நவம்பர் 24 முதல் நவம்பர் 30 குறைந்த மழை பெய்தபோது அதற்கு உரிய அளவு நீர் திறந்து விடப்பட்டது, பின்பு அதிக அளவிலான மழை பெய்ய நேரிடும் என்று வானிலை அறிக்கை தெளிவாக குறிப்பிட்ட போதும் அதை கவனத்தில் கொள்ளாது , செம்பரப்பாக்கத்தில் ஏற்கனவே அதிக அளவு தண்ணீரை (29,000 கன அடி) தேக்கி வைத்திருந்தனர், இதுதான் பின்பு செம்பரப்பாக்கம் அளவுக்கு அதிகமான தண்ணீரை கொண்டிருந்தது. அதை வெடித்து விடாமல் இருக்க சென்னை நகரை மூழ்கடிக்க வேறு வழி இல்லாமல் திறந்து விட்டனர். டிசம்பர் 1 ம் தேதி தேக்கத்தில் இருந்து .பின்பு 31,000 கன அடி தண்ணீர்... நீர் மேலாண்மை அதிகாரிகளின் செயலற்ற தன்மை தான் இந்த மொத்த அழிவுக்கும் காரணம் என்றால் மிகையாகாது. இதில் யார் குற்றவாளிகள்? பதில் எல்லோருக்கும் தெரிந்ததுதான் செயலற்ற அரசு ? வெறும் பிரசாரங்களை நம்பி அம்மா துதி பாடும் கலாசாரம்
The Hindu Chembarambakkam reservoir near Chennai on November 24, 2015. The Tamil Nadu government, it is learnt, is considering a move to reduce the set storage level in the reservoir. Photo: B. Jothi Ramalingam Official data from the Metro Water for the last 20 days suggest that the high precipitation and reservoir outflows on November 16 and December 1 respectively were primarily responsible for swelling the rivers.
The Hindu Chembarambakkam reservoir near Chennai on November 24, 2015. The Tamil Nadu government, it is learnt, is considering a move to reduce the set storage level in the reservoir. Photo: B. Jothi Ramalingam Official data from the Metro Water for the last 20 days suggest that the high precipitation and reservoir outflows on November 16 and December 1 respectively were primarily responsible for swelling the rivers.
As the flood water recedes in Chennai, serious questions are being
raised about reservoir management in the city. Much of the flooding and
subsequent waterlogging was a consequence of the outflows from major
reservoirs into swollen rivers and into the city following heavy rains.
The release of waters from the Chembarambakkam reservoir in particular
has received much attention.
Official data from the Chennai Metropolitan Water Supply and Sewerage
Board for the last 20 days suggest that the high precipitation and
reservoir outflows on November 16 and December 1 respectively were
primarily responsible for swelling the rivers. On November 17, 18,000
cusecs was released from the reservoir in Chembarambakkam.
However, from November 24 to November 30, when the city experienced
minimal rainfall, the outflows from the reservoir were limited, even as
the storage levels were maintained at almost 85-88% of the total
capacity of 3645 mcft. When heavy rains to the tune of nearly 48 cm fell
on the reservoir on December 1, 29,000 cusecs was released over 12
hours.
Experts raise the question as to why storage was set at such high
levels. Professor Janakarajan of the Madras Institute of Development
Studies also argues that the outflow management from the reservoir was
improper. If storage levels were set at less than 75% and sluice gates
were opened to allow for outflow from the reservoir in a way that it
exceeded the inflows in the last week of November, the blow in the form
of the high outflow on December 1 could have been softened, he asserts.
Officials formerly with the PWD say if the risk of releasing a
particular volume prior to the heavy rainfall day had been taken, there
would have been lesser floods in places like K.K.Nagar.
It is reliably learnt that the government is considering a move to
further reduce the set storage level in the reservoir. Now the level is
at two feet below the brim, and discussions are under way to change this
to four feet.
Reservoir managers ignored warnings of heavy downpour
On November 17, 18,000 cusecs was released from the reservoir in
Chembarambakkam, causing massive flooding in areas such as Mudichur,
West Tambaram, and Manapakkam among others.
However, from November 24 to November 30, when the city experienced
minimal rainfall, the outflows from the reservoir were limited.
Officials in the Public Works Department asserted that the inflow of
31,000 cusecs (26,000 before 6:00 p.m. owing to the high rainfall)
resulted in the high outflow of 29,000 cusecs from the reservoir on
December 1 and that they couldn’t hold the reservoir beyond a point.
Former officials of the department, however, said if they had taken the
risk of releasing a particular volume from the reservoir prior to the
heavy rainfall day, water received from some tanks like Porur and
Mudichur could have been stored.
The decision to conservatively hold storage despite early warnings from
various meteorological agencies about heavy rainfall in the offing in
late November and early December, clearly exacerbated the disaster that
followed.
This was in addition to the structural issues in Chennai with
floodplains and drainage systems being constrained by unplanned
urbanisation.
Storage levels in Chembarambakkam and other reservoirs are decided based
on drinking water requirements for the city and other areas in summer.
That the authorities should have hedged on the side of flood management
over concerns on drinking water is now evident in hindsight.
(With inputs from K. Lakshmi and Ramya Kannan)
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