Transport paths and morphology change were calculated for tide only, wave only, and combined
tide and wave forcing by application of coupled circulation, wave, and sediment transport-
morphology change models. Wave forcing was exaggerated by specification of a relatively large
wave angle to induce strong morphologic response over short simulation intervals. This
approach allows rapid testing to determine if calculated transport and morphologic change
patterns are representative of those observed in nature.
The circulation model M2D (Militello and Zundel, 2003) has been coupled to the steady
spectral wave model (STWAVE) (Smith et al. 2001) through the Surfacewater Modeling System
(SMS). This coupling provides a method for representing multiple scales of motion, a situation
prevalent in coastal dynamics owing to the presences of the tide, waves, and interaction of these
processes including wave transformation and breaking (Militello et al. 2000). Radiation stress
gradients from the wave model are mapped to the circulation model for calculation of the wave-
induced current. Depth-integrated currents from the circulation model are mapped to the wave
model for calculation of wave-current interaction. Sediment transport is calculated through the
total sediment load formulation of Watanabe (1987) as one of several sediment-transport formula
options. This coupled system calculates tidal propagation; the current driven by the tide, waves,
and wind; sediment transport; and bottom morphology change.
COUPLED MODELS
Combined circulation and wave modeling was conducted with the Steering Module, a
component of the SMS interface developed in the U.S. Army Corps of Engineers' Coastal Inlets
Research Program that couples models at user-specified time steps called "steering intervals"
(Zundel et al. 2000; Zundel et al. 2002). The Steering Module provides three options for
coupling of M2D and STWAVE: (1) 1-way coupling STWAVE to M2D. Radiation stress
gradients from STWAVE are input to M2D for wave-driven current calculations; (2) 1-way
coupling of M2D to STWAVE. Current fields from M2D are input to STWAVE for calculation
of wave-current interaction; and (3) 2-way coupling. Both 1-way coupling options are conducted
to calculate wave-driven currents and wave-current interaction. For all simulations in this study
that involved combined waves and tidal forcing, 2-way coupling was invoked. Coupling of the
circulation and sediment transport models was achieved by implementing the Watanabe (1987)
total-load formulation directly into M2D. Current velocity, ambient depth, water level, and
bottom stress were input to the sediment transport model every 100 s. Sediment transport rates
and updated values of depth over the model domain were calculated. The updated depths were
then input to the circulation model so that the hydrodynamic responses to change in bathymetry
were calculated. Sediment transport rates (median grain size of 0.2 mm) were output
periodically, from which sediment-transport paths can be identified. Time-varying depths were
also output to examine morphology change.
SIMULATION SPECIFICATIONS
An idealized grid was developed such that the inlet, channel, ebb shoal, and bay dimensions
approximate those of Shinnecock Inlet. Ocean and inlet grid dimensions are 15 km alongshore,
5 km from the shoreline to the ocean boundary, and inlet length and width of 500 m and 300 m,
respectively. Bay dimensions are 1.5 km 5 km, with depth of 5 m, giving a total volume of
37.5 M m3, approximating that of Shinnecock Bay. Inlet depth was specified as 5 m, and the
minimum depth of the spherical ebb shoal was 2 m, similar to that at Shinnecock Inlet, and at the
approximate same distance offshore (Fig. 1). (The idealized grid is rotated approximately 90 deg
Militello and Kraus
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