3.1.2.2- Sediment Sources, Cells and Budgets

Coastal Systems and Processes

Sediment Sources

Sediment- loose beach material e.g. silt, sand, shells and shingles

Sources- point of origin

Sources of Sediment at the coast include:

1. River sediment: Coming from a delta or estuary (from land to sea). This sediment comes from outside the coastal system as an input. 

2. Human Activity: May input sediment to the coastal system through beach nourishment or replenishment. 

3. Wave action or erosion: Provides cliff face sediment within the coastal system. Weathering (e.g. by frost action or freeze-thaw) and sub-aerial processes of mass movement (e.g. rockfall or landslides) also contribute sediment material from cliff faces. Indeed, cliff erosion is the major source of beach sediment. 

4. Biogenic input:  There is also an input of sediment from shells.

5. Offshore Sediment Deposits: Sediment may be transported along the coast by longshore drift, or onshore by tides and current, from offshore sediment deposits e.g. those left on the sea floor (sea bed) after the last Ice Age.

6. Offshore or Longshore Bars: Exposed at low tide, may be a source of sediment, carried beachward by onshore winds. Wind action may also transport sediment within the system from beaches and sand dunes.

Sediment may be lost to the coastal system if they are:

• Blown inland
• Transported offshore out of the coastal system to the sea system
• Removed by human activity e.g. sand mining uses sediment as aggregate for the building industry

Sediment (Littoral) cells.

• Sediment cells are the basic unit of shorline, management in England and Wales. They are used to aid planning and management of sections of the coastline. 

Distribution (spread/location/layout/where they are)

• 11sediment cells can be identified along the coastlines of England and Wales.
• Sediment cells are found within well defined physical bondaries such as between headlands (e.g. Landsend) and stretches of open, deep water (e.g. the River Severn Estuary)
• There are more cells/ a higher concerntration along the west coast (5 in total) than along either the south (3) or east (3) coasts. 
• Three cells make up the coastline of Wales; at 8, England has 12.
• Sediment cells are of unequal size- one of the smallest cells lies in the south…