How does the coast operate as an open system, and what processes move energy and sediment through it?
The coastal landscape as an open system within a sediment cell; sources of energy and sediment; marine and sub-aerial processes; and the concept of dynamic equilibrium.
An Eduqas A-Level Geography answer to coastal systems and processes in Component 1, covering the coast as an open system within a sediment cell, sources of wave, wind, tide and current energy, marine and sub-aerial processes, the sediment budget and dynamic equilibrium, with UK examples.
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What this dot point is asking
Eduqas wants you to treat the coast as an open system within a sediment cell, identify its sources of energy and sediment, explain the marine and sub-aerial processes that operate, and use the ideas of the sediment budget and dynamic equilibrium to show how the system stays in balance.
The answer
The coast as an open system
Treating the coast as an open system with inputs, stores, transfers and outputs is the foundation Eduqas builds the whole landscape option on. Energy and sediment enter, are stored in landforms, are transferred along the coast, and leave the cell. England and Wales are divided into eleven major sediment cells for management, each subdivided into sub-cells, so reasoning at the scale of the cell is essential: what is defended in one place affects another downdrift.
Sources of energy and sediment
Besides waves, tides set the vertical range over which marine processes act, and currents (including longshore and rip currents) redistribute sediment. Sediment is supplied by rivers at their mouths, by cliff erosion of weak or jointed rock, by offshore sources moved onshore by constructive waves, and by longshore drift entering the cell. Coasts are classified by energy (high-energy, exposed, erosional versus low-energy, sheltered, depositional) and by geology: concordant coasts (rock bands parallel to the sea) form coves, while discordant coasts (bands at right angles) form headlands and bays.
Marine and sub-aerial processes
Marine erosion works by hydraulic action (compressed air and water forced into joints), abrasion (sediment hurled at the cliff), attrition (particles rounding each other) and solution (dissolution of carbonate rock). Sediment is transported by traction, saltation, suspension and solution, and along the coast by longshore drift, driven by the dominant wave approach. Deposition occurs where energy falls below the transport threshold, in sheltered bays and behind obstructions. Sub-aerial processes act on the cliff from the land side: mechanical weathering (freeze-thaw, salt crystallisation), chemical weathering (carbonation, oxidation) and biological weathering weaken the rock, and mass movement (rockfall on resistant cliffs, rotational slumping on saturated clays) then delivers material to the cliff foot.
Examples in context
Example 1. The eleven sediment cells of England and Wales. For management, the coast of England and Wales is divided into eleven major sediment cells, each largely self-contained between major headlands, and these are subdivided into sub-cells. Treating the coast this way underpins shoreline management plans: because longshore drift carries sediment within a cell, a groyne field or sea wall that traps or reflects sediment at one point reduces the supply reaching beaches further along, so decisions cannot be made stretch by stretch in isolation. This cell framework is the practical reason the open-system idea matters.
Example 2. The Holderness coast, East Yorkshire. Holderness shows the energy and sediment inputs of a high-energy system. Weak glacial till cliffs meet a long North Sea fetch and a narrow beach, so wave energy is high and cliff erosion supplies large volumes of fine sediment that is quickly carried south by longshore drift towards the Humber. Sub-aerial slumping after wet winters reshapes the cliff face, and marine processes remove the slumped debris. The cell is in surplus of fine sediment but the coast still retreats at roughly m a year because that sediment does not stay to build protective beaches, illustrating how inputs, transfers and outputs together set the coastal form.
Try this
Q1. Define the term sediment cell. [2 marks]
- Cue. A length of coastline, usually bounded by headlands, within which the movement of sediment is largely self-contained, with its own sediment budget.
Q2. Explain how the sediment budget influences whether a coast erodes or accretes. [3 marks]
- Cue. A positive budget (inputs exceed outputs) builds beaches and favours deposition; a negative budget (outputs exceed inputs) narrows beaches and exposes cliffs to erosion; a balanced budget gives dynamic equilibrium.
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 2019 (style)5 marksUsing Figure 1 (a labelled sediment cell), describe the movement of sediment within the cell.Show worked answer →
A low-tariff AO3 resource question: read the figure and describe it in coastal terms rather than reciting a learned cell.
Read off the dominant longshore drift direction from the arrows, identify the sources (cliff erosion and river inputs at the updrift end), the transfers (drift carrying sediment along the coast) and the sinks (spits and offshore bars at the downdrift end).
State that the cell is largely closed, bounded by headlands, so sediment cycles within it, and quote any volumes the resource labels.
Markers reward precise reading of the resource and correct coastal terminology.
Eduqas 2021 (style)8 marksExplain how marine and sub-aerial processes both contribute to the coastal system.Show worked answer →
Define the coast as an open system of inputs, stores, transfers and outputs, then explain both process families and how they interact.
Marine processes act from the sea: erosion by hydraulic action, abrasion, attrition and solution, transport by longshore drift and the swash-backwash system, and deposition where energy falls.
Sub-aerial processes act from the land: weathering (freeze-thaw, salt crystallisation, carbonation) and mass movement (rockfall, slumping) that retreat cliffs and supply sediment.
The key link is that marine processes remove the debris that sub-aerial processes deliver, exposing fresh rock to renewed attack, so the two are interdependent rather than separate.
Markers reward sequenced processes from both families and an explicit link between them.
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Sources & how we know this
- Eduqas A-level Geography specification (from 2016) — Eduqas (2016)