The components and functioning of coastal systems

Coastal systems are the dynamic zones where land interacts with the sea. These natural systems operate through a balance of inputs, outputs, flows, and stores involving both sediment and energy, shaping the coastal landscape over time.

Key elements of coastal systems

• Inputs into the system - Sediment enters through various sources, while energy is introduced via wind, waves, tides, and currents.
• Outputs from the system - Sediment can be carried out to sea or deposited elsewhere along the coastline.
• Flows and transfers within the system - Processes like erosion, weathering, transportation, and deposition move sediment through the coastal zone.
• Stores within the system - Landforms such as beaches, dunes, and spits act as temporary storage areas for sediment.

Dynamic equilibrium in coastal environments

Coastal systems often strive to maintain a balance between inputs and outputs, a state known as dynamic equilibrium. Changes in the system can trigger feedback mechanisms that either restore balance or amplify the change.

Feedback mechanisms in coastal systems

• Negative feedback processes - These occur when a change prompts opposing effects to restore balance. For instance, when a cliff erodes, the fallen material accumulates on the beach below, offering protection and reducing further erosion.
• Positive feedback processes - These happen when a change leads to additional changes in the same direction. For example, when sand builds up on a barrier spit, it can capture more sediment, enlarging the landform until a new balance is achieved.

Energy sources driving coastal processes

Energy in coastal systems is transferred through air and water, powering the processes that shape coastlines. The primary sources include wind, waves, tides, and currents, each contributing uniquely to coastal dynamics.

Wind as an energy source

• Formation of wind - Generated by air moving from high-pressure to low-pressure areas.
• Impact of pressure gradients - Stronger gradients, often during storms, result in more powerful winds.
• Role of prevailing winds - Consistent winds from a single direction produce more energetic waves compared to variable winds.

Waves and their characteristics

• Creation of waves - Formed by wind blowing over the sea surface, causing friction that results in circular water motion.
• Factors affecting wave impact - Wave height, influenced by wind speed and fetch (the distance wind travels over water), determines the energy delivered to the coast.
• Wave breaking process - Waves break near the shore due to friction with the seabed.
• Swash and backwash dynamics - Swash is the water moving up the beach after a wave breaks, while backwash is the water returning to the sea.

Types of waves and their effects

Tides and their influence

• Cause of tides - Result from the gravitational pull of the Moon and Sun, causing the periodic rise and fall of the ocean surface.
• Effect on coastal processes - Tides determine where waves break on the beach, with most coastal landforms shaped in the zone between high and low tide.

Currents and sediment movement

• Nature of currents - Represent the general flow of water in a specific direction, driven by wind or differences in water temperature and salinity.
• Role in coastal systems - Currents transport sediment along coastlines, influencing erosion and deposition patterns.

Differences between high-energy and low-energy coasts

Coastal environments vary significantly based on the energy levels they experience, which affect the types of waves, landforms, and dominant processes present.

Characteristics of high-energy coasts

• Wave conditions - Dominated by large, powerful waves due to strong winds, long fetches, and steeply shelving offshore zones.
• Typical landforms - Feature sandy coves and rocky structures, shaped by intense wave action.
• Dominant process - Erosion rates generally exceed deposition, leading to retreating coastlines.

Characteristics of low-energy coasts

• Wave conditions - Characterised by small, gentle waves resulting from mild winds, short fetches, and gentle offshore slopes, often in sheltered locations.
• Protection factors - May be shielded by offshore reefs or islands, reducing wave energy.
• Typical landforms - Often include saltmarshes and tidal mudflats, formed in calmer conditions.
• Dominant process - Deposition rates typically exceed erosion, leading to coastline growth.

Sediment sources and budgets in coastal systems

Sediment is a critical component of coastal systems, sourced from various locations and managed within defined zones. The balance of sediment movement determines whether a coastline advances or retreats.

Sources of sediment in coastal systems

• River contributions - Rivers transport eroded material from inland areas to the coast.
• Impact of sea level rise - Rising sea levels can inundate river valleys, creating estuaries that supply sediment to coastal areas.
• Cliff erosion processes - Waves, weathering, and landslides break down cliffs, releasing sediment into the system.
• Marine organism remains - Crushed shells from sea creatures add to the sediment pool.
• Offshore deposits - Material is brought in from underwater stores through wave and current action.

Understanding sediment budgets

• Definition of sediment budget - Represents the balance between sediment entering and leaving a coastal system.
• Positive sediment budget - Occurs when more sediment enters than leaves, causing the coastline to build seaward.
• Negative sediment budget - Happens when more sediment leaves than enters, resulting in coastal retreat.

Concept of sediment cells

Sediment cells, also known as littoral cells, are distinct sections of coastline where sediment movement is largely self-contained. Sediment typically does not transfer between different cells, meaning each operates as an independent coastal system.