To improve waterflow during monsoon and to strengthen the walls of the underground British-era storm water drains (SWD) in Mumbai, the Brihanmumbai Municipal Corporation (BMC) is set to implement a geopolymer coating on the walls of the drains beginning this month.

There is currently a 36-km-long labyrinth network of arch-drains underneath the surface of island city. Some of them are even horseshoe-shaped and constructed on the masonry model, which includes the use of bricks and stones.

These drains were constructed during the erstwhile British era and could be found only in the island city, since during the 18th and 19th centuries, the suburban belt of the city was not fit for human habitation.

Since all these drains were in a dilapidated condition, the BMC in February 2022 had initiated a survey to assess their structural condition. Following which the decision to implement geopolymer coating on the walls of these drains were taken. According to civic officials, the coating would strengthen the life span of the drains and would lead to prevention of road cave-in incidents.

“The primary objective is to avoid digging and trenching of the road surface. All these drains are either arch-shaped or horse-shoe shaped and, therefore, the coating will be applied on the existing walls. These drains are over 100 years old and all the walls have become corroded,” a civic official said.

Further, civic officials said that to identify corroded portions of SWD walls, the BMC had deployed sensor-based cameras, following which the locations were geotagged.

In 2015, the BMC had replaced arch drains on Pedder Road, after a road cave-in in 2012 led to massive traffic disruption in south Mumbai.

Mumbai has a 70-km-long network of British-era drains, of which arch drains cover 36 km and the remaining consists of pipe drains.