3. Sédiment Transport
41
In general, if sédiment is moved by alongshore transport, it will not return
to its initial position. The cross-shore transport moves sédiment over the
beach profile. The beach profile is adapted only to the momentary wave
characteristics.
In the surf zone breaking wave induces high orbital velocities which
are responsible for the significant suspended sédiment concentration. In
addition, the wave-generated longshore current in the surf zone can cause
high longshore sédiment transports. In the offshore, the same principles are
valid as in the surf zone (wave-induced suspended sédiment concentrations,
longshore sédiment transport), however being less intensive.
The wave propagating towards shallow water depth influences the sédiments at the bottom when its oscillatory motion begins to feel the sea
bed. Initially, only the material of very low density (such as organic and
other seaweed matters) gets initiated. These particles oscillate back and
forth with the orbital motion of the waves. For a given wave condition
in deep water, the wave height increases as the depth decreases towards
the shore (to be correct first a slight decrease of the wave height occurs).
This increasing wave height and decreasing the depth produce an increasing orbital velocity. At a certain location, the orbital velocity, exert adéquate shear to initiate the sédiment particles. The sédiments then leads
to formation of ripples with the crests parallel to the wave crests. These
ripples are typically uniform and periodic, and the sand moves from one
side of the crest to the other with the passage of each wave. When the
waves become even higher and finally break, the orbital velocities continue
to increase. Finally, the orbital motion will exceed the critical velocity of
sheet flow. At this point, the ripples are flattened. A layer of sédiment
now moves over the bottom resulting in higher concentration of suspended
sédiments.
Littoral transport results due to the interaction of waves, currents, tides,
sédiments, gradients, winds and other process in the surf zone. The présent
chapter discusses the processes which are involved in sédiment motion which
can be divided into three categories namely, the forces which cause the
longshore current, the sédiment sources and the transport mechanism.
The définitions are given in the terms used and the axis-system.
3.4 Définitions
Prior to describing the processes involved in sédiment motion, it is necessary
to define the terms used in the field of Coastal engineering like “beach”,
41
In general, if sédiment is moved by alongshore transport, it will not return
to its initial position. The cross-shore transport moves sédiment over the
beach profile. The beach profile is adapted only to the momentary wave
characteristics.
In the surf zone breaking wave induces high orbital velocities which
are responsible for the significant suspended sédiment concentration. In
addition, the wave-generated longshore current in the surf zone can cause
high longshore sédiment transports. In the offshore, the same principles are
valid as in the surf zone (wave-induced suspended sédiment concentrations,
longshore sédiment transport), however being less intensive.
The wave propagating towards shallow water depth influences the sédiments at the bottom when its oscillatory motion begins to feel the sea
bed. Initially, only the material of very low density (such as organic and
other seaweed matters) gets initiated. These particles oscillate back and
forth with the orbital motion of the waves. For a given wave condition
in deep water, the wave height increases as the depth decreases towards
the shore (to be correct first a slight decrease of the wave height occurs).
This increasing wave height and decreasing the depth produce an increasing orbital velocity. At a certain location, the orbital velocity, exert adéquate shear to initiate the sédiment particles. The sédiments then leads
to formation of ripples with the crests parallel to the wave crests. These
ripples are typically uniform and periodic, and the sand moves from one
side of the crest to the other with the passage of each wave. When the
waves become even higher and finally break, the orbital velocities continue
to increase. Finally, the orbital motion will exceed the critical velocity of
sheet flow. At this point, the ripples are flattened. A layer of sédiment
now moves over the bottom resulting in higher concentration of suspended
sédiments.
Littoral transport results due to the interaction of waves, currents, tides,
sédiments, gradients, winds and other process in the surf zone. The présent
chapter discusses the processes which are involved in sédiment motion which
can be divided into three categories namely, the forces which cause the
longshore current, the sédiment sources and the transport mechanism.
The définitions are given in the terms used and the axis-system.
3.4 Définitions
Prior to describing the processes involved in sédiment motion, it is necessary
to define the terms used in the field of Coastal engineering like “beach”,