Page 414 - Laboratory Manual in Physical Geology

Panel on Climate Change (IPCC) of the United Nations surges. A storm surge is an abnormal rise of
Environment Programme (UNEP) has suggested that sea water pushed landward by high winds and/or low
level will continue to rise and is now expected to achieve a atmospheric pressure associated with storms. The storm
mean global rise of at least 0.17–0.32 m (6.7–13.6 inches) surge is over and above the normal tide, and NOAA
by 2046–2065. Note that these figures are for mean expresses it as the height above the expected tide level.
(average) changes of global sea level. Specific locations may NOAA also measures storm tide —which it defines as
experience more or less of a rise in sea level. For example, the water level height caused by a combination of the
although TOPEX/Poseidon satellite altimetry indicates normal tide level and the storm surge. Storm surges can
that sea level is rising at a global rate of 2.9 mm/yr, NOAA cause the ocean to rise by about 1–10 feet above the
tide gauge records indicate that sea level at Ocean City, normal astronomical tide, depending on the magnitude
Maryland (FIGURE 15.7), has been rising nearly twice as fast of the storm and other factors. However, except for
(5.48 mm/yr since 1975). hurricanes, most storm surges are in the range of
Sea level also fluctuates both above and below 2–3 feet.
mean sea level during daily tidal cycles and storm

Breakwater
(Offshore sea wall) Jetties Groins
Harbor
Sea wall

Wind
Longshore current

FIGURE 15.6 Coastal structures. Sea walls are constructed along the shore to stop erosion of the shore or extend the shoreline (as
sediment is used to fill in behind them). Breakwaters are a type of offshore sea wall constructed parallel to shoreline. The breakwaters stop
waves from reaching the beach, so the longshore drift is broken and sand accumulates behind them (instead of being carried down shore with
the longshore current). Groins are short walls constructed perpendicular to shore. They trap sand on the side from which the longshore current
is carrying sand against them. Jetties are long walls constructed at entrances to harbors to keep waves from entering the harbors. However,
they also trap sand just like groins.

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