The process of reclaiming land from the sea has not changed much in the 230-odd years since the Hornby Vellard was completed in 1785. The sea wall, named for Governor William Hornby, was laid by dumping boatloads of stone in the marsh near Worli creek.
The rubble came from hills of basalt around Bombay that were flattened. The ‘vallado (Portuguese for fence or divider)’ became the prototype for future embankments as the city continued to expand to the north.
The 7.4-km-long barricade that props up the Mumbai Coastal Road has a similar core layer of stone. Rocks of 60kg to 300kg are held together by granular material that binds them into flat surfaces. The inner layer is covered by a geo-textile made of woven material that resembles a net but with none of its weakness. This structure is surmounted by two layers of armour rock of different sizes, 1-3 tonnes in weight. The rocks are cut to different specifications to ensure stable interlocking. What’s more, unlike the tetrapods on Marine Drive, the armour rock carved out of quarries and hills in Navi Mumbai can sustain marine life. Over the years, its surface is likely to be lined with moss and algae and attract fauna.
The wall slopes as it rises, resembling a ramp that rises 6-10 metres from the sea bed. The Worli and the Amarsons stretch are where the sea bed is at its deepest and the wall rises to its maximum height. “These are also stretches where the waves are the most turbulent,” said a BMC engineer.
Apart from being sturdier, the significant distinction between the Coastal Road wall and the causeways that came up along Mumbai’s shore is that this one is relatively more future-proof. The engineers have factored in an average sea level rise of 5mm every year for the next 100 years while designing the wall. Protection against storm surges or tsunamis may be the most unlikely of spin-offs from Mumbai’s infrastructure showpiece.
The rubble came from hills of basalt around Bombay that were flattened. The ‘vallado (Portuguese for fence or divider)’ became the prototype for future embankments as the city continued to expand to the north.
The 7.4-km-long barricade that props up the Mumbai Coastal Road has a similar core layer of stone. Rocks of 60kg to 300kg are held together by granular material that binds them into flat surfaces. The inner layer is covered by a geo-textile made of woven material that resembles a net but with none of its weakness. This structure is surmounted by two layers of armour rock of different sizes, 1-3 tonnes in weight. The rocks are cut to different specifications to ensure stable interlocking. What’s more, unlike the tetrapods on Marine Drive, the armour rock carved out of quarries and hills in Navi Mumbai can sustain marine life. Over the years, its surface is likely to be lined with moss and algae and attract fauna.
The wall slopes as it rises, resembling a ramp that rises 6-10 metres from the sea bed. The Worli and the Amarsons stretch are where the sea bed is at its deepest and the wall rises to its maximum height. “These are also stretches where the waves are the most turbulent,” said a BMC engineer.
Apart from being sturdier, the significant distinction between the Coastal Road wall and the causeways that came up along Mumbai’s shore is that this one is relatively more future-proof. The engineers have factored in an average sea level rise of 5mm every year for the next 100 years while designing the wall. Protection against storm surges or tsunamis may be the most unlikely of spin-offs from Mumbai’s infrastructure showpiece.