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Embed code for: 9. Sediment
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The coastal sediment cell system is a simplified model that examines coastal processes and patterns in a given area.
Sources of sediment at the coast include:
the sediment transported by rivers and the wind
the biogenic input (e.g. shells)
marine deposits transported either along the coast by longshore drift or onshore by tide and currents from offshore deposits (e.g. those left on the sea floor during the last ice age).
Sediment may be lost to the coastal system if they are blown inland, transported offshore or removed by human action.
There are 11 sediment cells on the England and Wales coastline running around Britain from St Abb’s Head of the north east Scottish Border to the Solway Firth in the west.
A sediment cell (also known as a littoral cell) is defined as a length of coastline that is relatively self-contained as far as the movement of sand or shingle is concerned, and where interruption to such movement should not have a significant effect on adjacent sediment cells.
Each major sediment cell is divided into a number of sub-cells.
Material in a sediment cell can be considered in the form of sediment budget, with losses and gains.
Losses from the system involve deposition in sediment sinks, whereas gains tend to involve coastal erosion or sediment brought into the system by rivers or from offshore sources.
In principle, the sediment budget seeks to achieve a state of dynamic equilibrium where erosion and deposition are balanced.
This balance can be upset by events such as a surge in river discharge following floods introducing vast amounts of sediment into the system.
This, in turn, leads to deposition in the river estuary.
A severe storm may also upset the balance by eroding a beach and transferring the sediment outside the system.
Key – all values in thousand m3/yr
Direction & movement of sediment by LSD
Input of sediment
Removal of sediment
This figure shows the main inputs from coastal erosion together with the transfers along the East Anglican coastline.
By comparing the values of sediment movement, it is possible to identify loses and gains at points around the coast and to make assertions about the location of sediment sinks or alternative sources of sediment.
However, the map on the previous slide illustrates how difficult it is in obtaining data for all components of a sediment cell.