July. The flood drainage system has been improved in localities such as S. Kolathur, Pallikaranai and Mudichur Road. If projects proposed worth ₹3,000 crore under the Chennai City Partnership Programme are accelerated, permanent mitigation would be possible. Funds have been sought from the World Bank for comprehensive flood mitigation and conservation in Chennai Metropolitan Area, an official added.

Come monsoon, complaints of water pollution and sewage spillover do arise in the city. R. Narasimhan, Chief Engineer (Operation and Maintenance), Chennai Metrowater, said: “We are monitoring 609 locations prone to sewer obstructions. Special monitoring officers have been appointed to check out residents’ complaints. While 3,000 water samples are being tested daily for residual chlorine and total dissolved solids, an additional 300 samples are being tested for various parameters by the Quality Assurance Wing.”

Corporation confident

Amid the complaints of delay in minor works and inadequate funds for desilting drains in many wards, the GCC is confident of facing the impact of the monsoon. GCC Commissioner G. Prakash noted that works to provide new infrastructure and desilting of waterbodies this year would help face the monsoon. The stormwater drain network, especially in the core parts running to 400 km, was desilted with funds from the Chennai Mega City Development Mission and other projects.

Officials said that given the city’s flat terrain and the city’s stormwater drains designed to accommodate only up to 42 mm of rainfall per hour in core parts, it would take several hours for rainwater to recede. In extended areas, new stormwater drains have been built as per international standards to accommodate 68 mm of rainfall.

L. Nandakumar, Chief Engineer (General), noted the high tide and low tide also played a significant role in draining floodwater into the sea. On October 29, the high tide delayed discharge of rainwater. The pre-monsoon stormwater drain work helped to keep the city largely free of inundation. Rainwater should not stagnate for more than two hours as per international standard.

Nearly 25,000 tonnes of hyacinth, silt and garbage were removed from minor waterways to ensure free flow of rainwater. Measures to install 30,000 silt catch pits in the inlet points of the stormwater drains and 2,000 sunken wells in the parks and abandoned wells helped in rainwater harvesting in public spaces.

About one lakh rainwater harvesting structures in the city houses were made functional, he said.

The pandemic has delayed the Integrated stormwater drain in north Chennai areas such as Manali, Madhavaram and Tondiarpet. The work to build macro-canals in 10 locations in the merged areas of north Chennai would have been completed had it not been for the lockdown, said GCC officials.

However, Velachery residents complained that the pre-monsoon work was inadequate. Citing the construction of the flyover and widening of the Velachery Main Road, S. Kumararaja said the Velachery canal had been blocked with concrete to make way for the road and the macro-canal in the widened portion of Velachery-Taramani Link Road lay neglected.

Recurring encroachments

Though large-scale projects have been initiated and implemented successfully in various areas, departments like the WRD continue to grapple with issues like recurring encroachments and sewage flow into waterbodies and waterways.

WRD officials said an eight-km stretch of the Kosasthalaiyar river beneath the Karanodai bridge, which often breached leading to spillover of floods, had now been restored. “We found the bund cut open in 50-60 locations. Controlling illegal sand mining is a challenge,” said an official.

Cleaning various surplus courses, which carry rainwater to the Adyar, in the neighbourhood of Porur and Manapakkam was another challenge. In some narrow stretches, water hyacinth had to be removed manually as machines could not be deployed. Water hyacinth, too, returned over waterways as sewage continues to flow. Missing links in the Paruthipattu and Madhavaram surplus courses too pose a challenge.

S. Thirunavukkarasu, former Public Works Department engineer, notes that frequent readings of flow into reservoirs once in 30 minutes during heavy rainfall would help to tackle flash floods. More ‘lascars’ (irrigation assistants) should be deployed to monitor reservoirs.

Meanwhile, weather experts note that monsoon preparedness is more focussed on tackling urban floods. But it is also about drought preparedness and harnessing rainwater. It is essential for the State government to develop an elaborate plan to tackle water security next year in case the monsoon fails to bring sufficient rainfall.

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