Cyclone and Storm Surge - Iczmpwb.org

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All the islands are situated within the middle reaches of the Hooghly estuary. Some of these are:
nayachara, Ghoramara, Lohachara, Bedford, Sagar, Sikarpur, Kankramari, Mahisani, Jambu, and
Chuksar. Lohachara and Khasimara islands are already eroded in the estuarine environment.
Ghoramara and Bedford islands are gradually being reduced in their size. Parts of Sagar Island
(Bisalakshipur, Beguakhali, and Sikarpur) are also eroded by faster tidal currents (Paul 2002).
The 11.5km long stretches of the sea front of the Sagar Island on its southwestern side, parts of the
Jambu Island, and the seaward side of the Chuksar Island are dominated by shoreline features and
backshore dune fields. Waves and currents deposit sand in the shore zone of open sea-facing
islands of the Hooghly estuary. Strong onshore winds, particularly in the pre-monsoon season,
transport sand from the sea beach to the back-shore areas where dense vegetation cover attracts
sand particles to accumulate into sand dunes. Dunes are less frequent weher abundant sand supply
is absent (Paul 1994).
The most extensive landforms found in the Hooghly estuary channels are the tidal flats, which are
mostly restricted to intertidal zone. Tidal flats occur in the sloping sides of estuary channel and minor
tidal channel, and also on the island and bar surface. According to Paul (2002), there are two types
of tidal flats in the Hooghly estuary – the sheltered flat and the open-sea tidal flat. Variation of wave
heights and tidal ranges controls the geomorphic positions and morphologies of the tidal flats.
Islands, bars, and deltaic flats of the inland estuarine section are usually sheltered from the effects of
wind-driven waves. The sheltered section of the estuary with large tidal range enhances the
deposition of fine-grained silts and clays to form mud flats and marshes in the islands and deltaic
flats. Nayachara Island, Bedford Island, Sikarpur Island and Kankramari Char are good examples of
such extensive growth of tidal flats.
The shorelines of Sagar Island, Jambu Island, Chuksar Island, Frasergunj, and Bak-khali are
exposed to wave attacks at the lower reaches of the Hooghly estuary. Here, the accumulation of
sediment deposited by waves and currents has produced beaches in the shore zone.
The human habitation within the islands is guarded by circuit embankments, which act more like
polders. Some of the embankments (like those in Sagar Island) are looked after by the Kolkata Port
Trust (KoPT), and the rest by the Irrigation and Waterways Department (I&WD) of the Government of
West Bengal. However, the retired embankments (the embankment that is situated some distance
away from the riverbank) are less prone to damages which can be severe due to the cyclinic strom
surges. KoPT has prepared a scheme for river training works in the interior of the estuary on the
basis of recommendations of various expert committees and on the basis of the results of Hydraulic