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Lesson N°10 :
Sea level fluctuations and changes :
Dynamic changes in sea level on the order of hours to a few decades
reflect response of the water surface to meteorological and
oceanographic processes as well as tides and can be thought of as
periodic or episodic deviations about mean sea level. They affect the
level at which wave action occurs and thus have an effect on coastal
erosion, transportation and deposition.
In addition to tides produced by the gravitational force of the moon
and the sun , short-term fluctuation in sea level occur as a result of
strom surge , seasonal variations in pressure and wind patterns and
changes in weather patterns on a scale of years to decades.
There are a large number of causes of changes in sea level which vary
in their magnitude and on the time scale over which they operate .
We can think of sea level as the average level of the sea at a point
along the coastline,or in the open ocean ,and thus fluctuations due to
tides ,meteorological conditions and short-term variations in ocean
temperature and currents can be seen as departures above and below
this level.
Tides and coastal processes :
Along ocean coasts tides produce a regular daily rise and fall of sea
level that may range from a few decimeteres to as much as 15 m in a
few places .
These fluctuations are termed astronomical tides because they are
produced by the gravitational influence of the moon and sun , and this
distinguishes them from other
short-term changes in sea level
produced , for example , by strong winds or changes in barometric
pressure which are sometimes termed meteorological tides.
Short- term dynamic changes in sea level :
Temperature , pressure and ocean current effects :