2.3 Coasts

Formation and Characteristics:

• Dynamic Interface: Where land meets the sea, subject to constant change due to the action of waves, tides, and currents.
• Landforms: Coastal landforms include cliffs, headlands, bays, beaches, spits, bars, and stacks, shaped by erosion, transportation, and deposition processes.
• Processes: Erosion (by hydraulic action, abrasion, attrition, and solution), transportation (by waves, currents, and longshore drift), and deposition (of sediment) shape coastal features.

Coastal Erosion:

• Waves: Generated by wind, waves erode the coast through hydraulic action (force of water), abrasion (erosion by materials carried by waves), attrition (erosion as particles collide), and solution (erosion by chemical action).
• Headland and Bay Formation: Differential erosion of hard and soft rock creates headlands and bays along coastlines.
• Cliff Retreat: The gradual erosion of cliffs by wave action results in cliff retreat over time.

Coastal Transportation:

• Longshore Drift: The movement of sediment along the coast in a zigzag pattern, driven by wave action at an angle to the shoreline.
• Beach Drift: The movement of sediment along the beach by swash and backwash of waves.
• Spits and Bars: Deposition of sediment by longshore drift can form spits (extended beaches) and bars (submerged ridges).

Coastal Deposition:

• Beaches: Accumulations of sand and shingle deposited by wave action, influenced by wave energy, sediment size, and supply.
• Bars and Tombolos: Sand and shingle bars formed offshore by deposition, connecting headlands or islands to the mainland.
• Sand Dunes: Formed by the deposition of sand by wind, often stabilized by vegetation.

Coastal Management:

• Hard Engineering: Structures such as sea walls, groynes, and revetments are built to protect coastlines from erosion and flooding.
• Soft Engineering: Sustainable measures such as beach nourishment, dune stabilization, and managed retreat aim to work with natural processes to manage coastal erosion.
• Integrated Coastal Zone Management (ICZM): Holistic approaches that consider the environmental, social, and economic aspects of coastal management to achieve sustainable outcomes.

Human Impacts and Coastal Change:

• Coastal Development: Urbanization, tourism, and infrastructure development can disrupt natural coastal processes and increase vulnerability to erosion and flooding.
• Climate Change: Rising sea levels, increased storm intensity, and coastal erosion are exacerbated by climate change, posing significant threats to coastal communities and ecosystems.
• Pollution: Pollution from coastal development, industry, shipping, and agriculture can degrade coastal environments and impact marine life.

East Purbeck Coast Case Study

• Location and General Information:
• Location: Eastern part of the Isle of Purbeck, on the Jurassic Coast in Dorset, England.
• World Heritage Status: Part of the UNESCO World Heritage Site, recognized for its geological and geomorphological significance.
• Key Coastal Features and Statistics:
• Lulworth Cove:
• Formation: Created by the erosion of softer clays and sands behind a harder band of Portland limestone.
• Dimensions: Approximately 500 meters wide.
• Visitors: Attracts over 500,000 visitors annually.
• Durdle Door:
• Type: Natural limestone arch.
• Height: Arch stands about 30 meters high.
• Geology: Made of Portland limestone.
• Visitors: Popular tourist attraction with hundreds of thousands of visitors each year.
• Old Harry Rocks:
• Formation: Chalk stacks formed by the collapse of caves and arches due to erosion.
• Height: Old Harry stack is approximately 20 meters high.
• Location: Near Swanage, marking the start of the chalk cliffs that run to the Needles on the Isle of Wight.
• Coastal Processes:
• Erosion:
• Hydraulic Action: Waves compress air in cracks, causing pressure and breaking the rock.
• Abrasion: Rocks and pebbles grind against the cliffs, wearing them down.
• Corrosion: The chemical action of seawater dissolves minerals in the rocks.
• Weathering:
• Mechanical Weathering: Freeze-thaw cycles cause rock fragmentation.
• Chemical Weathering: Acidic rainwater reacts with minerals in the rocks.
• Human Interaction and Management:
• Tourism:
• Generates significant local revenue.
• Lulworth Estate: Private estate managing access to Lulworth Cove and Durdle Door.
• Coastal Management:
• Swanage: Sea walls and groynes protect the town and manage sediment transport.
• Beach Nourishment: Sand and shingle are added to beaches to combat erosion.
• Managed Retreat: Allowing certain areas to erode naturally to reduce impact on more valuable land.
• Challenges:
• Erosion and Coastal Retreat: Average erosion rate of 1-2 cm per year, with storm events causing more significant losses.
• Impact of Tourism: Path erosion, litter, and damage to natural features from high visitor numbers.
• Climate Change: Rising sea levels and more frequent storms increase the risk of coastal erosion and flooding.
• Conservation Efforts:
• Jurassic Coast Trust: Manages and conserves the natural and cultural heritage of the coast.