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Projected Sea Level Rise of Coastal Sunderbans

Gautam Kumar Das

Indian part of the Sunderbans, stands on the Hooghly-Matla estuarine complex, a type example of highly destructive tide-dominated delta, has faced wave vigour and tidal action twice daily in the semi-diurnal tidal situation. As a result, coastal dunes have gradually been eroded and the sediments are transported towards the sea side zone. The coastal Sunderbans is ornamented with the abundant linear sand bars formed due to accumulation of sands eroded away from the coastal dunes at present. But even in the eighties of the last century, coastal sand dunes stand in the supratidal zone protecting the inland area from the intrusion of saline water from the sea. Coastal dunes generally have not migrated and are formed with the association of a few halophytic herbs, creepers and grasses. These types of plants like Ipomoea pescaprae, Sesuvium portulacastrum etc assist the initiation and precise growth of the coastal dunes. The halophytic herbs and creepers arrest sands and help formation of mature dunes from an embryonic one. The roots and rootlets of these halophytic plants acting as sediment binders have manifold roles for the formation and stabilization of dunes.

Of late waves of greater heights on the coastal Sunderbans thrash the coastline dashing those sand dunes. Coastal Sunderbans once studded with lines of sand dunes in the Henry Island, Fedrick Island, Bakkhali, Fraserganj, Baliara of Mousuni Island, Gangasagar of Sagar Island faces destruction for wave action as a result of sea level rise due to climatic change increasing water height due to sea level rise makes the differences as the vigour of wave remain almost the same as the Geological Survey of India reported on the wave parameters of the coastal stretch of Digha – Sankarpur, adjacent to the coastal Sunderbans.

Wave Parameters

Data Collected

Average Wave Height (H)
Average Wave Period (T)
Average Wave Length (L) at a water depth of 1.5 m
Wave Steepness (H/L)
Surf Scaling Factor (Ɣ)
Wave Energy (E)
Average Beach Slope
Average Beach Width
Grain Size

49 cm
17 cm
65.21 m
0.065
4.60
282.5
0.450 to 1.430 (< 50)
80 m to 290 m
Fine grained sand admixed with clayey silt


Huge water mass thrash the coastal dunes and even the vigour of wave have gradually been increasing due to sea level rise as a result of climate change. Sea level rise gradually been rising as Till J.J. Hanebuth reported that the global sea level is considered to have been stable during the 18th century, while it is assumed an overall eustatic rise of 60 mm in the 19th century and 190 mm in the 20th century.

Global Sea Level Rise


Time Period

Sea Level Rise

18th Century
19th Century
20th Century
21st Century

Stable
60 mm
190 mm
31 to 1311 mm (Projected)


The projected global sea level rise including the areas of the coastal Sunderbans at the end of the 21st century varies from 1 ft to 4.3 ft, which would inundate the entire coastal Sunderbans areas. Remedial measures should be taken much well before facing such panic incidents as a result of sea level rise, particularly for the denizen of the people living in the coastal areas of the Sunderbans.

May 7, 2019


Gautam Kumar Das ektitas@gmail.com

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