A hurricane (unnamed) coincided with spring tide on the New England
coast on 21 September 1938. Property damage and loss of life were both
high. A storm of this magnitude was estimated to occur about once every
150 years. A study of the beach changes along a 12-mile section of the
Rhode Island coast (Nichol and Marsten, 1939) showed that most of the
changes in the beach profile were temporary. The net resuit was some
cliff érosion and a slight rétrogression of the beaches.
Beach changes from Hurricane Donna which hit Florida in September
1960 were more severe and permanent. In a study of the southwestem
coast of Florida before and after the storm, Tanner (1961), concluded
that "Hurricane Donna appears to hâve done 100 year’s work, considering
the typical energy level thought to prevail in the area."
On 1 April 1946, a tsunami struck the Hawaiian Islands with runup in
places as high as 55 feet above sea level. (Shepard, et al., 1950.) The
beach changes were similar to those inflicted by storm waves although "in
only a few places were the changes greater than those produced during normal storm seasons or even by single severe storms." Because a tsunami is
of short duration, extensive beach changes do not occur, although property
damage can be quite high.
Several conclusions can be drawn from the above examples. If a beach
has a sufficient sand supply and fairly high dunes, and if the dunes are
not breached, little permanent modification will resuit from storms, except
for a brief accélération of the normal littoral processes. This accélération will be more pronounced on a shore with low-energy wave conditions.
M NEARSHORE CURRENTS
Nearshore currents in the littoral zone are predominantly wave-induced
. motions superimposed on the wave-induced oscillatory motion of the wate^
The net motions generally hâve low velocities, but because t ey
whatever sand is set in motion by the wave-induced water motions, they are
important in determining littoral transport.
only slight exchange of fluid between the offshore and the
--- .
take nlace in a number of ways, which
There is u.x7 oxx6„u
b______
surf zone. Onshore-offshore flows take place in a number
at présent are not fully understood.
Ml WAVE-INDUCED WATER MOTION
circular motion
2-4, Section
c water particles hâve a
In idealized deepwater wave ,
crest (Fig*
t n
in a vertical plane perpendicular
enough to affect se
cjrcu2.235) , but this motion does not r
affected by the bott°m’- s to move.
the bottom. In depths where waves
e
the bottom beg
lar motion becomes elliptical. “^ate in« nearly straight Unes
At
In shallow water, the ellipses el°Xe complicated, but even rn the sur._
breaking, particle motion becomes £ kward in paths that are
passage
zone, the water moves forward an
_t|cai motions produce
>
zontal, with brief, but intense, ve
4-39
coast on 21 September 1938. Property damage and loss of life were both
high. A storm of this magnitude was estimated to occur about once every
150 years. A study of the beach changes along a 12-mile section of the
Rhode Island coast (Nichol and Marsten, 1939) showed that most of the
changes in the beach profile were temporary. The net resuit was some
cliff érosion and a slight rétrogression of the beaches.
Beach changes from Hurricane Donna which hit Florida in September
1960 were more severe and permanent. In a study of the southwestem
coast of Florida before and after the storm, Tanner (1961), concluded
that "Hurricane Donna appears to hâve done 100 year’s work, considering
the typical energy level thought to prevail in the area."
On 1 April 1946, a tsunami struck the Hawaiian Islands with runup in
places as high as 55 feet above sea level. (Shepard, et al., 1950.) The
beach changes were similar to those inflicted by storm waves although "in
only a few places were the changes greater than those produced during normal storm seasons or even by single severe storms." Because a tsunami is
of short duration, extensive beach changes do not occur, although property
damage can be quite high.
Several conclusions can be drawn from the above examples. If a beach
has a sufficient sand supply and fairly high dunes, and if the dunes are
not breached, little permanent modification will resuit from storms, except
for a brief accélération of the normal littoral processes. This accélération will be more pronounced on a shore with low-energy wave conditions.
M NEARSHORE CURRENTS
Nearshore currents in the littoral zone are predominantly wave-induced
. motions superimposed on the wave-induced oscillatory motion of the wate^
The net motions generally hâve low velocities, but because t ey
whatever sand is set in motion by the wave-induced water motions, they are
important in determining littoral transport.
only slight exchange of fluid between the offshore and the
--- .
take nlace in a number of ways, which
There is u.x7 oxx6„u
b______
surf zone. Onshore-offshore flows take place in a number
at présent are not fully understood.
Ml WAVE-INDUCED WATER MOTION
circular motion
2-4, Section
c water particles hâve a
In idealized deepwater wave ,
crest (Fig*
t n
in a vertical plane perpendicular
enough to affect se
cjrcu2.235) , but this motion does not r
affected by the bott°m’- s to move.
the bottom. In depths where waves
e
the bottom beg
lar motion becomes elliptical. “^ate in« nearly straight Unes
At
In shallow water, the ellipses el°Xe complicated, but even rn the sur._
breaking, particle motion becomes £ kward in paths that are
passage
zone, the water moves forward an
_t|cai motions produce
>
zontal, with brief, but intense, ve
4-39