Drawing lessons from May 26 rain, BMC to widen Mumbai’s drains to avoid flash floods, waterlogging

“In Mumbai, the original width of the major drains was able to handle around 25 mm of rainfall every hour. After the 2006 deluge, it was decided that all these drains would be widened so that they could handle 55 mm of rainfall water in an hour. The works were taken up in a phased manner. However, following the rains last month, it has now been decided that the overall width of the existing major drains needs to be further widened to tackle heavy rainfall of 120 mm,” a senior official said.

Mumbai has a vast network of drains, comprising 261.52 km of major nullahs (1.5 metres or wider) and 411.56 km of minor nullahs (less than 1.5 metres wide), along with other types of drains, such as arch and roadside drains.

The overall network of drains in Mumbai is approximately 3,800 km.

These nullahs play a crucial role in the city’s drainage system.

The origin of these drains dates back to the colonial era in the mid-20th century.

“Since the population and demography of the city have changed drastically in the past decades, the quantum of water flow has also increased. Meanwhile, the pattern of rainfall has undergone a significant change in the past few years, resulting in frequent incidents where a large quantity of rainfall occurs within a short period. Therefore, there is a need now to widen the existing width of the drains to improve their carrying capacity,” the official said.

Civic officials said that a larger number of flooding spots in Mumbai remain in the island city.

Therefore, the need for widening the drains in the island city is of utmost importance to the civic authorities.

The BMC will appoint a dedicated agency, such as the Indian Institutes of Technology (IIT) or Veermata Jijabai Technological Institute (VJTI), to conduct a survey of these drains and determine the margin by which each drain will be widened.

Following this, the widening work will be carried out.

Civic officials said that instead of undertaking large-scale widening works, the civic body is also exploring local-level interventions to enhance the smooth flow of water.

“We will also ask the local ward officers to submit to us their observations regarding the drainage in their area so that we can implement local-level interventions like the installation of mesh to prevent the deposit of floating waste and sludge inside the drains. The primary objective is to improve the water flow of the drains to ensure that they don’t overflow following a heavy spell of rain within a short period,” the official added.