Challenges of retrofitting the world’s biggest elevated water reservoir: Tala tank of Calcutta

The Tala water tank in Kolkata, India, is the largest water tank in the world with an active capacity of 41 Ml. The tank is an integral part of the first organised water supply system of the city since its commissioning in 1911. It was introduced to relieve the upstream supply pumps of stresses caused by fluctuating downstream demand. The tank structure is robust with an overall dimension of 97 m square and total 6 m height. The steel frame staging is supported on multiple types of trussed grouped columns with only one inlet-cum-delivery pipe. The tank was constructed in steel riveted joints and staged over 28 m from the ground level. The framed staging comprises 295 columns with a combined length of steel members measuring over 80 km. There are inclined rafters securing its walls by connecting to its floor. The bottom plate is made of flat steel riveted sheets of 6 m square panels. It has four compartments with an isolation facility. Kolkata Municipal Corporation has taken up a project to rehabilitate and retrofit this unique asset. This paper identifies the extremely technical and logistical challenges faced in the refurbishment and retrofitting of this engineering marvel.