The problem of obtaining wind information for wave hindcasting is
discussed, and spécifie instructions for estimating wind paraneters are
given.
Water levels continuously change. Changes due to astronomical tides
are predictable, and are well documented for many areas. Fluctuations due
to meteorological conditions are not as predictable, and are less well
documented.
Many factors govern water levels at a shore during a storm. The
principle factor is the effect of wind blowing over water. Some of the
largest increases in water level are due to severe storms, such as hurricanes, which can cause storm surges higher than 25 feet at some locations
□n the open coast and even higher water levels in bays and estuaries.
Estimating water levels caused by meteorological conditions is complex,
even for the simplest cases; and unfortunately, the best approaches available for predicting these water levels are elaborate computational techniques which require the use of large digital computers.
3.2 CHARACTERISTICS OF OCEAN WAVES
The earlier discussion of waves was concemed with idealized, monochromatic waves. The pattern of waves on any body of water exposed to
atmospheric winds generally contains waves of many periods. Typical
records from a recording gage during periods of steep waves (Fig. 3-1)
indicate that heights and periods of real waves are not as constant as is
assumed in theory. Wavelengths and directions of propagation are also
variable. (See Figure 3-2.) The prototype is so complex that some
idealization is required.
3.21 SIGNIFICANT WAVE HEIGHT AND PERIOD
An early idealized description of océan waves postulated a significant
height and significant period, that would represent the characteristics of
the real sea in the form of monochromatic waves.
The représentation of a wave field by significant height and period
has the advantage of retaining much of the insight gained from the theoretical studies. Its value has been demonstrated in the solution of
engineering problems. For some problems this représentation appears
adéquate; for others it is useful, but not entirely satisfactory.
lo apply the significant wave concept it is necessary to define the
height and period parameters from wave observations. Munk (1944) défined
signvfioant wave height, as the average height of the one-third highest
waves, and stated that it was about equal to the average height of the
waves as estimated by an experienced observer. This définition, while
useful has some drawbacks in wave-record analysis. It is not always
clear which irregularities in the wave record should be counted to deterthe JJ0**1Tomber of waves on which to compute the average height of
simplyCH hlrd hlghest’ 7116 significant wave height is written as H1/3 or
3-2
discussed, and spécifie instructions for estimating wind paraneters are
given.
Water levels continuously change. Changes due to astronomical tides
are predictable, and are well documented for many areas. Fluctuations due
to meteorological conditions are not as predictable, and are less well
documented.
Many factors govern water levels at a shore during a storm. The
principle factor is the effect of wind blowing over water. Some of the
largest increases in water level are due to severe storms, such as hurricanes, which can cause storm surges higher than 25 feet at some locations
□n the open coast and even higher water levels in bays and estuaries.
Estimating water levels caused by meteorological conditions is complex,
even for the simplest cases; and unfortunately, the best approaches available for predicting these water levels are elaborate computational techniques which require the use of large digital computers.
3.2 CHARACTERISTICS OF OCEAN WAVES
The earlier discussion of waves was concemed with idealized, monochromatic waves. The pattern of waves on any body of water exposed to
atmospheric winds generally contains waves of many periods. Typical
records from a recording gage during periods of steep waves (Fig. 3-1)
indicate that heights and periods of real waves are not as constant as is
assumed in theory. Wavelengths and directions of propagation are also
variable. (See Figure 3-2.) The prototype is so complex that some
idealization is required.
3.21 SIGNIFICANT WAVE HEIGHT AND PERIOD
An early idealized description of océan waves postulated a significant
height and significant period, that would represent the characteristics of
the real sea in the form of monochromatic waves.
The représentation of a wave field by significant height and period
has the advantage of retaining much of the insight gained from the theoretical studies. Its value has been demonstrated in the solution of
engineering problems. For some problems this représentation appears
adéquate; for others it is useful, but not entirely satisfactory.
lo apply the significant wave concept it is necessary to define the
height and period parameters from wave observations. Munk (1944) défined
signvfioant wave height, as the average height of the one-third highest
waves, and stated that it was about equal to the average height of the
waves as estimated by an experienced observer. This définition, while
useful has some drawbacks in wave-record analysis. It is not always
clear which irregularities in the wave record should be counted to deterthe JJ0**1Tomber of waves on which to compute the average height of
simplyCH hlrd hlghest’ 7116 significant wave height is written as H1/3 or
3-2