The Tallah tank
The first overhaul of the Tallah tank has to wait till the 105-year-old structure that towers over the city at 110ft gets a lift.
Engineers tasked with the repair have realised that it would be impossible to haul men and machinery from the ground to the world’s largest overhead reservoir in the absence of an elevator.
Mayor Sovan Chatterjee had last week cleared a Rs 70-lakh proposal for the installation of a lift at the reservoir. “We will soon invite a tender. The lift should be capable of carrying at least 15 people,” said Bibhas Kumar Maity, the director-general (water supply) in the Calcutta Municipal Corporation.
The 190-step inspection staircase, that reaches till the balcony of the tank at a height of 90ft, is too old and narrow for lugging up repair materials.
The tank, which supplies water to most of the city, is in need of an overhaul following decades of corrosion, worsened by air pollution.
Teams of engineers and scientists have examined the tank since the civic body ordered the repair last year. The lifespan of a steel structure is 50-70 years but the experts feel the Tallah tank can serve the city another 50 years if it is repaired properly.
The full tank contains nine million gallons of treated water, enough for the city proper for a day. The 16ft deep and seven bigha in area Tallah tank is divided into four compartments. There is a valve, 12 square feet in size, in each compartment so that parts of the tank can be repaired without drying up the entire tank and thus disrupting the city’s water supply.
Engineers have described the tank’s structural integrity as excellent. Over more than a century, it has sprung only a handful of leaks that could be repaired quickly, without disrupting the water supply. The tank had last undergone minor repairs in 2009 on its centenary year.
The lift needs to be installed immediately, explained Maity, because the first step of the repairs is to replace the valves that are not functioning properly. Replacement of valves will involve expenditure to the tune of about Rs 60-70 lakh.
“I will request the municipal affairs minister Firhad Hakim to allot some fund for the repair of the Tallah tank. Even if the overhaul is later funded under the JNNURM scheme, the state government would have to shell out 35 per cent of the proposed expenditure of Rs 77 crore. The amount we spend now could become a part of the state government’s contribution later,” said mayor Sovan Chatterjee.
“The valves are to be tailor-made in a Howrah firm. Instead of using galvanised steel we have decided to stainless steel”, said the director general Maity.
Clayton, Son and Co of Leeds had been the contractor for the tank commissioned in August 1907 and completed two years later. The material used in building the structure included special anti-corrosive plates shipped to Calcutta from the UK. Sir Edward Baker, Lt Governor of undivided Bengal under the British, had inaugurated the tank on November 18, 1909, in the presence of A. Earle Esq, an officer of the erstwhile Indian Civil Service who was then the chairman of the corporation.
The tank had been targeted by the enemy not only during World War II but also the two subsequent wars with Pakistan. On one occasion, artificial grass cover was put on the roof of the tank to make it look like a playground to the pilots of enemy aircraft.