Mumbai: BMC trying to avoid repeat of Marine Drive flooding this monsoon

Tetrapods are seen placed away from outfall to prevent pebbles, other waste from blocking stormwater outlet at Marine Drive. Pic/Anurag Ahire

After Marine Drive flooded last year due to small rocks getting stuck in the rainwater outfall at Patan Jain Road, the coastal road department reinstalled tetrapods around the outfall as per the instructions from the stormwater department (SWD). The Brihanmumbai Municipal Corporation (BMC), however, is not sure whether this will prevent rubble from entering the outfall during extreme high tides.

The landscape of the city changes every decade as more of sea area is reclaimed, resulting in unusual situations such as the flooding of the Marine Drive stretch, between Churchgate and Marine Lines railway stations, on July 27, 2023. As a result of the flooding, vehicular traffic was affected while Western Railway (WR) services were disrupted for more than two hours.

A WR spokesperson at the time said that outfall culverts were operating at half capacity and all manholes on the west side of the tracks till Marine Drive were overflowing. Afterwards, the BMC issued a statement that small rocks that were swept away by powerful waves got stuck in the outfall of Patan Jain Road. Though the outfall site is beyond the construction boundary of the Coastal Road, tetrapods in and around the outfall were removed for the construction of the project's sea wall.

Rubble at the same spot last year; (right) The rainwater outfall at Patan Jain Road, Marine Drive

Learning from the experience, the coastal road department started reinstalling tetrapods from the south side of the project for a few metres up to Marine Lines Police Gymkhana.

"As per the SWD's instructions, we rearranged tetrapods around the outfall which may hinder the movement of pebbles or rubble but do not stop water flow from the drain. But the outfall gets submerged even during low tide and with the heavy force of waves during extreme high tide, this measure cannot be effective," said a senior official. He added that continuous observation and frequent cleaning of the site are the only solution which can be done by the SWD and it is applicable for the other outfalls of the area.

Officials of the SWD department are sure about the arrangements. "There are four other outfalls till Nariman Point which were protected by tetrapods during heavy tides all these years. Only Patan Jain outfall was open to high tide waves in the absence of tetrapods, which were removed for the work of the coastal road, and was choked due to rubble. Placing tetrapods will solve the issue," said a concerned SWD official.

Abhijeet Bangar, additional commissioner of BMC and in-charge of SWD said, "After last year's experience, tetrapods have been arranged properly to prevent pebbles from getting into the outfall. But they may not offer 100 per cent protection, especially from extreme waves so we will keep inspecting the area to avoid repeating last year's incident."

Other outfalls till Girgaon

Coastal Road officials said the rearrangement of tetrapods beyond Police Gymkhana up to Girgaon Chowpatty will start only after the rainy season and the metal piles will prevent the force of heavy tides till then.

There are at least four other outfalls under the Coastal Road to Girgoan Chowpatty. The Coastal Road department claimed that they have made similar arrangements for other outfalls. "The new tetrapod arrangement will take care of the Patan Jain, Shantiniketan and Police Gymkhana outfalls, which are below the low tide level, and a small outfall at Bal Bhavan drain, which is about the tide level. There isn't much place to install floodgates at these outfalls. But we have merged three outfalls at the Police Gymkhana, Taraporewala Aquarium and Grant Medical College gymkhana into a large three-by-three-metre drain, which will be more than enough. The outfalls and drains from Marine Lines to Worli are still with the coastal road department and haven't been handed over to us. Though the work is mostly complete, they will hand over it after the rainy season. But we are preparing to keep the city flood-free," said an SWD official.