Coastal Systems

• Coastal system

  An open system that receives inputs from outside and transfers outputs away from the coast into other systems (terrestrial, atmospheric or oceanic) and can include rock, water and carbon cycles.
• The coastal system is impacted and impacts upon processes which occur in the five oceans of our planet and the smaller seas of which they are part of
• Sediment cells

  Sections of a coast often bordered by prominent headlands, where the movement of sediment is almost contained and the flows of sediment act in dynamic equilibrium
• Dynamic equilibrium

  The maintenance of a balance in a natural system, despite it being in a constant state of change, where inputs and outputs constantly change to maintain the balance
• Human interventions

  Can upset the dynamic equilibrium in the long term
• Natural variations

  Can interrupt the dynamic equilibrium in the short term
• Subcells

  Smaller sections within a sediment cell, often used when planning coastal management projects
• When you are learning something in this unit, always link it back to the key features:

  Inputs: May refer to material or energy inputs.

  Marine: Waves, Tides, Salt Spray

  Atmosphere: Sun, Air Pressure, Wind speed and direction.

  Humans: Pollution, Recreation, Settlement, Defences.

  Outputs: May refer to material or energy outputs: Ocean Currents, Rip tides, Sediment Transfer, Evaporation.

  Stores: Refer to stores and sinks of sediment and material: Beaches, Sand Dunes, Spits, Bars and Tombolos, Headlands and Bays.
• Transfers/Flows: The processes that link the inputs, outputs and stores in the coastal system.

  -Wind Blown Sand

  -Mass Movement processes

  -LSD

  -Weathering

  -Erosion

  -Transportation

  -Deposition
• Feedback Loops

  The coastal systems has mechanisms which enhance changes within a system, taking it away from dynamic equilibrium or mechanisms which balances changes, taking the system back towards equilibrium.
• Negative feedback loop-this lessens any change which has occurred within the system. For example a storm could erode a large amount of a beach, taking the beach out of dynamic equilibrium as there is a larger input of sediment into the system that output.
• Positive feedback loop-this exaggerates the change making the system more unstable and taking it away from dynamic equilibrium.
• Sediment Sources

  Rivers:

  Most of the sediment in the coastal zone is a result of an input from rivers, especially in high rainfall environments where significant river erosion occurs.

  Sediment may be deposited in estuaries which are brackish areas where rivers flow into the sea.
• Sediment Sources

  Cliff erosion:

  Very important in areas with unconsolidated cliffs that are eroded easily. In some areas coastlines can retreat by up to 10m per year providing a significant sediment input.
• Sediment Sources

  Wind:

  The wind is a coastal energy source and can cause sand to be blown along or up a beach.

  Sediment transport by winds may occur where there are sand dunes.
• Sediment Sources

  Glaciers:

  In some coastal systems such as in Antartica, Greenland, Alaska glaciers flow directly into the ocean depositing sediment.

  This occurs when glaciers calve, a process where ice breaks off the glacier.
• Sediment Sources

  Offshore:

  Sediment is transferred to the coastal zone when waves, tides and currents erode offshore sediment sinks such as offshore bars.

  Storm surges or tsunami waves may also transfer sediment into the coastal zone.
• Sediment Sources

  Longshore Drift:

  Sediment is moved along the beach, due to prevailing winds which alter the direction of the waves. This allows sediment to be transported from one section of coastline to another stretch of coastline.

  The swash approaches the coast at an angle due to the prevailing winds, transferring sediment along the beach. The backwash pulls the sediment directly back down the beach. The swash then transfers the sediment along the coastline and then the process repeats.
• Sediment Budgets-They use data of inputs, outputs and stores and transfers to assess the gains and losses of sediment within a sediment cell.
• The Littoral Zone - The littoral zone is the area of land between the cliffs or dunes on the coast and the offshore area that is beyond the influence of the waves.
• The littoral zone

  Constantly changing because of:

  Short term factors like tides and storm surges.

  Long term factor like changes in sea level and human intervention.
• Sun

  Primary source of energy for all natural systems
• Waves

  Main energy source at the coast, formed offshore, most commonly generated by wind, less frequently tectonic activity or underwater landslides causing tsunami waves
• Wave Formation

  1. Winds move across the surface of the water, causing frictional drag which creates small ripples and waves

  2. As the seabed becomes shallower towards the coastline, the orbit of the water particles becomes more elliptical, leading to more horizontal movement of the waves

  3. Wave height increases, but wavelength and wave velocity both decrease

  4. This causes water to back up from behind the wave until the wave breaks and surges up the beach
• The sun has a direct influence on the formation of waves, which occur when wind moves across the surface of the water
• Winds move across the surface of the water, causing frictional drag (resistance to the wind by the water) which creates small ripples and waves
• As the seabed becomes shallower towards the coastline, the orbit of the water particles becomes more elliptical, leading to more horizontal movement of the waves
• Wave height increases, but the wavelength (distance between two waves) and wave velocity both decrease
• This causes water to back up from behind the wave until the wave breaks (collapses) and surges up the beach
• When waves move up the beach, it is known as swash and when it moves back down the beach into the sea into the sea, this is known as the backwash
• Strength of the Wind

  • Wind is essentially air that moves from an area of high pressure to an area of low pressure
  • The larger the difference in pressure between two areas (pressure gradient) the stronger the winds
  • As waves are caused by the wind, stronger winds also mean stronger waves
• Duration of the Wind

  • The longer the wind is active, the more energy the waves will build up and increase
• Size of the Fetch

  • The distance over which the wind blows, the larger it is, the more powerful the waves will be
  • It could also be thought of as the distance to the nearest land mass in a particular direction
• Constructive waves

  Tend to deposit material, which creates depositional landforms and increase the size of beaches
• Destructive waves

  Act to remove depositional landforms through erosion, which work to decrease the size of a beach
• Formation of Constructive Waves

  1. Formed by weather systems that operate in the open ocean

  2. Long wavelength

  3. 6-9 Per Minute

  4. Low waves, which surge up the beach

  5. Strong swash, weak backwash

  6. Occurs on gently sloped beaches
• Formation of Destructive Waves

  1. Localised storm events with stronger winds operating closer to the coast

  2. Short wavelength

  3. 11-16 Per Minute

  4. High waves, which plunge onto the beach

  5. Weak swash, strong backwash

  6. Occurs on steeply sloped beaches
• In summer

  Constructive waves dominate
• In winter

  Destructive waves dominate
• Constructive waves

  May become destructive waves if a storm begins