CHAPTER 3
WAVE AND WATER-LEVEL PREDICTIONS
3.1 INTRODUCTION
Chapter 2, treated phenomena associated with surface waves as though
each phenomenon could be considered separately without regard to other
phenomena. Surface waves were discussed from the standpoint of motions
and transformations without regard to wave génération. Furthermore, the
water level, stï/L'Lvate'r tevel (SWL), on which the waves propagated was
assumed known.
In this chapter, wave observations are presented to show characteristics of surface waves in nature. The characteristics of real waves are
much less regular than those implied by theory. Also presented are procedures for representing the complexity of the real sea by a small number
of parameters. Déviations between the actual waves and the parameter
values are discussed.
Theory for wave génération is reviewed to show progress in explaining
and predicting the actual complexity of the sea. Wave prédiction is
called hindcasting when based on past meteorological conditions, and forecasting when based on predicted conditions. The same procedures are used
for hindcasting and forecasting; the only différence is the source of
meteorological data. The most advanced prédiction techniques currently
available can be used only in a few laboratories, because of the need for
electronic computers, the sophistication of the models, and the need for
correct weather data. However, simplified wave prédiction techniques,
suitable for use by field offices or a design group are presented.
While simplified prédiction Systems will not solve ail problems, they
can be used to indicate probable wave conditions for most design studies.
Simplified wave prédiction can also be used to obtain statistical wave
data over several ypars.
Review of prédiction théories is presented to give the reader more
perspective for the simplified prédiction methods that are presently
available. This will justify confidence in some applications of the
simplified procedures, will aid in recognizing unexpected difficulties
when they occur, and will indicate some conditions in which they are not
adéquate.
The graphs in Sections 3.5, Simplified Wave Prédiction Models, and
3.6, Wave Forecasting for Shallow Water Areas, may be read with the précision justified by the underlying theory. The équations were derived
originally from graphs, and do not provide any physical understanding.
Calculations with the graphs should be carried out to tenths or hundredths
where this is feasible, and then rounded off in the final resuit.
Prédictions are compared with available observations wherever possible
to indicate their accuracy. Calibration of techniques applied to a spécifie géographie area by comparison with available observations is always
désirable.
3-1
WAVE AND WATER-LEVEL PREDICTIONS
3.1 INTRODUCTION
Chapter 2, treated phenomena associated with surface waves as though
each phenomenon could be considered separately without regard to other
phenomena. Surface waves were discussed from the standpoint of motions
and transformations without regard to wave génération. Furthermore, the
water level, stï/L'Lvate'r tevel (SWL), on which the waves propagated was
assumed known.
In this chapter, wave observations are presented to show characteristics of surface waves in nature. The characteristics of real waves are
much less regular than those implied by theory. Also presented are procedures for representing the complexity of the real sea by a small number
of parameters. Déviations between the actual waves and the parameter
values are discussed.
Theory for wave génération is reviewed to show progress in explaining
and predicting the actual complexity of the sea. Wave prédiction is
called hindcasting when based on past meteorological conditions, and forecasting when based on predicted conditions. The same procedures are used
for hindcasting and forecasting; the only différence is the source of
meteorological data. The most advanced prédiction techniques currently
available can be used only in a few laboratories, because of the need for
electronic computers, the sophistication of the models, and the need for
correct weather data. However, simplified wave prédiction techniques,
suitable for use by field offices or a design group are presented.
While simplified prédiction Systems will not solve ail problems, they
can be used to indicate probable wave conditions for most design studies.
Simplified wave prédiction can also be used to obtain statistical wave
data over several ypars.
Review of prédiction théories is presented to give the reader more
perspective for the simplified prédiction methods that are presently
available. This will justify confidence in some applications of the
simplified procedures, will aid in recognizing unexpected difficulties
when they occur, and will indicate some conditions in which they are not
adéquate.
The graphs in Sections 3.5, Simplified Wave Prédiction Models, and
3.6, Wave Forecasting for Shallow Water Areas, may be read with the précision justified by the underlying theory. The équations were derived
originally from graphs, and do not provide any physical understanding.
Calculations with the graphs should be carried out to tenths or hundredths
where this is feasible, and then rounded off in the final resuit.
Prédictions are compared with available observations wherever possible
to indicate their accuracy. Calibration of techniques applied to a spécifie géographie area by comparison with available observations is always
désirable.
3-1