Mumbai News: BMC Strengthens 100-Year-Old Stormwater Drains Using Trenchless Geopolymer Technology To Boost Flood Resilience

Mumbai, April 3: The BMC has undertaken the strengthening of Mumbai’s 100-year-old underground stormwater arch drains using geopolymer lining with trenchless technology. This will extend their lifespan by at least 50 years, improve water flow efficiency, and enable faster drainage during heavy rainfall, helping reduce waterlogging, claims the official.

Aging drainage system shows structural issues

Mumbai, bounded by the Arabian Sea to the west and crisscrossed by creek systems, relies on tidal fluctuations for the efficient discharge of stormwater through its arch-type (masonry) and closed drainage networks.

While these underground drains undergo regular cleaning and desilting, recent CCTV inspections by the BMC’s Operations and Maintenance (O&M) department have revealed structural deficiencies in ageing sections, including cracks, displaced masonry, deteriorated mortar joints, and localised roof collapses.

Climate change driving urgency

"In recent years, due to climate change, Mumbai has experienced instances of nearly 1,000 mm of rainfall in just a few days during the monsoon. Such extreme downpours occasionally lead to waterlogging in low-lying areas of the city. Against this backdrop, efforts are being made to double the capacity of the stormwater drainage system," said a senior civic official.

Phase-wise rehabilitation underway

A total of 56 drains, spanning 23,548 metres, were identified as defective, with 27 drains covering 14,285 metres (Phase 1) requiring urgent rehabilitation. To address this, the BMC has initiated restoration work, and lining operations are currently underway along a 14-kilometre stretch to reinforce structural integrity and enhance hydraulic performance.

The O&M department consulted with the Indian Institute of Technology (IIT) Mumbai and Veermata Jijabai Technological Institute (VJTI) to determine the most suitable technology for rehabilitating ageing arch-type stormwater drains.

Trenchless technology adopted

Following their recommendations, the Technical Advisory Committee, in a November 2022 meeting, approved the use of trenchless geopolymer lining technology, which is currently being implemented as the most effective rehabilitation method.

"In Phase 1, the stormwater drainage department has commenced the rehabilitation of city-area arch-type drains using trenchless geopolymer lining technology," said a senior civic official.

This method, being implemented by the BMC, is the first of its kind in the country. Similar techniques are predominantly employed for such works in other countries, particularly in the United States.

Officials highlight long-term benefits

Kalpana Raul, Chief Engineer (Stormwater Drainage), said, "Rehabilitation is currently underway on 27 underground arch-type stormwater drains, spanning a total of 14,285 metres, which are nearly 100 years old. This work is expected to extend the service life of these drains by at least 50 years while improving water flow efficiency. Importantly, the trenchless geopolymer lining technology being used is environmentally sustainable."

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Drainage network extent

Island city: 495 km of stormwater drains.

Eastern suburbs: 63 km; Western suburbs: 63 km.

Total network length: 621 km of arch-type and closed drains.

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