Experts give contrasting recommendations for Malabar Hill reservoir
MUMBAI: After completing their assessments on the 135-year-old Malabar Hill reservoir, two teams of experts have submitted their final reports with contrasting recommendations. A final call on the future course of action will be taken by Brihanmumbai Municipal Corporation (BMC) commissioner and administrator Iqbal Singh Chahal.
The first group, comprising professors RS Jangid, V Jothiprakash and Dasaka Murty from IIT Bombay and BMC engineer C H Kandalkar have proposed an initial cleaning phase followed by a series of tests. These tests will play a decisive role in determining whether reconstruction or repairs are necessary for the reservoir located below the iconic Hanging Gardens.
In contrast, the second group consisting of IIT Bombay professor Alok Goyal, structural engineer VV Nori, and citizen representatives Alpa Sheth and architect Rahul Kadri have not expressed the need for reconstruction, stating that the projected lifespan of a reservoir is 15 years. They have, however, highlighted concerns about the comprehensiveness of visual inspections and recommended implementing a contingency standby plan to address potential issues that may arise.
What the first group says
In their final report on the reservoir, which supplies water to 18 lakh people, the Iit-bombay experts have recommended that the first step in safeguarding its integrity involves prioritising the cleaning of its tanks. The comprehensive cleaning process will encompass desilting, removal of root intrusions within tank walls, clearance of vegetation atop tanks, and eradication of rust from pipes and structural components. By initiating these immediate short-term measures, the experts have stated, the reservoir can mitigate potential risks and optimise its operational efficiency. The second step recommended is construction of an alternative tank.
A pivotal aspect of enhancing the reservoir’s capacity involves the construction of a new tank with a usable capacity of 52.44 million litres. The alternative tank will be strategically aligned with the existing hydraulic head of the reservoir to ensure uninterrupted water supply to citizens. The experts have suggested emptying interconnected tanks while constructing the alternative tank. Since the existing reservoir is more than 100 years old with structural and non-structural damage, it is suggested to carry out scientific structural and hydraulic audit of the tanks.
The final report further said, “A rigorous visual inspection of the tanks shall be carried out to assess the structural damage. In addition, the hydraulic conditional assessment of the pipes and valves of the reservoir tanks shall be performed. Non-destructive tests of the structural elements of the tanks shall be carried out. Load tests on the roof of the tanks shall be performed to assess the present load-carrying capacity as well as the inherent elasticity.”
The report has recommended that seismic safety of the existing tanks to current codal requirements should be assessed. Based on the outcome of all the abovementioned tests, the IIT-B experts will take a decision to either repair or reconstruct the existing tanks.
What second team says
While Goyal, Nori, Sheth and Kadri in their final report have ruled out reconstruction of the reservoir, they have stated that it is crucial to note that visual inspections may not provide a “comprehensive assessment of the reservoir’s condition”.
The report said, “For instance, areas of the floor submerged in knee-deep silt were inaccessible for inspection, raising concerns about potential water leakage through the floor. Given the reservoir’s role in supplying potable water to a large population, thermal imaging techniques should be employed to detect any hidden distress or weaknesses accurately. Additionally, preparing detailed as-built drawings with numbered grids is essential for recording construction details, defects, and other pertinent information.”
The structural condition of the reservoir is deemed satisfactory by these four experts as reported by HT last month eliminating the need for demolition or reconstruction in the next 10-15 years.
“No structural distress, such as cracks or deformation, was observed in any of the five compartments during the limited visual inspection. However, as a precautionary measure, the BMC should conduct annual inspections and prepare detailed reports. To prolong the reservoir’s lifespan, the BMC may consider repairing the roof, particularly sections exhibiting signs of corrosion in the reinforcing steel. These repairs should be conducted gradually, with special precautions to minimise disruption to water supply and ensure workers’ safety,” the final report elaborated. These four experts have recommended a contingency plan for a standby reservoir of suitable capacity that avoids uprooting old trees. They have also stated that the old building near the pump house needs to be replaced/retrofitted as decided by the BMC. “In the coming two-three years, the BMC should develop a maintenance scheme for the continuous use of the present reservoir,” the report concluded.