166
.
R.H. Charlie r and Chr. P. De Meyer
Unlike incident waves, limited by breaking to the surf zone, edge waves can grow
during storms and may dominate the zone. The broad aspect of the morphology
after a storm is usually consistent with edge wave generation.
It could lead one to conclude that the dominant storm erosive mechanism be edge
waves.
2.5
Tidal Effects
Tides, and superimposed storm surges, rise the water level, thereby flood low
elevation coastal land and by pushing landward the surf zone, let waves attack
directly set-back areas. Perigean spring tides, particularly at syzygy, raise
considerably water levels entraining erosion. So do storm surges. Areas not
affected by wave attack become suddenly subjected to it. Coastal dikes have been
built as protective structures.
2.6
Nearshore Currents
Nearshore currents are created by wave breaking. Waves may strike a shore
perpendicularly or at a more or less significant angle. One end of the spectrum of
angles is waves parallel to shore - and dominant nearshore currents are a cell
circulation with rip currents going seaward - the other with a~ o > 5 ° to 10 ° - and
longshore current is continuous along shoreline.
Rip currents are concentrated jets able to carry water seaward through the breaker
zone, very noticeable when long, high waves produce wave set-up on the beach,
viz. a superelevation of the water surface over normal surge elevation due to
onshore mass transport of the water by wave action alone.
Some other localized sea-wall flowing currents are due to concentrated flows
down gullies in the foreshore (beach face), and still others are caused by
interaction of wave- and edge-wave phenomena.
Generally, rip currents carry sand off-shore, even beyond the breaker zone and
create embayments of different extension in the process. When these cut through
the entire beach berm, substantial erosional effects ensue.
.
R.H. Charlie r and Chr. P. De Meyer
Unlike incident waves, limited by breaking to the surf zone, edge waves can grow
during storms and may dominate the zone. The broad aspect of the morphology
after a storm is usually consistent with edge wave generation.
It could lead one to conclude that the dominant storm erosive mechanism be edge
waves.
2.5
Tidal Effects
Tides, and superimposed storm surges, rise the water level, thereby flood low
elevation coastal land and by pushing landward the surf zone, let waves attack
directly set-back areas. Perigean spring tides, particularly at syzygy, raise
considerably water levels entraining erosion. So do storm surges. Areas not
affected by wave attack become suddenly subjected to it. Coastal dikes have been
built as protective structures.
2.6
Nearshore Currents
Nearshore currents are created by wave breaking. Waves may strike a shore
perpendicularly or at a more or less significant angle. One end of the spectrum of
angles is waves parallel to shore - and dominant nearshore currents are a cell
circulation with rip currents going seaward - the other with a~ o > 5 ° to 10 ° - and
longshore current is continuous along shoreline.
Rip currents are concentrated jets able to carry water seaward through the breaker
zone, very noticeable when long, high waves produce wave set-up on the beach,
viz. a superelevation of the water surface over normal surge elevation due to
onshore mass transport of the water by wave action alone.
Some other localized sea-wall flowing currents are due to concentrated flows
down gullies in the foreshore (beach face), and still others are caused by
interaction of wave- and edge-wave phenomena.
Generally, rip currents carry sand off-shore, even beyond the breaker zone and
create embayments of different extension in the process. When these cut through
the entire beach berm, substantial erosional effects ensue.