Ocean Waves and Coastal Processes Notes

Ocean Waves - How Do They Work?

• The power of waves is a significant force of coastal change.
• Waves are created by wind blowing over the surface of the sea.
• Friction is created as wind blows over the sea, producing a swell in the water.
• The energy of the wind causes water particles to rotate inside the swell, moving the wave forward.

Wave Terminology

• Crest: The top of the wave.
• Trough: The low area between two waves.
• Wavelength: The distance between two crests or two troughs.
• Wave Height: The distance between the crest and the trough.
• Wave Frequency: The number of waves per minute.
• Velocity: The speed that a wave is traveling, influenced by wind, fetch, and water depth.
• Swash: The movement of water and load up the beach.
• Backwash: The movement of water and load back down the beach.

Factors Increasing Wave Energy and Size

1. How long the wind has been blowing.
2. The strength of the wind.
3. How far the wave has traveled (the fetch).

Wave Movements

• Waves of Oscillation: Circular paths of particles due to oscillations from passing waves.
• Frictional interaction of the wave with the seabed causes particle orbital circles to stretch as wave energy is dissipated.
• After the wave breaks, the remains move as chaotic surf until it spreads onto the beach as swash.

Constructive and Destructive Waves

Constructive Waves

• Low wave height in proportion to length.
• Strong swash.
• Weak backwash.

Destructive Waves

• High wave height in proportion to length.
• Tall breaker that breaks downwards with great force.
• Weak swash.
• Strong backwash.

Coastal Erosion and Weathering Processes

• Weathering and erosion do the most damage at the weakest points.
• Weathering weakens rocks, making them more susceptible to erosion.

Sub-aerial Weathering

• Rain and surface run-off.
• Freeze-thaw.
• Biological Weathering:
  • Burrowing organisms.
  • Roots from trees/plants.
• Chemical Weathering:
  • Solution/salt crystallization.

Erosion Processes

• Abrasion.
• Hydraulic pressure (air compressed by the force of water entering cracks).
• Wave pounding.
• Solution.
• Attrition and wave scouring.

Headlands and Bays

• Headland: A piece of land that sticks out into the sea.
• Bay: An indented area of land normally found between two headlands.
• Bays form due to rapid erosion of less resistant rocks (e.g., clay/sands and gravels).
• Headlands are left sticking out as rocky outcrops where hard rock has resisted erosion (e.g., chalk/limestone).
• Once formed, the headland is more vulnerable to erosion, and the wave energy is concentrated there.
• When formed, the bays become sheltered by the headlands and so less eroded.

Deposition along the Coast

• Deposition is a geological process where soil, rocks, sand, and other sediments are added to an existing landscape.
• Longshore Drift: The process where sediment is transported and deposited on the lower end of the beach due to prevailing winds.

Landforms

1. Beach: The accumulation of sand between the lowest and highest spring tides, made of sand, shingle, and/or pebbles. Material comes from longshore drift, constructive waves, cliff erosion, and river discharge.
2. Spits: Unstable, narrow, long stretches of sand that extend out into the sea, formed by longshore drift.
   • Tombolos: Depositional landforms that develop when spits or bars connect the mainland to an island.
   • Bars: Form when spits grow across bays, joining two headlands on either side of a bay.

Coastal Management

• Building Groynes (barriers/walls to prevent erosion) can reduce erosion and the build-up of beaches.
  • Advantages:
    • Prevents erosion.
    • Allows build-up of beach.
    • Boosts tourism.
  • Disadvantages:
    • Costly to build and maintain.
    • Can be seen as unattractive.