How do transportation and deposition processes influence coastal landforms?

These processes vary depending on wave energy and sediment size. The most important factor in shaping coastal landforms is longshore drift, which moves material along the coast.

Longshore Drift: The Coastal Conveyor Belt

Longshore drift is the primary process that transports sediment along the shoreline.

Longshore Drift

• The prevailing wind drives waves and usually hits the coast at an angle.
• The swash carries material up the beach at this angle.
• The backwash, pulled by gravity, brings the material straight back down the beach at 90°.
• This repeated zig-zag motion gradually moves sediment along the coast.

Longshore drift is essential for feeding depositional landforms like spits, bars, and beaches with sediment.

Constructive Waves and Coastal Deposition

Deposition occurs when waves lose energy and drop the sediment they’re carrying.

The characteristics of a constructive wave

A constructive wave is a type of wave that builds up beaches by depositing sediment. Constructive waves are the leading cause of deposition. Their characteristics include:

• Strong swash (movement of water up the beach)
• Weak backwash (water returning to the sea)
• Low height and long wavelength
• Low frequency (6–8 waves per minute)
• Deposit sediment as they push it up the beach, but take little away

Deposition is most common in sheltered bays, during calmer weather, and where wave energy is reduced by friction or depth change.

Beaches: Built by the Sea

Beaches are created by the deposition of sediment along the coastline.

• Usually found in bays, where the wave energy is low.
• Sediment is sorted: larger material is left at the top of the beach, and finer material settles near the shoreline.
• In stormy weather, berms (ridges of shingle) may be thrown up by destructive waves.

Beach profile diagram

Over time, constructive waves build up the beach, forming a gently sloping profile made of sand, shingle, or a mixture of both.

Spits: The Coastal Tail

Spits are long, narrow ridges of sand or shingle that project out from the coastline into the sea.

How spits form:

• Longshore drift moves sediment along the coast.
• Where the coastline changes direction or ends (e.g. near a river mouth), wave energy drops.
• Sediment is deposited, forming a spit that builds out to sea.
• Changes in wind direction may create a hooked end.
• The sheltered water behind the spit encourages the formation of salt marshes or mudflats.

The formation of a spit

Spurn Point on the Holderness Coast is a well-known example of a UK spit.

Bars: Nature’s Coastal Barriers

Bars form when a spit extends across a bay and joins two headlands.

• This traps a lagoon of water behind it, forming a bar.
• Bars are often found in sheltered, low-energy environments.
• They can also form offshore due to wave action moving material from beaches and depositing it further out.

The formation of a bay bar

These features are essential for coastal protection, but they also change the natural flow of water and sediment.