Wind forcing was not included in the simulation, so wind-driven setup and
setdown in the bay and near the coast were not represented. Although this forcing of
water level would potentially alter tidal flushing through the inlet, breaking of waves
and transport pathways of sediment on the ebb-shoal, its control on the
hydrodynamics and sediment dynamics is expected to be secondary to waves and
Additionally the sediment transport module was designed for a uniform grain
size. In general the ebb and flood shoals, bypass bar and beaches are comprised of
fine to medium sand (0.20 0.35 mm) and an assumed uniform grain size would
produce reasonable results. However, the main navigation channel through the throat
of the inlet could contain more coarse material including gravel and shell hash. This
material would be more resistant to erosion and would not have scoured as rapidly as
predicted by the present transport model.
There are certain weaknesses inherent in the condensed forcing approach of the
modeling system, as well as limitations associated with the sediment transport
module. Calculations of morphology and water levels are expected to improve by
modeling the complete time period between surveys (8/13/97 through 5/28/98), and
including time-varying wind stress in the momentum equations. Implementation of
non-uniform grain sizes in the IMS is a planned enhancement, and once available
simulations at Shinnecock Inlet will be conducted to take advantage of this capability.
Evolution of morphology at Shinnecock Inlet between August 13, 1997 and May
28, 1998 was found to be associated with the westward migration of the main
channel. A coupled circulation, wave, and sediment transport modeling system was
applied to calculate morphology change and to determine the primary controls on
channel migration. General trends of natural sediment bypassing, growth of the ebb
shoal, scour in the throat, and channel migration were reproduced by the IMS-M2D
version forced by accurate tides and waves.
In summary, major measured morphologic change observed in at the inlet and ebb
shoal was simulated successfully in the IMS. These changes were associated with the
westward deflection of the channel seaward of the inlet, which include erosion of the
western flank along the channel, shallowing of the eastern flank of the ebb shoal, and
deposition along the seaward edge of the ebb shoal where the ebb jet terminates.
Channel deflection is controlled primarily by tidal processes consisting of
periodic ebb jet formation and advection of the jet by the coastal tidal current. Waves
originating from southeast enhance channel migration.
This research was sponsored by the Inlet Modeling System Work Unit of the
Coastal Inlets Research Program, Coastal and Hydraulics Laboratory, U.S. Army