Waves, beaches, & sand transport
Surface waves on the ocean play a major role in shaping
coastlines, beaches and moving sand and sediment along them.
Some important ocean wave facts:
* Waves transmit energy, not water mass, across the oceans.
Energy is “deposited” where waves break. Not all waves
are visible at the surface (e.g., internal waves or tsunami).
* Wave behavior depends on the relation between wave
length (not height) and the depth of water through which it
is moving.
* Waves change direction by refraction and diffraction, can
interfere with one another, and reflect from solid objects.
* Most surface waves are from wind energy transfer.
* Wind-wave energy is absorbed by the coastline upon which
the waves break.
Waves are energy passing through the water,
not water transport.
A particle (even a water
molecule) is moved in a circle
by passing wave energy.
Only a slow drift occurs in
the direction of wave travel
due to slight friction.
Surfing is the process of using
the slope of the wave (and
gravity) to move ahead of it;
the energy is still not
imparted to the surfer.
Prove this to
yourself in
the wave
tank.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Factors Affecting Wind Wave Development
Wind strength - wind must be moving faster than the wave crests for
energy transfer to continue.
Wind duration - winds that blow for a short time will not generate large
waves.
Fetch - the uninterrupted distance over which the wind blows without
changing direction.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Wave features
Wave Types
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Wind Waves Approaching Shore
Plunging waves break violently, collapsing an air-filled tube between the
crest and foot of the wave. These are formed when waves approach a shore
over a steeply sloped bottom.
Spilling waves occur on more gradually sloped bottoms. A spilling wave
slides down the face of the wave as it breaks.
In either case, the wave’s energy is spent on the beach and moves it.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Beaches
A beach is a zone of loose particles that covers a shore.
Note that larger particles
are associated with
more sloped beach.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Wave energy erodes points and
fills in bays & coves.
Figure
11.18
Beaches
The features of a beach.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Figure
11.21
Large Scale Features of Active Coasts
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Coastal Cells
Sections of coast in which sand input
and sand output are balanced are
referred to as coastal cells.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Sediment & sand supply
are critical to maintaining
beaches. It comes from
rivers, bluffs, offshore
bars, and other beaches.
What you see today isn’t
the same stuff that was
there a few months ago.
A few of the many
measures taken to
slow beach
erosion. Some of
these methods are
actually
counterproductive.
In most cases,
these only remind
us that shorelines
and beaches are
constantly
changing and are
not under human
control.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.