4
Harbor Response to Wind
Waves and Swell
Numerical model studies of the harbor response to wind waves and swell
were directed primarily toward assessing the operational performance of
alternative harbor sites and establishing design wave and water levels. Results
are summarized in this chapter. Amplification factors are discussed in the
following section. The next section gives Hs values exceeded 10 percent of the
time, a result more directly applicable to operational performance, and values
exceeded 1 percent of the time, an indicator of more extreme conditions. The Hs
values are derived from a combination of amplification factors from the
numerical model and wave hindcast information outside the harbor. They are
compared to operational criteria for wind waves and swell. The final section
gives extreme wave and water level information for design.
Amplification Factors
Each CGWAVE model run produces wave height results over the model
domain. Results were saved along output lines representing the four alternative
harbor sites, as discussed in Chapter 3. Wave height results were converted to
amplification factor results, where amplification factor is defined as the ratio of
local wave height to incident wave height. Amplification factors from the
various CGWAVE runs are then weighted and combined to represent
directionally spread shortwave spectra in the form of (Aamp)eff for the variety of
wind wave and swell conditions in the 5-year hindcast summary.
Amplification factors from the CGWAVE runs, before computation of
(Aamp)eff , can be somewhat variable because of the discrete values of wave period
and direction being modeled in each run. However, they are the basis for the
directional spectral calculations, and they can illustrate some basic characteristics
of wind wave and swell response at the study sites. Amplification factors for
each wave direction, with values for the various wave periods (6, 8, 10, and
12 sec) averaged together, Figure 14. They illustrate the impact of incident wave
direction on amplification factor at the study sites. Points shown in the figure
begin with the southernmost point on the Anasosopo output line and proceed
north and counterclockwise, as illustrated in Figure 13. At Anasosopo, waves
from the south have heights about 0.6 times the incident wave height. At Aua,
waves from the south also have the biggest impact. At Leloaloa, waves from
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Chapter 4 Harbor Response to Wind Waves and Swell
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