adapted to HTML from lecture notes of Prof. Stephen A. Nelson Tulane
Waves and Beaches
Waves are the result of water oscillating in a circular motion. The water
is not actually travelling like most people seem to think. (Imagine a
"wave" at a baseball game, with the people as water particles.)
Close to the beach, the circular water particle motion gets broken up as
the cycling water hits the bottom. This causes the wave to rise up (as the
water piles up on itself) and break.
Waves rarely hit the beach head on (at a flat angle). Most of the time,
there is some small angle between the line of the beach and the line of
As a result a Long Shore Current forms.
Berms - Areas that result from sand deposited on the recreactional beach
in fair weather during periods of relatively low wave energy. During
storms or periods of high wave energy the beach is eroded.
Seacliff - During storms the dunes may be eroded leaving a cliff scarp.
Rip Currents are areas of strong back-current under the surface that
returns breaking wave water to deeper regions.
On the west coast of the US the Pacific ocean has larger waves during the
winter which results in erosion of the recreational beach. On the east
coast the periods of larger waves are more related to storm activity which
may be associated with hurricanes in the summer of fall and northeasters
mainly in the winter.
Strong waves enough energy to carry sand away from the beach after they
break resulting in erosion of the recreational beach. Most of this sand is
deposited in bars just off shore. Gentler waves lose most of their energy
when they break, and so carry sand from the off-shore bars and deposit the
sand on the beach.
As a result of this, the sizes and features of recreational beach and
off-shore bars vary significantly.
Headlands are regions where the land thrusts out into the water.
Embayments are regions between headlands.
Headlands tend to be the focus of wave energy, whereas waves tend to
diffuse and weaken when in embayments. As a result of this, sediment is
eroded off of headlands, and deposited in embayments, which eventually
results in the eventual flattening of the coastline.
Sea cliffs are a result of wave erosion eroding away the base of a cliff
face. The face subsequently slumps due to lack of support.
Long Shore Currents and
Human Erosion Control
Long shore currents transfer sand down-current. When they run into a
barrier, such as a groin (a pile or rocks stretching into the water), the
sand is caught on the upstream side of the groin.
Littoral Drift is the same thing as longshore current.
Jetties - Are used to protect inlets. Jetties keep the river or inlet
openings from migrating.
-Sand builds up on upstream jetty, and severe erosion takes place on the
down-current side of the opposing jetty.
they have existed for many thousands of years. As sea level has risen they
have migrated towards the shore line. Currently, sea level is rising at
about 30cm a century at Long Island.
A typical barrier beach system:
During a storm, sand can be overwash the island ending up in the lagoon.
Repeated storms along with sea level rise results in the barrier beach
migrating shoreward as sand is removed from the ocean side and added in
During winter or storms, sand gets carried off into an offshore sand bar
(usually below the surface of the water).
This sand is replaced during the summers or low-storm periods.
When you have a sea wall (A large wall-like structure running parallel to
the beach used to stop the waves from eroding beaches), everything in
front of the sea wall gets eroded away during winters or storm times, and
then the gentle summer waves have no beach slope upon which to redeposit
the sand. As a result, erosion in front of the sea wall takes place at a
much faster rate, and isn't replaced.
Sea walls, due to the fact that they are constantly being pounded on by
waves, tend to eventually break down, and are often very costly to repair.
Opinions on Coastal Processes
Among environmental geologists, there are several points of agreement with
regard to coastal processes and engineering. They are:
Coastal Erosion is a natural process rather than a natural hazard;
erosion problems occur when people build structures in the coastal
Any shoreline construction causes change.
Stabilization of the coastal zone through engineering structures
protects the property of relatively few people at a larger general
expense to the public.
Engineering structures designed to protect a beach may eventually
Once constructed, shoreline engineering structures produce a trend
in coastal development that is difficult if not impossible to reverse.
Hurricanes - Hurricanes raise up the sea level around them as they travel
closer to shore. This is referred to as a Storm surge, as it causes a
"surge" in the water level and wave energy when the hurricane hits shore.
The wind in a hurricane in the northern hemisphere rotates
counterclockwise. Thus as the hurricane moves northerly, as it does at
higher latitudes, the winds on the east side of the eye of the hurricane
will be much faster than elsewhere around the eye. Likewise the winds on
the west side of the eye will be much slower than elsewhere. See the
Possible storm surge patterns around New York City and Long Island if the
eye of a hurricane crosses just west of NYC.