Tidal flushing
results in the significant variability of the vertical
and horizontal shear of tidal currents during the tidal
cycle. In the homogeneous case with only tidal forcing,
the along-isobath tidal current in the NB/MHB channel
is almost uniform in the vertical during the early flood,
with a maximum speed in the center of channel and decreasing
toward the coast (Fig. 2: upper-left). This pattern remains
unchanged until the maximum flood, during which a velocity
reversal occurs on the northern coast due to flow separation
and the axis of the maximum tidal current shifts toward
the southern side (Fig. 2: middle-left). Two hours after
the maximum flood, however, a strong vertical shear occurs
in the deep channel, with maximum current near the bottom,
decreasing toward the surface (Fig. 2: lower-left). At
this time, the water in the upper 10 m tends to move toward
the southern coast, which is consistent with the formation
of a large clockwise eddy in the southern coastal area.
The velocity returns to a uniform vertical profile again
during the early phase of the ebb period, with a maximum
outflow on the slope of the channel about 2 km away from
the coast on both sides of the transect (Fig. 2: upper-right).
A significant vertical shear of tidal currents occurs
at the maximum ebb, with the maximum velocity at the surface
with depth
|
(Fig.2: mid-right). The vertical profile
of tidal currents becomes much more complex in the later
phase of the ebb period, during which the outflow is stronger
on the southern coast than on the northern coast and is
strongest at the surface (Fig. 2: lower-right). |
