Cyclone and Storm Surge - Iczmpwb.org

2.11
2.4.1. Physical features
The major portion of South Bengal including the Sundarban had been formed mainly by the service
tendered by the magnificent river Ganga in transporting millions tons of silt every year from the
Mighty Himalayas through the Bhaqirathi Hooghly channel. Land was formed at the head of delta due
to deposition of silt in suspension when the strong current in the river is checked by coming in contact
with the sea. Ganges like other delta builders, began to approach the sea in several diverging
branches enclosing the intersecting the delta already built so as extend it towards the sea by
dropping their silt load near about their mouths. But the raising would have beer, exceedingly slow as
floods occur only in limited period during the monsoon. Hence Nature has requisitioned the service of
tide who pick up vast reservoir of unconsolidated silt at their mouths almost to the saturation point
and flow inland twice a day during flood tide through out the year and drops a part at low velocity
stage on the entire basin below tide level and within tide limits and thus raise the delta already built.
The process of delta building was very high for the two following factors -
i) The steep slope of the Himalays, the highest mountain in the world which aided by the
torrential character of the rain and the rather indifferent conditin of the catchment basin has
been furnishing the building material in abundance during the monsoon.
ii)
The abnormally high tidal range due to the funnel shape of the Bay of Bengal which has been
helping in distributing these materials twice daily throughout the year. But, silt is less in
winter season particularly.
The formation of delta in Southern Bengal continued at a very fast rate upto 12th Century. Between
the l2th and 16th centuries A.D., the main course of the Ganga fluctuated between the Bhagirathi-
Hooghly and the present course further eastwards called the Padma, and from the 16th century
onwards the Padma has become the main course. With this diversion of the main Ganga through the
Padma, all the branches of the Ganga Bhagirathi system in this region, which were carriers of silt
were deprived of their head water supply except during the few monsoon months. As such these
rivers have lost their role in building the delta. At the moment, new land formation is dependent on
tides. The old river channels excepting Hooghly exist as tidal creeks with the additional function as
drainage carriers of the area.
2.4.2. Topography
The depth of silt deposited by upland floods is the maximum close to the river banks where the