Lecture 16-Coastal Oceanography I Flashcards Preview

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Flashcards in Lecture 16-Coastal Oceanography I Deck (56):

What is the definition of the coastal zone?

-the region that is affected by coastal processes that make the environment different from that of the open ocean -wave breaking, erosion, river outflow


What are the differences between the coastal zone and the open ocean? (3)

1.Waves= don't break on the open ocean but do on the coast -the energy is released by wave breaking, imparts the energy on the coast 2.Erosion 3. River outflow= freshwater interacts with salt water


Does the distance from shore of boundary between open ocean and coastal region vary?

-varies greatly depending on ocean depth and the relative importance of waves, erosion and river outflow -get regions where it is short as there is drop off to the depth -so the ocean ground profile determines the lengths of coastal zone -competing influences change


What are the processes that are active in the coastal zone? (6)

1. Waves and wave breaking 2. Erosion 3. Sediment transport 4. Tides 5. River outflows and estuaries 6. Strong effect on biology -wave breaking leads to erosion -erosion is highly dependent on the material on the coast -very different from place to place and the resulting sediment transport is very different depending -the sediment can be dumped in different places= accretion -tides= occur in open ocean too but in coastal= change the level of sea -impacts on bioloigcal processes -many humans settled on estuaries


What is a wind driven wave?

-an instability arising from the relative motion of two fluids of very different densities (air and water, water= 1000x different density than air and they are in relative motion)


What is the source of energy of wind-driven waves?

-wind -wind imparts energy on the surface of the ocean -almost all the time the wind is faster -leads to wave generation


Do waves transport mass horizontally?

-no, not until they break

-currents do that

-motion of the object is circular

-the transport is in a circle for a wind driven ocean wave

-so the bird bill bob up and down and from side to side

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What is a crest?

-the top bit of the wave


What is a trough?

-the bottom part of a wave


What is wave height?

-vertical distance between trough and crest


What is wave amplitude?

-1/2 of wave height -vertical distance from still water level to the crest


What is still water level?

-the average of the height of the crest and the trough, the average between the two, height of the water if there were no waves


What is wavelength?

-distance between two crests


What is frequency of a wave?

-number of wave crests passing point A or B each second

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What is period of a wave?

-time required for wave crest at point A to reach point B

(period= usually several seconds, frequency= 0.2 if period is 5 seconds)

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What is the path of an individual water molecule on water surface in a wave?

-orbital path

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What is the generation of waves over open ocean like?

- wind creates small ripples, these travel

-become bigger depending on the wind

-then become fully developed and change into swells eventually

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What are swells?

-remotely generated waves that and propagated/moved into another region

-waves can travel in regions without wind, they travel from the region where they were generated to wind calm areas

-over 1000s of km

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What is a fetch?

-distance over which the wind blows in the same direction

-the longer the fetch the more energy the wave can get

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What are fully developed waves/seas?

no longer extracting any energy from the wind


What does the point where waves become fully developed depends on?

so the point in which it becomes fully developed depends on the fetch distance and duration


What happens as wave approaches shore?

-bottom friction slows it down -the amount of energy is then concentrated in a smaller volume (as it is traveling slower) -this pushes the wave up -when the top moves faster than the bottom (which is slowed down by bottom drag) the wave breaks


What is true of high waves?

-the higher the wave the more energy is needed to keep it up -when close to shore


What is a storm surge?

-dome of water pushed ahead of a strong large storm by winds -not a wave, it is a pressure gradient effect -the wind is pushing the water up, elevating the sea level


What is a storm surge generated by?

-tropical cyclone -mid-latitude low pressure system -also a seconary effect from lower atmospheric pressure in center of these storms sucking the sea upwards= inverse barometer effect


Where are the most damaging aspects of tropical cyclones?

-on the coast


What kind of wave is a tsunami?

-not wind driven, different type of wave


What causes tsunamis?

-earthqake generated (or asteroid strike or landslides), -one column of water gets pushed upwards (happens at places where two tectonic plates meet) -the column up= creates a wave, not very visible at sea (only via tsunami monitoring device) -water rises in shallow water as the wave has tremendous energy -so the energy gets concentrated in a smaller volme as it slows down= goes up -then breaks, damaging, plus flooding -really fast


What are the aspects of a tsunami wave that distinguish it from wind-driven waves?

--travel much faster (100km/h) -small in the open ocean and can be huge as they approach the coastline (1m amplitude at open sea is a big one) = would have 10s of meters upon hitting the coastline


How fast do the tsunamis travel?

-above 200m/s -700 km/h -much faster than wind waves


What is the amplitude of tsunamis in the open ocean?

-small, often below 1 meter -then get pushed up as they slow down on approaching land


What are the types of waves? (5)

1. wind-driven waves

2. tsunami

3. tide

4.seiche= harbour wave

5.capillary wave/ripple

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What does disturbing force mean?

-the force that supplies the energy for the wave to form


What does restoring force mean?

-the force that is trying to eliminate the force providing the energy (gravity = pulling the wave down)


What is the period, disturbing and restoring force of a wind-driven wave?

-period= in single digits seconds (1-10s) =the disturbing force is the wind =restoring force- gravity


What is the period, disturbing and restoring force of a tsunami?

-period is about 20 mins (1000s) -disturbing force is seismic disruption, landslides or an asteroid strike -restoring force is gravity


What is the period, disturbing and restoring force of tides?

-period is 12 hrs usually -disturbing force is gravity(gravity of the moon and sun) -restoring force is gravity (gravity of the Earth)


What is the period, disturbing and restoring force of seiche (harbour wave)?

-period is 100s -disturbing force is wind -restoring force is gravity


What is the period, disturbing and restoring force of capillary waves/ripples?

-period is 1/100 of a second to 1/10 of a second -the disturbing force is wind - the restoring force is surface tension(=intermolecular attraction of water molecules on the surface of water


How does the distance between wave crests change as they approach the coast?

-get closer together


What is happening in this picture?

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-region of the point not as shallow water is attracting more wave energy= get more erosion -the really shallow water= less energy attracted, get sediment transport not as much erosion(less energy) -so sand taken from the erosion region (the point) and transported onto the shallower water, the beach


What do tides mark?

-mark regions of highest water


What is nearshore?

-where the waves are typically breaking (that is where the high tide comes in)

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What is a longshore bar?

-when waves break they have stuff in them= sediment, this is being deposited when the waves break= get formation of longshore bars= self-maintaing as the water there becomes shallower so the waves are more likely to break there

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What is foreshore?

-the region that is only occassionaly wave indentated, waves affected by smashing


What is backshore?

-the region that is not commonly indentated by waves


What is swash?

-wave coming onshore


What is backwash?

-wave going offshore


What is the relationship between wave energy and sediment deposition?

1.LOW ENERGY--if wave energy not high the amount of water coming up on the coast is small and sediment is pushed up and wants to go back but can't as there isn't enough water to bring it back down, backwash is inefficient in low energy waves 2.HIGH ENERGY- excess water dumped on the shore, enough to take the sediment back, efficient back wash= get coastal erosion of beaches with high energy waves


What are the types of beaches?

-range from sandy to rocky


How is the type of a beach determined?

-the steepness of the slope; the flatter the beach the more fine-grained the material -on steep slopes, backwash dominates and finer particles are swept out to sea -energy of the waves -on beaches with high wave energy,backwash dominates and scours smaller particles


What conditions would you have to have to get a rocky beach?

-either steep slope or really high energy waves (steep slopes in mediterranean, not so in australia)


How can sediment be transported along the shore?

-sediment can come onshore but it can also go also transport along the shore

-transaltion along the shore depends on the angle of the wave hitting the coastline

-path followed by the sand grains in first perpendicular to the wave crest, when it goes down it goes down the foreline, the steepest diretcion dictated by the beach slope = get coastward sediment transport

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Why is longshore sediment transport important?

-longshore sediment transport is important -can take sediment from places where erosion happens and dump it where erosion is not occurring


How are rips formed?

-rip is generated by the longshore going and meeting, swim parallel to the shore

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What are the offshore depositions, bars and barrier islands?

-lot of different structure in places where longshore current

-heterogenous coast

-creates all of this

-barrier island protects the bit against

-stand pit= is smaller and bar is bigger

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