2 Coastal Processes Flashcards
What are the 6 factors that influence coastal processes?
Waves
Tides
Currents
Aeolian
Geology
Human Activity
What are waves?
The transfer of energy through the water, produced by wind exerting a frictional drag on the ocean’s surface - not the transfer of water
What energy do waves input?
Major input of kinetic energy into the coastal system
-Potential energy by virtue of the water’s height above the trough of the wave
Energy allows work (e.g. erosion)
Describe the movement of a molecule of water as a wave passes through
The waves impart a circular motion to the individual water molecules
What is the wave crest/trough?
Highest/lowest point of a wave
Define wavelength
Average distance between successive wave crests
Define wave height
The vertical distance between a wave trough and crest
Define wave velocity
The speed at which the wave travels
Define wave steepness
The ratio of wave height to wave length
Define wave period
The average time between successive waves
Define wave frequency
The average number of waves per minute
Define wave power
The square of wave height multiplied by wave period (P=H^2T)
Describe the characteristics of swell waves
Long wavelength
Gentler gradient
Long wave period (up to 20secs)
Generated by distant winds blowing in the open ocean
Describe the characteristics of storm waves
Short wavelength
Steeper
Short wave period
Generated by local winds
What is the equation for calculating the wave power?
P (wave power) = H^2 (height) T (wave period)
Why do waves break?
-In deep water, not affected by friction (long wavelength and low wave height)
-Shallower water, slowed by friction with the sea bed
-Front is slowed earlier than the back, causing the back of the wave to ‘catchup’ with the front (shortens wave length and increases wave height)
-Base slowed more than the top so top ‘overshoots’ the base, and distorts the circular orbits of water molecules to be more elliptical
-When wave depth is <x1.3 wave height, the wave becomes too top-heavy and unstable, and it breaks
Describe spilling waves
Steep waves breaking onto gently sloping beaches; water spills gently forwards as the wave breaks
Describe plunging waves
Moderately steep waves breaking onto steep beaches; water plunges down vertically as the crest curls over
Describe surging waves
Low angle waves breaking onto steep beaches; the wave slides forward and may not actually break
Describe the characteristics of constructive waves
Low waveheight
Long wavelength
Gentle steepness
Long period
Low frequency (6-8/min)
Long fetch (distant winds)
Broken wave spills up beach
Swash stronger than backwash - long period means backwash returned to sea before next wave arrives, so incoming swash is not disrupted
Material pushed from lower to upper beach, creating steeper upper beach features such as berms
Describe the characteristics of destructive waves
High waveheight
Short wavelength
Steep steepness
Short period
High frequency (12-14/min)
Short fetch (local winds)
Wave breaks vertically down in a plunging motion
Backwash stronger than swash - plunging motion means little energy directed up the beach, and short period means backwash of one wave will disrupt incoming swash
Material combed from upper beach and deposited on lower beach, creating features such as breakpoint bars
Draw a sketch of constructive and destructive waves
What shape of coastline results in wave refraction?
Irregular-shaped
What two coastal landforms in particular encourage refraction?
Headlands and bays