Coastal Erosion Processes

Coastal Environments

• Coastal processes involve wave generation (fetch, energy, refraction, breaking waves, swash, backwash), marine erosion (hydraulic action, cavitation, corrasion, solution, attrition), sub-aerial processes (weathering, mass movement), and marine transportation/deposition (sediment sources, characteristics, sediment cells, longshore drift).

Coastal Landforms

• Erosional landforms include cliffs, wave-cut platforms, caves, arches, stacks.
• Depositional landforms include beaches (cross-section/plan, swash and drift-aligned beaches), spits (simple and compound), tombolos, offshore bars, barrier beaches, coastal dunes, tidal sedimentation in estuaries, coastal salt marshes, and mangroves.
• Sea level change plays a critical role in coastal landform formation.

Coral Reefs

• Coral reefs are characterized by their structure, distribution, and method of formation.
• Types include fringing reefs, barrier reefs, and atolls.
• Coral growth is influenced by specific environmental conditions.
• Conservation and management strategies are important for coral reefs, particularly given threats like global warming, sea-level rise, pollution, and physical damage.

Sustainable Management of Coasts

• Coastal management involves analyzing the problems and evaluating the effectiveness of management strategies to protect coastlines.
• Case studies are a significant component of assessing coastal management solutions.
• Case studies encompass both hard and soft engineering approaches.

Erosional Landforms

• Cliffs and wave-cut platforms form due to wave energy eroding the base of a cliff, leading to overhang collapse and cliff retreat.
• Cliff heights increase through rock type erosion rates, and wave action.
• Wave-cut platforms are flat areas extending from the cliff.
• Rock type and structure (resistant vs less resistant) affect cliff formation.
• Composite cliffs consist of multiple rock types, leading to differential erosion rates.
• Faults in rock decrease rock resistance, leading to more rapid erosion.
• Dips (inclination of bedding planes) affect cliff profiles.
• Marine processes (hydraulic action and cavitation) affect cliff material removal (breaking apart).
• Sub-aerial processes like freeze-thaw weathering further weaken rock.

Development of Cliffs and Wave-Cut Platforms

• Wave energy erodes the base of cliffs, creating wave-cut notches.
• The unsupported weight of cliffs leads to overhang collapse, causing them to retreat.
• Cliffs made of hard rock (e.g. chalk) result in steep cliffs.
• Wave-cut platforms form by the horizontal erosion of the cliff base.
• Cliff erosion continues until the wave-cut platform extends to a point where water no longer reaches the cliff base.

Coastal Landforms: Depositional Section

• Beaches: The zone of loose sediment between the mean low tide line and where the material/physiographic form changes.
  • Beach profiles are cross-sectional views from the sea to the cliff base.
  • A beach is characterized by 5 zones (onshore, backshore, foreshore, nearshore, offshore).
  • Beach profiles are affected by factors such as tidal range, and type/amount of sediment. Wide beaches are related to smooth sand; narrower beaches to shingle.
  • Beach profiles are affected by seasonal changes: Winter (steeper beach gradient, less steep offshore gradient) and Summer (less steep beach gradient, steeper offshore gradient).
• Sand Dunes: Small ridges of sand found above the maximum reach of waves. Conditions needed for dune development include sand availability, dry sand, large tidal range, and large flat areas with obstructions. Types of Aeolian transport (creep, saltation, suspension) are important components of dune development. Plant succession is crucial to dune development; the sequence of vegetation changes based on plant tolerances to increasingly dry/nutrient-poor conditions.
• Barrier Beaches/Barrier Islands/Bars: Linear ridges of sand/shingle across a bay, connected to land on both sides. They form from longshore drift, create lagoons, and can be caused by rising sea levels.
• Spits: Narrow stretches of sand extending into the sea from land, sometimes attaching to other pieces of land or islands. Prevailing winds will influence their shape and development.
• Tombolos: Ridge or sand attaching an offshore island to mainland areas.
• Offshore Bars: Ridges located offshore that are often made of sand or shingle.
• Cuspate Forelands: Low-lying triangular headlands formed from coastal sediments when longshore currents converge on the shoreline. They are influenced by opposing currents.
• Salt Marshes and Mudflats: Coastal wetlands that are regularly flooded by tides, contain grasses and herbs, and are found on low-energy coastlines, behind spits or barrier islands. Mudflats often are sediment deposits in fluid medium from rivers.

Role of Sea Level Change

• Eustatic Change: Global changes in sea level, related to temperature (melting ice and thermal expansion).
• Isostatic Change: Local changes in land elevation (uplift or subsidence), often due to glaciation.
• Eustatic and isostatic changes profoundly impact coastal landform formation and evolution. Rising sea levels result in coastal submergence (flooded valleys or fjords) and, with falling sea levels, coastal emergence (raised beaches with relict features).