I FORE I OFFSHORE -
SHORE
BEACH ZONE
IWINTER SURF ZONE
"
Effects of Waves
107
' -J RANGE
OF TIDE
Fig. 4.9. Beach profile (southern California). The summer profile shows the buildup of the berm at
the expense of the bars. During winter the surf removes sand from the berm, and the bars reform.
Note the breakers over the bars (arrows marked B) The vertical scale is exaggerated. Gradients in
sandy beaches are mostly around a few degrees, the finer the sand, the more gentle the slope.
[W. Bascom, 1960, Sci. Am. 203 [2] 80; modified]
currents disperse. They also can carry sediment, and produce channels and ripple
marks within the breaker zone.
Water transported by waves also causes longshore currents, which can move sediment parallel to the beach. Since the breakers are very efficient in suspending the
sediment, the longshore currents (velocities up to I m/s) can move a large amount of
material (Fig. 4.IOa). On both the US East and West Coasts, the longshore drift is
predominantly from north to south. On the shores of Southern California, sand
brought by rivers moves south till it is intercepted by the head of a submarine canyon.
Thus, south of submarine canyons, beaches tend to be starved for sand (Fig. 4.IOb).
The submarine canyon acts as a funnel, moving beach sediment as well as kelp and
other debris down to the deep-sea floor (Fig. 4.11) .
Where beaches are narrow or missing altogether, storm breakers can hit the coast
with full force. Armed with gravel or sand, breakers can dig a deep notch into cliffs,
even if these are made of hard rock. When the notches and sea caves become large
and deep enough, the overlying material collapses and cliff erosion results. By grinding up the fallen rocks, waves produce additional beach sand (Fig. 4.12).
SHORE
BEACH ZONE
IWINTER SURF ZONE
"
Effects of Waves
107
' -J RANGE
OF TIDE
Fig. 4.9. Beach profile (southern California). The summer profile shows the buildup of the berm at
the expense of the bars. During winter the surf removes sand from the berm, and the bars reform.
Note the breakers over the bars (arrows marked B) The vertical scale is exaggerated. Gradients in
sandy beaches are mostly around a few degrees, the finer the sand, the more gentle the slope.
[W. Bascom, 1960, Sci. Am. 203 [2] 80; modified]
currents disperse. They also can carry sediment, and produce channels and ripple
marks within the breaker zone.
Water transported by waves also causes longshore currents, which can move sediment parallel to the beach. Since the breakers are very efficient in suspending the
sediment, the longshore currents (velocities up to I m/s) can move a large amount of
material (Fig. 4.IOa). On both the US East and West Coasts, the longshore drift is
predominantly from north to south. On the shores of Southern California, sand
brought by rivers moves south till it is intercepted by the head of a submarine canyon.
Thus, south of submarine canyons, beaches tend to be starved for sand (Fig. 4.IOb).
The submarine canyon acts as a funnel, moving beach sediment as well as kelp and
other debris down to the deep-sea floor (Fig. 4.11) .
Where beaches are narrow or missing altogether, storm breakers can hit the coast
with full force. Armed with gravel or sand, breakers can dig a deep notch into cliffs,
even if these are made of hard rock. When the notches and sea caves become large
and deep enough, the overlying material collapses and cliff erosion results. By grinding up the fallen rocks, waves produce additional beach sand (Fig. 4.12).