MIDDAY EXPLAINS: Why is Gargai dam important to Mumbai?

The Gargai dam will be located neaed the Modak Sagar dam. File Pic

The new Gargai dam, planned by the BMC, is located near the Modak Sagar dam, which has received the highest rainfall among major dams over the last five years, ensuring that the Gargai dam will also benefit from substantial rainfall. A 2-km tunnel could connect the new dam with Modak Sagar, enabling BMC to link the Gargai supply to Modak Sagar's existing infrastructure, which is already operational to supply water to Mumbai. The proposed Gargai project is situated in Palghar, 110 km north of Mumbai.

With an estimated cost of Rs 5,000 crore and a construction period of five years, the BMC has high expectations from the dam as the city's water demand continues to outpace supply. Saurabh Deshpande, an assistant engineer from the Water Supply Department, said, "The Gargai dam is near Modak Sagar, which generally receives the highest rainfall. This will ensure that the new dam also gets good rainfall."

Over the last four years, Modak Sagar has received more than 3,300 mm of rainfall, the highest among the five major dams that supply water to the city. While lakes like Tulsi and Vihar receive more rainfall than Modak Sagar, they provide only 2 per cent of the total water supply, and there is no potential for another lake in Mumbai.

The BMC has yet to receive forest and wildlife protection approvals for the proposed dam, as it is located within the Tansa Wildlife Sanctuary and involves the removal of over 400,000 trees. A second tree census is going on and the BMC will plan compensatory plantations based on the findings.

While the Gargai dam will help alleviate water shortages, it won't fully resolve the city's water cut issues. Currently, Mumbai requires 4,463 MLD of water, but only 3,950 MLD is supplied. The Gargai dam, with a capacity of 440 MLD, can help reduce the supply-demand gap, but even if construction proceeds smoothly, the dam will take at least five years to become operational, by which time demand will have further increased.

"Gargai will act as a cushion, but the city will need additional water sources for future needs. In case of drought, there won't be any option other than water cuts," said a BMC official. The BMC is also considering building a water weir between the Middle Vaitarna and Modak Sagar reservoirs. Both reservoirs are unable to store all the rainfall they receive, often requiring the release of excess water.

"The idea of constructing a water weir to store more water is under preliminary study," said Purushottam Malavade, chief engineer of the BMC's hydraulic department. "The amount of water saved, as well as the site and cost, is still being evaluated," added an official from the Water Supply Department.