The greatest potential for loss of life related to a
hurricane is from the storm surge, which historically has claimed nine of ten
Storm surge is simply water that is
pushed toward the shore by the force of the winds swirling around the storm.
This advancing surge combines with the normal tides to create the hurricane
storm tide, which can increase the mean water level 15 feet or more. In
addition, wind waves are superimposed on the storm tide. This rise in water
level can cause severe flooding in coastal areas, particularly when the
storm tide coincides with the normal high tides. Because much of the United
States' densely populated Atlantic and Gulf Coast coastlines lie less than 10
feet above mean sea level, the danger from storm tides is tremendous.
The level of surge in a particular area
is also determined by the slope of the continental shelf. A shallow slope off
the coast (right, top picture) will allow a greater surge to inundate coastal
communities. Communities with a steeper continental shelf (right, bottom
picture) will not see as much surge inundation, although large breaking waves
can still present major problems. Storm tides, waves, and currents in confined
harbors severely damage ships, marinas, and pleasure boats.
The intensity of the storm (as given by
Saffir-Simpson Hurricane Scale)
affects the possibility of flooding from storm surge at two locations. Storm
surge also affects rivers and inland lakes, potentially increasing the area that
must be evacuated.
Obviously, the more intense the storm,
and the closer you are to its right-front quadrant, the larger the area you will
have to evacuate. The problem is, how do you know what category storm is going
to hit you?
Wave and current action associated with
the tide also causes extensive damage. Water weighs approximately 1,700 pounds
per cubic yard; extended pounding by frequent waves can demolish any structure
not specifically designed to withstand such forces.
The currents created by the tide
combine with the action of the waves to severely erode beaches and coastal
highways. Many buildings withstand hurricane force winds until their
foundations, undermined by erosion, are weakened and fail.
In estuaries and bayous, intrusions of
salt water endanger the public health and send animals, such as snakes, fleeing
from flooded areas.