The cross-shore variation of the long-term average
longshore current velocity was formed owing to the
difference between the wave and wind conditions when
the northward and southward longshore currents developed.
When the northward current developed, the offshore
wave height was relatively small and the frequency of the
southward wind velocity was almost equal to that of the
northward one. Consequently, the northward current
developed only near the shore, in the narrow surf zone;
outside the surf zone, the northward current velocity
decreased to zero. On the other hand, when the southward
current developed, the offshore wave height was relatively
large and the southward wind velocity was predominant.
Hence, the southward longshore current developed not
only in the wide surf zone but also outside the surf zone,
and the cross-shore variation of the longshore current
velocity became relatively uniform. The superposition of
the two cross-shore variations produced cross-shore variation
of the long-term average longshore current velocity
with a northward velocity near the shore and a southward
velocity far from the shore. The conclusions suggest that
the direction of net longshore sediment transport offshore
may be the opposite to that near the shore.