Sediment Transportation Flashcards
Explain the process of longshore shift?
The strongest longshore drift occurs when waves approach the beach at an angle of 30 degrees.
Swash carries beach sediment up the beach at the same angle of the waves.
Backwash carries the sediments back down the beach at right angles to the shore, under the influence of gravity. It moves sediment along the coast until it meets an obstacle.
Predominant wind direction determines direction of longshore drift.
Explain the sediment cell concept.
A sediment cell has sources, transfers and sinks (‘closed system’).
Erosion in one place in the system is balanced by deposition in another with transfers of sediment within the cell by processes like longshore drift and currents.
What is a sediment budget?
The amount of sediment gained from sources and lost to sinks.
Why is the sediment cell concept useful?
For assessing the extent of coastal change and for evaluating coastal management strategies.
What are the sources within sediment cells?
Erosion of cliffs, land sediments transported by rivers, wind-blown sediment from land, onshore currents bringing sediment to shore.
What are the transfers within a sediment cell?
Longshore drift, waves, tides, currents and wind.
What are the sinks within sediment cells?
Depositional features on the backshore, foreshore, nearshore and offshore.
What is negative feedback in the context of sediments cells?
They tend to maintain in equilibrium, for example where wave erosion causes rock falls, which then protect the base of the cliff from further erosion.
What is positive feedback in the context of sediment cells?
It tends to increase change in the system until a new equilibrium is reached, for example a ‘blow out’ in a sand dune allows more sand to be eroded by the wind, reducing vegetation cover further. Often humans cause this.
