Curious case of Mumbai’s Mithi River leaves BMC concerned

On multiple occasions this year, the city has witnessed a delay in the time taken for logged water to recede from the streets or nullahs, following heavy rain in some flooding spots

On multiple occasions this year, the city has witnessed a delay in the time taken for logged water to recede from the streets or nullahs, following heavy rain in some flooding spots. The Brihanmumbai Municipal Corporation (BMC) has also noticed that the Mithi River took longer to drain its water into the sea in the past two or three instances after a downpour. This has caused some storm water drains in the suburbs – that empty water into the Mithi River – to stock up to full capacity, leading to waterlogged streets. This has also led to an apprehension if Mumbai is staring at more floods in the coming years.

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On Friday morning, Mithi’s water level rose to 3.9 metres (m), prompting BMC to evacuate residents who live on the river’s banks. A senior civic official said, “The area received 200mm of rainfall between 4am and 8am on Friday morning, which led to the swelling of the river. Previously, a combination of factors – over-flowing of the Powai lake, that discharges its water into the Mithi River; and high tide, due to which water from this river cannot empty into the sea – had contributed to similar situations.”

The official said, “On Friday, Powai lake did not overflow, and there was no high tide during the four hours of heavy rainfall. Despite this, Mithi took longer to drain water into the sea.”

Civic officials ruled out lack of desilting of the city’s storm water drains. P Velrasu, additional municipal commissioner in-charge of BMC’s storm water drains department, said, “We noticed that Mithi was taking longer to drain its water into the sea on Friday. Because of this, some nullahs that empty water into Mithi, such as the nullah at Kalpana Cinema in Kurla, also filled up and the areas that these nullahs cater to were inundated. I inspected Mithi and other waterlogged areas on Friday. However, I have noticed that water has receded fast enough from other streets throughout the monsoon. So this is not due to improper desilting. Mithi is a natural rain water draining system, and has been doing its job properly. There is no problem as such with it.”

Civic officials are not sure why Mithi’s water level rose to 3.9 metres with only one factor in play, that is 200mm rainfall in just four hours. The senior civic official said, “Over the past few years, Mumbai has seen erratic rainfall patterns. As per the natural topography, Mithi should drain all its water into the sea. However, if the sea is not accepting the water, an in-depth study will be needed to know if this is attributed to climate change or rising sea levels.”

Experts believe that it is time that BMC starts integrating climate change in its policy making. “For example, the Brimstowad project (aimed at overhauling drains) has no mention of rising sea levels. The CRZ (Coastal Regulation Zone) notification of 1998 says plains that are likely to get inundated with sea water, especially during monsoon, should have no construction, but we have ignored them. Also, we have destroyed to a large extent Mithi’s floodplains, which is bound to affect the water flow,” said Debi Goenka, executive trustee of non-profit organisation Conservation Action Trust (CAT).

City-based naturalist writer-photographer Sunjoy Monga said, “The delay in the time taken for water to recede from the city is attributed to a lot of reasons, including nullahs being over clogged with garbage and muck. We need to inculcate civic sense among the citizens of Mumbai. Rampant construction and concretisation without understanding the dynamics of water over the years are an invitation to situations where we will face such problems repeatedly.”