ERDC/CHL CETN-IV-25
June 2000
1 .2
w aves
and
L -S
c u rre n t
w aves only
larg e-scale (L-S) cu rrent only
0 .8
0 .4
0 .0
0
200
400
600
800
1000
C ro s s -S h o re D is ta n c e (m )
Figure 4. Simulation of the effect of a large-scale current
on a wave-generated nearshore current
The example concerns wave transformation on flood and ebb currents. An inlet channel is
simulated with a water depth of 4 m at the throat and linearly sloping offshore to a depth of 12 m
(assumed boundary for this inlet). Waves are assumed to travel along the channel (0 incident
wave angle), and the tidal current (flood or ebb) decreases linearly from the throat to the offshore
end of the channel where it was set to 0 (at the 12-m water depth corresponding to x = 0 in
Figure 5). The deepwater rms wave height was 1.0 m, and the mean wave period 8 sec (typical
for Shinnecock Inlet). Standard parameter values were employed in the NMLong-CW
simulations.
Figure 5 displays the results of the simulations for two different current speeds at the inlet throat
for flood, ebb, and no-current cases. In the no-current case, a small increase in wave height is
observed because of shoaling, whereas for the flood current the waves experience a reduction in
height as they approach the inlet. The opposite trend occurs if the waves encounter an ebb flow
and a pronounced wave height increase might take place. For example, in the case of an ebb
current of 3.0 m/sec at the inlet throat, wave breaking occurs because of the limitation in wave
steepness, causing a reduction in wave height, as seen in Figure 5 (note that the waves propagate
along the x-axis to allow qualitative comparison with Figure 6). Also, for the larger ebb current,
wave blocking is taking place before the waves reach the inlet throat. Figure 6 is a photograph
taken from the east jetty at Shinnecock Inlet and shows wave breaking and blocking on an ebb
current. Note that the waves cannot penetrate against the current, with turbulent water to the left
(south) and calm water to the north, inside the inlet.
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