each output line. For each recreated observation, the corresponding wave height
at a harbor point is:
( H s )harbor = ( Aamp )eff ( H s )incident
(1)
where
(Hs)harbor = significant wave height at a point in the harbor
(Aamp)eff = spectral amplification factor calculated from model results for
the periods and directions in Table 4 to represent Tp and θp in
the incident wave time-history
(Hs)incident = incident deepwater significant wave height
The time-history of (Hs)harbor at each point along the output lines was sorted
into descending order, and the value of Hs which was exceeded 10 percent of the
time, H10, was identified. The Hs value which was exceeded 1 percent of the
time, H1, was also identified. The Hs with 1-percent exceedance relates to a more
demanding operational condition which may be relevant to heavily used
commercial docks.
Along the alternative harbor sites considered, H10 values are between 0.15 m
(0.5 ft) and 0.6 m (2.0 ft), except for a value of 0.64 m (2.1 ft) at the most
exposed point at Anasosopo and very low values at Anua (Figure 16 and
Table 6). 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. The highest values of H10 occur at Anasosopo, which is the site
nearest the embayment entrance and most exposed to incident waves. At
Anasosopo, H10 ranges from 0.5 to 0.6 m (1.5 ft to 2.1 ft). These values are
significantly reduced from the offshore incident wave heights, mainly because of
considerable sheltering of the site by Breakers Point.
At Aua, H10 drops to the range of 0.2 to 0.3 m (0.5 ft to 1.0 ft), except for two
higher points affected by a local bathymetric hump discussed previously. Aua is
significantly more sheltered than Anasosopo. It lies deeper into the Pago Pago
Harbor embayment. Breakers Point, Niuloa Point, and Tulutulu Point all afford
sheltering to the Aua site. In addition, a large lobe in the fringing reef just south
of the site adds to the local sheltering.
The Leloaloa site, although deeper into the embayment than Aua, is less
protected from incident waves. The Leloaloa site has a more direct exposure to
the commonly occurring waves from southeast directions. Values of H10 at
Leloaloa range from 0.3 to 0.4 m (1.1 ft to 1.4 ft) along most of the line,
dropping to 0.2 m (0.5 to 0.6 ft) at the more sheltered end of the line. The
Leloaloa site benefits from sheltering by Breakers Point and Tulutulu Point. The
west end of the Leloaloa line also benefits from sheltering by Goat Island Point, a
major impact which also benefits existing harbor facilities further west.
25
Chapter 4 Harbor Response to Wind Waves and Swell