The first five hâve periods that range from a few minutes to a few
days; the last two hâve periods that range from semi-annually to many
years. Although important in long-term changes in water élévations,
climatological and secular variations are not discussed here.
Forces caused by the graviational attraction between the moon, the
sun, and the rotating earth resuit in periodic level changes in large
bodies of water. The vertical rise and fall resulting from these forces
is called the tide or astronomical tide; the horizontal movements of
water are called tidal currents. The responses of water level changes to
the tidal forces are modified in Coastal régions because of variations in
depths and latéral boundaries; tides vary substantially from place to
place. Astronomical tide generating forces are well understood, and can
be predicted many years in advance. The response to these forces can be
determined from an analysis of tide gage records. Tide prédictions are
routinely made for many locations for which analyzed tide observations
are available. In the United States, tide prédictions are made by the
National Océan Survey, National Océanographie and Atmospheric Administration
Tsunamis are generated by several mechanisms: submarine earthquakes,
submarine landslides, and underwater volcanos. These waves may travel
distances of more than 5,000 miles across an océan with speeds at times
exceeding 500 miles per hour. In open océans, the heights of these waves
are generally unknown but small; heights in Coastal régions hâve been
greater than 100 feet.
Seiches are long-period standing waves that continue after the
forces that start them hâve ceased to act. They occur commonly in
enclosed or partially enclosed basins.
Voue setup is defined as the supere levât ion of the water surface due
to the onshore mass transport of the water by wave action alone. Isolated
observations hâve shown that wave setup does occur in the surf zone.
Surges are caused by moving atmospheric pressure jumps and by the
wind stress accompanying moving storm Systems. Storm Systems are significant because of their frequency and potential for causing abnormal water
levels at coastlines. In many Coastal régions, maximum storm surges are
produced by severe tropical cyclones called hurricanes.
Prédiction of water level changes is complex because m^ny types of
water level fluctuations can occur simultaneously. It is not unusual
for surface wave setup, high astronomical tides, and storm surge to occur
coïncidently at the shore on the open coast. It is difficult to détermine
how much rise can be attributed to each of these causes. Although astronomical tides can be predicted rather well where levels hâve been recorded
°C l"°5e’ there are many locations Where this information is not
shaîinw
Furthermore> the interaction between tides and storm surge in
shallow water is not well defined.
3-70
days; the last two hâve periods that range from semi-annually to many
years. Although important in long-term changes in water élévations,
climatological and secular variations are not discussed here.
Forces caused by the graviational attraction between the moon, the
sun, and the rotating earth resuit in periodic level changes in large
bodies of water. The vertical rise and fall resulting from these forces
is called the tide or astronomical tide; the horizontal movements of
water are called tidal currents. The responses of water level changes to
the tidal forces are modified in Coastal régions because of variations in
depths and latéral boundaries; tides vary substantially from place to
place. Astronomical tide generating forces are well understood, and can
be predicted many years in advance. The response to these forces can be
determined from an analysis of tide gage records. Tide prédictions are
routinely made for many locations for which analyzed tide observations
are available. In the United States, tide prédictions are made by the
National Océan Survey, National Océanographie and Atmospheric Administration
Tsunamis are generated by several mechanisms: submarine earthquakes,
submarine landslides, and underwater volcanos. These waves may travel
distances of more than 5,000 miles across an océan with speeds at times
exceeding 500 miles per hour. In open océans, the heights of these waves
are generally unknown but small; heights in Coastal régions hâve been
greater than 100 feet.
Seiches are long-period standing waves that continue after the
forces that start them hâve ceased to act. They occur commonly in
enclosed or partially enclosed basins.
Voue setup is defined as the supere levât ion of the water surface due
to the onshore mass transport of the water by wave action alone. Isolated
observations hâve shown that wave setup does occur in the surf zone.
Surges are caused by moving atmospheric pressure jumps and by the
wind stress accompanying moving storm Systems. Storm Systems are significant because of their frequency and potential for causing abnormal water
levels at coastlines. In many Coastal régions, maximum storm surges are
produced by severe tropical cyclones called hurricanes.
Prédiction of water level changes is complex because m^ny types of
water level fluctuations can occur simultaneously. It is not unusual
for surface wave setup, high astronomical tides, and storm surge to occur
coïncidently at the shore on the open coast. It is difficult to détermine
how much rise can be attributed to each of these causes. Although astronomical tides can be predicted rather well where levels hâve been recorded
°C l"°5e’ there are many locations Where this information is not
shaîinw
Furthermore> the interaction between tides and storm surge in
shallow water is not well defined.
3-70