The coastal system
- Created by: rchapman99
- Created on: 11-11-17 22:17
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- The coastal system
- Coasts are natural systems
- Inputs, e.g. sediment can be brought into the system in various ways Energy inputs come from wind, waves, tide and currents.
- Outputs, e.g. sediment can be washed out to sea, or deposited further along the coast.
- Flows, e.g. processes such a erosion, weathering, transportation and deposition, can move sediment within the system
- Stores - landforms, such as beaches, dunes and spits, are stores of sediment.
- Coastal systems are often in dynamic equilibrium (balanced inputs and outputs).
- Coastal systems experience feedbacks
- Negative - neutralises the effects of changes to the system. E.g. as a beach is eroded, the cliffs behind it are exposed to wave attack. Sediment eroded rom the cliffs is deposited on the beach, causing it to grow in size again.
- Positive - amplifies changes to the system. E.g. as a beach starts to form, it slows down waves, which can cause more sediment to be deposited, increasing the size of the beach. The new equilibrium is reached when long-term growth of the beach stops.
- There are lots of sources of energy in coastal systems
- Wind: created by air moving from areas of high pressure to areas of low pressure; strong winds can produce powerful waves; in some areas, wind consistently blows from the same direction (prevailing wind) which causes higher-energy waves than winds that change direction frequently.
- Waves: created by the wind blowing over the surface of the sea; the friction between the wind and the surface of the sea gives the water a circular motion; wave height is affected by the wind speed and the fetch (maximum distance of sea the wind has blown over); a high wind speed and a long fetch create powerful waves; as waves approach the shore, they break.
- Backwash: water washing back towards the sea.
- Swash: water washing up the beach.
- Destructive waves: high and steep; circular cross profile; high frequency (10-14/min); strong backwash removes material from the beach.
- Constructive waves: low frequency (6-8/min); low and long; elliptical cross profile; powerful swash carries material up the beach and deposits it.
- Tides: periodic rise and fall of the ocean surface, caused by the gravitational pull of the Moon and the Sun; affect the position at which waves break on the beach; the area of land between maximum high tide and minimum low tide is where most landforms are created and destroyed.
- Currents: the general flow of water in one direction; it can be caused by wind or by variations in water temperature and salinity; move along the coast.
- Coasts can be high and low energy coasts
- Low-energy coasts: receive low inputs of energy in the form of small, gentle waves. These can be caused by gentle winds, short fetches and gently sloping offshore zones. Some coastlines are low energy because there is a reef or island offshore, which protects the coast from the full power of waves. Often have saltmarshes and tidal mudflats. The rate of deposition is often higher than the rate of erosion.
- High-energy coasts: receive high inputs of energy in the form of large, powerful waves. These can be caused by strong winds, long fetches and steeply shelving offshore zones. Tend to have sandy coves and rocky landforms, e.g. cliffs, caves, stacks and arches. The rate of erosion is often higher than the rate of deposition.
- There are lots of sediment sources in coastal systems
- There are lots of inputs of sediment into the coastal system
- Rivers carry eroded sediment into the coastal system from inland.
- Sea level rise can flood river valleys, forming estuaries. Sediment in the estuary becomes part of the coastal system.
- Sediment is eroded from cliffs by waves, weathering and landslides.
- Sediment can be formed from the crushed shells of marine organisms.
- Waves, tides and currents can transport sediment into the coastal zone from offshore deposits.
- The difference between the amount of sediment that enters the system and the amount that leaves is the sediment budget.
- Negative sediement budget: if more sediment leaves than enters and the coastline retreats.
- Positive sediment budget: if more sediment enters than leaves and the coastline builds outwards.
- Sediment cells
- Processes going on in one cell don't affect the movement of sediment in another cell.
- Lengths of coastline that are entirely self-contained for the movement of sediment.
- Coast is divided into sediment cells.
- There are lots of inputs of sediment into the coastal system
- Coasts are natural systems
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