View source for Floods in Chennai

==November==
[https://indianexpress.com/article/explained/explained-why-chennai-received-heaviest-rainfall-since-2015-7610977/  Arun Janardhanan, Nov 9, 2021: ''The Indian Express'']

The heavy rain that lashed Chennai led to flooding in at least 40 busy residential and commercial neighbourhoods in the city. The overnight rain, which was reportedly the heaviest since 2015, was part of a formation of a low pressure over the Bay of Bengal.

''' Overnight Impact '''

The rains caused flooding in several city neighbourhoods including T Nagar, Vyasarpadi, Adyar, Velachery, Royapettah and Mylapore.
Jawaharlal Nehru Nagar, Madhavram, Tondiarpet High Road, Northern Trunk Road, Royapuram, Teynampet, Khader Nawaz Khan Road, interior areas of Velachery, several stretches of Sholinganallur in the city suburb were among those areas reported flooding or water inundation early morning on Sunday.

According to a government release, 500 Cusecs of water from Puzhal reservoir will be released around 11 am and the local authorities issued alerts to people living in low-lying habitations on the banks of the surplus canal. The government has also announced that the water from the Chembarambakkam reservoir will be released.

''' Heaviest rain after 2015 '''

Data from two rain recorders – Nungambakkam in Chennai city and Meenambakkam in the city suburb – shows that the city and suburbs received 21.5 cm and 11.3 cm rains respectively.

In one of the heaviest episodes of rain witnessed in 2015, on November 15 to 16, Chennai recorded 24.6 cm rainfall in 24 hours, which was breaking the previous record of 14.2 cm from November 2005.

But the maximum rainfall recorded in 24 hours time may be from November 1976, when Chennai had recieved 45.2cm of rainfall. Another record rainfall, in two days, was registered in 1985 – which was November 12 (25cm) and November 13 (33cm). The 14.2 cm rainfall in 2005 was the next.

''' North East monsoon bring rains to Chennai '''

Chennai’s monsoon is largely about the Northeast Monsoon, rains during October to December, with easterly winds starting from mid-October, precisely the usual onset that begins between October 10 to 20. It is the Northeast Monsoon, also known as the ‘primary monsoon of Tamil Nadu,’ that brings sufficient rains to the state when all other states depend on the South West monsoon for rains that sets in from May, June and July. The South West monsoon, after a prolonged summer, helps Tamil Nadu to maintain the ground water tables, it is the North East monsoon that elevates the table.

Tamil Nadu’s coastal districts get 60% of the annual rainfall and the interior districts get about 40-50% of the annual rainfall from the North East monsoon.

''' Low pressure formation ''' 

The meteorological department predicts a likely formation of low pressure over the Bay of Bengal moving towards the northern Tamil Nadu coast with moderate rain in the coming days ahead of the formation of the low pressure.

“An upper air cyclonic circulation lies over southeast Bay of Bengal and adjoining equatorial Indian Ocean extending up to 3.1 km above mean sea level. Under its influence, a low-pressure area is likely to form over southeast Bay of Bengal and neighbourhood around November 9. It is likely to become more marked during subsequent 48 hours and move towards the north Tamil Nadu coast,” said a statement from the Regional Specialised Meteorological Centre – Tropical Cyclones. It also predicts chances of squally winds of 40 kmph to 50 kmph gusting to 60 kmph might prevail over the sea from November 9, and along and off the Tamil Nadu coast and south Andhra Pradesh coast from November 11 and 12.

A heavy rainfall warning also has been issued for November 10 as a thunderstorm with heavy to very heavy rain is likely to occur at isolated places over Chennai, Tiruvallur, Kancheepuram, Chengalpet, Villupuram, Cuddalore, Mayiladuthurai, Nagapattinam, Tiruvarur, Thanjavur and Pudukottai districts of TN, Puducherry and Karaikal.




===As on Nov 11===
[https://timesofindia.indiatimes.com/city/chennai/chennai-shows-how-not-to-manage-monsoon/articleshow/87657467.cms  Komal Gautham, Nov 12, 2021: ''The Times of India'']

[[File: Rainfall from October 1 to November 11, 2021.jpg|Rainfall from October 1 to November 11, 2021 <br/> From: [https://timesofindia.indiatimes.com/city/chennai/chennai-shows-how-not-to-manage-monsoon/articleshow/87657467.cms  Komal Gautham, Nov 12, 2021: ''The Times of India'']|frame|500px]]

''' Chennai shows how not to manage monsoon '''

CHENNAI: Soon after the December 2015 floods, the blame for the devastation caused was placed on encroachments in water bodies, blocks in major canals, lack of storm water drains in many places and the absence of data on critical areas.

Nearly six years later, after heavy rain has caused almost similar destruction, the question is whether Greater Chennai Corporation was better prepared to deal with the crisis. Experts say the city administration did better, but residents, who had to bear the brunt of nature’s fury, feel otherwise.

They say the corporation built drains over 900km since 2018, but when it mattered, some were blocked and some connected to those on elevated roads such as near Inner Ring Road in North Chennai didn’t work. In the central region, the dumping of debris for the Mambalam canal improvement work just ahead of the monsoon led to a disaster, while in the south lakes filled during the southwest monsoon overflowed, flooding homes and entire localities.

Since May, a senior corporation official told TOI, a lot of garbage and debris was removed from road sides and slum. The civic body de-silted 900km of the 2,500km of drains, de-silted 30,000 catchpits. New drains were constructed in Velachery, Nandanam and other areas and a response system was also put in place. This, he claimed, helped keep water away from major most bus route roads.

KK Nagar, pockets of Alwarpet, Velachery, Ashok Nagar, Kilpauk, Subramania Puram and Aziz Nagar in Kodambakkam, Pulianthope, Broadway, Choolai and Madipakkam were all declared high risk in 2019 and details of how the drains didn’t have enough carrying capacity was submitted to the civic body by experts. Yet, it was in these areas that drain work didn’t take place in the last five years. “We had submitted the proposals. It will be completed in a year,” said an official.

Another reason for the flooding, officials said, was that the November 7 rain had already inundated major areas. This week’s rain only caused more havoc.

M V Ramanamoorthy, director of National Centre for Coastal Research, said there was a lot of improvement in the system. “In 2015, we were not prepared for heavy rain. Earlier, we used to have distributed rainfall over two months. Now, the entire rainfall is received within a few days. It is difficult for any city to accommodate this much water. The administration has done a lot by clearing many bottlenecks. However, a comprehensive plan for the entire city is needed as in the future more such events are likely to take place often,” he said.

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