Coastal landscapes as systems

What is a coast

• a narrow strip of shoreline where the sea and land interact and is shaped and influenced by both natural and human activity within a powerful ‘system’

• land, air, and sea meet at the coast, making it a constantly changing environment

• also is affected by human activity

• unique combination creates a dynamic environment where change occurs frequently

The coastal zone

What is a system

• a system is a set of interrelated stores and processes that are connected together to form a working unit

• open system - a system in which energy and matter can flow in and out of the system, both energy and matter can cross the system boundary to and from the surrounding environment

• closed system - a system in which energy can flow in and out but mater cannot leave and cannot be added, the matter is cycled within the system and only energy transfers across the system boundary to or from the surrounding environment

Energy inputs into the coastal system

• the coastal system is driven by flows of energy within the inshore and foreshore zones, these flows of energy are the ones that enables work to be carried out by the natural geomorphic processes to shape the landscape

Flows of energy:

Solar energy - from the sun, it is responsible for atmospheric processes such as winds which generate waves

Kinetic energy - generated originally from solar energy, energy flows from the movement of wind, water and ocean currents

GPE - the movement of material downslope under gravity. Also, energy from the sun and moon converts to energy in tides

Geothermal energy - responsible for tectonic activity which can happen in coastal locations close to plate boundaries or faults

Inputs of energy

• Thermal/Solar

• GPE

• Kinetic energy

Geomorphic processes

• Weathering

• Erosion

• Mass movement

• Transportation

• Deposition

Outputs of energy

• Energy is used up in geomorphic processes

Stores of sediment

• Beach

• Spit

• Bar

• Tombolo

• Delta

• Salt marsh

Inputs of matter

• Longshore drift from another stretch of coast

• Offshore zone

• Aeolian transport from sand dune

• Cliff erosion - scree

• Fluvial input from river

Outputs of sediment

• Longshore drift to another stretch of coast

• Aeolian transport to sand dunes

• Offshore zone

The coastal zone and equilibrium

Equilibrium - inputs and outputs of energy and matter are balanced

• Coasts are dynamic - they change frequently

• these changes caused by changes in energy flows e.g. wave energy in a storm

• then, the system undergoes self-regulation and changes in order to restore the equilibrium

• e.g. the shape of the coastline changes in response to the increased energy input

• the system is then in a state of dynamic equilibrium - when equilibrium is in the the process of being restored

• the system’s response is known as negative feedback

Negative feedback loop

• this is a stabilising mechanism acting to oppose changes to coastal inputs and re-establish equilibrium

• they have the opposite effect of the initial change

• they can restore equilibrium quickly e.g. where sediment is involved, or over a longer timescale e.g. where rocky landform are involved

Negative feedback loop when a storm heavily erodes beach sediment

• sediment eroded from the shore forms an offshore bar

• this causes friction between the bar and incoming waves which dissipates its kinetic energy and forms a low energy constructed wave and deposits sediment on the beach

Negative feedback loop when a cliff erosion results in the formation of a wave cut platform

• wave cut platform creates friction for the wave which dissipates its kinetic energy

• so when the wave reach the back of the WCP, the energy of the wave is too little to erode the cliff

• so no more sediment is added from the cliff so equilibrium is restored

Positive feedback loop

• in contrast positive feedback pushes a coastal away from equilibrium and amplifies the initial change

• e.g. at a cliff in equilibrium, high energy waves erode the cliff releasing angular sediment - this will then further erode the cliff via abrasion

Sediment cells

• sediment cells are long stretches of coastline where sediment is sourced (inputs of sediment), where sediment flows (sediment is transferred due to inputs of energy), and where sediment is stored

• the geomorphic processes of erosion, transportation, deposition, mass movement and weathering all take place and are largely contained within the sediment cells

• a sediment cell is a closed system so no sediment is transferred from one cell to another

Sediment cells operating as a system

• cells function independently from each other, the boundaries of the cells are determined by the topography and shape of the coastline

• large features e.g. headlands such as the Llyn Peninsula in Wales act as huge natural barriers that prevents the transfer of sediment

• coarse sediment is not exchanged between cells but fine sediment (sand) in suspension might be

• it is unlikely that cells are fully closed because variations in wind direction and tidal currents might cause some sediment to be transferred between cells which makes them more open than the theory suggests

• there are also many sub-cells of a smaller scale existing within the major cells