IGCSE Geography / Coastal environments

Longshore drift and coastal deposition revision notes

Edexcel International GCSE Geography (4GE1), chapter 2: Coastal environments, specification point 2.1a. Free lesson.

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The sea transports its load in four ways, while longshore drift moves material along the coast in a zigzag. Deposition happens when waves lose energy and can no longer carry as much material.

How the sea carries its load

The load is the material carried by the sea. It moves in four ways, depending on the size of the material and whether it dissolves in the water. Traction rolls large pebbles and boulders along the sea bed. Saltation bounces smaller pebbles along the sea bed in short hops. Suspension carries fine sand and silt inside the water. Solution carries minerals that have dissolved in the sea water.

How longshore drift moves material along the coast

Longshore drift is a transport process. It moves material along the coastline, but it does not explain why material is dropped.

Where and why deposition happens

Deposition is when the sea drops the load it was carrying. The reason is always that waves lose energy: waves with less energy cannot carry as much material. In a sheltered bay, headlands on either side take the force of the waves, so the water in the bay is calmer and material is deposited. In shallow water, friction with the sea bed slows the waves down. At a bend in the coast, such as at a river mouth, drifting material can be carried into calmer water and dropped. Behind an obstacle, such as a groyne, longshore drift is blocked and sand piles up against it. The wider…

Explain deposition in a sheltered bay

A three-mark answer links the sheltered bay to reduced wave energy, then explains why the load is dropped and what builds up.

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