HOW DO WAVES EXERT ENERGY ON BEACHES? Waves are generated by the friction of winds passing over water, they therefore represent an expression of differences in atmospheric pressure resulting from the interaction of the Earth system with insolation.

Oscillatory wavesTranslatory waves

Wind

Oscillatory waves Merely a transfer of potential energy (up and down)

Oscillatory waves Impacts felt progressively less with depth

Oscillatory waves Impacts felt progressively less with depth Wavelength, λ d≥ λ/2

Oscillatory waves D< λ/2 Friction of circular motion with the sea bed, slows lower water layers, causing wave front to steepen

Oscillatory waves d≥ λ/2 Translatory waves Kinetic Energy Water moving

Oscillatory waves d≥ λ/2 d h H = 0.8 d Wave breaks Translatory waves

WHAT CAUSES WAVE ENERGY TO CHANGE? 1.Wind Speed. Direct linkage between waves as agent of erosion and “external” energy.

WHAT CAUSES WAVE ENERGY TO CHANGE? 1.Wind Speed. Direct linkage between waves as agent of erosion and “external” energy. 2.Wind Fetch. The greater the fetch then the more distance over which there is to exchange energy between the atmosphere and the ocean surface. Gulf of Mexico ATLANTIC

WHAT CAUSES WAVE ENERGY TO CHANGE? 1.Wind Speed. Direct linkage between waves as agent of erosion and “external” energy. 2.Wind Fetch. The greater the fetch then the more distance over which there is to exchange energy between the atmosphere and the ocean surface. 3.Duration. The longer the wind blows in one direction the more consistently the energy (waves) will be generated and not interfere with each other.

Wind Speed June 1995 Wave Height June 1995 Summer Winter Summer Winter

New Zealand Australia Cape Horn South America ANTARCTICA Cape of Good Hope South Africa

λ/2 Shallow Deep Beach WIND DIRECTION ENERGY AND SEDIMENT TRANFER ALONG BEACHES FROM WAVE ACTION

λ/2 Shallow Deep Beach TIME = 0 Oscillatory wave approaching from deep ocean at right angles to wind direction. Equal energy per unit length of wave front.

λ/2 Shallow Deep Beach TIME = 1 Each unit length of wave front has moved an equal distance (equal velocity) in unit of time

λ/2 Shallow Deep Beach TIME = 1 Each unit length of wave front has moved an equal distance (equal velocity) in unit of time Unit of wavefront closest to shore has now reached the critical depth of λ/2 and wave energy begins to interact with bed. A)Wavefront section becomes translatory B)Energy released to bed material. C) Friction causes wavefront to slow (loss of energy to bed).

λ/2 Shallow Deep Beach TIME = 2 Each unit length of wave front in deep water has moved an equal distance (equal velocity) in unit of time

λ/2 Shallow Deep Beach TIME = 2 Each unit length of wave front in deep water has moved an equal distance (equal velocity) in unit of time Most shoreward section of wavefront has lower velocity (d<λ/2), therefore it has not travelled as far in unit time, causing apparent “bending” of less energetic wave

λ/2 Shallow Deep Beach TIME = 2 Each unit length of wave front in deep water has moved an equal distance (equal velocity) in unit of time Most shoreward section of wavefront has lower velocity (d<λ/2), therefore it has not travelled as far in unit time, causing apparent “bending” of less energetic wave Unit of wavefront next closest to shore now reaches the critical depth of λ/2 and wavefront section becomes translatory

λ/2 Shallow Deep Beach TIME = 3 Deep water wavefront sections all move at equal velocity.

λ/2 Shallow Deep Beach TIME = 3 Deep water wavefront sections all move at equal velocity. Most shoreward section of wavefront loses velocity and steepens

λ/2 Shallow Deep Beach TIME = 3 Deep water wavefront sections all move at equal velocity. Most shoreward section of wavefront loses velocity and steepens Wavefront unit slows and steepens after becoming translatory

λ/2 Shallow Deep Beach TIME = 3 Deep water wavefront sections all move at equal velocity. Most shoreward section of wavefront loses velocity and steepens Wavefront unit slows and steepens after becoming translatory Next wavefront unit reaches the critical depth of λ/2 and wavefront section becomes translatory

λ/2 Shallow Deep Beach TIME = 4 Deep water wavefront sections all move at equal velocity.

λ/2 Shallow Deep Beach TIME = 4 Deep water wavefront sections all move at equal velocity. Most shoreward sections of wavefront continue to lose velocity and steepens

λ/2 Shallow Deep Beach TIME = 4 Deep water wavefront sections all move at equal velocity. Most shoreward sections of wavefront continue to lose velocity and steepens Translatory wavefront units becoming slower and steeper.

λ/2 Shallow Deep Beach TIME = 4 Deep water wavefront sections all move at equal velocity. Most shoreward sections of wavefront continue to lose velocity and steepens Point at which wavefront encounters critical depth, λ/2, moves down beach Translatory wavefront units becoming slower and steeper.

λ/2 Shallow Deep Beach TIME = 5 Deep water wavefront sections all move at equal velocity.

λ/2 Shallow Deep Beach TIME = 5 Deep water wavefront sections all move at equal velocity. H=0.8d Most shoreward section now sufficiently grown in height to exceed critical value to break. Release of energy.

λ/2 Shallow Deep Beach TIME = 5 Deep water wavefront sections all move at equal velocity. H=0.8d Most shoreward section now sufficiently grown in height to exceed critical value to break. Release of energy. Waves Steepening

λ/2 Shallow Deep Beach TIME = 5 Deep water wavefront sections all move at equal velocity. Oscillatory/ translatory point H=0.8d Most shoreward section now sufficiently grown in height to exceed critical value to break. Release of energy. Waves Steepening

λ/2 Shallow Deep Beach TIME = 5 Deep water wavefront sections all move at equal velocity. Most shoreward section now sufficiently grown in height to exceed critical value to break. Release of energy. Oscillatory/ translatory point Translatory wavefront units becoming slower and steeper. H=0.8d Waves Steepening

λ/2 Shallow Deep Beach TIME = 6 Deep water wavefront sections all move at equal velocity. H=0.8d Waves Steepening

λ/2 Shallow Deep Beach TIME = 6 Deep water wavefront sections all move at equal velocity. Breaking wave H=0.8d Waves Steepening

λ/2 Shallow Deep Beach TIME = 6 Deep water wavefront sections all move at equal velocity. Breaking wave Translatory wavefront units becoming slower and steeper. Waves Steepening H=0.8d

λ/2 Shallow Deep Beach TIME = 6 Deep water wavefront sections all move at equal velocity. Breaking wave Oscillatory/ translatory Translatory wavefront units becoming slower and steeper. Waves Steepening H=0.8d

λ/2 Shallow Deep Beach TIME = 7 Deep water wavefront sections all move at equal velocity. Waves Steepening H=0.8d

λ/2 Shallow Deep Beach TIME = 7 Deep water wavefront sections all move at equal velocity. Waves Steepening H=0.8d Most shoreward section of wave now slowed sufficient that almost parallel to beach

λ/2 Shallow Deep Beach TIME = 7 Deep water wavefront sections all move at equal velocity. Breaking wave Waves Steepening H=0.8d Most shoreward section of wave now slowed sufficient that almost parallel to beach

λ/2 Shallow Deep Beach TIME = 7 Deep water wavefront sections all move at equal velocity. Breaking wave Oscillatory/ translatory Waves Steepening H=0.8d Most shoeward section of wave now slowed sufficient that almost parallel to beach

λ/2 Shallow Deep Beach TIME = 8 Deep water wavefront sections all move at equal velocity. Breaking wave Oscillatory/ translatory Waves Steepening H=0.8d Most shoreward section of wave now slowed sufficient wavefront is parallel to beach

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory 0

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory 0 1

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory 0 12

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory 0 123

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory 0 12 Direction of Energy Gradient through Time

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory Direction of Energy Gradient through Time

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory Direction of Energy Gradient through Time

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory Direction of Energy Gradient through Time

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory Direction of Energy Gradient through Time

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory Direction of Energy Gradient through Time

λ/2 Shallow Deep Beach H=0.8d Time when wave changes from Oscillatory to Translatory Direction of Energy Gradient through Time

λ/2 Shallow Deep Beach H=0.8d Time when wave broke 0

λ/2 Shallow Deep Beach H=0.8d Time when wave broke 0 5

λ/2 Shallow Deep Beach H=0.8d Time when wave broke 0 56

λ/2 Shallow Deep Beach H=0.8d Time when wave broke 0 567

λ/2 Shallow Deep Beach H=0.8d Time when wave broke

λ/2 Shallow Deep Beach H=0.8d Time when wave broke 0 56 Direction of Energy Gradient through Time

λ/2 Shallow Deep Beach H=0.8d Time when wave broke 0 67 Direction of Energy Gradient through Time

λ/2 Shallow Deep Beach H=0.8d Time when wave broke 0 78 Direction of Energy Gradient through Time

λ/2 Shallow Deep Beach H=0.8d 0 LONGSHORE CURRENT Associated with Breaking Waves Associated with Oscillatory→ Translatory

λ/2 Shallow Deep Beach H=0.8d 0 LONGSHORE CURRENT Father Mother Child

λ/2 Shallow Deep Beach H=0.8d 0 LONGSHORE CURRENT Father Mother Child

Vilamoura, Algarve, Portugal.

What the tourist/businessman sees. Thousands of E.U. tourists come for sun, sea and sand

What the tourist/businessman sees Marina for wealthy boat owners to dock and stay.

What the tourist/businessman sees Sandy beaches along the sea front and right in front of the hotels.

What the Coastal Geomorphologist sees Waves approaching from deep water, obliquely to the coast line.

What the Coastal Geomorphologist sees Waves “bending” and steepening as they come in shore.

What the Coastal Geomorphologist sees Breaker zone.

What the Coastal Geomorphologist sees Longshore current and transfer of sediment (sand).

Human Interventions Construction of long stone jetties, or piers, to prevent transported sediment filling in the harbor entrance.

Human Interventions Construction of stone or wooden “groynes” out to beyond the low tide mark..

Human Interventions 1. Protect the beach immediately “downwind of the groyne from energy of waves, by forcing waves to break on groyne Protected area of the beach

Human Interventions 1. Provide a “dam” to trap any sediment eroded and transported from further up the coast

Human Interventions Note the “U” shape of the beaches between the groynes – “upcoast” protected from erosion, “downcoast” captures any sand moved.

When it comes to sediment, one person’s gain is indeed another person’s loss!