The Bengal government plans to construct a robust and ecologically sustainable ‘bioshield’ along the state’s coastline and the Sunderbans islands in order to strengthen Kolkata’s and the rest of the state’s defence against devastating cyclonic storms, such as Amphan, which are expected to increase because of climate change.
The plan is to build earth embankments, plant 36 species of resilient mangrove species and set up a geo-textile cover on embankments, and a second line of embankment on the east-facing concave coastline, where erosion is highest.
Chief minister Mamata Banerjee herself proposed a multi-layer vegetation shield as a protective layer against storms, erosion and ingress of saline water in coastal Bengal. Last month, she had set up a 24-member committee of experts, headed by state pollution control board chairman Kalyan Rudra, a river expert. The exhaustive report by the committee, which came up with the details of the plan, was recently approved by chief secretary H K Diwedi as the master guide for any work in that eco-sensitive zone.
The impact of climate change is most severe in the Bengal delta region, where the sea-level rise is the highest globally. The global mean sea level has been rising at 3.6mm per year between 2006 and 2015. The sea-level off the coast of Bengal is rising at around 4mm per year. The impact of sea-level rise in the Sunderbans is further accelerated due to slow subsidence of land, at 2.9mm per year. That effectively makes the sea level rise more than 6.9mm per year.
The committee has proposed a “climate-resilient” multi-layer vegetation shield: three-layer shields along the sea coast, and two along the river-embankments in the Bengal delta.
“The 36 species of mangrove and mangrove associates and blue and green algae were chosen on the basis of their resilience, ability for propagation, height, salinity resistance and tidal influence,” said Rudra. “The invasive species were avoided. The vegetative shield, unlike the capital-intensive concrete embankment, systematically helps develop sand dunes off the coasts, which effectively act as a wave-breaker, apart from replenishing the beaches,” he added.
The irrigation and waterways department has identified 378 stretches of different rivers in the state, that have a total length of 559km, as vulnerable, of which 207 stretches, with a combined length of 324km, have been marked “extremely vulnerable”. These are mostly east-facing concave banks, where breaching of embankments is highest. A second line of embankment has been planned in such zones to minimise the impact of cyclones and erosion.
If the frontal old embankment is located along the high tide line, the buffer area between the old and new dykes may ideally be 200m, and would be declared “no-construction zones”, in compliance with the Coastal Zone Regulation, 2019. Also, the eroded beaches in East Midnapore and the Sunderbans have become so narrow and low that the wave-breaking zones have moved nearer to land. Since there is hardly any area along the southern front of Sagar Island to create a proper bioshield, an artificial off-shore reef barrier has been proposed by experts from IIT-Madras, Rudra added.
Source: Times of India