Topic 5Waves and Wave DepthsTopic 5Waves and Wave Depths
If the wind blows hard enough (speed) and longenough (duration) over a long enough area(fetch), waves become fully developed.If the wind blows hard enough (speed) and longenough (duration) over a long enough area(fetch), waves become fully developed.
When the wind stops, they become swells.When the wind stops, they become swells.
As swells reach shore they change into breakingwaves.As swells reach shore they change into breakingwaves.
Wave EnergyWave Energy
Deep water waves – ocean depth isgreater than half the wavelengthDeep water waves – ocean depth isgreater than half the wavelength
–D > ½ λ–D > ½ λ
Wave energy extends only to a depth ofhalf the wave length.Wave energy extends only to a depth ofhalf the wave length.
In open ocean the energy of swells do nottouch bottom.In open ocean the energy of swells do nottouch bottom.
As energy moves through the water it setsthe water particles in orbital motion.As energy moves through the water it setsthe water particles in orbital motion.
D > ½ λD > ½ λ
•Half the wavelength beneath the surface of the water and deeper, there is no movement ofthe water molecules
•Orbits decrease as depth increases
Shallow water wave:Shallow water wave:
–When the water depth is less than 1/20 thewavelength–When the water depth is less than 1/20 thewavelength
–D<1/20 λ–D<1/20 λ
Transitional waves:Transitional waves:
–As the swells flatten they become waveshaving wavelength greater than twice but lessthan 20 times the waters depth.–As the swells flatten they become waveshaving wavelength greater than twice but lessthan 20 times the waters depth.
–Includes wind waves that have moved intoshallower water.–Includes wind waves that have moved intoshallower water.
–1/2 λ >D>1/20 λ–1/2 λ >D>1/20 λ
Peaking Wave:Peaking Wave:
–The water is pushed up off the bottom forminghigher steeper waves–The water is pushed up off the bottom forminghigher steeper waves
–Because of friction between the water particles andthe seafloor, the top of the wave begins to movefaster than the deeper parts–Because of friction between the water particles andthe seafloor, the top of the wave begins to movefaster than the deeper parts
–The front of the wave becomes steeper than theback surface.–The front of the wave becomes steeper than theback surface.
Breaking wave:Breaking wave:
–The top of the wave travels so fast that it begins tospill over and fall down the front surface–The top of the wave travels so fast that it begins tospill over and fall down the front surface
–develop when:–develop when:
The crest of the wave forms an angle less than 120o.The crest of the wave forms an angle less than 120o.
The height is greater than 1/7 of the wavelength.The height is greater than 1/7 of the wavelength.
The wave height is ¾ of the water depth.The wave height is ¾ of the water depth.
Topic 6Wave-Coast InteractionTopic 6Wave-Coast Interaction
Typical Coastal FeaturesTypical Coastal Features
Coast – a strip of land of indefinite width,extending from the shoreline inland to thefirst major change in land features.Coast – a strip of land of indefinite width,extending from the shoreline inland to thefirst major change in land features.
Beach – The zone of loose gravel, sand orother material that extends landward fromthe low waterline, either to the line ofpermanent vegetation or to where there isa marked change in substrate.Beach – The zone of loose gravel, sand orother material that extends landward fromthe low waterline, either to the line ofpermanent vegetation or to where there isa marked change in substrate.
Foreshore + Backshore!
Nearshore – an indefinite zone extending seawardfrom the shoreline to beyond the breaker zone.Nearshore – an indefinite zone extending seawardfrom the shoreline to beyond the breaker zone.
Foreshore – that part of the shore between the upperlimits of the wave wash and the water’s edgeForeshore – that part of the shore between the upperlimits of the wave wash and the water’s edge
Backshore – The zone of the beach between theforeshore and the point on the coastline wherebeach berms are located.Backshore – The zone of the beach between theforeshore and the point on the coastline wherebeach berms are located.
Onshore – the direction landward from the water.Onshore – the direction landward from the water.
Offshore – the direction seaward from the breakerzoneOffshore – the direction seaward from the breakerzone
C
D
E
Offshore
Coastline – the indefinite line that forms theboundary between the coast and the shore.Coastline – the indefinite line that forms theboundary between the coast and the shore.
Shoreline – the line formed when the watertouches the beach at high tideShoreline – the line formed when the watertouches the beach at high tide
Bay of Fundy
Dunes – ridges or mounds of loose windDunes – ridges or mounds of loose wind
blown material, usually sand.blown material, usually sand.
Scarp – a steep slope along a beach caused bywave erosion.Scarp – a steep slope along a beach caused bywave erosion.
Berm – nearly horizontal part of the backshore ofthe beach formed by the erosion of material bywave action.Berm – nearly horizontal part of the backshore ofthe beach formed by the erosion of material bywave action.
Rip Feeder Channel – a drop off parallel to thebeach formed at the final breaking point ofwaves just before the rush up the beachRip Feeder Channel – a drop off parallel to thebeach formed at the final breaking point ofwaves just before the rush up the beach
Bar – an embankment of sand or gravel depositedin shallow water by waves or current.Bar – an embankment of sand or gravel depositedin shallow water by waves or current.
Surf zone – the area extending from wherewaves begin to peak to the highest uprush ofthe wave – zone where waves breakSurf zone – the area extending from wherewaves begin to peak to the highest uprush ofthe wave – zone where waves break
Breaker zone – area where deep water wavestouch bottom and become shallow water waves;unstable peaked wavesBreaker zone – area where deep water wavestouch bottom and become shallow water waves;unstable peaked waves
Plunge Point – The point at which plungingwaves curl over and fall.Plunge Point – The point at which plungingwaves curl over and fall.
Breaker – an unstable wave that is breaking onshore or over a reef or other object.Breaker – an unstable wave that is breaking onshore or over a reef or other object.
Peaking wave – a wave that hasPeaking wave – a wave that has
begun to change from a roundedbegun to change from a rounded
swell to a higher steeper andswell to a higher steeper and
less stable pointed wave.less stable pointed wave.
