useful for present purposes (though they are stated to be applicable only for
fishing vessels, coasters, freighters, ferries, and Ro-Ro vessels). The operational
criteria for maximum velocity vary with size of ship, but they can be summarized
as: maximum horizontal velocity less than 0.3- to 0.6-m/sec (1- to 2-ft/sec).
Maximum velocity decreases as ship size increases, with 0.3 m/s (1 ft/sec)
representing an 8,000-DWT ship and 0.6 m/sec (2 ft/sec) representing a
1,000-DWT ship.
Horizontal velocity was computed over the Pago Pago Harbor embayment
for the nine selected resonant conditions (Figures 25 through 27). Velocity
magnitude is directly related to longwave height. Longwave height was 10 cm
(0.3 ft) in the simulations, as in a recent study of Kahului Harbor (Thompson and
Demirbilek 2002). Since velocities along existing docks significantly exceeded
the PIANC criteria, velocities were scaled down to represent a 1-cm (0.03-ft)
incident longwave height, which produced velocities that are at least qualitatively
consistent with the operability of existing docks. Although these are velocities of
the water resulting from long wave motion rather than moored ship velocities (as
in the PIANC criteria), they still provide a relevant metric for comparing harbor
sites.
Horizontal velocity because of resonant oscillations in the Pago Pago Harbor
embayment is strongly related to local water depth. The deeper areas
consistently show velocities well below the PIANC criteria. Reef areas and the
shallow Aua embayment show velocities exceeding the PIANC criteria for many
of the resonant cases, especially the shorter period cases. For the 454.6-sec
resonance (Peak 2), velocities of about 0.3- to 0.6-m/sec (1- to 2-ft/sec) are
evident in most of the western tip of the harbor, including the Anua site.
Since three of the four alternative sites (Anasosopo, Aua, and Leloaloa) are
adjacent to reef areas, they may be affected by strong velocities due to resonant
oscillations. In practice, dock facilities in these areas which are sufficiently deep
and offset from the reef may not experience operational difficulties due to long
waves.
39
Chapter 5 Harbor Oscillations
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