Waves ???
FINDNOTES
At B the waves move on with without any change due to the island.
As a result the waves bend or refract around the island. Wave energy is focused on that part of the island facing the waves and erosion increases.
In the sheltered lee of the island at C there is a drop in water energy as turbulence increases.
Waves??
As the part of the wave at A enters shallow water it contacts the bottom and slows down.
At B the wave continues at its original speed.
As a result the entire wave bends in such a way that it becomes parallel to the coast.
The wave is now parallel to the coast.
Longshore Current formation
At A the wave strike the shoreline at an angle as it breaks . Water rushes up on shore and goes to zero velocity.
At B the water returns straight back offshore.
Water rushes up on shore and goes to zero velocity on shore by the next incoming wave
The water returns back offshore again and the process repeats itself over and over.
The result is a longshore current - the flow of water parallel to the shoreline.
Longshore Current
The flow of water parallel to the shoreline.
How a wave breaks NEED WAVE PIC
- The wave moves towards the shoreline.
- As the wave move into shallower water the orbits touch the bottom, the waves slow down and begins to break.
- The waves bunch up and wavelength decreases. Wave height increases as water is forced upward. Wave orbits flatten out as the wave runs out of room.
Instead of the orbital motion there is a distinct back and forth motion to the water beneath the wave.
- The wave reaches a height and speed where it is no longer stable and it falls over.
- Final wave energy is expended as the water rushes up the swash zone. This is often a thin, fast moving layer of water.
- The water reaches zero velocity and stops. Some water infiltrates into the shoreline
- Water that remains on the surface returns back offshore as a bottom current.
Edge Wave
An edge wave is a wave that travels parallel to the shoreline. The crest of an edge wave is perpendicular to the shoreline. Edge waves are wind generated waves.
Edge waves are
wind generated waves.
How do edge waves travel?
PARALLEL to the coast because that was the direction the wind was blowing. They may also travel parallel to the coast because of wave refraction.
Beach Cusp (SEE PHOTO)
A beach cusp is a regular pattern of sediment distribution in the swash zone that includes a raised “horn” and low “embayment.
Beach Cusp Formation (SEE PHOTOs)
along a coastline there can be two patterns of waves. At C these two wave crests meet to make one larger crest (positive interference).
At D, two wave troughs meet to make one lower trough (positive interference).
A- larger waves breaking further on shore
B- smaller waves breaking lower on the shoreline
As a result of wave interference there is an alternating pattern of larger (A) and smaller waves (B) breaking on the shoreline.
The larger waves create the low embayments composed of finer sand and the combination of return flow from the embayment and the smaller waves create the horns and the corse sediment in them.
along a coastline there can be two patterns of waves.
- waves moving toward the coast with crests parallel to the coast (A)
- waves travelling parallel to the shoreline.
Positive/constructive interference
?
Spit formation
A a longshore current moves sediment along the coast to form a beach. Where the coast changes direction the long shore current may continue to into deeper, offshore water. Sediment continues to be deposited as current velocity decreases. The result is a spit.
Spit
An extension of the coast and beach into deeper, offshore water.
Barrier island
A barrier island is a linear ridge of sediment parallel to the coast that is some distance offshore.
Formation of a barrier island
- Form is a spit becomes detached from the coast.
- Form is an offshore berm grows in size and is exposed above sea level.
when: can happen during a storm.
Formation of a Beach Step
On a shoreline the upward motion as a wave breaks (I) meets the return flow from the swash zone (II)
As a result of this mixing of water, coarse sediment is concentrated and a depositional feature called a step is formed.
