zone is the principal cause of longshore currents - currents that flow
parallel to the shoreline within the surf zone. These longshore currents
are largely responsible for the longshore sédiment transport.
There is some mean exchange between the water flowing in the surf
zone and the water seaward of the breaker zone. The most easily seen of
these exchange mechanisms are the rip currents (Shepard and Inman, 1950),
which are concentrated jets of water flowing seaward through the breaker
zone.
4.123 Tides and Surges. In addition to wave-induced currents, there are
other currents affecting the shore that are caused by tides and storm
surges. Tide-induced currents can be impressed upon the prevailing waveinduced circulations, especially near entrances to bays and lagoons and
in régions of large tidal range. (Notices to Mariners and the Coastal
Pilot often carry this information.) Tidal currents are particularly
important in transporting sand in shoals and sand waves around entrances
to bays and estuaries.
Currents induced by storm surges (Murray, 1970) are less well known
because of the difficulty in measuring them, but their effects are undoubtedly significant.
The change in water level by tides and surges is a significant factor
in sédiment transport, since, with a higher water level, waves can then
attack a greater range of élévations on the beach profile. (See Figure
1-7.) The appropriate theory for predicting storm surge levels is discussed in Section 3.8.
4.124 Winds. Winds act directly on b^e*nb^*°"in (sXge’Sd^oodbeaches (déflation) and by depositing
finer material, leaving
house, 1968.) Déflation usually removes th
r
seaward from
behind coarser sédiment and shell fragmen .
not lost> but is
the beach usually falls in the surf
Sand blown landward from
introduced into the littoral transpor
y
•
b deposited in
the beach may form dunes, add to existing dunes, or
P
lagoons behind barrier islands.
. -r- ont ouantity of sand must be available
For dunes to form, a significan q
trap the moving sand.
for transport by wind, as must features
végétation are the
Topographie irrégularités, the dunes themselves,
principal features that trap sand.
are foredunG8 - tne
The most important dunes in
hpach
They usually form beline of dunes immediately landward o
g beach will trap sand
own
cause beachgrasses growing just lan wa
barrier to prevent waves an
landward off the beach. Foredunes act a
a reservoir of sand to replenhigh water from moving inland, an pr
hore érosion.
ish the nearshore régime during seve
on the water surface is
The effect of winds in producing curren s
(Bretschneider,
well documented, both in the laboratory and in
4-5
parallel to the shoreline within the surf zone. These longshore currents
are largely responsible for the longshore sédiment transport.
There is some mean exchange between the water flowing in the surf
zone and the water seaward of the breaker zone. The most easily seen of
these exchange mechanisms are the rip currents (Shepard and Inman, 1950),
which are concentrated jets of water flowing seaward through the breaker
zone.
4.123 Tides and Surges. In addition to wave-induced currents, there are
other currents affecting the shore that are caused by tides and storm
surges. Tide-induced currents can be impressed upon the prevailing waveinduced circulations, especially near entrances to bays and lagoons and
in régions of large tidal range. (Notices to Mariners and the Coastal
Pilot often carry this information.) Tidal currents are particularly
important in transporting sand in shoals and sand waves around entrances
to bays and estuaries.
Currents induced by storm surges (Murray, 1970) are less well known
because of the difficulty in measuring them, but their effects are undoubtedly significant.
The change in water level by tides and surges is a significant factor
in sédiment transport, since, with a higher water level, waves can then
attack a greater range of élévations on the beach profile. (See Figure
1-7.) The appropriate theory for predicting storm surge levels is discussed in Section 3.8.
4.124 Winds. Winds act directly on b^e*nb^*°"in (sXge’Sd^oodbeaches (déflation) and by depositing
finer material, leaving
house, 1968.) Déflation usually removes th
r
seaward from
behind coarser sédiment and shell fragmen .
not lost> but is
the beach usually falls in the surf
Sand blown landward from
introduced into the littoral transpor
y
•
b deposited in
the beach may form dunes, add to existing dunes, or
P
lagoons behind barrier islands.
. -r- ont ouantity of sand must be available
For dunes to form, a significan q
trap the moving sand.
for transport by wind, as must features
végétation are the
Topographie irrégularités, the dunes themselves,
principal features that trap sand.
are foredunG8 - tne
The most important dunes in
hpach
They usually form beline of dunes immediately landward o
g beach will trap sand
own
cause beachgrasses growing just lan wa
barrier to prevent waves an
landward off the beach. Foredunes act a
a reservoir of sand to replenhigh water from moving inland, an pr
hore érosion.
ish the nearshore régime during seve
on the water surface is
The effect of winds in producing curren s
(Bretschneider,
well documented, both in the laboratory and in
4-5