Cyclone and Storm Surge - Iczmpwb.org

2.21
Considering all the interdependencies in relation to the distribution of the flows over the many river
sections, proposed human interventions to alter or to stabilize the course, the size and the shape of
any section should not only be valued on their effects on the local situation and their sustainability but
also on the changes these interventions might initiate in the pattern of flows and discharges in the
adjacent river sections.
At present not much information is available about the configuration, the fluctuations of the water
levels and the pattern of flows which are the results of the combination of storage and the
propagation of the tide.
Whatever the configuration of the maze of waterways might be and whatever the sizes and the
shapes of the river sections might have, their various average depths are smaller during low tide than
during high tide. Incoming tide starts with certain depths and these depths will increase till the end of
the incoming tide. With outgoing tides however the depths will become less from its start till its end.
Due to this and the effects on the propagation velocity, the period of incoming tide will become
shorter and the outgoing tide will become longer for the river sections according as their distance to
the sea. As the volumes that are moving in and out are about equal, the incoming currents are
stronger than the outgoing for all sections except those very close to the sea; where the currents are
equally strong. This phenomenon is important for the process of erosion and sedimentation in the
estuary.
2.4.9. Role of tidal channels
The energy which creates the tidal flow, viz. attraction of the sun and the moon in the deep sea, is
manifested partly as potential energy viz. rise in tide level and partly as Kinetic energy viz. velocity of
flow. The formal causes the tidal flow up the rivers and the latter determines its power of transporting
silt. As the velocity of tide when it enters the mouths of these tidal rivers is high and as there is a vast
reservoir of unconsolidated silt in suspension along the delta-face, the tide as it flows up these rivers,
is highly charged with silt. The duration of Ebb tide in a tidal river is much longer than that of the flow
tide in upper reach. Hence the average velocity of Ebb is less than that of the flow. Thus the Ebb tide
is unable to transport back fully the silt carried by flow tide. Even a slight deposition of the silt will go
on accumulating as the tides function twice daily through out the year. Thus the tide channels
perform the most important function of raising the delta up to highest tide level and made fit for
human habitation unless there is human interference. If the tidal channels and creeks are allowed to
perform their above responsibility of raising land to optimum elevation the drainage of the land thus