6
Conclusions and
Recommendations
Studies of the wave response of alternative sites for Pago Pago Harbor have
produced information to assist in planning for future harbor facility requirements.
The numerical model CGWAVE was used to simulate the behavior of the Pago
Pago Harbor embayment, including four alternative harbor sites. Model results
are compared with criteria for operational acceptability and with experience in
the existing harbor to the extent possible. The effectiveness of proposed new
harbor areas for wind wave and swell protection often has little relationship to
protection from oscillations. These two aspects of pier operability are both
considered in judging suitability of the alternative sites. Extreme wave and water
level information for design is also presented.
Key input information for the study was available with varying degrees of
accuracy. Detailed recent bathymetry was provided by HED for the entire Pago
Pago Harbor embayment, including reef areas. The offshore wave climate
incident to the study area was developed from summary tables of a 5-year
hindcast of deepwater, open ocean waves near Western Samoa. This wave
climate is expected to be reasonably representative but, if better definition of the
incident wind wave and swell climate becomes available in the future, a more
accurate assessment of the harbor sites will be possible. Very little information
was available relative to long waves and this area appears to behave differently
than more typical harbors studied previously. No data on incident longwave
conditions exist, and no information about longwave response in Pago Pago
Harbor embayment exists other than qualitative experience at existing docks.
Thus, the long wave part of the study is primarily qualitative.
An overview of performance of the alternative sites is given by their success
relative to a simple, meaningful criterion. For wind waves and swell, success
was defined as having Hs> 0.3 m (1 ft) less than 10 percent of the time. This
criterion is often used for small, shallow-draft vessel mooring areas, but it can
also be a meaningful metric for operational suitability of deep-draft docks. A
less demanding criterion, which may be more applicable to larger moored
vessels, was also considered, namely Hs> 0.6 m (2 ft) less than 10 percent of the
time. This secondary criterion may suffice, depending on the vessel types and
sizes to be using the dock and the flexibility of their calling schedules. A similar
overview of site performance for harbor oscillations could be developed only in
relative terms, since quantitative longwave information was lacking.
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Chapter 6 Conclusions and Recommendations
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