Mumbai monsoon audit:A spot check of chronic flooding areas

The upcoming monsoon will be a big test for the Brihanmumbai Municipal Corporation (BMC), as it claims to be in a better position to handle waterlogging in Mumbai, compared to the past two years.

Of the 273 flooding-prone spots identified across the city over 2017 and 2018, BMC said it has tackled 178 flooding-prone spots before this monsoon.

Moreover, 49 other flooding-prone spots, of the 273, are localised flooding-prone spots — where waterlogging takes place owing to a local and temporary reason such as very heavy rainfall over a short duration combined with high tide. These 49 spots are not chronic waterlogging spots, hence they do not face the threat of submerging every monsoon.

Over the past two years, BMC has been looking for ways to deal with waterlogging spots, an issue that resulted in a wide public backlash against the civic body after Mumbai was inundated for hours during the monsoons of 2017 and 2018.

June 9 and 10, 2018 saw a situation similar to the deluge of August 29, 2017, when Mumbai remained submerged in waist- deep water in several places, for hours after it had stopped raining, as it recorded more than 100mm of rain in short time. This brought the city to a standstill, delaying suburban trains owing to waterlogged tracks and diverting bus routes and traffic because of waterlogged roads.

After last monsoon, then municipal commissioner Ajoy Mehta changed the methodology by micro-planning to deal with flooding. He directed BMC officials to study each chronic flooding spot individually, define why the area floods every monsoon, and then come up with personalised solutions for each spot to prevent waterlogging. While this method did not replace the earlier plan of cleaning water entrances, laterals and desilting drains and nullahs, it was expected to aid flood mitigation.

After this, the stormwater drains (SWD) department took measures such as drain augmentation, construction of additional drains, adding floodgates, remodelling drains, culvert uplifts, strict policy about laying utilities in drains, and resorting to new technology for cleaning drains such as the robots it purchased.

A senior civic official from the SWD department said, “Work on some flooding-prone spots is still going on, so they are likely to see some flooding this monsoon, but we have the situation largely under control.”

Some areas where work has been completed, include Masjid Bunder where floodgates were fixed; Deonar Municipal Colony, Devkabai Chawl in Ghatkopar, the junction of JK Bhasin Road and Jaymal Singh Road near Sion, the area around KEM Hospital — where drain augmentations were undertaken; Tardeo market where additional stormwater drains were installed; Homi Bhabha Road in A ward, Sarang Road in B ward, and a portion of Chamdavadi nullah near Bandra, where an old small culvert has been demolished and a six-metre wide box drain is being installed. Areas where work is still going on are Hindmata junction at Dadar East and the junction at Byculla Police station.

VH Khandkar, chief engineer of the SWD department, said, “When BMC says it has tackled waterlogging spots, it does not mean the spot will never be waterlogged ever again. We have to wait and observe what this monsoon has in store for us. For example, the capacity of our drains to carry water is 50mm per hour. If it rains over 100mm or 150mm, how will we be able to prevent flooding entirely. However, if it rains 35mm per hour and still the area is waterlogged, then BMC is doing something wrong.”

Audit results

HT inspected three flooding-prone spots across the city. These were Hindmata junction at Dadar East, Nana Chowk at Grant Road, and LBS Road near Ghatkopar.

While Hindmata and Nana Chowk are natural low-lying areas prone to flooding, experts have attributed flooding in these spots to narrow drains and shortcomings in the engineering of British-era drains, which were built to cater to the needs of that time, lack of proper cleaning of laterals and water entrances, as at many places HT encountered garbage in the water entrances such as Hindmata, or Kemps Corner at Peddar Road (run-off water from this area reaches Nana Chowk and contributes to its flooding), excessive concretisation and no open space where water can percolate into the soil.

HT found at least three dewatering pumps at Nana Chowk and Hindmata, which will help drain water faster in case of flooding.

The spot at LBS Road near Ghatkopar is also a Metro construction site. Construction of a missing link in the drains was going on, but the remaining drain was too narrow for water to flow out.

Rohit Shinkre, one of the experts who accompanied HT on the audit, said, “Flooding is unavoidable in certain areas such as Hindmata or Nana Chowk, which are low-lying areas.” He added, “Mumbai has seen development in many mangroves, mudflats, and wetlands, which are natural retention beds, which has aggravated flooding. Obstruction or diversion of many rivulets such as Mithi has also aggravated the problem. We need to look at the problem holistically, rather than only as a problem of stormwater drains.

Experts also blamed excessive concretisation and new construction for waterlogging. Pankaj Joshi, an expert on the panel, said, “The compounds of new buildings in most areas such as Parel, Mahalaxmi, Lower Parel and Dadar, are raised substantially. This means all water runs on to the road, and the road is expected to act as a natural drain.”

According to experts, although stormwater drains might be functioning, they are not designed to cater to 100% run-off from the site. In such cases, SWD department alone cannot be blamed for waterlogging. Joshi said, “It is a fundamental issue in planning. No drain, in cities across the world, is designed to cater to 100% run off, and some water needs to percolate into the ground.”

Over the past five years, flooding-prone spots in Mumbai increased from 40 in 2014, to 273 in 2019. After the June 9 and 10 floods last year, then civic chief Ajoy Mehta said, “New flooding-prone spots have emerged in the city owing to multiple infrastructure projects under construction.” During the same time, Mehta had also attributed flooding to shoddy cleaning work by contractors. He had said, “At one spot, we opened the drains and noticed a bunch of loose utility wires in the drain, that were getting in the way of the drain’s water-carrying capacity.”

Following this, BMC got a robot to enter drains and clean them and take photographs of the drains simultaneously, and awarded a two-year contract at ₹60 crore for the purpose. It assigned cleaning 70km of drains to the robots, of which 36km were British-era arched drains, and the remaining were new drains. However, the robot was not successful in cleaning the drains, and BMC had to drop the venture midway. It then resumed end-to-end mechanical cleaning of drains.

Role of pumping stations

After the 2005 deluge , the Brihanmumbai Stormwater Disposal System (BRIMSTOWAD) project was announced to overhaul the stormwater drains system in the city. This system planned eight pumping stations across the city. Of these, only six have been completed so far — Haji Ali station, Lovegrove station near Lotus Colony in Worli, Cleveland Bunder near Worli Koliwada, Irla pumping station in Vile Parle, Britannia pumping station near Reay Road, and Gazdarbandh pumping station at Khardanda.

Of these, Britannia pumping station was commissioned in 2016, and was expected to give relief to areas of Parel, Dadar, and Matunga.

However, despite this, the areas of Fitwala Lane, Hindamata, and Kings Circle continued to flood in subsequent monsoons.

A BMC survey revealed that the drains in this area also need to be augmented. Following this, BMC undertook augmentation of the drainage system at Hindmata in January 2018.

The Gazdarbandh pumping station that was completed in May 2019 is expected to provide relief to Juhu, Santacruz and Vile Parle areas. This is the first monsoon when the pumping station will be operational. The 7th and 8th pumping stations planned under BRIMSTOWAD, the Mahul and Mogra pumping stations, expected to give relief to Wadala and Santacruz respectively, have not kick-started yet.