Different parameters are used for the long wave tests. The reflection
coefficient was set to 1.0 for all boundaries, since long waves generally reflect
very well from a coastal boundary. Long waves are more affected by bottom
friction than short waves, so a value greater than zero is appropriate. The value
is best determined by calibration with field data when possible. Since no field
data are available in this area, a value of 0.02 was selected, based on previous
calibration at Kahului Harbor, Maui, Hawaii (Thompson and Demirbilek in
preparation). These and other parameters are summarized in Table 3.
Test Procedures and Calculations
Incident wave conditions
A range of short- and longwave conditions incident to the Pago Pago Harbor
embayment was considered. A representative range of wave periods and
directions which could cause damaging waves inside the harbor was included,
based on the hindcast wave climate and buoy data.
The shortwave periods and approach directions considered are given in
Table 4. The range of wave periods shown was tested for each direction shown.
These conditions provide reasonable coverage of the wave climate. Directions
were chosen to cover the full directional exposure of the harbor entrance, in
22.5-deg increments (Figure 12). These incident wave components can be
expected to give a good representation of the directional spectrum in post-
processing.
Table 4
Summary of Incident Shortwave Conditions
Wave Period (sec)
Wave Direction (deg az., coming from)
6
90.0
8
112.5
10
135.0
12
157.5
180.0
202.5
225.0
For the study of alternative harbor sites, CGWAVE was run with shortwave
periods of 6 to 12 sec and the full set of directions in all possible combinations.
Wave heights of 1.5, 2.5, 3.5, 5, and 7 m (4.9, 8.2, 11.5, 16.4, and 23.0 ft) were
run for each period/direction combination. Model results were then properly
weighted and recombined to represent a directional spectrum for each bin in the
5-year incident wave climate summary. Selected longer-period cases (14 to
20 sec) were run with a single wave height of 2 m and direction of east southeast.
The longest period represents a very long swell condition. These cases, which
are outside the normal wave climate, were run in the event some special concerns
related to long period swell should need to be addressed in the future.
18
Chapter 3 Numerical Model
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