When Chennai went under

Print edition : December 25, 2015

Water being released from the Chembarambakkam lake after it reached full capacity, on November 24. Photo: B. Jothi Ramalingam

THE rain in November and on December 1 and 2 cut such a deadly swathe of destruction across the coastal districts that Chief Minister Jayalalithaa called it “a mammoth adversity”. Prime Minister Narendra Modi flew to the naval air station INS Rajali at Arakkonam, about 60 kilometres from Chennai on December 3, and inspected the destruction caused by the floods from a helicopter. Jayalalithaa separately saw the destruction from a helicopter the same day. When the two met at INS Adyar in Chennai, Jayalalithaa told Narendra Modi that it was an “unprecedented magnitude of calamity” that had struck the coastal districts of Chennai, Cuddalore, Kancheepuram and Tiruvallur.

What worsened this situation was the release of water from reservoirs in Andhra Pradesh, which flows into the waterbodies and drainage systems in the northern districts [Chennai, Kancheepuram and Tiruvallur] of Tamil Nadu, Jayalalithaa told Modi. The major drainage systems for all this water is through Chennai by the Adyar, the Cooum and the Kosasthalaiyar rivers. Heavy surplus outflow from the four major reservoirs of Chembarambakkam, Cholavaram, Poondi and the Red Hills, which form the catchment areas for Chennai, further inundated the low-lying areas in Chennai. “There has been extensive damage to infrastructure including roads, bridges, water supply and electricity systems,” she told Modi.

After two weather systems pounded Chennai, Cuddalore, Kancheepuram and Tiruvallur districts and the Union Territory of Puducherry with non-stop rain from November 8 to 16, two more weather systems merged on November 30 to pummel these districts again with rain on November 30, December 1 and December 2, causing all-round destruction. The first trough of low pressure formed this time near the south Andaman Sea on November 25 and the next trough of low pressure began forming on November 29 off Sri Lanka. Both the systems merged and became one intense weather system in south-west Bay of Bengal on November 30.

During the 24 hours ending 8.30 a.m. on December 2, this combined system unleashed “extremely heavy rainfall” of 49 cm at Tambaram in Kancheepuram district, 47 cm at Chembarambakkam in Tiruvallur district, 42 cm at Marakkanam in Tiruvallur district, 39 cm each in Chengalpattu (Kancheepuram district) and Ponneri (Tiruvallur district), and 38 cm each in Sriperumbudur and Cheyyur (both in Kancheepuram district), 35 cm at Chennai airport , and 34 cm in Mamallapuram, Poonamallee, Red Hills and Chennai city. Taramani, the information technology hub of Chennai, north Chennai, Cholavaram and Thamaraipakkam (both in Tiruvallur district), and Madurantakam received between 28 cm and 30 cm.

The resultant floods, brought on also by the PWD discharging surplus waters from the Chembarambakkam reservoir into the Adyar river, were unprecedented, submerging hundreds of houses in Varadarajapuram, CTO Colony, Bharathi Nagar, Jothi Nagar, Thirumudivakkam and Harita Enclave, all near West Tambaram. The water level in most of these settlements rose to the first floor-level. Velachery was flooded again. In Tiruvallur district, Ambattur, Ponneri, Maduravoyal, Tiruvottriyur and Madhavaram areas were marooned.

The rainfall was so heavy on December 1 that the entire inflow of 20,000 cubic feet per second into the Chembarambakkam reservoir was let into the Adyar river, flowing through Chennai. Chennai District Collector E. Sundaravalli issued a flood alert, asking people living on the banks of the Adyar river to move to safer places. According to official figures, about 44,000 cubic feet of water per second flowed into the Bay of Bengal. In other words, the State had made no plans to store the surplus waters of the Adyar. The river overflowed its banks, leading to a couple of hundreds of the Tamil Nadu Slum Board tenements being marooned in Kotturpuram. Water, rising to a height of several feet, barrelled through Madipakkam, Adambakkam, Nanganallur, Velachery, Medavakkam, Madambakkam and Selaiyur, where lakhs of people live. If the Poondi reservoir received 29,922 cubic feet a second, PWD officials decanted 30,200 cubic feet a second into the Kosasthalaiyar. Water was also discharged from the Krishnapuram reservoir into the Kosasthalaiyar. Andhra Pradesh released water from the Pichatur dam into the Araniyar river. This led to breaches in 15 lakes in Tiruvallur district. All these releases combined to maul Chennai and its suburbs on December 1, 2 and 3.

In a statement on December 1, Jayalalithaa said the combined storage in the reservoirs of Chembarambakkam, Cholavaram, Poondi and Red Hills, situated in Kancheepuram and Tiruvallur districts, stood at 83.8 per cent. (These reservoirs supply water to Chennai.) Surplus water was being let out to safeguard the reservoirs. Besides, surplus water was being discharged from 45 big reservoirs out of 89 big reservoirs under PWD control in the State. Out of 14,098 lakes maintained by the PWD, 6,971 lakes were full, the Chief Minister said.

The lakes which were full in Kancheepuram and Tiruvallur districts included those at Madurantakam, Chengalpattu, Nallambakkam near Vandalur, Kadambadi, near Mamallapuram, Manimangalam, Irumpuliyur, Mannivakkam, Perungalathur, Selaiyur, and Chitalapakkam. Water from the Madurantakam lake flooded the Kallaru river and it reached the Kesavaram anaicut via Takkolam, near Arakkonam. This water, too, was let into the Kosasthalaiyar river. So, villages such as Manimangalam, Sivapuram and Narasingapuram were flooded. Flood water mangled a big bridge at Muthukondapuram, across the Kosasthalaiyar river in Tiruvallur district. This led to Muthukondapuram, Cauvery Rajapuram and Koorma Vilasapuram being cut off from other areas. In the interior Krishnagiri district, a big lake at Uthangarai Theerthagiri Valasai breached and the waters submerged Krishnangiri-Tiruvannamalai Road for many hundred metres.

People rubbed their eyes in disbelief when even the perennially bone-dry Palar river went into spate after two decades and its waters flowed over a bridge at Thenambakkam, near Kancheepuram.

T.S. Subramanian

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