Coastal Landscapes
Sediment Cells
What are Sediment Cells?
Sediment cells, also known as littoral cells, are distinct areas of the coastline where sediment is sourced, transported, and deposited. Each cell is generally regarded as a self-contained system with its own inputs, transfers, and outputs of sediment and is, therefore, regarded as a closed system. These cells are crucial for managing coastal processes and understanding how coastal features are formed and maintained.
Characteristics of Sediment Cells
Sediment cells have several defining characteristics:
- Boundaries:
- Each sediment cell is bounded by natural or human-made features that prevent significant sediment transfer to adjacent cells. These boundaries can include headlands, estuaries, groynes, or breakwaters.
- Sources:
- Rivers, cliff erosion, and offshore deposits are sediment sources within a cell. These inputs provide the material that is transported and deposited along the coast.
- Transfers:
- Sediment is transported within the cell through processes such as longshore drift, tidal currents, and wave action. The direction and rate of sediment transport depend on prevailing wind and wave conditions.
- Sinks:
- Sediment sinks are locations where material is deposited and stored, such as beaches, dunes, and offshore bars. These features act as temporary or permanent storage sites for sediments.
Components of a Sediment Cell
To understand how sediment cells function, it is essential to recognize their key components:
- Sediment Sources:
- River Inputs: Rivers transport sediments from inland areas to the coast, where they enter the sediment cell.
- Cliff Erosion: Eroding cliffs contribute sediments to the coastal system.
- Offshore Deposits: Sediments from the seabed can be transported onshore by wave action.
- Sediment Transfers:
- Longshore Drift: The movement of sediment along the coast by wave action at an angle. This process plays a significant role in sediment transport within cells.
- Tidal Currents: Tides move sediments in and out of estuaries and along the coast.
- Wave Action: Waves can erode, transport, and deposit sediments, shaping coastal features.
- Sediment Sinks:
- Beaches: Accumulations of sand, pebbles, and other materials along the shoreline.
- Dunes: Wind-blown sand forms dunes, which act as sediment storage sites.
- Offshore Bars: Submerged ridges of sand or gravel formed by wave action.
Importance of Sediment Cells
Sediment cells are crucial for several reasons:
- Coastal Management:
- Understanding sediment cells helps in developing effective coastal management strategies. By recognising the sources, transfers, and sinks of sediment, managers can implement measures to maintain or restore natural processes and protect coastal areas.
- Erosion and Deposition:
- Sediment cells help explain patterns of erosion and deposition along coastlines. By studying these cells, geographers can predict how coastal features will change over time and the impacts of human activities on sediment dynamics.
- Sustainable Development:
- Knowledge of sediment cells is vital for sustainable coastal development. It ensures that construction projects like ports, sea defences, and tourist facilities do not disrupt the natural sediment balance and lead to unintended consequences like increased erosion or sediment starvation.
Case Studies
To illustrate the concept of sediment cells, let’s look at a couple of examples:
- The Holderness Coast, UK:
- The Holderness Coast is one of the fastest-eroding coastlines in Europe. It forms part of a sediment cell where material eroded from the cliffs is transported southwards by longshore drift, eventually depositing at Spurn Head.
- The Nile Delta, Egypt:
- The Nile Delta is a significant sediment sink, where sediments carried by the Nile River are deposited, forming extensive deltaic landforms. The delta is part of a larger sediment cell influenced by river inputs and Mediterranean wave action.