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Wednesday, June 16, 2021

‘De-silting target during Mumbai’s nullah cleaning increased by 95% this year, will help hold more rainwater’

The BMC is preparing for the upcoming monsoon. P VELRASU, additional municipal commissioner (projects), speaks to The Indian Express on steps it has taken to ensure that parts of the city do not get submerged after a heavy downpour

Written by Laxman Singh |
Updated: May 30, 2021 8:13:03 pm
Mumbai, Mumbai monsoonIn Mumbai, monsoon arrives in the first week of June and the BMC aims to finish the pre-monsoon infrastructure work by May 31. For roads and nullah works, the deadline is June 7. (Express Photo by Amit Chakravarty/File)

The BMC is preparing for the upcoming monsoon. P VELRASU, additional municipal commissioner (projects), speaks to The Indian Express on steps it has taken to ensure that parts of the city do not get submerged after a heavy downpour.

What is the overall progress of pre-monsoon works? How are we going to ensure that flooding does not take place?

We have, for the first time, increased the target for silt to be removed during nullah cleaning. This will help in holding more rainwater in these major nullahs. For the Mithi river, which is the cause of flooding in many parts of the suburbs, we have doubled the quantity of silt to be removed. This year’s target is 2.74 lakh metric tonnes, an increase of 95 per cent as compared to last year. For major nullahs, the desilting quantity has been increased to 4.16 lakh metric tonnes as compared to previous year’s 3.12 metric tonnes. For Mithi river and major nullahs, 89 per cent pre-monsoon silt has been removed till May 28, and that too against the increased quantity target. So far, about 4.72 lakh metric tonnes of silt has been moved from major nullahs and Mithi with the help of 28,400 vehicle trips. Overall, we have already exceeded the nullah cleaning work target compared to last year. There are 405 flooding spots, of which 125 will be tackled this year. So far, 54 works have been completed and rest are in progress.

What is the status of the construction of the two pumping stations at Mogra Nullah and Mahul?

For Mogra pumping station (Andheri West), we have finalised the agency and, soon, a proposal will be tabled before the standing committee for final approval. We are hopeful of getting the work approved before monsoon. Project will take three years to complete and, since we are constructing the pumping station over the nullah, no land acquisition will be required. For Mahul, we are still awaiting a nod from the salt commissioner. In the last many years, multiple letters have been written to the department of industry and internal trade (DPIIT) but there has been no response. We also checked the feasibility of constructing the pumping station over the nullah like in Mogra, but it will not work out. If nothing happens (permission from DPIIT), then we will study if there is another way to do it, such as a change of location.

At what stage is the city’s first underground water tank project to tackle flooding, and are we planning any more such tanks?

This year, we are doing sump-based pumping systems at two locations, Hindmata and Gandhi Market. Both are known flooding spots. At Gandhi Market, we don’t have underground tanks but have created sumps, and four motors that can push 16,000 cubic metres of water per hour will be stationed. We are laying a 1,200 mm pipeline through which water will be pushed and then discharged into the nearest Bharat Nagar railway culvert. Apart from that, we will have three flood control gates in three nullahs connected to Gandhi Market. It will be similar to the one we did in Kalanagar, Bandra East, last year, which was successful. About 90 per cent work has been completed and, by the first week of June, it will be made operational.

The Hindmata flood management system is much more advanced than Gandhi Market’s. It will have two massive water holding tanks: one at Pramod Mahajan Udyan, Dadar West, with a capacity of 60,000 cubic metre and St Xavier Ground, Parel, with a capacity of holding 40,000 cubic metre. But this monsoon, we are only doing it one-third only. In phase one, roughly 30,000 cubic metre holding capacity can be created before the monsoon. That means, this tank can hold water, during a spell of heavy rain of 70 mm to 80 mm for an hour and a half. But our ultimate aim is to create a capacity of 1 lakh cubic metre that can hold rainwater for four hours. So, the second phase of Hindmata flood management system will be completely ready before the next monsoon.

Hindmata is a pilot project to see how efficiently it works. If this technology is successful, then we can identify more such spots where there is frequent flooding. To create such a complex flood management system, we have to see a lot of aspects. We have to go for energy-based storm water drains rather than depending on gravity.

Even though the civic body takes steps to mitigate flooding, why do new flooding spots come up every year?

This is an old city where most drains are designed for 25 mm rain per hour. Rainfall pattern keeps changing, and the city is getting higher rainfall frequently. Over the past year, the average rainfall has crossed 200 mm thrice in just a few hours, especially in South Mumbai. Now, this drain with 25 mm capacity cannot handle that. Development works such as Metro, coastal road are also on. All have planned with new connections (drains). For coastal road, if you see, a massive channel has been created near Hindu Gymkhana. We have also put cameras to check clogging and internal damage to drains. All clogging has been identified and cleared. Near Babulnath Temple, there was no storm water drain network and now, this year, we are constructing a new drain as the entire area was flooded.

We have conducted a meeting with MMRDA (Mumbai Metropolitan Region Development Authority), Metro and coastal road, and requested for an increase of the 30 mm outfall to 60 mm. But that is a long-term plan and will take time.

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