Combined impact at dock
Wave propagation through Apra Harbor entrance and diffraction in the
harbor occurs simultaneously with local wave generation inside the harbor.
Significant wave height at the dock resulting from these two components can be
estimated by assuming that the total energy density in the sea surface is equal to
the sum of the energy densities due to each wave component. Since energy
density is proportional to wave height, this gives:
H sdock = H s2diff + H s2loc
(19)
where
Hsdock = total significant wave height at the dock
harbor entrance
Waves also partially reflect from the dock. Interaction between incident and
reflected waves effectively increases significant wave height adjacent to the
dock by a factor of one plus the reflection coefficient. Assuming waves are
symmetric about the swl, one-half of the significant wave height will rise above
the swl. Finally, the elevation reached by the crest of the significant wave
incident to the dock can be calculated as
WLs = swl + 0.5 * H sdock (1 + Cr )
(20)
where
WLs = elevation reached by crest of significant wave
swl = still-water level due to tide and storm effects
Cr = reflection coefficient at dock face
Reflection coefficient values used in this study are 0.5 along the exposed dock
face with southwest exposure and 0.1 along the relatively protected dock face
with exposure to the south.
These relationships are included in the Fortran program HARBOR so that a
time-history of WLs can be easily calculated for each typhoon modeled.
Empirical Simulation Technique
Storm damage reduction programs and design of coastal structures typically
require a storm-surge analysis to obtain a peak water-surface elevation for design
water levels. Because typhoons and hurricanes occur infrequently at a given site,
abundant storm-surge stages are generally not available and standard ranking
27
Chapter 3
Modeling Approach
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