Sediment Budget and Transport in Sediment Cells

Coastal systems are often divided into sediment cells, also known as littoral cells, which are closed coastal systems for the purpose of sediment management.

Definition: A sediment cell is a section of coastline and nearshore area within which sediment movement is self-contained.

The sediment budget is a key concept in understanding coastal dynamics:

Vocabulary: The sediment budget is the difference between the amount of sediment that enters a coastal system and the amount that leaves it.

There are two possible outcomes for a sediment budget:

1. Positive sediment budget: More sediment enters than leaves, resulting in coastline build-up
2. Negative sediment budget: More sediment leaves than enters, leading to coastline retreat

Highlight: Understanding the sediment budget is crucial for coastal equilibrium systems and feedback mechanisms, as it directly impacts the balance of erosion and deposition.

Sediment inputs to coastal systems come from various sources:

1. Rivers carrying eroded sediment from inland
2. Sea level rise flooding river valleys and forming estuaries
3. Erosion of cliffs by waves, weathering, and landslides
4. Sediment formed from crushed shells of marine animals
5. Transportation of offshore sediment deposits by waves, tides, and currents

Example: The East Anglian coast in the UK receives significant sediment input from cliff erosion, contributing to the formation of beaches and spits along the coastline.

Wave erosion plays a crucial role in shaping coastlines and contributing to the sediment budget. The main processes of wave erosion include:

1. Corrasion (abrasion): Rock and sediment transported by waves grind against cliffs and rocks
2. Hydraulic action: Compressed air in cliff cracks exerts pressure when waves crash
3. Cavitation: Expanding air in receding waves breaks off pieces of rock
4. Wave quarrying: Wave energy directly breaks off rock fragments
5. Solution (corrosion): Seawater gradually dissolves soluble rocks like limestone
6. Attrition: Rock fragments in water break into smaller pieces by colliding with each other

Quote: "Understanding sediment sources, cells, and budgets is essential for effective coastal management and predicting future changes in coastlines."

These processes of erosion, transportation, and deposition work together to shape coastlines and maintain the dynamic equilibrium of coastal systems. By studying sediment budget and transport in sediment cells, coastal managers can make informed decisions about shoreline protection, beach nourishment, and other coastal management strategies.

Coastal Systems and Equilibrium

Coastal systems are complex natural environments that operate in a state of dynamic equilibrium. This equilibrium is maintained through various inputs, outputs, flows, and stores within the system.

Definition: Coastal equilibrium refers to the balanced state of inputs and outputs in a coastal system, where processes of erosion and deposition are in relative balance.

The main components of coastal systems include:

1. Inputs: Sediment from rivers, cliff erosion, and marine organisms
2. Outputs: Sediment transported out to sea or along the coast
3. Flows: Movement of sediment by waves, tides, and currents
4. Stores: Landforms such as beaches, dunes, and spits that hold sediment

Highlight: Coastal systems are dynamic, constantly changing due to the interaction of various processes and energy sources.

Energy inputs in coastal systems come from:

• Tides
• Currents
• Wind
• Waves

These energy sources drive the processes that shape coastlines, including:

• Erosion
• Weathering
• Transportation
• Deposition

Example: Wave action can erode cliffs, creating sediment that is then transported along the coast and deposited to form beaches or spits.

Feedback mechanisms play a crucial role in maintaining coastal equilibrium:

1. Negative feedback: Causes changes with the opposite effect, restoring balance to the system
2. Positive feedback: Causes changes that have a similar effect, potentially creating a new equilibrium

Vocabulary: Negative feedback is a self-regulating mechanism that helps maintain stability in a system.

Coasts can be classified as high energy or low energy:

1. High energy coasts:

   • Receive high inputs of energy from large, powerful waves
   • Often have sandy coves and rocky landforms (cliffs, caves, stacks, and arches)
   • Erosion rate typically higher than deposition rate

2. Low energy coasts:

   • Receive low inputs of energy from small, gentle waves
   • Often have salt marshes and tidal flats
   • Deposition rate typically higher than erosion rate

Example: A high energy coastline example UK would be the rugged cliffs of Cornwall, while a low energy coastline example UK might be the mudflats of the Thames Estuary.

Understanding these coastal systems and their equilibrium mechanisms is crucial for effective coastal management and predicting future changes in coastlines.