Cool Coasts Notes

Definition of the Coast

The coast can be defined as the narrow overlapping zone where land meets the sea. This area is characterized by constant change due to natural forces, including waves and tides, which play pivotal roles in shaping the coastal landscape by forming various landforms through processes of erosion and deposition.

Causes of Waves

Factors Influencing Wave Formation

  1. Wind Strength: The intensity of the wind directly impacts wave formation; stronger winds generate larger waves.

  2. Duration: The length of time the wind blows also plays a critical role; longer durations contribute to wave building.

  3. Direction of Prevailing Wind: The direction from which the wind predominantly blows determines the characteristics of the waves produced.

  4. Distant Storms: Storms occurring far from the coastline can generate waves that travel vast distances to shore.

  5. Fetch: This term refers to the distance over open water that the wind blows.

    • Example:

      • Thurso: 7500 km

      • North America: 8000 km across the Atlantic Ocean

      • North Sea: 650 km

      • Blackpool: 300 km

      • Lands End: Scolt Head: Southend: South America: varying distances.

Relationship Between Fetch and Wave Size

  • More wind leads to increased wave size.

  • A larger fetch results in larger waves.

Wave Breaking Mechanism

Waves break due to the following reasons:

  1. Friction from the wind adds energy to the waves, causing them to increase in height.

  2. The upper portion of the wave, which continues to move at speed, becomes unstable due to increased height and eventually collapses when it reaches shallow water.

Terminology in Waves

  • SWASH: The movement of the wave as it washes up the beach at an angle.

  • BACKWASH: The flow of water moving straight back down the beach after the wave has broken.

Wave Structure

  • Crest: The highest point of the wave.

  • Trough: The lowest point of the wave.

  • Wave Height: The vertical distance between the crest and trough.

  • Wave Length: The horizontal distance between two successive crests or troughs.

  • Water Depth: The depth of the water in relation to the wave.

Types of Waves

  1. Constructive Waves: These waves arrive at a frequency of 6-8 per minute and typically have less energy, promoting the build-up of sandy beaches due to the processes of swash being more substantial than backwash.

  2. Destructive Waves: Characterized by a higher frequency of 12-14 waves per minute, they possess greater energy which leads to significant beach erosion where the backwash is stronger than the swash.

Rip Currents

A rip current is defined as a strong surface current that moves away from the beach, creating a channel through the breaking waves.

Types of Coastal Erosion

Mechanisms of Coastal Erosion

Waves contribute to wearing away the coastline through four primary types of erosion:

  1. Abrasion: Involves rocks being hurled against the coastline, scouring it similarly to sandpaper.

  2. Attrition: This process involves rocks colliding with one another, causing them to break down into smaller and rounder pieces.

  3. Hydraulic Action: Waves crashing against cliffs compress the air in cracks, which as the wave recedes, can expand and widen the cracks further.

  4. Solution: A chemical reaction occurs with certain rocks (e.g., limestone) when they react with mildly acidic water, leading to their dissolution.

Landforms of Coastal Erosion

Coastal erosion leads to the creation of various landforms:

  1. Caves: Formed when waves find weaknesses in rock and widen existing cracks.

  2. Arches: Result from the enlargement of caves that erode through a headland.

  3. Stacks: The remaining seaward side of an eroded arch once it collapses.

  4. Wave-cut Platforms: Created as cliffs erode, leaving behind a flat surface exposed at low tide.

    • Example: Durdle Door in Dorset, and the 12 Apostles along the Great Ocean Road.

Coastal Management Strategies

Managing coastal areas involves balancing environmental concerns with economic and human activities. Key methods of coastal management include:

  1. Beach Replenishment: Involves pumping sand dredged from offshore back onto the beach to combat erosion.

  2. Groynes: Structures built perpendicular to the coastline to trap sediment and prevent longshore drift, ultimately aiding in beach development.

  3. Sea Walls: Cement structures designed to deflect wave energy and protect the land behind them.

  4. Revetments: Sloped wooden structures that absorb wave energy.

  5. Doloses: Concrete blocks strategically placed along the coast to absorb wave energy, designed by Eric Merrifield.

  6. Gabions: Wire cages filled with rocks that serve to absorb wave energy while holding the rocks in place.

  7. Rip Rap: Composed of large stones placed along the shoreline, providing a buffer against wave action; however, they can be easily reshaped by wave action.

Case Study: Bournemouth

The coastal defenses observed in Bournemouth are a practical example of the various strategies employed in managing coastal areas for protection against erosion and human development.