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The study of coastal landscapes begins with understanding the littoral zone as a dynamic, open system shaped by the interaction of terrestrial, marine and atmospheric processes. This lesson addresses the foundation of Edexcel A-Level Geography Paper 1, Topic 2B: Coastal Landscapes and Change and specifically supports Enquiry Question 1: Why are coastal landscapes different and what processes cause these differences? By the end of this lesson you will be able to define the littoral zone, explain how coasts function as open systems, apply the concept of sediment cells and dynamic equilibrium, and classify coasts according to their physical characteristics.
The littoral zone is the area where the land meets the sea. It is not a simple line — it is a zone that extends from the landward limit of marine influence (including cliffs, dunes and salt marshes affected by storm waves and salt spray) to the seaward limit where waves begin to interact with the seabed (the wave base, typically at a depth of approximately half the wavelength of the dominant wave). The littoral zone therefore varies in width from a few metres on steep, rocky coasts to several kilometres on gently shelving coastlines with extensive tidal flats.
The littoral zone is conventionally divided into several sub-zones, each experiencing different combinations of marine and terrestrial processes:
| Sub-Zone | Location | Key Characteristics |
|---|---|---|
| Backshore | Above the normal high-tide mark | Affected only during storms and exceptionally high tides; includes cliff faces, dune systems and coastal marshes |
| Foreshore | Between the average high-tide and low-tide marks | The intertidal zone; regularly submerged and exposed; where most wave action occurs |
| Nearshore | From low-tide mark to the point where waves begin to break | Includes the surf zone and breaker zone; sediment is actively moved by wave energy |
| Offshore | Beyond the nearshore, to the limit of wave influence on the seabed | Waves are unbroken; sediment transport is primarily by tidal and ocean currents |
Understanding these zones is essential because different processes dominate in each. Erosion is concentrated in the foreshore and nearshore, while deposition tends to dominate in the backshore (dune building, marsh accretion) and in sheltered offshore areas.
Exam Tip: When the specification refers to "the coast as a system," it means the entire littoral zone — not just the beach or cliff face. Always define the littoral zone in terms of the full range of marine and terrestrial influences operating across its sub-zones.
In physical geography, a system is a set of interrelated components through which energy and matter flow. The coast operates as an open system, meaning it exchanges both energy and matter with its surroundings. This distinguishes it from a closed system, which exchanges energy but not matter.
The coastal system can be analysed using the standard framework of inputs, outputs, stores (components) and flows (transfers and transformations):
graph LR
subgraph INPUTS
A["Wave energy"]
B["Tidal energy"]
C["Wind energy"]
D["Sediment from rivers, cliffs, offshore"]
E["Precipitation"]
F["Solar energy (weathering)"]
G["Gravitational energy"]
end
subgraph STORES
H["Beaches"]
I["Sand dunes"]
J["Mudflats & salt marshes"]
K["Cliff faces"]
L["Offshore sediment deposits"]
end
subgraph OUTPUTS
M["Sediment lost offshore"]
N["Sediment lost to adjacent cells"]
O["Evaporation"]
P["Solution loss"]
end
A --> H
B --> J
C --> I
D --> H
E --> K
F --> K
G --> K
H --> M
H --> N
I --> N
J --> P
K --> H
Stores are where energy or matter is held within the system. The principal sediment stores are beaches (the most dynamic store, constantly gaining and losing sediment), sand dunes (longer-term storage, built by aeolian processes), mudflats and salt marshes (fine sediment stored in low-energy estuarine and sheltered environments), cliff faces (a potential source of sediment when eroded) and offshore deposits (sediment resting below the wave base).
Flows describe how energy and matter move through the system:
Outputs represent losses from the system. Sediment may be lost offshore beyond the wave base, transported out of the local system by longshore drift into an adjacent sediment cell, or removed in solution (dissolved material carried away by seawater or runoff).
Exam Tip: In exam answers, always structure your systems analysis using these four categories (inputs, outputs, stores, flows). Examiners reward candidates who apply the systems framework explicitly rather than simply listing processes.
The concept of sediment cells (also called littoral cells) is central to understanding coastal sediment budgets. A sediment cell is a length of coastline that is largely self-contained in terms of the movement of sediment. Within a sediment cell, sediment is sourced, transported and deposited in a broadly circular pattern. The boundaries of sediment cells are defined by natural features that interrupt longshore drift, such as headlands, estuaries, tidal inlets and deep-water channels.
The coastline of England and Wales has been divided into 11 major sediment cells for the purposes of coastal management. Each cell is further subdivided into sub-cells. These cells were defined by a joint research programme (SCOPAC and others) and form the basis of Shoreline Management Plans (SMPs).
| Cell Number | Approximate Extent | Key Features |
|---|---|---|
| 1 | St Abb's Head to Flamborough Head | Includes the Holderness coast (rapid erosion) |
| 2 | Flamborough Head to The Wash | Includes Spurn Head spit |
| 3 | The Wash to Thames Estuary | Includes the north Norfolk coast, Happisburgh |
| 4 | Thames Estuary to Selsey Bill | Includes the Blackwater Estuary (Essex) |
| 5 | Selsey Bill to Portland Bill | Includes the Solent and Isle of Wight |
| 6 | Portland Bill to Start Point | Includes Chesil Beach (a tombolo) |
| 7 | Start Point to Hartland Point | South Devon and north Cornwall |
In theory, what happens within one sediment cell should not affect adjacent cells. In practice, boundaries are permeable — some sediment does leak between cells, particularly during storm events. This is why the term "largely self-contained" is more accurate than "completely closed."
Within each cell, the balance between sediment inputs and outputs determines whether the coast is accreting (gaining sediment), eroding (losing sediment) or in equilibrium (inputs balance outputs). This balance is called the sediment budget.
graph TD
A["Sediment Budget"] --> B["POSITIVE budget<br/>Inputs > Outputs<br/>Coast accretes (builds out)"]
A --> C["BALANCED budget<br/>Inputs = Outputs<br/>Coast in equilibrium"]
A --> D["NEGATIVE budget<br/>Outputs > Inputs<br/>Coast erodes (retreats)"]
B --> E["Example: Dungeness foreland,<br/>growing through longshore drift"]
C --> F["Example: Stable pocket beach<br/>in a sheltered bay"]
D --> G["Example: Holderness coast,<br/>losing ~2 million m³/year"]
Understanding the sediment budget is essential for coastal management decisions. If a groyne traps sediment on one beach (increasing the local sediment store), it starves the downdrift coast of sediment, potentially causing erosion. This interconnected thinking is a key part of the systems approach.
The coast is in a state of dynamic equilibrium — a condition in which the system is constantly adjusting to changing inputs and outputs while maintaining an overall balance over time. Unlike static equilibrium (where nothing changes), dynamic equilibrium involves continuous change at short timescales that averages out over longer timescales.
Beach profiles: A beach may be eroded during a winter storm (destructive waves remove sediment, creating a flatter profile with an offshore bar). During calmer summer conditions, constructive waves return sediment onshore, rebuilding the berm and steepening the profile. Over a full year, the beach may remain roughly the same size — dynamic equilibrium is maintained.
Cliff retreat and platform extension: As a cliff is eroded, it retreats landward. The debris accumulates at the cliff base and is reworked by waves, contributing to the widening of a wave-cut platform. The widening platform itself dissipates wave energy, reducing the rate of cliff erosion — a negative feedback mechanism that slows the process over time.
Salt marsh growth: A salt marsh accretes vertically as sediment is trapped by vegetation during tidal flooding. As the marsh surface rises, it is flooded less frequently, reducing sediment supply and slowing the rate of accretion. This is another negative feedback loop.
Dynamic equilibrium can be disrupted by changes to inputs or outputs, which may be natural (e.g., a major storm, sea level rise, tectonic uplift) or human (e.g., dam construction reducing river sediment supply, groyne construction trapping longshore drift, dredging removing offshore sediment). When equilibrium is disturbed, the system adjusts towards a new equilibrium — but this adjustment may involve significant erosion, flooding or habitat loss during the transition.
Exam Tip: The concept of dynamic equilibrium is a powerful evaluative tool. In essay questions, you can argue that many coastal management problems arise from human disruption of dynamic equilibrium — for example, building a groyne creates a local positive sediment budget but a downdrift negative budget, merely displacing the erosion problem rather than solving it.
Coasts can be classified in many ways. The Edexcel specification expects you to understand classification by geology, process dominance and sea level change history. These classifications are not mutually exclusive — a coast may be, for example, both rocky and emergent.
| Classification | Description | Example |
|---|---|---|
| Rocky (cliffed) | Dominated by resistant bedrock forming cliffs, platforms and headlands | Flamborough Head, Yorkshire; Dorset coast (Portland limestone) |
| Sandy | Low-lying coasts with extensive beaches, dunes and barrier systems | North Norfolk coast (Holkham, Brancaster) |
| Estuarine | Drowned river valleys dominated by tidal processes and fine sediment (mud, silt) | Blackwater Estuary, Essex; Severn Estuary |
| Coral | Built by biological processes (coral reef growth) in warm, clear tropical waters | Maldives atolls; Great Barrier Reef |
| Classification | Description | Characteristic Landforms | Example |
|---|---|---|---|
| Emergent | Land has risen relative to the sea (or sea level has fallen) | Raised beaches, relict (abandoned) cliffs, coastal terraces | Western Scotland (isostatic rebound after deglaciation) |
| Submergent | Sea has risen relative to the land (or land has subsided) | Rias (drowned river valleys), fjords (drowned glacial troughs) | Kingsbridge Estuary, Devon (ria); Sognefjorden, Norway (fjord) |
| Classification | Characteristics |
|---|---|
| High-energy | Exposed to powerful waves with long fetch; dominated by erosion; typically produces cliffed, rocky coasts with wave-cut platforms. Example: Atlantic coast of Cornwall |
| Low-energy | Sheltered from dominant wave directions; dominated by deposition; typically produces beaches, salt marshes and mudflats. Example: The Wash, East Anglia |
graph TD
A["Coastal Classification"] --> B["By Geology"]
A --> C["By Sea Level History"]
A --> D["By Energy/Process"]
B --> B1["Rocky / Cliffed"]
B --> B2["Sandy / Beach"]
B --> B3["Estuarine / Muddy"]
B --> B4["Coral"]
C --> C1["Emergent<br/>Raised beaches, relict cliffs"]
C --> C2["Submergent<br/>Rias, fjords"]
D --> D1["High energy<br/>Erosion dominant"]
D --> D2["Low energy<br/>Deposition dominant"]
Understanding how a coast is classified helps explain why it looks the way it does and how it is likely to change in the future. A high-energy, discordant, submergent coast will behave very differently from a low-energy, concordant, emergent coast. Classification also informs management decisions — hard engineering is more commonly applied on high-value, high-energy cliffed coasts, while managed retreat may be more appropriate for low-lying, low-energy estuarine coasts.
Feedback mechanisms are critical to understanding how coastal systems self-regulate (or fail to self-regulate):
Negative feedback counteracts change and promotes stability. Example: cliff erosion widens the wave-cut platform, which dissipates more wave energy, which reduces the rate of cliff erosion. The system moves back towards equilibrium.
Positive feedback amplifies change and promotes instability. Example: cliff erosion removes vegetation from the cliff top, which reduces root binding and increases infiltration, which accelerates weathering and mass movement, which increases the rate of cliff erosion. The system moves further from equilibrium.
In reality, both types of feedback operate simultaneously. The balance between them determines whether a coast is stable, gradually changing or experiencing rapid transformation.
| Feedback Type | Effect | Coastal Example |
|---|---|---|
| Negative | Counteracts change; promotes equilibrium | Platform widening reduces cliff erosion rate |
| Positive | Amplifies change; promotes instability | Vegetation loss accelerates cliff retreat |
Exam Tip: When answering questions about coastal change, explicitly identify feedback mechanisms. This demonstrates high-level systems thinking and is rewarded in the upper mark bands for 12- and 20-mark questions.
This lesson establishes the systems framework for Edexcel A-Level Geography Paper 1, Topic 2B. The next lesson examines how geological structure and lithology create distinctive coastal landscapes.