96
11
R.H. Charlier and Chr. P. DeMeyer
two-layer concentration profile with rather large concentration gradients in
the near-bed layer (,~ 3 ripple heights) and smaller concentration gradients in
tile upper layer, in case of non-breaking waves over a rippled bed,
strong influence of the ripples giving relatively large concentrations in the
near-bed layer due to eddy-generated motions,
increasing concentrations in the upper layers by spilling breaking waves,
strongly increasing concentrations in the near-bed layer and in the upper layer
by plunging breaking waves (factor 5 larger than in spilling breaking waves).
2.3
Sediment Transport Rates
Sediment transport rates under wave action have been investigated by several
authors. Most of the experiments were carried out with flat (oscillating) beds.
Transport rates were generally small.
Based on these results, the transport rate in the sheet flow regime seems to be
dependent on approximately the third power of the velocity : qw = (0) 3.
Sawamoto and Yamashita (1987) did similar experiments in a wave tunnel in the
sheet flow regime. Sand material with particle sizes of 200 ~tm, 700 Ism and 1800
~tm was used. Coal and plastic material was also used. Based on their results,
these investigators have found that the transport rate in the sheet flow regime is
related to (t')l.s or (08) 3.
Summarizing, it can be concluded that the net transport rate under wave action
strongly depends on the transport mode and on the type of bedfonn :
1. bed load or suspended load overflat bed : net transport rate is always in the
direction of the largest peak velocity
2. dominantly bed load over rippled bed : net transport rate is in the direction of
the largest peak velocity
3. dominantly suspended load over rippled bed : net transport rate is against the
direction of the largest peak velocity.
11
R.H. Charlier and Chr. P. DeMeyer
two-layer concentration profile with rather large concentration gradients in
the near-bed layer (,~ 3 ripple heights) and smaller concentration gradients in
tile upper layer, in case of non-breaking waves over a rippled bed,
strong influence of the ripples giving relatively large concentrations in the
near-bed layer due to eddy-generated motions,
increasing concentrations in the upper layers by spilling breaking waves,
strongly increasing concentrations in the near-bed layer and in the upper layer
by plunging breaking waves (factor 5 larger than in spilling breaking waves).
2.3
Sediment Transport Rates
Sediment transport rates under wave action have been investigated by several
authors. Most of the experiments were carried out with flat (oscillating) beds.
Transport rates were generally small.
Based on these results, the transport rate in the sheet flow regime seems to be
dependent on approximately the third power of the velocity : qw = (0) 3.
Sawamoto and Yamashita (1987) did similar experiments in a wave tunnel in the
sheet flow regime. Sand material with particle sizes of 200 ~tm, 700 Ism and 1800
~tm was used. Coal and plastic material was also used. Based on their results,
these investigators have found that the transport rate in the sheet flow regime is
related to (t')l.s or (08) 3.
Summarizing, it can be concluded that the net transport rate under wave action
strongly depends on the transport mode and on the type of bedfonn :
1. bed load or suspended load overflat bed : net transport rate is always in the
direction of the largest peak velocity
2. dominantly bed load over rippled bed : net transport rate is in the direction of
the largest peak velocity
3. dominantly suspended load over rippled bed : net transport rate is against the
direction of the largest peak velocity.