Explained: Why is Chennai under water?
..Thank you Indian Express
Unusually heavy rain has exposed the city’s broken urban planning, revealed its stolen natural waterways, and exposed its tolerance of illegal construction.
The Indian Express article "Why is Chennai under water" is interesting to read. It has tried to give some scientific reasoning for the deluge
Chennai floods: Almost the whole of Chennai
city (map on the right) is flooded. The low-lying area between Velachery and
Sholinganalur is especially badly affected.
The catastrophic
flooding in Chennai is the result of the heaviest rain in several decades,
which forced authorities to release a massive 30,000 cusecs from the
Chembarambakkam reservoir into the Adyar river over two days, causing it to
flood its banks and submerge neighbourhoods on both sides. It did not help that
the Adyar’s stream is not very deep or wide, and its banks have been heavily
encroached upon over the years.
Similar flooding
triggers were in action at Poondi and Puzhal reservoirs, and the Cooum river
that winds its way through the city.
While Chief Minister J Jayalalithaa said,
during the earlier phase of heavy rain last month, that damage during the
monsoon was “inevitable”, the fact remains that the mindless development of
Chennai over the last two decades — the filling up of lowlands and choking of
stormwater drains and other exits for water — has played a major part in the
escalation of the crisis. On the evidence of what is currently unfolding in
Chennai, city authorities would appear to have the abandoned the concept of
stormwater drains — the fundamental instrument of flood-fighting — altogether
over the years. Experts at Chennai Metropolitan Development Authority (CMDA)
pointed out that the key parameter of rain intensity measure — which ought to
be at least 1 inch per hour — has been ignored while planning multicrore
drainage projects. -
While Chief Minister J Jayalalithaa said,
during the earlier phase of heavy rain last month, that damage during the
monsoon was “inevitable”, the fact remains that the mindless development of
Chennai over the last two decades — the filling up of lowlands and choking of
stormwater drains and other exits for water — has played a major part in the
escalation of the crisis. On the evidence of what is currently unfolding in
Chennai, city authorities would appear to have the abandoned the concept of
stormwater drains — the fundamental instrument of flood-fighting — altogether
over the years. Experts at Chennai Metropolitan Development Authority (CMDA)
pointed out that the key parameter of rain intensity measure — which ought to
be at least 1 inch per hour — has been ignored while planning multicrore
drainage projects. -
While stormwater drains
are supposed to be planned on the basis of detailed topographical data, their
linkage with water bodies, construction along their course, and the design of
roads have rarely been seen as part of a whole. As a result, drains constructed
over the past decade have repeatedly proved inefficacious — and showed up
problems of poor urban planning nearly every monsoon.
Planning officials said
contractors are rarely briefed on the topography or the flood character of
sites. A top civic official said even the water log data of the last 10 years
are often not considered as officials “hurry to complete works” before the
allocated funds lapse. A former CMDA planner said mandatory standards based on
data on sea level and water flows are not followed, resulting in situations
like Koyambedu, the neighbourhood that saw expensive stormwater drain projects,
but has still gone under.
Across Chennai, illegal
construction has been making neighbourhoods unrecognisable — what may have been
a tank, lake, canal or river 20 years ago, is today the site of multistorey
residential and industrial structures. There are over 1.5 lakh illegal
structures in the city, according to a report submitted by CMDA to the Madras
High Court. Despite several HC orders ordering their demolition, the buildings
stand — often after appeals to the Supreme Court, and due to the inefficiency
of the CMDA’s legal wing. Hundreds of stay orders against demolition orders
have been obtained by both business houses and individuals.
As the illegal
structures sprouted in the city and suburbs, over 300 water bodies disappeared.
The irreversible destruction of the city’s natural water paths can be seen in
the flooding in Mudichur, Velachery, and several other areas that have come up
on wetlands or river basins.
After a major flood in
2005, Chennai had commissioned a project to prepare laser terrain maps,
scanning the entire city from a helicopter, instead of depending on topographic
maps. But this project remains unimplemented — just like the early warning
system that was prepared by the Department of Remote Sensing at Anna University
to understand the run-off pattern of rainwater.
El Niño to blame, other factors too
An exceptionally strong
El Niño, along with a rare “coincidence of various factors”, has resulted in
the heavy rain in Tamil Nadu this northeast monsoon season, officials at India
Meteorological Department (IMD) said.
The El Niño phenomenon —
an unusual warming of surface waters in the equatorial Pacific Ocean — is
“intensely strong” at present, Additional Director-General of Meteorology
(Research) at IMD, B Mukhopadhyay, said. “In a strong El Niño year like the
present one, the summer (southwest) monsoon is adversely affected, while the
northeast monsoon or the winter monsoon is favourably affected.”
However, Mukhopadhyay
added, “the present very heavy rain is exceptional and not normal.”
The 2015-16 El Niño
could turn out to be the strongest ever recorded — in fact, by one measure, it
has already reached that milestone. In mid-November, the sea surface
temperature in the central tropical Pacific was 3 degrees Celsius warmer than
normal, the largest positive deviation in recorded history. To officially beat
the 1997-98 El Niño as history’s worst, sea surface temperatures must stay at
these levels for three months.
Other than the El Niño,
a strong upper air divergence and high moisture content at lower levels, have
contributed to the rain, Mukhopadhyay said. “These two factors, along with
formation of low pressure systems have resulted in the heavy rainfall,” he
said.
— PARTHA SARATHI BISWAS
— PARTHA SARATHI BISWAS
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