waves, beaches, & sand transport surface waves on the ocean play a major role in shaping...

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.

© 2002 Brooks/Cole, a division of Thomson Learning, Inc.

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.

Waves are energy passing through the water, not water transport.

© 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.

Wave energy erodes points and fills in bays & coves.

Figure 11.18

© 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Beaches

The features of a beach.

Figure 11.21

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Large Scale Features of Active Coasts

© 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Sections of coast in which sand input and sand output are balanced are referred to as coastal cells.

Coastal Cells

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.

© 2002 Brooks/Cole, a division of Thomson Learning, Inc.

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.