L4 Coastal transport processes

Coastal Processes

Overview of Coastal Processes

• Key Process: Longshore Drift (LSD)

• Direction of Material Movement: Material is transported along the coast due to prevailing wind and wave action.

• Features Extended from the Beach: These are called spits, bars, and beaches.

Sediment Transportation & Deposition Processes

Coastal Transport and Landforms

• Sediment Movement: Influenced by longshore drift and constructive waves.

• Effects on Coastal Landscapes:

  • Spits: Narrow stretches of sand jutting into the sea.

  • Beaches: Accumulated sediment from waves hitting the shore.

  • Bars: Form when a spit grows across a bay, connecting two headlands.

Transportation Processes

Types of Sediment Movement

• Traction:

  • Larger pebbles and cobbles are rolled along the sea bed.

• Saltation:

  • Small pebbles bounce along the sea bed due to impacts.

• Suspension:

  • Very fine sediment (silt and clay) is suspended in water and transported with currents.

• Solution:

  • Minerals dissolved in seawater are transported invisibly, often from chalk or limestone cliffs.

Longshore Drift (LSD) Process

Steps in Longshore Drift

1. Prevailing Winds: Winds hit the beach at an angle.

2. Wave Action: Waves propagate toward the shore at the same angle.

3. Swash: Material is moved up the beach at an angle.

4. Backwash: Gravity pulls material straight back down to the sea.

• Pattern of Movement: This creates a zigzag motion of material along the coast.

Factors Influencing Beach Formation

Types of Waves

• Constructive Waves:

  • Needed for beach formation; characterized by a strong swash and weak backwash.

• Destructive Waves:

  • Not conducive for beach formation; they erode rather than deposit.

Composition of Beaches

Beach Formation

• Made up of eroded material transported from elsewhere.

• Occurs in areas with limited wave energy, typically sheltered bays.

Spit and Bar Formation

Formation of Spits

• Causes:

  • Change in landscape shape

  • River mouth impacting sediment deposition.

Formation of Bars

• Process:

  • When a spit extends across a bay, connecting two headlands, creating a barrier.

• Resulting Features:

  • Salt marshes may develop behind the spit in low energy zones.

  • Lagoons are formed behind bars as water becomes trapped.

Review & Knowledge Check

Summary of Key Terms

• Longshore Drift: Process of sediment transport along coast.

• Constructive Waves: Build beaches with strong swash.

• Bar: Sediment feature formed across a bay.

• Spit: Jutting sand or shingle feature created by deposition.

Questions for Review

1. Describe how the sea transports material along the coast. (4 marks)

2. Identify the direction of longshore drift based on visual aids.