The ‘green’ story behind India’s longest sea bridge

Insights into the engineering behind the iconic project, from S V DESAI , Whole-time Director & Senior EVP (Civil Infrastructure), Larsen & Toubro.

It is perhaps one of the most defining pieces of infrastructure in the Maximum City, that will make one of the strongest ‘green’ statements in recent times. The 21.9-km-long Atal Bihari Vajpayee Sewri–Nhava Sheva Atal Setu, or the Mumbai Trans Harbour Link will connect Mumbai with its satellite city of Navi Mumbai, reducing average commute time by half to about 20 minutes, with the potential to substantially save on fuel consumption per annum.

The challenge before us, as responsible builders of infrastructure, was to build a ‘green’ bridge deploying the most sustainable methods of construction. Apart from executing in an ecologically sensitive zone, for the Sewri mud flats are earmarked as an Important Birding Area (IBA) and home for a variety of birds including the pink-necked flamingos, our challenge was to build without interfering with the lives of the birds, flora and fauna around, and keeping their habitat pristine.

Drilling softly: By deploying special piling rigs and world-class Reverse Drilling Machines, we managed to keep noise and vibrations to less than 78 dBA. Special mufflers fitted to generators reduced noise and carbon emissions, with sound maintained at 72 dBA with the help of a generator silencer. Several dosimeters installed at site, especially in the marine and intertidal zones, monitored noise levels every fortnight.

Away from the bright lights: Warm-white coloured, eco-friendly LED Philips lights with 3,000 kelvin temperatures, with an average surface illuminance of 30 lux, protected the birds and aquatic life from the strong light rays.

To keep them out of harm’s way: A special sheet barricade was erected to demarcate the construction area from the habitat of the birds, that was short enough for the birds to fly over them.

Breathing easy: Construction activity normally generates dust and emissions that harm the quality of air - air quality meters, installed at several sensitive locations, monitored air quality on a weekly basis: PM2.5, PM10, SO2, NO2, O3, CO, Ni, As, and C6 H6.

Maintaining the ecological balance: We collected and tested samples from three zones – the mudflats, intertidal, and marine areas – every quarter to monitor the species of phytoplankton and zooplankton in the waters and the benthic sediments to understand if the productivity of the mudflats was maintained. Water quality was checked once a quarter on primary parameters like pH, DO, colour and odour, floating matter, suspended solids, oil & grease, and heavy materials. Geological studies were conducted every quarter to check the soil quality and sedimentation process. Periodic tests also monitored  the health of the environment. NABET-qualified labs were appointed with locations pre-qualified as per MoEF&CC guidelines to integrate the approved monitoring programme for the following:

Efficiently disposing waste: Pile muck generated during the construction of piles was collected in separate bins and transported to a designated deposition area to protect the marine body. The fabrication and construction activities over the seabed were carried out with special care to protect the sea from any foreign particles, allowing the aquatic life to continue following their usual pattern of life. Waste was collected at source, segregated, stored, and transported to recycling units. Oil spillage sensors were installed in all Plant & Machinery.

Drinkable water in the sea: A filtration system ensured that the drinking water met the Pollution Control Board’s prescribed standards. Water at the office, site, yards, and labour camps was tested every quarter, and our managers ensured site compliance.

A unique way to answer nature’s call: On a construction area spread over 10 hectares, answering nature’s call can be a difficult proposition, especially when dealing with a workforce of around 5,500. To address this issue, the site put up Bio Toilets, a patented technology with inoculum, developed by DRDO, that generates zero sludge and the treated wastewater is discharged into drains after meeting the standards.

India’s longest sea bridge is ready for the nation and as nation builders we are proud to have built another landmark of the future, but this time, the 24,000+ flamingos and marine life in the region have cause to thank us too, for leaving their habitat as it was before.