Five underground silos to tackle Mumbai’s flooding woes
The Brihanmumbai Municipal Corporation (BMC) is constructing five underground water silos at vulnerable spots in the island city to mitigate the flooding that usually happens during the monsoon
The Brihanmumbai Municipal Corporation (BMC) is constructing five underground water silos at vulnerable spots in the island city to mitigate the flooding that usually happens during the monsoon. Two chronic waterlogging spots have been identified for the pilot project currently under construction: One at Hindmata Junction in Dadar (East) and the other at Gandhi Market near Matunga, both on Babasaheb Ambedkar (BA) road. Both spots get inundated up to over two feet of water during every heavy spell of rain. The road is one of the main connectors of the eastern suburbs to the island city.
According to officials, of the five silos, two will be at Hindmata (one under Hindmata flyover, and one under the northbound carriage of BA road). Water from these silos will be channelled from underground pipes to two other bigger underground silos — one at Pramod Mahajan Udyan on Senapati Bapat Road, near Elphinstone station, and one under St Xavier’s ground in Parel.
From these two bigger silos, water will either flow into the sea through underground pipes, or used for non-potable purposes. In the long run, BMC plans to set up water-filling points at the two bigger silos at Elphinstone and Parel, for refilling water tankers for non-potable purposes.
One more underground silo is being constructed at Gandhi Market under the south-bound carriageway on BA road, which is yet another low-lying area. Three dewatering pumps will pump the surface water into this tank, from where underground pipes will discharge it at the railway culvert near Matunga.
P Velarasu, additional municipal commissioner, in-charge of BMC’s stormwater drains (SWD) department, said, “Since this is the first time we are trying the concept in the city, we have selected these two waterlogging spots. Depending on the success with this project, construction of similar silos in other waterlogging-prone spots will begin after monsoon 2021.” Other similar spots identified by the civic body are Postal Colony, Chembur; Oberoi Mall in Goregaon; and the area around Mahalaxmi in South Mumbai.
While the silos at Hindamata with a capacity to hold 1,000 cubic metres of water or 1,000,000 litres, each, and the silo at Gandhi Market with the capacity to hold 1,200 cubic metres of water, will be completed before this monsoon, the two silos at Parel and Elphinstone will be completed by monsoon 2022. Velarasu said, “The two silos at Parel and Elphinstone, where work is going on right now, will be completed and used for monsoon 2021. But we have dug up only a portion of both these open spaces. There is more scope to create another silo at each of these open spaces. This will be phase two of the project, taken up after monsoon 2021. We didn’t want to dig up the entire open space in one go.” The total water holding capacity of the tanks at Parel and Elphinstone alone is 50,000 cubic metres, once completed. The first phase, to be completed before this monsoon, will have a total water-holding capacity of 16,000-17,000 cubic metres, Velarasu said.
The cost of the first phase is Rs60 crore, while the cost of the entire project is Rs130 crore.
Velarasu added, “The project has been designed by the SWD department of BMC) with a local consultant. A local contractor is constructing the silos. SWD department is taking remarks from the civic bridges department, for the silo under the Hindmata flyover.” BMC has maintained it is safe in terms of the structural stability of the flyover, to have silos underneath it, as they are nowhere near the pillars of the flyover.
Manoj Baraskar, independent structural auditor, said, “Foundations of flyovers are Pile foundations and go pretty deep. As long as sufficient distant is maintained between the pillars and the tank, it should cause no problem for the structural integrity of the flyover. As far as structural integrity of the road is concerned (near Gandhi Market) we need to regular inspection chambers. Beams of carriageways are likely to be in contact with water accumulated on the surface of the road, so steal in the beams may rust, and need regular inspection. Otherwise there should be no problem at all, and is a good idea.”
The idea to construct underground water tanks to hold monsoon flood water was first mooted for Mumbai in early 2019, along the lines of underground water tanks constructed in Tokyo in Japan, to mitigate flooding. BMC was also in the process of signing a memorandum of understanding (MOU) with Japan International Cooperation Agency (JICA) for the project. Bids were floated in 2019 for constructing underground water silos in Mulund and Bhandup, so as to divert excess rainwater from Mithi river.