Wave types and coastal processes of weathering, mass movement, erosion, transport and deposition; erosional and depositional landforms; and the costs and benefits of hard and soft coastal management.

What this dot point is asking

This is AQA GCSE Geography (8035) Paper 1, Section C (3.1.3 Physical landscapes in the UK). AQA expects you to distinguish constructive and destructive waves, explain the full set of coastal processes (weathering, mass movement, erosion, transport and deposition), describe and explain how erosional and depositional landforms develop in a sequence, and evaluate the costs and benefits of hard engineering, soft engineering and managed retreat. Coasts is one of three landscape options; you study it plus at least one of rivers or glaciation.

Waves and coastal processes

Waves form when wind blows over the sea surface, transferring energy to the water. The energy of a wave depends on its fetch (the distance of open water the wind has blown over), wind strength and how long the wind blows. The North Sea coast of Holderness has a long fetch, so its waves carry high energy.

Constructive waves are low and long, with a strong swash (water rushing up the beach) and a weak backwash. They deposit more material than they remove, so they build up beaches. Destructive waves are tall and steep with a weak swash and a strong backwash that drags sediment back out to sea, so they erode the coast. Storms generate destructive waves; calm spells favour constructive waves, which is why a beach profile changes through the year.

Sediment is transported along the coast by longshore drift. The prevailing wind drives waves onto the beach at an angle, so the swash carries material up the beach diagonally; gravity then pulls the backwash straight back down the steepest slope. The result is a zig-zag movement of sediment along the coast in the direction of the prevailing wind. Deposition occurs where waves lose energy, for example in sheltered bays or where the coast changes direction.

Erosional landforms

A wave-cut platform forms as a cliff retreats. Destructive waves erode a wave-cut notch at the base of the cliff between the tide marks; the overhanging rock collapses, the cliff retreats landward, and the gently sloping rocky surface left behind (exposed at low tide) is the wave-cut platform.

Depositional landforms

Where waves lose energy, deposition forms beaches: sandy beaches are gently sloping (constructive waves), shingle beaches are steeper. A spit forms where the coast suddenly changes direction; longshore drift carries sediment past the bend and deposits a ridge of sand and shingle out into the sea, and a change in the wind curls the end into a recurved hook (Spurn Head at the mouth of the Humber). Sheltered water behind the spit allows a salt marsh to develop. A bar forms when a spit grows right across a bay, trapping a lagoon behind it.

Coastal management

Coastal management balances the cost of defences against the value of what is protected. A cost-benefit analysis decides whether to "hold the line", "advance the line" or, increasingly, allow "managed realignment".

• Hard engineering: sea walls (reflect wave energy, very effective but expensive at thousands of pounds per metre), groynes (trap sediment to build a wider beach, but starve down-drift coasts), rock armour (rip-rap absorbs energy) and gabions. Effective but costly and can look unnatural or shift erosion along the coast.
• Soft engineering: beach nourishment (adding sand to widen the beach) and dune regeneration work with natural processes, are cheaper and more natural, but need regular and repeated maintenance.
• Managed retreat (managed realignment): deliberately allowing low-value land to flood, creating salt marshes that absorb wave energy and create habitat. It is cheap and sustainable but means losing farmland and sometimes homes, so it is socially difficult.

Try this

Q1. Explain how a stack is formed. [4 marks]

• Cue. Erosion widens a crack into a cave, the cave is eroded through the headland to form an arch, the arch roof collapses to leave a stack.

Q2. Evaluate the use of hard engineering to manage the coast. [6 marks]

• Cue. Benefits such as effective protection and tourism confidence, against costs such as expense, unnatural appearance and increased erosion further along the coast.