Notes · GeographyUK · A-Levels

Coastal Systems and Landscapes

A physical-landscape option that treats the coast as a dynamic open system in which energy from waves, tides and currents interacts with sediment to erode, transport and deposit material. It develops the sediment-cell concept, the marine and sub-aerial processes, the sequence of erosional and depositional landforms, the effects of sea-level change, and the evaluation of coastal management.

6 sections~22 min reading time3 competenciesLevel Standard 4 · Advanced 2

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Exam profile

AO1 · Understand the coastal system, its sediment budget, and marine and sub-aerial processes and landformsAO2 · Apply process understanding to explain named landforms and evaluate coastal management for a placeAO3 · Interpret OS maps, coastal photographs and wave, sediment and management data

Operators:explainanalyseassessevaluateto what extentdescribe the distributioninterpret

basic level

At AS-Level the focus is on describing the main coastal processes and landforms and reading coastal maps and photographs.

higher level

The full A-Level requires the sediment-cell system, the sequence of landform development, sea-level change and evaluative judgement about management.

Depth

Text

Contents · 6 sections

Coastal Systems and Landscapes

The coast as a system and the sediment budget#

StandardAQA 7037 3.1.3DfE GCE Geography - coastal systems

A coastal sediment cell

Fig. 1Within a sediment cell, sediment moves from sources through transfers to sinks; the balance is the sediment budget.

The coast is best understood as an open system with inputs, outputs, stores and flows. The inputs are energy (from wind, waves, tides and currents) and sediment (from rivers, cliff erosion, offshore and, on some coasts, wind and organisms). The stores are the beaches, dunes, spits and nearshore sediment bodies. The flows are the movements of sediment by longshore drift and by on- and offshore currents. The outputs are the loss of sediment to the deep sea, to estuaries and to the wind. Reading the coast this way turns a list of features into a connected system.

The organising concept is the sediment cell: a largely self-contained stretch of coastline, bounded by prominent headlands or by changes in the direction of drift, within which the movement of sediment is effectively enclosed. England and Wales, for example, are divided into eleven major sediment cells, each further split into sub-cells. Within a cell, sediment moves from sources (where it enters, such as eroding cliffs and river mouths) along transfers (the beaches and drift pathways) to sinks (where it is deposited and stored, such as spits, offshore bars and deep water). The boundaries are rarely perfectly closed, but the concept lets managers treat a cell as a single unit.

The sediment budget is the balance between the sediment entering a cell and the sediment leaving it, and it determines whether the coast advances or retreats. A positive budget (inputs exceed outputs) means net deposition, so beaches grow and the coastline builds seaward; a negative budget (outputs exceed inputs) means net erosion, so beaches shrink and the coast retreats. When inputs and outputs are balanced, the coast is in dynamic equilibrium - individual grains keep moving but the overall form is stable. This budget is the coastal equivalent of the water balance.

Feedback operates within the cell. If a beach is eroded, the exposed cliff behind it may be attacked and eroded faster, releasing sediment that can rebuild the beach - a negative feedback that tends to restore equilibrium. Human interference commonly breaks the budget: building a groyne or a harbour wall traps drift and starves the coast downdrift, tipping its budget negative and accelerating erosion there. Recognising that the cell is a connected system is exactly why interfering in one place has consequences elsewhere - the key idea behind modern shoreline management.

Worked example

Reasoning with the sediment budget

A stretch of coast has a river supplying sediment and eroding cliffs, but a new harbour wall now blocks longshore drift into the bay. Explain what happens to the sediment budget and the coastline downdrift of the wall.

Identify the change
The harbour wall intercepts sediment moving along the coast by longshore drift, so the input of sediment to the coast downdrift is cut off.
Effect on the budget
Downdrift, outputs (continued drift and offshore loss) now exceed inputs, so the sediment budget becomes negative.
Effect on the coast
With a negative budget the beach shrinks and the coastline retreats faster - the wall protects one place but starves and erodes another.

Result: The wall makes the downdrift budget negative, so its beach is starved of sediment and erosion there accelerates.

Typical mistakes

Treating a sediment cell as completely closed - the boundaries leak, and the cell is only a useful management approximation.
Forgetting that trapping drift updrift starves the coast downdrift - the cell is connected, so local action has knock-on effects.

Active revision

Explain why building a groyne field to protect one beach can increase erosion further along the coast within the same sediment cell.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for geography (Department for Education) · AQA A-level Geography 7037 specification (AQA)

Waves, tides and marine and sub-aerial processes#

StandardAQA 7037 3.1.3DfE GCE Geography - coastal processes

Classification of coastal processes

Fig. 2Marine and sub-aerial processes together shape the coast; each erosional and transport process has a distinct mechanism.

Waves are the main source of energy at the coast. They form as wind drags across the sea surface, and their energy depends on the fetch (the distance of open water the wind blows over), the wind speed and its duration. In open water the water particles move in circular orbits; as a wave enters shallow water the orbit is distorted, the wave steepens and breaks, sending the swash rushing up the beach and the backwash draining back. Wave energy is concentrated on headlands and dissipated in bays by wave refraction - the bending of wave crests as they slow in shallow water - which is why headlands are eroded and bays receive deposition.

The distinction between constructive and destructive waves controls whether a beach grows or shrinks. Constructive waves are low, long and infrequent (a low frequency of around 6-8 per minute); their strong swash carries sediment up the beach and their weak backwash lets it settle, so they build the beach. Destructive waves are high, steep and frequent (10-14 per minute); their weak swash and strong backwash drag sediment back down the beach and offshore, so they erode it. Storms bring destructive waves; calmer weather brings constructive waves, and beaches often show a seasonal cycle between the two.

Tides and currents add further energy and set the vertical and lateral limits of processes. Tides - the regular rise and fall of the sea caused by the gravitational pull of the Moon and Sun - determine the tidal range, and therefore the width of coast over which marine processes can act; a large range spreads energy over a wide zone, while a small range concentrates it. Currents, including rip currents and longshore currents, move water and sediment along and away from the shore.

Two families of process shape the coast. Marine processes are those of the sea: erosion (hydraulic action - the force of water and trapped air; wave quarrying; abrasion - the grinding of sediment against the rock; attrition - the wearing of the sediment itself; and solution - the chemical dissolving of rock), transport (longshore drift, and traction, saltation, suspension and solution within the water) and deposition. Sub-aerial processes act on the land above the waterline: weathering (mechanical, such as freeze-thaw and salt crystallisation; chemical, such as carbonation) and mass movement (rockfall, landslides and slumping). The interplay of the two families produces the coast's landforms.

Worked example

Constructive versus destructive waves

A beach is surveyed in summer and again after a series of winter storms and is found to have lost sediment. Explain, using wave type, why the profile changed.

Summer conditions
Calm weather brings constructive waves - low, long, infrequent - whose strong swash and weak backwash push sediment up the beach and build a steeper berm.
Winter storms
Storms bring destructive waves - high, steep, frequent - whose weak swash and strong backwash comb sediment down the beach and carry it offshore.
Net change
Over the winter the destructive waves remove more than the constructive waves added, so the beach loses sediment and its profile flattens.

Result: Winter destructive waves eroded the beach through strong backwash, flattening the profile that summer constructive waves had built.

Typical mistakes

Confusing abrasion (sediment grinding the rock) with attrition (the sediment wearing itself down).
Saying constructive waves are 'weak' - they are low and long but their swash is strong; it is their weak backwash that lets sediment build up.

Active revision

Explain how wave refraction concentrates erosion on headlands and encourages deposition in bays.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for geography (Department for Education) · AQA A-level Geography 7037 specification (AQA)

Erosional processes and landforms#

StandardAQA 7037 3.1.3DfE GCE Geography - erosional landforms

A cliff and wave-cut platform

Fig. 3Undercutting at the notch causes the cliff to collapse and retreat, leaving a wave-cut platform.

Where a coast is exposed to strong wave energy and the rock is resistant, erosional landforms dominate. The large-scale pattern is set by geology: where bands of hard and soft rock meet the coast at right angles (a discordant coast), the soft rock is eroded into bays and the hard rock stands out as headlands. Once headlands form, wave refraction concentrates energy on them, so they become the focus of the erosion that produces the classic sequence of landforms.

Cliffs and wave-cut platforms form as the sea attacks the base of the land. Hydraulic action and abrasion cut a wave-cut notch at the high-tide level; as the notch deepens the rock above is undercut and eventually collapses, so the cliff retreats landward. Each retreat leaves behind a gently seaward-sloping wave-cut platform, exposed at low tide, marking where the cliff used to be. The steepness of the cliff reflects the rock's resistance and structure, and the width of the platform records how far the cliff has retreated.

On a headland, a further sequence develops as the sea exploits lines of weakness such as joints and faults. Erosion widens a weakness into a cave; if a cave is cut right through a narrow headland, or two caves meet, an arch forms. Continued erosion and weathering enlarge the arch until its roof can no longer be supported and collapses, leaving an isolated pillar of rock - a stack. The stack is then undercut and weathered until it too collapses to a low stump, visible mainly at low tide. This cave-arch-stack-stump sequence is the most frequently examined landform progression at the coast.

Explaining these landforms well means giving both the process and the sequence, and using the correct terms. A common error is to describe the shape of a stack without explaining that it is a former arch whose roof has collapsed. The strongest answers link the landform to the processes that made it (which erosion process attacked which weakness), to the geology that allowed it, and to time, since these features represent stages in a continuing retreat rather than fixed forms.

The cave-arch-stack-stump sequence

Fig. 4The sea exploits a weakness in a headland to produce, in turn, a cave, an arch, a stack and a stump.

Worked example

Explaining an arch and a stack

A photograph shows an arch on one headland and an isolated stack nearby. Explain how each formed and how they are related.

Start with the weakness
Waves attack a joint or fault in the headland by hydraulic action and abrasion, widening it into a cave.
From cave to arch
If erosion cuts the cave right through the headland, or two caves meet, an arch is left with a roof of rock spanning the gap.
From arch to stack
Continued erosion at the base and weathering of the roof remove support until the roof collapses, leaving an isolated stack - so the stack is a later stage of the same arch.

Result: The arch is a cave cut through the headland; the stack is what remains after the arch roof collapses - successive stages of one erosion sequence.

Typical mistakes

Describing a stack as simply a 'pillar of rock' without explaining it as a collapsed arch.
Assuming all coasts erode into these landforms - they require resistant rock, exposure to strong waves and lines of weakness to exploit.

Active revision

Explain how the geology and the pattern of wave energy along a discordant coastline produce headlands and bays.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for geography (Department for Education) · AQA A-level Geography 7037 specification (AQA)

Transport, deposition and depositional landforms#

StandardAQA 7037 3.1.3DfE GCE Geography - depositional landforms

A spit built by longshore drift

Fig. 5Where the coast turns, longshore drift extends a spit across the mouth; refraction curves its end and mud accretes behind it.

Longshore drift is the process that moves sediment along the coast and underlies most depositional landforms. When waves approach the beach at an angle (set by the prevailing wind), the swash carries sediment up the beach at that angle, but the backwash drains straight back down under gravity. Repeated many times, this zig-zag motion moves sediment steadily along the shore in the direction of the dominant waves. Where the coast changes direction or the energy falls, the sediment is deposited, building the depositional landforms.

Beaches are the simplest store, and their material and profile record the wave conditions: shingle beaches are steep because water percolates through the coarse material and the backwash is weak, while sand beaches are gentler. A spit is a long, narrow ridge of sand or shingle built by longshore drift out across a bay or estuary mouth, where the coastline changes direction; its end is often curved (a recurved end or hook) by wave refraction or a second wind direction, and the sheltered water behind it fills with mud to form a salt marsh or mudflat. If a spit grows right across a bay it becomes a bar, trapping a lagoon behind it; a spit joining an island to the mainland is a tombolo.

Where waves reach the shore with low energy and the tidal range is large, finer material is deposited to build salt marshes: the vegetation traps sediment, the marsh accretes, and a distinctive zonation of salt-tolerant plants develops from the pioneer species at the seaward edge to the climax community inland. Sand dunes form where sand is dried on a wide beach, blown inland and trapped by obstacles and vegetation such as marram grass; they show a succession (a psammosere) from embryo and fore dunes near the beach to fixed, vegetated dunes inland.

Explaining depositional landforms well means naming the process that supplies and deposits the sediment, and the condition that causes deposition (a change in coastline direction, a fall in energy, shelter or an obstacle). A frequent weakness is to describe a spit's shape without explaining the longshore drift that built it or the refraction that recurved its end. The strongest answers also note that these are living landforms in dynamic equilibrium, growing and being reshaped as the sediment budget and wave conditions change.

Worked example

Explaining the formation of a spit

An OS map shows a spit with a recurved end extending across an estuary mouth, with salt marsh symbols behind it. Explain the sequence of processes that formed it.

Sediment supply and movement
Waves approaching at an angle drive longshore drift, moving sediment along the coast towards the estuary mouth.
Deposition across the mouth
Where the coastline changes direction at the estuary, the water deepens and energy falls, so sediment is deposited and builds out as a spit.
Recurving and the marsh
Wave refraction (or a secondary wind) curves the growing end into a recurved hook; behind the spit the water is sheltered, so fine mud settles and a salt marsh develops.

Result: Longshore drift supplies sediment that is deposited where the coast turns, building a spit whose end is recurved by refraction and behind which a salt marsh accretes.

Typical mistakes

Describing a spit only as a 'finger of sand' without the longshore-drift process and the change in coastline direction.
Confusing a bar (a spit grown across a bay, trapping a lagoon) with a tombolo (a spit joining an island to the mainland).

Active revision

Explain how longshore drift and a change in the direction of the coastline combine to form a spit with a recurved end.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for geography (Department for Education) · AQA A-level Geography 7037 specification (AQA)

Sea-level change and emergent and submergent coasts#

AdvancedAQA 7037 3.1.3DfE GCE Geography - sea-level change

Causes and landforms of sea-level change

Fig. 6Eustatic (volume) and isostatic (land height) change combine to produce emergent and submergent coasts.

Sea level relative to the land changes for two distinct reasons, and distinguishing them is essential. Eustatic change is a worldwide change in the actual volume of water in the oceans - it falls when water is locked up in ice during a glacial period and rises when the ice melts, and it also rises as the ocean warms and expands. Isostatic change is a local change in the height of the land relative to the sea - the land is pushed down by the weight of an ice sheet and slowly rebounds upward once the ice melts (isostatic recovery), a process still raising parts of northern Britain today.

Because the two operate on different timescales - eustatic change is fast, isostatic recovery slow - a coastline can experience both, and their interplay over the glacial cycles produced the distinctive emergent and submergent coasts. When the land rises relative to the sea (or the sea falls), an emergent coastline is created; when the sea rises relative to the land, a submergent coastline is created. Each has its own set of relict landforms recording the former sea level.

Emergent coasts display landforms lifted above the present sea. A raised beach is a former beach, complete with its wave-worn platform, now stranded above the reach of the waves, often backed by a relict (abandoned) cliff with old caves and notches high and dry. These are common along coasts that have undergone isostatic recovery. Submergent coasts, by contrast, display drowned landforms: a ria is a drowned river valley, a winding inlet that deepens seaward; a fjord is a drowned glacial trough, deep, steep-sided and often with a shallow entrance sill; and a Dalmatian coast is a set of drowned valleys parallel to the coast, forming long offshore islands.

Understanding sea-level change is not only historical: contemporary eustatic rise from a warming, expanding ocean and melting ice is central to the management of coasts, because it raises the baseline on which storms and erosion act. The evaluation the specification rewards is to connect past sea-level change (which produced the inherited landforms and the sediment supply) with future change (which raises flood and erosion risk), and to recognise that the same processes that shaped these coasts over glacial cycles are now operating within a human lifetime.

Worked example

Identifying a coast type

A coastline has a flat platform with an old cliff, caves and a beach deposit standing several metres above the present shore. Classify the coast and explain how it formed.

Read the evidence
A wave-worn platform, cliff, caves and beach material now stranded above the waves are relict marine landforms that the sea no longer reaches.
Classify
Landforms lifted above the present sea indicate an emergent coastline - the land has risen relative to the sea.
Explain the cause
After the last glacial period the removal of the ice load allowed the land to rebound by isostatic recovery, lifting the former beach and cliff clear of the sea to form a raised beach.

Result: It is an emergent coast: a raised beach and relict cliff produced by isostatic recovery after deglaciation.

Typical mistakes

Using eustatic and isostatic interchangeably - one is a change in ocean volume, the other in the height of the land.
Confusing a ria (drowned river valley, V-shaped) with a fjord (drowned glacial trough, U-shaped and deeper).

Active revision

Explain how the interplay of eustatic and isostatic change since the last glacial period has produced both emergent and submergent coastlines.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for geography (Department for Education) · AQA A-level Geography 7037 specification (AQA)

Coastal management and a case study#

AdvancedAQA 7037 3.1.3DfE GCE Geography - coastal management

Hard versus soft engineering

Fig. 7Hard and soft approaches share the aim of reducing risk but differ in cost, sustainability and side-effects.

Coastal management aims to protect people and property from flooding and erosion, and it is grouped into hard and soft engineering. Hard engineering builds structures to resist the sea: sea walls reflect wave energy, groynes trap longshore drift to widen the beach, rock armour (rip-rap) and gabions absorb wave energy, and revetments break up the waves. These are effective and reassuring but expensive, visually intrusive, and often shift the problem elsewhere - groynes, for example, starve the coast downdrift by interrupting the sediment budget.

Soft engineering works with natural processes rather than against them. Beach nourishment adds sand to widen a beach so it absorbs wave energy; dune regeneration and marsh creation restore natural buffers; and beach re-profiling reshapes the material. These approaches are usually cheaper, more sustainable and less intrusive, but they require repeated maintenance and provide less certain protection in a severe storm. A third strategy, managed realignment (managed retreat), deliberately allows the sea to flood low-value land, moving the defence line landward and letting a new salt marsh form as a natural defence - controversial where it means abandoning land, but increasingly favoured as sea level rises.

Decisions are made through Shoreline Management Plans, which divide the coast (using the sediment cells) into lengths and assign each one of four policies: hold the line, advance the line, managed realignment, or no active intervention (do nothing). The choice rests on a cost-benefit analysis - weighing the value of what is protected against the cost of defending it - and, increasingly, on Integrated Coastal Zone Management, which coordinates all the users and interests along a whole stretch of coast rather than defending each settlement piecemeal.

Evaluating management is the core skill, and it demands a balanced, place-specific judgement rather than a verdict that one method is best. The right approach depends on the value of the land and property at risk, the rate of erosion, the sediment budget, the wishes of local players and the sustainability of the option as sea level rises. A strong case study - for example a rapidly eroding soft-rock coast such as Holderness in East Yorkshire, where defending the towns has starved and accelerated erosion elsewhere - shows exactly this trade-off: protecting one place imposes costs on another, so management is a matter of choosing whom to protect and at what price.

Worked example

Evaluating a management choice

A town on a rapidly eroding soft-rock coast is protected by a sea wall and groynes, but a village a few kilometres downdrift is now eroding faster. Evaluate whether continuing to defend the town is the right decision.

The case for defending
The town has high-value property and infrastructure, so a cost-benefit analysis may justify hard defences that protect a large rateable value and many residents.
The cost elsewhere
The groynes trap drift and the wall reflects energy, starving the downdrift coast of sediment, so the village's sediment budget turns negative and its erosion accelerates - a cost transferred, not removed.
Reach a judgement
A defensible conclusion is that defending the high-value town can be justified, but only within a shoreline management plan that compensates or manages the downdrift village - defending one place while ignoring the connected cell is neither fair nor sustainable.

Result: Defending the town may be economically justified, but because the sediment cell is connected the decision must be made at the scale of the whole coast, not town by town.

Typical mistakes

Claiming hard engineering is always best because it is strongest - it is costly, intrusive and often shifts erosion downdrift.
Treating managed realignment as simply 'giving up' - it is a deliberate strategy that creates a natural defence and can be the most sustainable option.

Active revision

'Managed realignment is a more sustainable response to coastal erosion than hard engineering.' Assess this view with reference to a case study.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for geography (Department for Education) · AQA A-level Geography 7037 specification (AQA)

References & sources

Sources

Department for Education

GCE AS and A level subject content for geography

AQA

AQA A-level Geography 7037 specification

Coastal Systems and Landscapes

6 sections~22 min reading time3 competenciesLevel Standard 4 · Advanced 2

Coastal Systems and Landscapes

Key points

Reasoning with the sediment budget

Key points

Constructive versus destructive waves

Key points

Explaining an arch and a stack

Key points

Explaining the formation of a spit

Key points

Identifying a coast type

Key points

Evaluating a management choice

Sources

Coastal Systems and Landscapes

Key points

Reasoning with the sediment budget

Key points

Constructive versus destructive waves

Key points

Explaining an arch and a stack

Key points

Explaining the formation of a spit

Key points

Identifying a coast type

Key points

Evaluating a management choice

Sources