Factors That Determine Wave Height (H) - Keynote pdf
Wave Interference - Keynote pdf
Wave Dispersion -Keynote pdf
Surf - Keynote pdf
Wave Refraction - Keynote pdf
Longshore Drift - Keynote pdf
Longshore Currents - Keynote pdf
Wave Reflection and Seawalls - Keynote pdf
Tsunamis - Keynote pdf
Large wind waves are generated in a sea - a storm region.
The height of the waves generated by the strong winds depends primarily on three
factors:
Duration - the time that the wind blows in a single direction.
Fetch - the distance that the wind blows in a single direction.
Wave heights increase as all three factors increase:
For a given wind speed, once the maximum fetch and duration are achieved, the sea is fully-developed.
Fully developed sea - the theoretical maximum height attainable by ocean waves given wind of a specific strength, duration, and fetch. Longer exposure to wind wind will not increase the size of the waves.
Oceanographers use the concept of wave interference to explain the chaotic
nature of the surface of the ocean.
Deep water waves are energy propagating across the surface of the ocean.
Non-breaking waves will pass through each other, but, as they do, they interfere
with one another to determine the elevation of the ocean surface.
Two types of interference:
Constructive Interference
Two types of constructive interference:
Crest-to-crest is when two wave crests come together and the elevation of
the ocean surface is the sum of both wave heights above sea level.
An example is when a 1 m crest passes through a 2 m crest and the resulting
ocean surface elevation in 3 m above sea level.
Trough-to-trough is when two wave troughs come together and the elevation
of the ocean surface is the sum of both wave heights below sea level.
An example is when a 3 m trough passes through a 2 m trough and the resulting
ocean surface elevation is 5 m below sea level.
In each instance, the ocean surface is higher or lower than either wave.
Destructive Interference
Destructive interference occurs when a wave crest coincides with a wave trough.
The crest and the trough totally or partially cancel each other.
An example is when a 2 m crest comes together with a 1 m trough and the resulting
ocean surface elevation is 1 m above sea level.
In the instance of destructive interference, the ocean surface is neither as
higher or as low as the largest wave, because it is partially canceled by the
smaller wave.
The elevation of the an individual point on the surface of the ocean, at any
given instant of time, is the sum of all of the waves are passing that point.
Because the elevation of the surface of the ocean is constantly changing as
different waves pass through each other, the term mixed interference pattern
is used.
Some rogue waves form by constructive interference when several wave crests coincide.
A deep-water wave is described as energy propagating across the surface of
the ocean, with no significant transport of mass.
A deep-water wave, also, is a wave in water deeper than L/2 (a wave stirs the
ocean to one half its wavelength).
After a wave enters water that is shallower than L/2, it interacts with the sea floor and the characteristics of the wave change:
Wave steepness is defined as wave height divided by wavelength (H/L).
As a wave approaches a coastline, its wave height increases as it wave length
decreases, which results in increasing wave steepness.
Once H/L >1/7, a wave breaks.
After a wave breaks, forming surf, water is moving in the direction of wave
propagation, which is generally towards the shore.
Breaking waves can be classified into three types of surf:
The type of surf that forms at a given location is a function of the gradient of the seafloor:
Spilling breakers form as the breaking waves release energy slowly and the
crest of the wave slowly spills down the face of the wave.
Plunging breakers form as the breaking waves release energy fast - the top of
the wave outruns the bottom of the wave and plunges over.
Surging breakers form as the breaking waves release energy all at once - the
wave breaks on top of the beach.
Spilling breakers commonly form along Waikiki Beach because the seafloor is
relatively flat.
Plunging breakers commonly form along North Shore beaches because the seafloor
is moderately steep.
Surging breakers commonly form along Yokohama Beach because the seafloor is
very steep.
Longshore drift is the transport of sand along a beach face.
Sand generally flows from one end of a beach to the other, which explains why
many beaches are thinner at one end.
Remember that when waves break water is moving in the direction of wave propagation.
Waves that approach a beach at an angle run up the beach face at an angle.
The water moves sand up the beach face at an angle, too.
After the wave stops, gravity pulls the water and the sand straight back into
the ocean.
This pattern is repeated with each subsequent wave.
The result is that sand moves in a zigzag pattern along the beach, moving in
the direction opposite to the direction that the waves approach from.
Longshore Drift and Shoreline Structures
If a structure along the shoreline, such as a groin, impedes the transport
of sand, sand will collect (deposition) on one side of the structure.
On the opposite side of the structure sand starvation (erosion) occurs.
The direction of the waves determines which side undergoes deposition or erosion.
Sand builds up on the side of the structure that waves approach from.