Unit 7 Topic 5 Waves and Wave Depths If the wind blows hard enough (speed) and long enough (duration) over a long enough area (fetch), waves become fully developed. When the wind stops, they become swells. As swells reach shore they change into breaking waves.

Wave Energy Deep water waves – ocean depth is greater than half the wavelength D > ½ λ Wave energy extends only to a depth of half the wave length. In open ocean the energy of swells do not touch bottom. As energy moves through the water it sets the water particles in orbital motion.

Deep water waves are characterized by the water to be at least half the wavelength deep. Half the wavelength beneath the surface of the water and deeper, there is no movement of the water molecules due to the wave.

Orbits near the surface have diameters approximately equal to the wave height. Deeper in the water, the orbits become smaller. Below a depth of ½ the wave length, water is unaffected. When wave energy reaches the bottom (begins to drag along the seafloor) the circular orbits are flattened.

Transitional waves: Peaking Waves: As the swells flatten they become waves having wavelength greater than twice but less than 20 times the waters depth. Includes wind waves that have moved into shallower water. Peaking Waves: The water is pushed up off the bottom forming higher steeper waves Because of friction between the water particles and the seafloor, the top of the wave begins to move faster than the deeper parts The front of the wave becomes steeper than the back surface.

Shallow water wave: Breaking wave: When the water depth is less than 1/20 the wavelength D<1/20 λ Breaking wave: The top of the wave travels so fast that it begins to spill over and fall down the front surface develop when: The crest of the wave forms an angle less than 120o. The height is greater than 1/7 of the wavelength. The wave height is ¾ of the water depth.

Topic 6 Wave-Coast Interaction Typical Coastal Features Coast – a strip of land of indefinite width, extending from the shoreline inland to the first major change in land features.

Beach – The zone of loose gravel, sand or other material that extends landward from the low waterline, either to the line of permanent vegetation or to where there is a marked change in substrate. Foreshore + Backshore!

Nearshore – an indefinite zone extending seaward from the shoreline to beyond the breaker zone. Foreshore – that part of the shore between the upper limits of the wave wash and the water’s edge Backshore – The zone of the beach between the foreshore and the point on the coastline where beach berms are located. Onshore – the direction landward from the water. Offshore – the direction seaward from the breaker zone

C D E Offshore

Coastline – the indefinite line that forms the boundary between the coast and the shore. Shoreline – the line formed when the water touches the beach at high tide Bay of Fundy

Dunes – ridges or mounds of loose wind blown material, usually sand.

Scarp – a steep slope along a beach caused by wave erosion. Berm – nearly horizontal part of the backshore of the beach formed by the erosion of material by wave action. Rip Feeder Channel – a drop off parallel to the beach formed at the final breaking point of waves just before the rush up the beach

Bar – an embankment of sand or gravel deposited in shallow water by waves or current.

Surf zone – the area extending from where waves begin to peak to the highest uprush of the wave – zone where waves break Breaker zone – area where deep water waves touch bottom and become shallow water waves; unstable peaked waves

Plunge Point – The point at which plunging waves curl over and fall. Breaker – an unstable wave that is breaking on shore or over a reef or other object. Peaking wave – a wave that has begun to change from a rounded swell to a higher steeper and less stable pointed wave.