164
R.H. Charier and Chr. P. De Meyer
Any condition promoting water saturation of the beach, destabilizes it. Among
these are disposal of storm waters from catchments, sub-beach rock shelves
concentrating ground water, seaward run-off, longshore walks blocking
temporary uprush of water during storms. Accumulation of water against a
vertical wall generates standing waves which increase the rate of sand removal.
2.4
Swell Waves
Swell waves are beach builders as they transport material landward, cover the
beach face in an uprush, water percolates down through the sand to the water
table, and diminished speed reduces carrying power so that suspended material is
deposited (fig. 2).
Beach accretion will be pursued as long as material is available off-shore to feed
incoming breakers. Material deposited is slightly compacted.
It is not far fetched to link this phenomenon and the feeder berm technique
recently developed. Once swell waves can no longer provide material, the beach
profile becomes virtually static from berm to off-shore ; they compact the beach
face by pounding it.
An oblique persistent swell will move sediment downcoast.
Swell waves return sand to the beach, often by bar decapitation. While the beach
is healed, rip currents, a swift flow fed by longshore currents on either side,
return to the sea water accumulated in the trough.
The intensity of erosion is a function of swell profile steepness. The more time
swell waves have to sweep off-shore material to the beach, the greater the beach
recession the next storm season.
"On land" structures should only be built at such distance of the shoreline that the
beach acts as a "bank" that can "feed" the bar.
As R. Silvester stressed at libitum, sufficient width of sedimentary material must
be available for bar fornlation to defend a coastline against erosion.
Waves reaching an "obstacle" will react in a variety of ways the two extremes
being fully dissipative (in case of flat shallow beaches that have large subaqueous sand storage) and highly reflective (in case of steep beaches with small
storage).
R.H. Charier and Chr. P. De Meyer
Any condition promoting water saturation of the beach, destabilizes it. Among
these are disposal of storm waters from catchments, sub-beach rock shelves
concentrating ground water, seaward run-off, longshore walks blocking
temporary uprush of water during storms. Accumulation of water against a
vertical wall generates standing waves which increase the rate of sand removal.
2.4
Swell Waves
Swell waves are beach builders as they transport material landward, cover the
beach face in an uprush, water percolates down through the sand to the water
table, and diminished speed reduces carrying power so that suspended material is
deposited (fig. 2).
Beach accretion will be pursued as long as material is available off-shore to feed
incoming breakers. Material deposited is slightly compacted.
It is not far fetched to link this phenomenon and the feeder berm technique
recently developed. Once swell waves can no longer provide material, the beach
profile becomes virtually static from berm to off-shore ; they compact the beach
face by pounding it.
An oblique persistent swell will move sediment downcoast.
Swell waves return sand to the beach, often by bar decapitation. While the beach
is healed, rip currents, a swift flow fed by longshore currents on either side,
return to the sea water accumulated in the trough.
The intensity of erosion is a function of swell profile steepness. The more time
swell waves have to sweep off-shore material to the beach, the greater the beach
recession the next storm season.
"On land" structures should only be built at such distance of the shoreline that the
beach acts as a "bank" that can "feed" the bar.
As R. Silvester stressed at libitum, sufficient width of sedimentary material must
be available for bar fornlation to defend a coastline against erosion.
Waves reaching an "obstacle" will react in a variety of ways the two extremes
being fully dissipative (in case of flat shallow beaches that have large subaqueous sand storage) and highly reflective (in case of steep beaches with small
storage).