STWave grid so that the temporal modulation of wave properties with changes in
water level was represented. Coupling between M2D and STWave was set at 3-hr
intervals.
Sediment transport and morphology change were calculated within M2D.
Combined wave- and tide-driven velocities were entered into computations of local
shear stress and sediment transport rates were calculated by the Watanabe (1987)
total load formulation,
(τ - τ )V
qt = A b cr
(4)
ρw g
where qt is the total load (both suspended and bed), τ b is the shear stress at the bed,
τ cr is the shear stress at incipient sediment motion, V is the depth averaged current
velocity as provided by the coupled model, ρ w is the density of water, g is the
2 for regular to irregular waves). For this investigation the sediment was
considered to be homogeneous medium sand. Transport rates for each M2D cell
were computed every 100 seconds. Through mass conservation, the bathymetry was
updated at 6-hr intervals giving morphology change of the inlet, shoals, and nearshore
region. At each bathymetric update, new depths were provided to the hydrodynamic
component of the model for calculation of velocity and water level response to
changes in morphology.
Grid Development
Bathymetric data for the M2D and STWave grids were obtained from several
sources including NOAA, GEODAS, Marine Science Research Center State
University of New York at Stony Brook, and USACE. Bathymetry covering the
region surrounding Shinnecock Inlet (ebb shoal, throat, and flood shoal) was obtained
from the August 13, 1997 and the May 28, 1998 SHOALS surveys. Model grids
cover all of Shinnecock Bay and extend up and downdrift of the inlet to regions
unaffected by the ebb-tidal shoal (Fig. 8). Seaward boundaries extend offshore to
30 m water depth, beyond the zone where wave shoaling takes place and beyond the
closure depth and farthest seaward extent of the ebb jet.
The STWave grid was specified to have 20-m spacing over its domain. This
spacing provides several cells per wavelength and adequately resolves the radiation-
stress gradients within the shoaling, breaking and surf zones, leading to more accurate
calculation of water levels and currents there. The M2D grid was developed such
that the cell spacing was 100 m in the deeper water offshore, and transitions to 10 m
near the coastline, inside the wave shoal zone, around the flood and ebb shoals, and in
the inlet throat (Fig. 9). Wave transformation in these regions takes place over
relatively short distances and greater resolution was specified in areas so that details
of the circulation and sediment transport would be reproduced. The two grids
(STWave and M2D) covered identical geographical regions (Fig. 8).
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