Floods come calling regularly now - Can Chennai escape?

Understanding why Chennai sinks each time it rains heavily, and why the problem is a century-old one

Floods come calling regularly now - Can Chennai escape?

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Read more on - Polity | Economy | Schemes | S&T | Environment

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• The story: In November 2015, Chennai received 1,049 mm of rain, compared with 915 mm till November 29 in 2021. There have been particularly heavy rains between November 6 and 7 (210 mm), November 10 (22mm), November 19 (32mm), and November 26 (29mm). Overall, Tamil Nadu and the neighbouring Union territory of Puducherry together received 630 mm of rainfall from October 1 to November 29, 2021, as against the average for these months of 350 mm. During the same time period the rainfall received in Chennai is 1,130 mm, which is 83% higher than the average.
• The devastation in 2015: In the 2015 tragedy, more than 400 people were killed in Tamil Nadu. The situation was worsened when water from the Chembarambakkam lake was released, flooding Chennai. Since then, the Tamil Nadu government has said that a ₹5,000 crore integrated stormwater project is being implemented, and in T Nagar alone, ₹9.3 crore has been spent on a drain under the “smart city” mission, and was completed in 2020.
• Why it happens: This expenditure includes work to construct collector, feeder and arterial drains, canals for the Adyar and Cooum basins, which were completed last year, and ongoing work for canals for the Kosasthalaiyar basin in northern Chennai and Kovalam in the south. And yet, Chennai floods.

1. The first reason is Chennai’s long history of vanishing lakes and water bodies, captured by rampant and unfettered urbanisation.
2. Only 15% of Chennai’s wetlands are left, according to a study by Chennai-based Care Earth Trust, a biodiversity research organisation. Their findings show that Chennai’s built-up area grew from 47 sq. km in 1980 to 402 sq. km in 2012, while wetlands declined from 186 sq. km to 71 sq. km.
3. Between 2017 and 2018, about 48 km of drains were built under the smart cities mission. Wherever these new drains have been laid, there was little to no flooding,. Places like T Nagar flood all the time mostly because there are old drains, which the municipality is re looking to reconstruct.
4. In the 1920s, a large reservoir called the Long Tank was filled up to build a residential colony in erstwhile Madras. It is now known as Thyagaraya Nagar, or T Nagar, a symbol of many things right and wrong in Chennai. Located in the heart of the city, it has rows of homes and a shopping hub where stores range from jewellery and clothing showrooms to street vendors. It was T Nagar that was picked to implement the Chennai “smart city” project. But now, it is synonymous with another Chennai image: Roads that turn into rivers, boats for vehicles, and people stranded in homes at the first hint of heavy rainfall. When Chennai received over 900 mm excess rainfall in November, the roads of T Nagar, and indeed other parts of Chennai, were completely submerged. It was the second highest rainfall recorded in the city in November since 2015, when it suffered massive floods.

• Low flood limit: In T Nagar, particularly, there was another problem. Contractors engaged in improvement work for the Mambalam canal, where all the water from T Nagar drains, had dumped debris all along a length of 1.7km that blocked inlets. An indication that the drains in the city failed to work during this monsoon comes from the overburdening of another department, the Chennai Metropolitan Water Supply and Sewerage Board, which manages the city’s water supply and sewage network.

1. It usually pumps out 585 mld (million litres per daily) of sewage everyday, which reaches the treatment plants, but since heavy rains began, it is pumping out 920 mld. The additional load is because the corporation is using heavy motors to drain rainwater from waterlogged streets into the sewerage pipes.
2. According to municipality records, there are more than 30,000 interior roads and 471 bus route roads in Chennai that add up to close to 5,000km and 300km, respectively, but the city’s drainage network is present in just around 2,000km. Many of these drains were built at least three decades ago.
3. The old drains were constructed for a rainfall capacity of 20mm per hour, whereas the new drains are being built for 70mm per hour. The old drains are built of brick and mortar so they are dilapidated and break easily.
4. Many areas in the city were flooded although they had roads with drains on both sides, found a field audit by Chennai-based Arappor Iyakkam, an anti-corruption NGO.
5. Corruption in awarding tenders as well as improper design where the drain slope is higher than the height of the road or the gradient not matching the water body to which it is linked are primary problems.

• Transparency: After years of demands by activists and environmentalists, the municipal corporation began releasing maps on its website on where drains are located, a crucial information gap till now. Only with these maps will people be able to understand where the drains are present, how they are connected and in which direction they drain. These maps show, for instance, a ward in T Nagar where the height of a manhole on the street is at 5m but the drain is at a height of 5.7m, impeding the flow of water, said Raj Bhagat, senior manager of Geoanalytics at research organisation World Resources Institute India, who is studying these maps.

1. The city’s drainage network is designed only to carry average rainfall, and that it cannot handle excess rainfall. It gets clogged further with solid waste and drain slits that are not cleaned regularly.
2. There is also a clear lack of coordination between various civic departments ranging from the Chennai Metropolitan Development Authority, which approves building constructions, the public works department that is in charge of de-silting water bodies, the municipal corporation which builds drains and Metro Water that lays pipelines under roads for water and sewage connections.

• What next: Based on the November rains, municipal authorities have identified pockets where drainage capacity has to be augmented. Drain construction will now follow prescribed standards. The World Bank’s standard, for example, is for bigger drains to take 70mm of rainfall per hour. But if 100mm rainfall falls and that has to be taken care of, the stormwater drains will be bigger and the roads will become smaller.

1. The corporation was looking at ways to bolster drainage even if there is stagnant water, like permanent pumps. As the city expands, many drains’ capacity has to be increased. And it’s not just the case in Chennai. It is the same for Bengaluru or Mumbai.
2. Another peculiar issue that GCC engineers identified during these rains were so-called saucer-type streets, where the constant relaying of roads resulted in them being at a higher level than homes in densely populated areas.
3. Ironically, the city faced a drought-like situation a few months after the northeast monsoon, which can be addressed if the urban run-off is stored. Water from drains should be diverted to existing water bodies, particularly those located outside Chennai, which will help in mitigating flooding as well as recharging aquifers.

• Summary: The city will continue to flood, due to some geographical disadvantages of being a flat city close to sea level. And also since for more than 70 years, it has encroached on all the natural water bodies. The failure is collective, that of officials, real estate and civil society.
• EXAM QUESTIONS: (1) Taking Chennai as an example, explain the imperatives of flood management in Indian cities. (2) Explain technically what went wrong with the urban planning model of Chennai, in the 20th century.

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