Figs. 4c and 5c show circulation model results at peak flood and peak ebb, respectively,
with the inclusion of wave-induced currents generated by 4-m, 12-sec obliquely-incident
waves (waves from right, 30 deg from shore normal). Fig. 4 shows strong currents
(1.8 m/sec) near the outer portion of the ebb shoal, a strong longshore current (1.3-
longshore currents represent a 500-m wide surf zone for this storm wave condition. In
contrast, the tidal current (Fig. 4a) shows little or no longshore component. Breaking of
obliquely incident waves is the driving mechanism of these longshore currents.
Fig. 5c shows the confluence of ebb tidal currents with wave-induced currents to the
left of the ebb shoal, strengthening the longshore current to approximately 1.6-1.8 m/sec.
Longshore currents on the right side of the inlet are approximately 1.3 m/sec. A lobe of
weak (null) currents is observed near the left, downdrift shoreline and currents increase
500 m further downdrift. This weak current zone suggests a corresponding weak sediment
transport zone and hence is a possible mechanism in the formation of a downdrift
attachment point.
Grays Harbor, Washington, Simulations
From the idealized inlet model coupling simulations, the significance of wave-induced
currents in the surf zone, wave-current interaction at the inlet entrance, surf zone
resolution, and finite-difference and finite-element grid resolution compatibility were
determined to be major factors in the coupling process. Coupling of the wave and
circulation models for the Grays Harbor application therefore required addressing these
considerations.
A finite difference mesh was developed for the Grays Harbor area (Fig. 6). Grid cells
range from 50 km near the offshore boundary to 25 m in the surf zone. The fine nearshore
resolution is required to accommodate the interpolation of radiation stress gradients from
the finite difference wave model domain to the finite element circulation model domain
(Fig. 7). Radiation stress gradients produced with the STWAVE model were transformed
to the ADCIRC domain to examine tidal plus wave-induced currents. Beyond the wave
model domain, radiation stress gradients were extrapolated to zero using a standard
sigmoidal function. Currents from the finite-element circulation model were transformed
from the finite-element model to the finite difference wave model to examine the influence
of currents on waves. Two-way passing between models was also accomplished. This
paper concentrates on the effect of waves on currents.
Results are presented for a 5-day ADCIRC simulation. The ADCIRC model was forced
with a spring tide and a) no waves, b) 5-m 13-sec west-northwest (WNW) wave, and c)
6-m, 14-sec west-southwest (WSW) waves. Ideally, radiation stress gradients would
be passed to the circulation model every 1-3 hr during the simulation to include variation
in water level on wave transformation through a tidal cycle. However, these single-wave
condition simulations coupled the models at the start, mid-simulation, and end to reduce
simulation time and simplify the analysis process. Radiation stress gradients from the three
STWAVE simulations were then temporally interpolated for every ADCIRC timestep.
Figs. 8 and 9 show flood and ebb tidal currents and wave-induced currents for WNW and
WSW waves. As in the idealized case, the flood tidal currents increase on approach to
Cialone, Militello, Brown, and Kraus
8