Changing Coastal Environments » Longshore Drift

What you'll learn this session

Study time: 30 minutes

The process of longshore drift and how it works
Key features created by longshore drift (spits, bars and tombolos)
How longshore drift affects coastal communities
Management strategies to deal with longshore drift
Real-world case studies of longshore drift in action

Introduction to Longshore Drift

Longshore drift is one of the most important coastal processes you'll need to understand for your iGCSE Geography. It's responsible for moving millions of tonnes of beach material along coastlines every year and creates some really distinctive coastal landforms!

Key Definitions:

Longshore Drift: The zigzag movement of sediment along a beach caused by waves approaching at an angle.
Swash: The movement of water up the beach after a wave breaks.
Backwash: The movement of water back down the beach after swash.
Sediment: Material like sand and pebbles that is transported along the beach.

🌊 How Longshore Drift Works

Longshore drift happens when waves approach the beach at an angle (rather than straight on). This creates a zigzag movement of beach material:

Waves approach the shore at an angle (usually due to the prevailing wind direction)
The swash carries beach material up the beach at the same angle as the incoming wave
The backwash pulls the material straight back down the beach under gravity
This creates a zigzag movement, gradually moving material along the coastline

Over time, this process can move huge amounts of sand and pebbles along a coastline!

🔎 Factors Affecting Longshore Drift

The strength and impact of longshore drift depends on several factors:

Wave energy: Stronger waves move more material
Wave angle: The greater the angle, the faster the movement
Beach material: Sand moves more easily than pebbles
Beach shape: The slope of the beach affects movement speed
Obstacles: Headlands, groynes or sea walls can interrupt the flow

Landforms Created by Longshore Drift

Longshore drift is responsible for creating several distinctive coastal landforms that you'll need to know for your exam. These features form when the transported material is deposited in certain locations.

🌊 Spits

A spit is a long, narrow ridge of sand or shingle that extends from the land into the sea. They form where:

The coastline changes direction suddenly
Material continues to be deposited in the original direction
The end often curves inward (called a recurved end) due to secondary winds

Example: Spurn Head in Yorkshire, UK

🌊 Bars

A bar is similar to a spit but connects two headlands across a bay. They form when:

Longshore drift carries material across a bay
The material eventually builds up enough to rise above the water
A lagoon may form behind the bar

Example: Slapton Ley in Devon, UK

🌊 Tombolos

A tombolo is a bar of sand or shingle that connects an island to the mainland. They form when:

Waves refract (bend) around an offshore island
This creates a zone of low energy behind the island
Sediment is deposited in this sheltered area

Example: Chesil Beach connecting Portland to mainland Dorset, UK

Human Impacts and Management

Longshore drift can have significant impacts on coastal communities and requires careful management.

Problems Caused by Longshore Drift

While longshore drift is a natural process, it can create several challenges for people living along coastlines:

⚠ Coastal Erosion

When longshore drift removes beach material from an area, it can leave the coastline more vulnerable to erosion. This is because beaches act as a natural buffer against wave energy. Without this protection, cliffs and coastal structures can be damaged more easily.

🏙 Harbour Siltation

Longshore drift can cause sediment to build up at harbour entrances, a process called siltation. This can block shipping channels and require expensive dredging operations to keep ports operational. Many coastal towns that rely on fishing or tourism can be severely affected.

Managing Longshore Drift

Engineers have developed several strategies to manage the effects of longshore drift:

🧭 Groynes

Wooden or rock structures built perpendicular to the beach that trap sediment moving along the coast. They help build up beaches in front of vulnerable areas but can cause erosion further down the coast.

🚧 Beach Nourishment

Artificially adding sand or shingle to beaches to replace material lost through longshore drift. This is expensive but creates a natural-looking solution without disrupting coastal processes elsewhere.

🛥 Dredging

Removing built-up sediment from harbours and shipping channels, often pumping it back to beaches 'updrift' to continue the natural cycle of movement.

Case Study Focus: Holderness Coast, UK

The Holderness Coast in East Yorkshire is one of the best examples of longshore drift in action:

The coastline is made of soft boulder clay which erodes easily
Prevailing winds from the northeast create waves that approach at an angle
Longshore drift moves material southwards at a rate of about 2 million tonnes per year
The coast is eroding at one of the fastest rates in Europe (1.5-2.5 metres per year)
Villages like Mappleton have built groynes to trap sediment and protect their coastline
However, this has increased erosion rates further down the coast (called 'terminal groyne syndrome')
The material eventually forms Spurn Head, a classic spit at the mouth of the Humber Estuary

This case study perfectly demonstrates both the natural processes of longshore drift and the challenges of managing its impacts.

Studying Longshore Drift

If you're conducting fieldwork on longshore drift, there are several techniques you can use:

🔬 Measuring Longshore Drift

Practical ways to investigate longshore drift include:

Painted pebbles: Mark pebbles and track their movement over time
Beach profiles: Measure the shape of the beach at different points
Sediment size analysis: Compare grain sizes along the beach
Groyne measurements: Measure beach height on either side of groynes

📝 Exam Tips

To score highly on longshore drift questions:

Use proper terminology (swash, backwash, deposition)
Explain the process step-by-step with clear diagrams
Link landforms to the process that created them
Discuss both natural processes and human management
Include specific details from case studies
Consider different perspectives on management strategies

Longshore Drift in a Changing Climate

Climate change is affecting longshore drift in several ways:

Rising sea levels are changing the position of beaches
More frequent storms can increase the rate of longshore drift
Changing wind patterns may alter the direction of drift
Management strategies need to adapt to these changing conditions

Understanding these changes is becoming increasingly important for coastal communities and planners.

🧠 Test Your Knowledge!