Why does Andheri subway keep getting flooded? Answer lies in its topography

The subway is located around 1 km away from the Andheri station and is known to be one of the low-lying areas in Mumbai. Even though the Brihanmumbai Municipal Corporation (BMC) set up dewatering pumps every year inside the subway, the problem of waterlogging continues to exist.

Last year, the subway was shut down at least 35 times between June and October during the monsoon since it got inundated during the rains. Before that, in 2023, the subway was shut down at least 21 times during this period. The subway closure leads to immense vehicular congestion in the suburban belt of Mumbai.

The location of the subway is saucer-shaped in nature, which means the entry and exit point of the subway is elevated and has a slope-like curvature due to which water from the adjoining areas, which are elevated in nature, travels downstream inside the subway through the slope.

Besides this, the Mogra nullah, which originates 2 km away from the subway, passes downstream, touching the subway, and whenever the water in the nullah overflows, it enters the subway and stays accumulated there.

Speaking to The Indian Express, Abhijit Bangar, Additional Municipal Commissioner (Projects), said, “One of the major challenges that we (BMC) are facing to keep this particular point flood-free is the topography of this subway.”

“This area is called the watershed area, and the gradient over there is very steep; therefore, water gushes inside the subway at a very high speed during the rain. Therefore, unless any large-scale structural intervention is carried out, it will continue to be a challenge to keep the subway entirely flood-free,” said Bangar.

Bangar also maintained that the drains’ carrying capacity is very low, mainly due to floating waste inside the drains. This leads to waterlogging during the monsoon season even after an above-moderate spell of rainfall. Bangar said the haphazard disposal of solid waste causes the drainage system to choke, leading to overflow.

“Often we see materials like suitcases, furniture, plastic items, bicycles, being disposed of in the drain when they are no longer used. These items obstruct the water flow, which in turn leads to overflow of the drains, causing flooding in the subway. We have been holding dialogues with local residents as well, however, no concrete result has happened yet,” said an official.

Mitigation measures planned, but not implemented

Last year, the BMC proposed a Rs 200-crore ambitious proposal to counter the flooding issue of the Andheri subway. The civic body’s objective was to augment the existing drainage system to increase the water-carrying capacity. The civic authorities also planned to create an additional drainage line that would divert the water flow in a separate direction towards the western side, eventually discharging the water to the nearby creek.

The two-phase project was supposed to begin in October last year and lead to full completion by May 2026. However, the project did not take off.

“During our feasibility study and estimation for the project, we found that the carrying capacity of the drains could be increased to tackle the average rainfall of 55 mm. At present, the carrying capacity is just 20 mm, and after the implementation of the proposed works, we would get only an additional cover of 35 mm of rainfall, which is not a wide range. Therefore, spending Rs 200 crore just to tackle 35 mm of rainfall will not be worth it, and we had to cancel this project to chalk out a more feasible project with a good cost-benefit ratio,” Bangar said.

Holding ponds, a possible solution

Civic officials said to mitigate this issue, the BMC is already in talks with the Indian Institute of Technology (IIT) Bombay to derive a key alternative for tackling the issue. Bangar said experts are mooting the construction of holding ponds to tackle the flooding at the Andheri subway.

A holding pond is like a detention basin that temporarily stores water during heavy rain. The water from a flood-prone area is routed to a nearby pond through pumps and pipelines, where the water is either kept in storage temporarily or channelled out to nearby outfalls using dewatering pumps. Besides tackling waterlogging during rains, holding ponds also act as a buffer between a particular area and its nearby water body, helping reduce waterlogging.

In Mumbai, a holding pond was started in the Hindmata junction of central Mumbai, a key flood-prone area. Following this, the issue of waterlogging in the area came down by a large margin.

“Setting up holding ponds could be the concrete solution to abate flooding at the Andheri subway. The experts are also supporting it, and since this technology has already been applied in Mumbai, we can take a cue from it and apply it here. This project will also bear a good cost-benefit ratio,” Bangar said.