Coasts as Systems

The coast is one of the most dynamic environments on Earth, shaped by the constant interaction of marine, atmospheric and terrestrial processes. At A-Level, AQA requires you to understand the coastline through the lens of systems theory — treating the coast as an open system with inputs, outputs, stores and transfers of energy and materials. This approach, rooted in General Systems Theory developed by Ludwig von Bertalanffy (1968), allows geographers to analyse how coastal landscapes change over time and space.

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The Systems Approach

A system is a set of interrelated components that work together as a complex whole. In geography, we distinguish between three types of system:

System Type	Characteristics	Coastal Example
Open system	Exchanges both energy and matter with its surroundings	A beach receiving sediment from rivers and losing it to longshore drift
Closed system	Exchanges energy but not matter	The global sediment budget (theoretical)
Isolated system	No exchange of energy or matter	Does not exist in nature

The coast is fundamentally an open system. It receives energy from waves, wind and tides, and matter in the form of sediment from rivers, cliff erosion and offshore sources. It loses energy through friction and wave breaking, and matter through sediment transport beyond the system boundary.

Key Definition: A coastal system is an open system in which inputs of energy and sediment are processed through a series of stores and transfers, producing outputs that shape the coastal landscape.

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Inputs to the Coastal System

Inputs are the driving forces that provide energy and material to the coast:

Energy Inputs

1. Wave energy — the primary input, generated by wind blowing over the ocean surface. The energy available depends on wind speed, wind duration, and fetch (the distance of open water over which the wind blows)
2. Tidal energy — produced by the gravitational pull of the Moon and Sun. Spring tides (when Sun, Moon and Earth are aligned) generate higher energy than neap tides
3. Wind energy — directly moves sediment through aeolian processes, particularly on beaches and sand dune systems
4. Solar energy — drives weathering processes (thermal expansion and contraction) and influences biological activity
5. Gravitational energy — drives mass movement processes such as rockfalls, landslides and slumping on cliffs

Material Inputs

1. Fluvial sediment — rivers deliver sand, silt, clay and gravel to the coast. The River Amazon alone delivers approximately 1.2 billion tonnes of sediment to the Atlantic annually
2. Cliff erosion — produces sediment directly at the coast. At Holderness, cliff retreat of 1.8 m/year supplies around 3.4 million m³ of material annually
3. Offshore sediment — material moved onshore from the continental shelf by constructive waves, particularly sand and shingle deposited during the last glaciation
4. Windblown material — aeolian transport of sand from inland areas or along the coast
5. Biological material — shells, coral fragments and organic matter from marine organisms

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Outputs from the Coastal System

Outputs represent the energy and material that leave the system:

• Sediment lost to deep water — material carried offshore beyond the wave base by destructive waves and rip currents
• Sediment transported along the coast — longshore drift moves material beyond the defined system boundary (sediment cell boundary)
• Solution loss — dissolved minerals carried away by chemical processes
• Wind removal — aeolian transport of fine sediment inland or offshore
• Human extraction — dredging, sand and gravel removal for construction

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Stores and Transfers

Within the coastal system, energy and material are temporarily held in stores (also called components or sinks) and moved between them by transfers (also called flows or processes):

Key Stores

Store	Description
Beaches	Accumulations of sand, shingle or pebbles between low and high water marks
Sand dunes	Aeolian deposits of sand stabilised by vegetation
Mudflats and salt marshes	Fine sediment deposited in sheltered intertidal areas
Cliffs	Rock faces that act as a store of potential sediment
Offshore bars	Submerged ridges of sediment parallel to the coast
Spits and bars	Elongated deposits of sediment formed by longshore drift

Key Transfers

• Erosion — removal of material from cliffs, beaches and the sea bed
• Weathering — in situ breakdown of rock (mechanical, chemical, biological)
• Mass movement — downslope transfer of material under gravity (rockfall, slumping, landslides)
• Longshore drift — net movement of sediment along the coast by wave action
• Tidal currents — movement of water and sediment by tidal flows
• Aeolian transport — wind-driven movement of sand particles

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The Sediment Cell Concept

One of the most important applications of systems theory to the coast is the sediment cell (also called a littoral cell). This concept was formalised in the UK by Motyka and Brampton (1993) for the Ministry of Agriculture, Fisheries and Food (MAFF).

Key Definition: A sediment cell is a largely self-contained stretch of coastline within which the movement of sediment is essentially a closed system — sediment is recycled within the cell with minimal exchange across its boundaries.

graph TD
    subgraph "Sediment Cell Model"
    A["Inputs: cliff erosion, rivers, offshore"] --> B["Beach Store"]
    B --> C["Longshore Drift Transfer"]
    C --> D["Spit / Bar Store"]
    D --> E["Outputs: deep water loss"]
    B --> F["Dune Store"]
    F --> B
    C --> B
    end

UK Sediment Cells

The coastline of England and Wales has been divided into 11 major sediment cells and 55 sub-cells. The boundaries between cells typically occur at major headlands, estuary mouths or stretches of deep water where sediment transport is negligible.

Cell Number	Location	Approximate Length
1	St Abb's Head to Flamborough Head	300 km
2	Flamborough Head to The Wash	200 km
3	The Wash to Thames Estuary	190 km
4	Thames Estuary to Selsey Bill	200 km
5	Selsey Bill to Portland Bill	170 km
6	Portland Bill to Land's End	350 km
7	Land's End to Hartland Point	330 km
8	Hartland Point to St David's Head	420 km
9	St David's Head to Great Orme	330 km
10	Great Orme to Solway Firth	370 km
11	Solway Firth to St Abb's Head	560 km

Sediment Budgets

Each sediment cell has a sediment budget — the balance between inputs and outputs:

• Positive budget: inputs > outputs → net deposition → coastline advances seaward (progradation)
• Negative budget: outputs > inputs → net erosion → coastline retreats landward (recession)
• Balanced budget: inputs = outputs → coastline is in dynamic equilibrium

Exam Tip: Questions on sediment cells often ask you to explain how human intervention in one part of a cell can disrupt the sediment budget elsewhere. A classic example is how groynes at Mappleton on the Holderness coast starved beaches downdrift at Cowden of sediment, accelerating erosion there from 1.8 m/year to over 4 m/year after the scheme was completed in 1991.

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The Littoral Zone

The littoral zone is the area of coastline directly influenced by marine processes. It can be subdivided:

Zone	Location	Key Processes
Backshore	Above the normal high tide mark, reached only by storm waves	Aeolian processes, weathering, mass movement
Foreshore	Between normal high and low tide marks (the intertidal zone)	Wave action, tidal processes, erosion and deposition
Nearshore	From low tide mark to the point where waves begin to break	Wave shoaling, longshore currents
Offshore	Beyond the wave base where waves do not affect the sea bed	Minimal direct coastal processes

Understanding these zones is critical because different processes dominate in each, producing distinct landforms and deposits.

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Dynamic Equilibrium and Feedback

Coastal systems tend towards a state of dynamic equilibrium — a condition where the system is constantly adjusting to maintain a balance between inputs and outputs. This does not mean the coast is static; rather, it fluctuates around an average condition.

Feedback Mechanisms

Two types of feedback operate in coastal systems:

Negative feedback (self-regulating): A change triggers a response that counteracts the original change, returning the system towards equilibrium.

Example: Storm waves erode a beach, moving sediment offshore to form a bar. The bar causes waves to break further from the shore, reducing their erosive power. Constructive waves then gradually return sediment to the beach.

Positive feedback (self-reinforcing): A change triggers further change in the same direction, pushing the system away from equilibrium.

Example: Cliff erosion removes vegetation from the cliff top, which reduces interception and infiltration, increasing surface runoff. This accelerates further erosion through gullying and mass movement. The cliff retreats faster and faster until a new equilibrium is established.

graph LR
    subgraph "Negative Feedback"
    A1["Storm removes beach sediment"] --> B1["Offshore bar forms"]
    B1 --> C1["Waves break further out"]
    C1 --> D1["Reduced erosion at beach"]
    D1 --> E1["Beach rebuilds"]
    end

graph LR
    subgraph "Positive Feedback"
    A2["Cliff erosion"] --> B2["Vegetation lost"]
    B2 --> C2["Increased runoff"]
    C2 --> D2["Accelerated erosion"]
    D2 --> A2
    end

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Temporal and Spatial Scales

Coastal processes and changes operate across multiple scales, and the AQA specification requires understanding of this:

Temporal Scales

Scale	Time Period	Examples
Short-term	Hours to days	Individual storm events, tidal cycles
Medium-term	Years to decades	Seasonal beach profiles, cliff retreat rates
Long-term	Centuries to millennia	Sea level change, isostatic adjustment, coastal evolution
Geological	Millions of years	Formation of coastlines, lithological change

Spatial Scales

Scale	Area	Examples
Micro	Individual landform	A single rock pool, a blow hole
Meso	Section of coast	A bay, a spit, a beach
Macro	Regional	A sediment cell, the Holderness coast
Mega	Continental/global	Global sea level patterns, plate tectonics

Exam Tip: In extended answer questions on coastal systems, explicitly reference the temporal and spatial scales at which processes operate. This demonstrates synoptic understanding and is rewarded in the AO2 marks for application. For example, note that while a storm event (short-term, micro-scale) may destroy a section of beach, the sediment budget of the wider cell (long-term, macro-scale) may remain in equilibrium.

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Evaluation of the Systems Approach

Strengths	Limitations
Provides a holistic framework for understanding coastal change	Over-simplifies complex, chaotic natural processes
Helps identify cause-and-effect relationships	Sediment cell boundaries are not truly closed — leakage occurs
Useful for coastal management planning and decision-making	Difficult to measure all inputs and outputs accurately
Allows prediction of consequences of human intervention	Does not fully account for episodic, high-magnitude events
Widely accepted by researchers and policymakers (e.g., DEFRA, Environment Agency)	Human activity often disrupts natural system operation

The systems approach remains the dominant framework used in UK coastal management, underpinning Shoreline Management Plans (SMPs) introduced from 1995 onwards. Despite its limitations, it provides an essential tool for understanding and managing one of the world's most dynamic environments.

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Summary

• The coast is an open system with inputs, outputs, stores and transfers of energy and sediment
• Sediment cells provide a framework for understanding sediment movement along the coast
• The littoral zone is divided into backshore, foreshore, nearshore and offshore
• Coastal systems tend towards dynamic equilibrium through negative feedback mechanisms
• Understanding temporal and spatial scales is essential for analysing coastal change
• The systems approach, while imperfect, remains the foundation of modern coastal management