Shinnecock Inlet experienced five intense wave events during the month of
November. For three of these events, wave heights exceeded 4 m and periods ranged
between 10 and 11 sec from the southeast quadrant. The two smaller events (wave
height of 2.5 to 3 m; period 7 to 9 sec) approached the inlet from the southwest.
Bathymetry changes at the end of November indicated increased deposition along the
bypass bar and seaward extent of the ebb jet, and continued westward deflection of
the main channel (Fig. 12).
Discussion
Wave conditions for the simulation varied from low energy in the months of
August and September to moderate and eventually high-energy environments for
October, 1997 and November, 1997 respectively. Morphologic changes computed
for the end of September indicated the regional influence of tidal transport was
localized around the throat and mouth of the inlet and the pathway of the ebb jet.
Westward migration of the channel thalweg was shown to occur during weak wave
forcing. Two tidal processes are responsible for this migration. The periodic
formation of the ebb jet scours the channel thalweg. In addition, the coastal tidal
current advects the jet toward the west, which translates the erosional stresses of the
jet westward. Together, these processes scour the western portion of the channel,
which realigns of the thalweg.
Scouring of the navigation channel in the throat of the inlet throughout the
simulation is consistent with the analytical relationship of Jarrett, 1976 (Eq. 1), and
previous observations of the inlet (Militello and Kraus 2001b). Additionally the ebb
shoal continued to evolve toward the equilibrium volume (Eq. 2) by accreting
14,370 m3 of sediment over the fifteen-week period. Calculated modes of natural
sediment bypassing were also in agreement with the theoretical stability ratio of
Bruun and Geritsen (1959). Observed transport pathways were associated with
channel flushing through the throat of the inlet and wave-driven transport along the
perimeter of the ebb shoal and bypass bar.
Previous investigations have attributed the westward deflection of the main
channel of Shinnecock Inlet attributes to: 1) continuous tidal deflection of the ebb jet
(Militello and Kraus 2001a), and 2) increased deflection of the ebb jet by wave-
driven longshore currents (Buonaiuto, 2003a). Other controls on the jet migration are
the bay channel geometry, flood shoal, and offset jetties. Simulations conducted in
this study indicate the continuous tidal deflection of the ebb jet is a dominant process
controlling the migration of the channel, and it can be enhanced or accelerated by
increased wave activity and littoral sediment supply. Further analysis is required to
discern to what degree the observed changes in the morphology of Shinnecock Inlet
between the 1997 and 1998 surveys were in response to an increase in sediment
delivery. Sediment supplied to the inlet was most likely derived from wave driven
erosion and transport of the beaches and surfzone along the eastern and western
barriers.
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