The coastal system
What is a coast? : The part of the land most affected by its proximity to the sea, and the part of the sea most affected by its proximity to the land. The components of the coastal system are interlinked- if one aspect changes (naturally or by humans), it will have a knock on effect on other components.
Inputs of a Coastal System:
- People- economics, tourism, sea defences, recreation etc.
- Land- Rock type/structure, tectonics
- Marine- tides and waves
- Atmosphere- weather and climate, solar energy, climate change
- Erosional Landforms- cliffs, stacks, wave cut platforms
- Depositional Landforms- beaches, spits, salt marshes, dunes
Processes: Deposition, Weathering/Mass Movement, Transportation and Erosion
Backshore: Area between the high water mark and the landward limit of marine activity. Changes normally only occur here in storm conditions.
Foreshore: Area lying between the high and low water marks. Most important zone for marine processes in times that aren't influenced by storm activity.
Inshore: Area between the low water mark and the points where waves cease to have any influence on the land between them.
Offshore: Area beyond the point where waves cease to have impact upon the sea bed and which activity is limited to deposition of sediments.
Sources:Sediment comes from a variety of sources including the sea bed, beaches, river channels, estuaries and cliff erosion. Sediment movements occur in distinct areas known as sediment cells where inputs and outputs are balanced.
Cells: Along the coastline of England and Wales, 11 cells have been identified. Sediment cells are distinct areas seperated from others by headlands and stretches of deep water. They can be regarded as closed systems where nothing is gained or lost although the finer sediments often can move into neighbouring cells. Cells can vary in size.
High energy coastlines: Have strong wave power for a large part of the year. Eg. West coast of the British Isles- the prevailing and dominant winds are westerly and face the direction of the longest fetch: waves have crossed the Atlantic.
Low energy coastlines: Estuaries, inlets and bays are environments where wave energy and heights are lower as waves spread outwards, dissipating their energy. This leads to deposition of transported material. The Baltic Sea is a good example of this.
A wave is a long body of water curling into an arched form and breaking on the shore. Waves are created by the wind giving the water energy, and are a movement of this energy in an orbital motion. Most energy is found at the top of the ocean, and decreases with distance from the surface.
Wave Frequency: Number of wave crests passing a point each second.
Wave Period: Time required for the wave at Point A to reach Point B.
Peak/Crest: The highest point of a wave
Trough: The lowest point of a wave
Wavelength: The distance between successive crests of a wave
There are 2 types of wave: constructive and destructive.
Formation: Local storms create a lot of wind in the close vicinity of the coastline.
Wave form: High plunging waves (over 1m), short wavelength and high frequency (10 waves per minute). High wave in proportion to length.
Wave Break: Weak swash, strong backwash. Tall breakers: break downwards with great force.
Beach: Loss- destructive
Profile: Steep beach results.
Formation: Distant weather systems generate waves in the open ocean.
Wave Form: Low surging waves (under 1m), long wavelenth (above 100m) and low frequency (6 per minute). Low waves in proportion to length.
Wave Break: Strong swash, weak backwash.
Beach: Gain- constructive
Beach Profile: Gentle
Creation of Waves
1. Wind moves over the ocean and as it drags over the surface, friction causes a disturbance, forming waves.
2. Forms part of a relatively static orbital motion with little horizontal movement of individual water molecules.
3. When the wave gets close to the coastline, the sea bed creates friction with the wave, slowing the base of it down.
4. This increases the height and steepness of the wave, as the water particles move in an increasingly elliptical orbit cauising the velocity and wavelength to decrease.
5. The upper part of the wave plunges forwards and breaks when the height: wavelength ratio reaches 1:7.
6. The water rushes up the beach as swash and runs back down at 90 degrees as backwash.
Wave Refraction and Tides
- As waves get nearer a coast, they take on the shape of the coast, so it looks like the waves are bending.
- This causes wave energy to be more concentrated on ares of the coast that protrude such as headlands, increasing rate of erosion here compared to surrounding bays.
- Tides are the periodic rise and fall in the levels of the sea, caused by the gravitational potential pull of the sun and moon. The moon has greater effect due to its proximity with earth.
- The moon pulls water towards it creating a high tide, with a compensatory bulge created on the opposite side of the earth.
- In the areas between 2 high tides, there are low tides.
- The tidal range is the vertical difference between the high tide and the succeeding low tide.
- When there is the largest tidal range (highest high tide and lowest low tide)
- Occurs when the moon and sun are aligned, every 2 weeks.
- These two gravitational pulls attract the water towards them.
- When there is the smallest tidal range (lowest high tide and highest low tide).
- Occurs when the moon and sun are at right angles with eachother, pulling in opposite directions, balancing eachother out keeping the water level relatively stable.