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contamination are also part of storm surge damage. With the present technology and
information, the occurrence of cyclones can be predicted but it would be still difficult to
pinpoint the exact nature and magnitude of the hazard that would occur in the coastal area.
Sometimes the magnitude of the cyclone is so large that it brings about devastation not only
in the coastal districts but also well interior into the hinterlands. Even the most developed
countries with sophisticated early warning systems suffer huge loss of property and lives in
the coastal areas due to flooding caused by hurricanes, typhoons, tidal waves, tsunamis and
storm surges.
Flooding due to river discharge in inland tidal water bodies (still water flooding):
Banks of water bodies get flooded due to rise of water level as a result of precipitation and
river discharge. This rise in the water level without the influence of wind leads to water
logging in the adjacent areas. Data is available in historical records with the Central Water
Commission/ irrigation departments and these flood lines are also depicted in the topo sheets
for certain areas. This flood line if demarcated shall also include the unforeseen rise of water
due to man’s intervention.
2.8.4 Sea level rise due to Greenhouse effect
Sea level rise is one of the major factors influencing coastal erosion. As the sea level
rises low lying areas will be inundated, the reach of active marine forces like the waves will
be raised relative to the land surface, which will lead to coastal erosion and drowning of
estuaries. Recent estimates of global sea level rise vary from a high scenario of one metre to a
low scenario of 15 cm during the next century.
2.8.5 Salt Water Intrusion
Many coastal communities rely on potable ground water for requirements of water.
Often it is the only reliable source, seawater not being potable without expensive
desalination. Both fresh and salt water seep into the coastal terrain; the fresh water, being
less dense, overrides the salt water often forming a shallow lens between the recharge and the
discharge zones. In these shallow, unconfined aquifers, permeability is often very high, due
to porous or even cavernous sediments, and consequently the through flow (transmissibility)
is rapid. Thus natural fluctuations in the in the freshwater head, often due to seasonal
factors., can have a marked effect on the position of the saltwater -freshw ater interface.
Several processes disturb this relationship. Perhaps the most common is the abstraction of
ground water by pumping. Lowering of the freshwater head encourages the incursion of salt
water, which can rapidly render the supply undrinkable. Removal or lowering of coastal
dunes has similar effect. Dunes act both as recharge zones and as support for an elevated
water table. Draining of coastal wetlands, and cutting or dredging of coastal navigation
channels may breach the brackish interfacia l zone often leading to increase in salinity. The
projected rises of world sea level in the next century may also lead to severe salt intrusion
problems. The shallow coastal aquifer is liable to pollution. Coastal ground water extraction
may lead to subsidence. Siting wells and boreholes further inland is not a long-term solution
and alternative supplies may have to be provided.
2.8.6 Tsunami
The devastating earthquake of magnitude 9 occurred off the west coast of northern
Sumatra which lies in the Andaman-Nicobar Island arc on December 26, 2004 at 06:28:50
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