❄️Earth Surface Processes Unit 10 – Coastal Landforms: Shoreline Evolution

Key Concepts and Terminology

• Coastal zone refers to the interface between land and sea, including both the shoreline and adjacent coastal waters
• Littoral zone encompasses the area between the high and low water marks, influenced by tides, waves, and currents
• Longshore drift (littoral drift) transports sediment along the coast parallel to the shoreline due to wave action and currents
• Fetch refers to the distance over which wind blows across open water, influencing wave size and energy
• Tides are the rise and fall of sea levels caused by the gravitational pull of the moon and sun
  • Tidal range is the vertical difference between high tide and low tide
• Wave refraction bends waves towards shallower water, causing them to approach the shoreline at a more perpendicular angle
• Coastal geomorphology studies the landforms and processes that shape the coast, including both erosional and depositional features

Coastal Processes and Dynamics

• Waves are the primary driver of coastal processes, generated by wind blowing over the ocean surface
  • Wave height, wavelength, and period determine the energy and erosive power of waves
• Tides influence the vertical and horizontal extent of the coastal zone, with high tides submerging more land and low tides exposing more of the shore
• Currents transport sediment and shape the coast, including longshore currents, rip currents, and tidal currents
• Sediment transport involves the movement of sand, gravel, and other materials along the coast, driven by waves, currents, and wind
  • Longshore drift moves sediment parallel to the shoreline
  • Cross-shore transport moves sediment perpendicular to the shoreline
• Storm surges are temporary increases in sea level caused by strong winds and low atmospheric pressure during storms, leading to increased erosion and flooding
• Sea level rise due to climate change amplifies coastal erosion, inundation, and the impact of storm surges

Types of Coastal Landforms

• Beaches are accumulations of sediment along the shoreline, shaped by waves and currents
  • Beach profile includes the backshore, berm, foreshore, and offshore zones
• Dunes are hills or ridges of sand formed by wind, providing a buffer against coastal erosion and flooding
  • Foredunes are the first line of dunes closest to the shore
  • Backdunes are older, more stable dunes further inland
• Cliffs are steep, vertical faces of rock or sediment formed by erosion, often found in areas with resistant bedrock and high wave energy
• Headlands are resistant rock formations that protrude into the sea, often separating bays or beaches
• Bays are concave indentations in the coastline, typically featuring calmer waters and gentler slopes than headlands
• Estuaries are partially enclosed coastal bodies of water where freshwater from rivers mixes with saltwater from the ocean, creating unique ecosystems
• Barrier islands are elongated, narrow islands that run parallel to the mainland, protecting the coast from waves and storms

Factors Influencing Shoreline Evolution

• Geology plays a crucial role in shoreline evolution, with resistant rocks (granite) eroding more slowly than softer rocks (sandstone)
  • Coastal lithology and structure control the shape and stability of the shoreline
• Climate influences the frequency and intensity of storms, precipitation, and wind patterns, which in turn affect coastal processes
• Sea level change, whether due to global climate change or local factors (land subsidence), alters the position and morphology of the shoreline
  • Rising sea levels lead to increased erosion, flooding, and landward migration of the coast
• Sediment supply from rivers, cliffs, and offshore sources determines the availability of material for beach nourishment and dune formation
  • Reduced sediment supply can exacerbate erosion and shoreline retreat
• Vegetation, such as salt marshes and mangroves, stabilizes sediment and dissipates wave energy, reducing erosion rates
• Human activities, including coastal development, dam construction, and beach nourishment, can significantly alter natural coastal processes and shoreline evolution

Erosion and Deposition Patterns

• Erosion is the removal and transport of sediment by waves, currents, and wind, leading to the landward retreat of the shoreline
  • Hydraulic action, abrasion, and attrition are key erosional processes
• Deposition is the accumulation of sediment in areas of lower energy, such as bays, estuaries, and the lee side of headlands
• Longshore drift creates patterns of erosion and deposition along the coast, with sediment eroded from one area and deposited downdrift
  • Groynes and jetties can interrupt longshore drift, causing accretion on one side and erosion on the other
• Beach erosion occurs during storms and high wave energy events, with sediment transported offshore to form sandbars
  • Beach accretion occurs during calmer periods, with sediment returning to the shore
• Cliff erosion is driven by a combination of wave action, weathering, and mass movements (rockfalls, slumps)
  • Cliff retreat rates vary depending on rock type, structure, and wave exposure
• Sediment budgets quantify the inputs, outputs, and storage of sediment within a coastal system, helping to understand erosion and deposition patterns

Human Impact on Coastal Systems

• Coastal development, including the construction of buildings, roads, and infrastructure, can disrupt natural coastal processes and increase erosion rates
  • Hardening the shoreline with seawalls and revetments can lead to increased erosion downdrift
• Dam construction on rivers reduces sediment supply to the coast, leading to increased erosion and shoreline retreat
  • Sediment trapping in reservoirs can starve beaches and deltas of necessary material
• Beach nourishment involves the artificial addition of sediment to the shore to combat erosion and maintain beach width
  • Nourishment projects can have limited long-term effectiveness and may require repeated applications
• Dredging of navigation channels and harbors can alter sediment transport patterns and contribute to erosion in adjacent areas
• Coastal pollution, including oil spills and marine debris, can degrade coastal habitats and impact the health of marine organisms
• Climate change-induced sea level rise and increased storm intensity exacerbate coastal erosion and flooding, threatening coastal communities and infrastructure

Case Studies and Real-World Examples

• The Holderness Coast in England experiences rapid cliff erosion due to soft glacial deposits and high wave energy from the North Sea
  • Average cliff retreat rates exceed 1 meter per year, with some areas losing up to 10 meters in a single storm event
• The Mississippi River Delta in Louisiana, USA, is experiencing significant land loss due to a combination of reduced sediment supply, subsidence, and sea level rise
  • Coastal wetlands and barrier islands are disappearing at an alarming rate, increasing the vulnerability of coastal communities to storms and flooding
• The Gold Coast in Australia has implemented a long-term beach nourishment program to combat erosion and maintain the region's famous sandy beaches
  • Sand is dredged from offshore sources and pumped onto the shore, with ongoing monitoring and maintenance to ensure the program's success
• The Maldives, a low-lying island nation in the Indian Ocean, faces an existential threat from sea level rise and coastal erosion
  • The government has invested in coastal protection measures, such as seawalls and artificial islands, to protect its population and infrastructure

Coastal Management and Conservation

• Integrated Coastal Zone Management (ICZM) is a holistic approach that balances the economic, social, and environmental aspects of coastal management
  • ICZM involves stakeholder participation, adaptive management, and the use of scientific knowledge to inform decision-making
• Coastal setbacks and building restrictions can help to minimize the impact of coastal development on natural processes and reduce the risk of damage from erosion and flooding
• Nature-based solutions, such as the restoration of coastal wetlands, dunes, and oyster reefs, can provide natural protection against erosion and storm surges while enhancing biodiversity
  • Living shorelines incorporate natural elements (vegetation, biodegradable materials) to stabilize the coast and create habitat
• Marine Protected Areas (MPAs) are designated regions where human activities are managed to conserve marine ecosystems and resources
  • MPAs can help to protect critical coastal habitats, such as coral reefs and seagrass beds, which provide natural coastal defense and support fisheries
• Coastal monitoring and research are essential for understanding the complex processes and interactions that shape the coast and informing effective management strategies
  • Remote sensing, GIS, and numerical modeling are valuable tools for monitoring coastal change and predicting future scenarios
• Public education and outreach are crucial for raising awareness about coastal issues, promoting sustainable practices, and fostering stewardship of coastal resources