Deposition and Landforms

Deposition

• Occurs when sediment becomes too heavy for water to carry, or if wave loses energy

• High-energy coastlines continue to transport smaller sediment, so larger rocks are deposited

• Low-energy coastlines have much smaller sediment, which is only deposited in these areas where there is a much lower water velocity

Sediment budget

The balance between sediment added to, stored within, and removed from a sediment cell over a given time period.

Beaches

A depositional landforms that stretches from roughly the low tide to the high tide line. Beach accretion occurs due to constructive waves during the summer. Beach excavation occurs due to to destructive waves in winter.

Barrier beach/bar P

A barrier beach (or bar) is a ridge of sand or shingle that forms across a bay or river mouth, blocking it.

• Longshore drift transports sediment along the coastline

• Deposition occurs when there is a decrease in wave energy, causing sediment to accumulate

• Over time, the deposited material extends across a bay or estuary, forming a barrier beach

• If the bar fully connects across the bay, it is called a bar

• A lagoon may form behind the bar as the water is trapped

Tombolo

A tombolo is a narrow ridge of sand or shingle that connects an island to the mainland or another island.

• Longshore drift moves sediment along the coastline

• Wave refraction around the island reduces wave energy, leading to deposition in the calmer water behind it

• Over time, sediment accumulates, forming a tombolo that links the island to the mainland

Offshore bar

An offshore bar is a submerged or partially exposed ridge of sand or shingle lying parallel to the coastline

• Destructive waves erode material from the beach and transport it offshore

• Deposition occurs as wave energy decreases, forming a submerged ridge

• Over time, the accumulation of sediment creates an offshore bar

• In some cases, if the bar rises above sea level, it can become a barrier beach

Saltation

The bouncing movement of sand-sized particles as they are lifted and dropped by water flow near the seabed.

Suspension

The transport of fine sediment particles within the water column, held aloft by turbulent flow.

Solution (transport)

The movement of dissolved minerals in seawater, whereby chemical ions are carried in solution.

Embryo dune

The first small ridge of sand formed when wind-blown grains accumulate around an obstacle above the high-tide line

Foredune

A larger, vegetated dune ridge formed when pioneering plants stabilise accumulated sand, parallel to the shoreline.

Mature dune (grey dune)

An inland dune stage with well-developed soils and diverse vegetation, often grey-green in colour.

Barrier island

A long, narrow offshore sand feature lying parallel to the coast, separated by a lagoon or bay, formed by wave and tidal action.

Estuarine mudflat

A flat expanse of fine mud deposited in the sheltered, intertidal areas of estuaries during low-energy conditions.

Saltmarsh

A coastal wetland dominated by salt-tolerant plants, forming on mudflats where fine sediments accumulate.