Cyclone and Storm Surge - Iczmpwb.org

2.18
All rivers have in general southerly course towards sea. Some of the above major rivers braids into
more than one channel before meeting the sea. Except river Hooghly and river Baratala all rivers are
actually tidal waterways without any upland discharge expecting run off of small localised catchment
and their water is as salty as the sea.
Between the large estuaries and rivers are innumerable streams and water courses called khals,
forming a net-work of channels, some ending ultimately in little channels that serve to draw off the
water from each block of land. Each block is formed like a saucer with high ground along the bank of
the Khals surrounding it, and with one or more depressions in the middle. The rain water in the block
is drained off by the little khals into the larger khals and ultimately to the Sea through the rivers during
Ebb tide, conversely when the water swells in the rivers during Flood tide it floods the country
through the same channels. Many of the khals connect two large ones, and consequently the tide
flows into them through both ends. Such khals are called “Do-Aniya" Khals. They are very useful as
affording communication between the larger khals, but have one serious defect that they are liable to
silt up at the point where the two tides meet, for the water in always still there.
Even the major rivers in the Sundarban region flowing East of the Hooghly river have relatively small
catchment areas and consequently the discharges from the hinterlands are small in comparison with
the volumes of water which flow in and out each tide. Therefore, the currents in the maze of rivers
and creeks of the Sundarban Region are almost entirely the results of the fluctuation of the sea level
in the Bay of Bengal and the way these fluctuations propagate themselves within the system of
waterways of the delta.
2.4.8. Tides
Tides are generated in the Bay of Bengal by the forces of attraction of mainly the sun and the moon
upon the rotating earth. The effect of tide is manifested in a regular alteration of rise and fall of the
water level of the sea and the estuarine channels and creeks, with the advent of rising tide, the water
level of the Sea Starts rising gradually and steadily till a highest level known as the “High Water
Level” (HWL) is attained. This rising phase of the tide is called the “Flood tide” or the “Flow tide”.
After the attainment of HWL the tide water level starts falling gradually and steadily till a lowest water
level (LWL) is reached. This falling phase of the tide is called “Ebb tide”. Thereupon the tide water
starts rising once again till the occurrence of the next HWL and so on. The difference in elevation
between a HWL and the next LWL is called the “Tidal range” and the period intervening any two