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:
- Positive sediment budget: More sediment enters than leaves, resulting in coastline build-up
- 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:
- Rivers carrying eroded sediment from inland
- Sea level rise flooding river valleys and forming estuaries
- Erosion of cliffs by waves, weathering, and landslides
- Sediment formed from crushed shells of marine animals
- 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:
- Corrasion (abrasion): Rock and sediment transported by waves grind against cliffs and rocks
- Hydraulic action: Compressed air in cliff cracks exerts pressure when waves crash
- Cavitation: Expanding air in receding waves breaks off pieces of rock
- Wave quarrying: Wave energy directly breaks off rock fragments
- Solution (corrosion): Seawater gradually dissolves soluble rocks like limestone
- 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.
