1.3.1 Coasts as Systems

• System


  A group of fundamental elements bound together by specific linkages
• Systems


  • May be open or closed
  • May change through time
• Key words in geography for systems

  • Energy
  • Matter
  • Transfer
  • Inputs
  • Outputs
  • Stores
  • Transfers
  • Flows
• Closed system

  Transfer of energy, but not matter, between the system and its surroundings
• Closed system

  • Planet Earth
• Open system


  Receives inputs and transfers outputs of energy or matter across the boundaries within it and with its surroundings
• Open systems


  • Water cycle
  • Carbon cycle
• Sediment cells


  Sections of the 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. The system has a tendency to counteract any changes imposed on the system in order to keep this balance, which is achieved by inputs and outputs constantly changing to maintain the balance
• Dynamic equilibrium in a sediment cell is where input and outputs of sediment are in a constant state of change but remain in balance
• The dynamic equilibrium may be upset in the long term by human interventions, or in the short term it may be interrupted by natural variations
• Within each sediment cell there are smaller subcells. Often the smaller subcells are used when planning coastal management projects
• Features of the coastal system


  • Inputs
  • Outputs
  • Stores/Sinks
  • Transfers/Flows
  • Energy
• Inputs


  May refer to material or energy inputs. Coastal inputs are not limited to but include three main areas: Marine, Atmosphere, Humans
• Outputs


  May refer to material or energy outputs such as ocean currents, rip tides, sediment transfer, evaporation
• Stores/Sinks


  • Beaches
  • Sand Dunes
  • Spits
  • Bars and Tombolos
  • Headlands and Bays
  • Nearshore Sediment
  • Cliffs
  • Wave-cut Notches
  • Wave-cut Platforms
  • Caves
  • Arches
  • Stacks
  • Stumps
  • Salt Marshes
  • Tidal Flats
  • Offshore Bands and Bars
• Transfers/Flows


  • Wind-blown sand
  • Mass-movement processes
  • Longshore drift
  • Weathering
  • Erosion (Hydraulic Action, Corrosion, Attrition, Abrasion)
  • Transportation (Bedload, In suspension, Traction, In solution)
  • Deposition (Gravity Settling, Flocculation)
• Energy


  • Wind
  • Gravitational
  • Flowing Water
• Negative feedback loop


  Mechanisms which balance changes, taking the system back towards equilibrium
• Positive feedback loop


  Mechanisms which exaggerate change, taking the system away from dynamic equilibrium
• Sediment sources


  • Rivers
  • Cliff erosion
  • Wind
  • Glaciers
  • Offshore
• 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 (as an output) to another stretch of coastline (as an input)
• Sediment budgets


  Use data of inputs, outputs, stores and transfers to assess the gains and losses of sediment within a sediment cell