3.5 Coastal transport and deposition

Describe the process of longshore drift

Swash carries material up the beach in the direction of the prevailing wind, and then backwash carries material directly down the beach under gravity. This is repeated until the water loses energy and deposits the sediment.

Describe the four main ways in which coastal sediment is transported

1. Traction— relatively large and heavy rocks are rolled along the seabed

2. Saltation- smaller and lighter rocks ‘bounce’ along the seabed

3. Suspension- when lighter sediment is carried in the water

4. Solution- when sediment is dissolved in the water

What is tidal range?

The relative difference between high and low tides

Describe how a spit is formed

They form on drift aligned beaches, and where sand and shingle is moving across the beach but the water flow suddenly changes direction. Sediment begins to build up across the estuary mouth, however will rarely extend across it because of the outflow of water. They curve on the end as wave refraction carries material round into the more sheltered wave behind the spit.

What makes a beach swash aligned?

Sediment moves up and down the beach with little transfer

What makes a beach drift aligned?

Sediment is transferred along the coast by longshore drift

How is an offshore bar formed?

Destructive waves erode sand from the beach with their strong backwash and deposit it offshore in bars

How is a barrier beach formed?

When a spit extends across a bay to join two headlands, and can trap water to form a lagoon

What is a tombolo and how is it formed?

It is a beach that forms between an island and the mainland. Deposition occurs where waves lose their energy and the tombolo begins to build up. They are usually covered at high tide, such as the tombolo at St Michael’s Mount, Devon

What is a cuspate foreland?

This is a triangular shaped headland that extends out from the main coastline, and is formed when a coastline is exposed to longshore drift from opposite directions, and sediment is deposited at the point where the two meet. An example of this is Dungeness in Kent.

Name the six stages of plant succession.

Embryo dunes, fore dunes, yellow dunes, grey dunes, dune stack, woodland (mature dunes)

What is the name of the first colonising plants in plant succession?

Pioneer species

What are the steps for dune development?

1. Embryo dunes are the first dunes to develop

2. As embryo dunes develop, they grow into bigger fore dunes, which are initially yellow in colour, but darken to grey as decaying plants add humus

3. depressions between dunes can develop into dune slacks, which are damper areas where the water table is closer to, or at, the surface

What are the steps of salt marsh formation?

1. as mud flats develop, salt tolerant plants begin to colonise and stabilise them

2. Halophytes, such as glasswort and cordgrass, help to slow down tidal flow and trap more mud and silt

3. as sediment accumulates, the surface becomes drier and different plants begin to colonise

4. creeks, which are created by water flowing across the estuary at low tide, divide up the salt marsh.