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A Secure Decentralized Disaster Management Information Network (SDDMIN) Using Rapidly Deployable Wireless Networking & Mobile Computing Technologies (Contd...)


8.  As a result of prolonged absence of non-freshets from upper portion of these deltaic channels of the block and domination of marine influence, new islands and bar plains are forming in some areas and eroding the embankments in many parts of the islands of the block. Removal of material is generally initiated by the tidal currents flowing through small creeks. As a result, bank erosion takes place in a piece meal manner which adds to the processes of lateral shifting of the river course. This leads to conclude that piece meal mechanism of bank erosion enhances the process of tidal river or tidal creek migration in addition to the processes applicable for the shifting of meandering streams having unidirectional flow. These phenomena resulted in further meandering and as a whole destructive erosion of the embankments.
9. The margin of all the islands dominated by a medium to low energy tropical meso-macro- tidal environment. The generally mesotidal coast (Tidal wave amplitude 2 - 4 m) is macrotidal (Tidal wave amplitude > 4 m) at the funnel mouths of estuaries and big rivers. Tidal wave amplitude varies between 2 to 5.5 meters.

10. Long shore tidal waves of the Bay of Bengal, coupled with predominant southwesterly monsoon winds and other easterly
to  southerly winds blowing onshore with occasional cyclones affect the block in the summer and post monsoon months, i.e., 
from March April to September-October.
11. Throughout the year, active tidal ingressions into the wetlands, lowlands, inlets and estuaries are caused by high tidal range (over 5 m).
12. Residence time of high tide and flow of water during low tide is about 18-20 hours per day.
13. The maximum wind velocity is 16.7 - 50 Km/hr (April - June) and minimum wind velocity is 10.7 - 11.8 Km/hr (December - February). The wind velocity during cyclones often ranges from 80 - 140 Km/hr, in some cases it crosses 180 Km/hr. 3 to 4 cyclones hit the block each year, average velocity of which reach about 80 - 120 Km/hr. Empirical records of cyclones showed that severe cyclone, velocity of which reach 150 - 200 Km/hr., hit the block at every 4 - 5 year.
14. All the margins of the block are affected by storms and associated wave related
phenomenon. Sediment mobilization is also very significant along the passage of cyclones over the wetlands, offshore and wide funnel shaped estuaries. Cyclones also initiate large scale littoral drift and lead to devastating coastal modification.

15. High and low risk zones are classified on the toposheet with database of latitude and
longitudes. Databases for shelters, Government buildings, Pakka houses, availability of
drinking water sources, rural hospitals, market areas etc. has also been done.




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