1.8 Coastal erosion processes

Coastal erosion shapes our shorelines, impacting coastal communities and ecosystems. It's driven by waves, tides, wind, and storms, creating diverse landforms like cliffs, caves, and stacks. Understanding these processes is crucial for developing effective coastal protection strategies.

Engineers study erosion types, factors influencing rates, and sediment transport to manage coastlines. They use various techniques to measure erosion and model future changes. This knowledge helps in developing strategies to protect property, infrastructure, and ecosystems from the impacts of coastal erosion.

Types of coastal erosion

• Coastal erosion processes play a crucial role in shaping coastlines and impact coastal resilience engineering strategies
• Understanding different types of erosion helps engineers develop effective protection and adaptation measures
• Erosion types often interact and compound, requiring comprehensive approaches in coastal management

Wave-induced erosion

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• Occurs when wave energy impacts shorelines, causing sediment removal and transport
• Wave characteristics (height, period, direction) influence erosion intensity
• Constructive waves build up beaches, while destructive waves erode them
• Creates distinctive coastal features (wave-cut platforms, notches)

Tidal erosion

• Results from the cyclical rise and fall of tides, exposing different parts of the shore
• Tidal range affects the vertical extent of erosion along the coast
• Generates unique landforms in areas with significant tidal variations (tidal flats, salt marshes)
• Interacts with wave action to amplify erosional effects during high tides

Wind erosion

• Involves the removal and transport of sediment by wind action
• Particularly significant in arid coastal areas or those with extensive sandy beaches
• Creates distinctive features like coastal dunes and blowouts
• Wind direction and strength influence sediment movement patterns

Storm surge erosion

• Occurs during extreme weather events, causing rapid and severe coastal erosion
• Combines effects of high waves, strong winds, and elevated water levels
• Can lead to significant shoreline retreat and destruction of coastal infrastructure
• Often results in long-term changes to coastal morphology and sediment distribution

Factors influencing erosion rates

• Erosion rates vary significantly along coastlines due to multiple interacting factors
• Understanding these factors is crucial for predicting future coastal changes and developing resilience strategies
• Engineers must consider both natural and anthropogenic influences on erosion processes

Geological composition

• Rock type and structure determine resistance to erosion (granite vs. sandstone)
• Presence of joints, faults, or bedding planes affects erosion susceptibility
• Softer materials (clay, unconsolidated sediments) erode more rapidly than harder rocks
• Influences the development of specific coastal landforms and erosion patterns

Beach profile

• Shape and slope of the beach affect wave energy dissipation and erosion potential
• Steep profiles typically experience more erosion than gently sloping beaches
• Beach width impacts the ability to absorb wave energy and protect the backshore
• Seasonal changes in beach profile influence erosion rates throughout the year

Sediment supply

• Balance between sediment input and removal determines long-term coastal stability
• Sources include rivers, cliff erosion, and offshore deposits
• Human activities (dams, coastal structures) can disrupt natural sediment supply
• Sediment characteristics (size, shape, composition) affect transport and deposition patterns

Wave energy

• Higher wave energy generally leads to increased erosion potential
• Factors include wave height, period, and approach angle
• Seasonal variations in wave climate influence erosion patterns
• Refraction and diffraction processes modify wave energy distribution along the coast

Sea level rise

• Accelerates coastal erosion by allowing waves to reach higher elevations
• Causes landward migration of the shoreline (Bruun Rule)
• Increases the depth of nearshore waters, potentially altering wave dynamics
• Interacts with local factors like subsidence or isostatic rebound to amplify effects

Erosion mechanisms

• Erosion mechanisms describe the physical processes by which coastal materials are removed and transported
• Understanding these mechanisms is essential for developing effective erosion control strategies
• Different mechanisms often work in combination, creating complex erosion patterns

Abrasion vs corrosion

• Abrasion involves mechanical wearing down of surfaces by sediment particles
  • Occurs when waves carrying sand, gravel, or pebbles impact coastal features
  • Creates smooth, polished surfaces on rocks and coastal structures
• Corrosion refers to chemical weathering processes in coastal environments
  • Involves dissolution of rocks by seawater, particularly in carbonate-rich areas
  • Can weaken rock structures, making them more susceptible to other erosion mechanisms

Hydraulic action

• Occurs when the force of water itself causes erosion and material removal
• Air trapped in cracks and crevices is compressed by incoming waves, creating pressure
• Repeated compression and decompression weakens rock structures over time
• Particularly effective in areas with jointed or fractured rock formations

Attrition

• Process where sediment particles collide and break down into smaller pieces
• Occurs as waves and currents move sediment along the coast
• Results in rounding and smoothing of rock fragments and beach materials
• Contributes to the overall reduction in sediment size along transport pathways

Solution erosion

• Chemical process involving the dissolution of soluble rock materials by water
• Particularly significant in limestone and chalk coastlines
• Creates distinctive karst features in coastal environments (solution pits, caves)
• Rate of erosion depends on rock composition, water chemistry, and climate factors

Coastal landforms from erosion

• Erosional processes create a variety of distinctive coastal landforms
• These landforms provide insights into the geological history and ongoing coastal processes
• Understanding landform evolution is crucial for predicting future coastal changes and hazards

Cliffs and platforms

• Cliffs form through wave erosion at the base, leading to undercutting and collapse
• Wave-cut platforms develop as cliffs retreat, creating flat or gently sloping surfaces
• Cliff retreat rates vary based on rock type, wave energy, and weathering processes
• Platforms act as natural wave energy dissipaters, influencing nearshore dynamics

Sea caves and arches

• Sea caves form when waves erode weaker rock sections in cliff faces
• Continued erosion can lead to caves extending through headlands, forming arches
• Arch formation requires differential erosion rates within the rock structure
• Represent transitional features in the erosion sequence of coastal headlands

Stacks and stumps

• Stacks are isolated rock columns formed when arches collapse
• Continued erosion at the base of stacks eventually leads to their collapse, forming stumps
• Illustrate the progressive nature of coastal erosion processes
• Often become iconic landscape features and tourist attractions (Old Harry Rocks, UK)

Headlands and bays

• Develop along coasts with varying rock resistance to erosion
• Headlands form in areas of more resistant rock, while bays form in softer materials
• Wave refraction around headlands concentrates erosion in adjacent bays
• Create distinctive coastline shapes and influence sediment transport patterns

Sediment transport processes

• Sediment transport is a key component of coastal erosion and accretion dynamics
• Understanding these processes is crucial for predicting shoreline changes and managing coastal areas
• Transport mechanisms interact with erosion processes to shape coastal morphology

Longshore drift

• Movement of sediment parallel to the shoreline due to oblique wave approach
• Creates distinctive beach features like spits and barrier islands
• Influenced by prevailing wind and wave directions
• Interruption of longshore drift (coastal structures) can lead to erosion downdrift

Cross-shore transport

• Involves sediment movement perpendicular to the shoreline
• Seasonal variations often result in offshore transport during storms and onshore during calm periods
• Influences beach profile changes and nearshore bar formation
• Critical for understanding beach recovery processes after erosion events

Rip currents

• Narrow, seaward-flowing currents that can transport sediment offshore
• Form due to variations in wave height and nearshore bathymetry
• Play a role in beach erosion during storm events
• Can create localized erosion hotspots along otherwise stable shorelines

Littoral cells

• Self-contained coastal compartments with distinct sediment sources, transport pathways, and sinks
• Boundaries often defined by natural features (headlands, river mouths) or artificial structures
• Understanding littoral cell dynamics is crucial for effective coastal management
• Sediment budgets within cells influence long-term coastal stability and erosion patterns

Measuring coastal erosion

• Accurate measurement of coastal erosion is essential for understanding processes and developing management strategies
• Combining multiple techniques provides a comprehensive view of erosion patterns and rates
• Advances in technology have greatly improved the accuracy and resolution of erosion measurements

Remote sensing techniques

• Satellite imagery and aerial photography enable large-scale erosion monitoring
• LiDAR (Light Detection and Ranging) provides high-resolution topographic and bathymetric data
• Synthetic Aperture Radar (SAR) allows for all-weather, day-and-night coastal monitoring
• Unmanned Aerial Vehicles (UAVs) offer flexible, high-frequency data collection capabilities

Field surveys

• Traditional methods involve physical measurements of beach profiles and cliff positions
• GPS surveying provides accurate positioning for repeated measurements
• Sediment sampling and analysis help understand material properties and transport patterns
• In-situ instrumentation (wave gauges, current meters) provides data on forcing factors

Historical map comparison

• Utilizes old maps, charts, and land records to reconstruct long-term coastal changes
• Requires careful georeferencing and consideration of historical surveying accuracies
• Provides valuable insights into centennial-scale erosion trends
• Helps identify cyclical patterns or long-term directional changes in coastal evolution

Shoreline change analysis

• Involves comparing shoreline positions over time to calculate erosion or accretion rates
• Digital Shoreline Analysis System (DSAS) automates calculations of shoreline change statistics
• Requires consistent definition of shoreline indicators (high water line, vegetation line)
• Results are used to predict future shoreline positions and assess coastal hazards

Impacts of coastal erosion

• Coastal erosion has wide-ranging impacts on natural and human systems
• Understanding these impacts is crucial for developing effective coastal management strategies
• Erosion effects often cascade through interconnected physical, ecological, and socioeconomic systems

Property loss

• Direct loss of land and buildings due to shoreline retreat
• Affects both private properties and public infrastructure
• Can lead to forced relocation of coastal communities
• Property values in erosion-prone areas may decrease due to perceived risks

Infrastructure damage

• Erosion threatens coastal roads, railways, and utilities
• Damage to port facilities and coastal protection structures
• Increased maintenance costs for infrastructure in erosion-prone areas
• May require relocation or redesign of critical infrastructure

Ecosystem disruption

• Loss of coastal habitats (beaches, dunes, wetlands) due to erosion
• Altered sediment dynamics can impact marine and estuarine ecosystems
• Changes in coastal morphology affect species distribution and migration patterns
• Erosion may expose and damage buried contaminants or waste sites

Economic consequences

• Direct costs of property and infrastructure damage
• Indirect costs from disruption to coastal industries (tourism, fishing)
• Increased insurance premiums and potential loss of insurability in high-risk areas
• Economic impacts on coastal communities from reduced property values and tax base

Erosion management strategies

• Coastal erosion management requires a balance between protection, adaptation, and natural processes
• Strategies must consider long-term sustainability and potential impacts on adjacent coastal areas
• Integrated approaches often combine multiple strategies to address complex erosion issues

Hard engineering solutions

• Involve construction of physical structures to protect coastlines
• Seawalls provide direct protection against wave action and flooding
• Groins and breakwaters interrupt longshore sediment transport to retain beach material
• Revetments and riprap armor shorelines against wave erosion
• Can lead to increased erosion in adjacent areas if not properly designed

Soft engineering approaches

• Work with natural processes to reduce erosion and enhance coastal resilience
• Beach nourishment adds sand to eroding beaches, widening them and dissipating wave energy
• Dune restoration and vegetation planting stabilize coastal sediments and provide natural barriers
• Managed realignment allows controlled flooding of low-lying areas to create buffer zones
• Generally more environmentally friendly but may require frequent maintenance

Managed retreat

• Involves planned relocation of assets and communities away from eroding coastlines
• Allows natural coastal processes to occur without intervention
• Can be cost-effective in the long term for highly vulnerable areas
• Requires significant social and political support for implementation
• May involve land acquisition, buyout programs, and relocation assistance

Integrated coastal zone management

• Holistic approach considering all aspects of coastal systems and stakeholders
• Combines multiple strategies tailored to specific coastal environments and needs
• Emphasizes long-term planning and adaptive management
• Incorporates climate change projections and uncertainty into decision-making processes
• Promotes collaboration between different levels of government and stakeholders

Climate change and erosion

• Climate change is altering coastal erosion patterns and intensifying erosion processes
• Understanding these changes is crucial for developing resilient coastal management strategies
• Impacts of climate change on erosion vary regionally and interact with local coastal dynamics

Accelerated sea level rise

• Increases the baseline water level, allowing waves to reach higher elevations
• Leads to more frequent and severe coastal flooding and erosion events
• Causes landward migration of the shoreline, following the Bruun Rule
• Interacts with local factors like subsidence to amplify erosion impacts

Increased storm intensity

• More powerful storms generate larger waves and storm surges
• Leads to episodic, severe erosion events that can rapidly reshape coastlines
• May overwhelm existing coastal protection structures
• Changes in storm tracks can alter long-term erosion patterns

Changes in wave patterns

• Alterations in wind patterns affect wave generation and direction
• Can lead to changes in longshore sediment transport rates and directions
• May cause erosion in previously stable coastal areas
• Affects the effectiveness of existing coastal protection measures

Permafrost thaw in arctic coasts

• Warming temperatures cause thawing of coastal permafrost
• Leads to increased erosion rates in arctic and subarctic regions
• Releases stored carbon, potentially accelerating climate change
• Threatens coastal communities and infrastructure in high-latitude areas

Case studies of coastal erosion

• Examining specific cases of coastal erosion provides insights into erosion processes and management strategies
• Case studies illustrate the complex interactions between natural processes and human interventions
• Learning from past experiences informs the development of more effective coastal management approaches

Holderness coast, UK

• One of Europe's fastest-eroding coastlines, retreating at up to 2 meters per year
• Composed of soft glacial till cliffs highly susceptible to wave erosion
• Historical loss of numerous coastal villages and infrastructure
• Management strategies include both hard defenses and managed realignment

Outer Banks, USA

• Chain of barrier islands along the North Carolina coast experiencing rapid erosion
• Longshore drift and frequent hurricanes contribute to shoreline changes
• Erosion threatens coastal communities, tourism industry, and unique ecosystems
• Management includes beach nourishment, property relocation, and habitat restoration

Gold Coast, Australia

• Popular tourist destination facing erosion issues due to natural processes and human interventions
• Extensive history of coastal engineering, including seawalls and artificial reef construction
• Regular beach nourishment program to maintain wide beaches for tourism and protection
• Demonstrates challenges of balancing development pressures with coastal protection needs

Waikiki Beach, Hawaii

• Iconic beach experiencing chronic erosion due to sea level rise and coastal development
• Historical shoreline hardening has exacerbated erosion problems
• Recent efforts focus on beach nourishment and innovative sand retention structures
• Illustrates challenges of managing erosion in a densely developed urban coastal environment

Modeling coastal erosion

• Erosion modeling is essential for understanding, predicting, and managing coastal changes
• Models range from simple empirical relationships to complex numerical simulations
• Advances in computing power and data availability have greatly improved modeling capabilities

Numerical models

• Simulate physical processes governing coastal erosion and sediment transport
• Include hydrodynamic models (waves, currents) coupled with morphodynamic components
• Examples include DELFT3D, XBeach, and MIKE21
• Allow for scenario testing and future projections under different conditions

Physical models

• Scaled representations of coastal systems built in laboratory settings
• Used to study specific erosion processes or test coastal protection designs
• Provide visual demonstrations of erosion mechanisms and management strategies
• Complement numerical models by providing validation data and insights into complex processes

Predictive erosion mapping

• Combines historical data, current measurements, and model projections
• Creates maps showing potential future shoreline positions and erosion rates
• Incorporates factors like sea level rise, storm frequency, and coastal development
• Used for long-term coastal planning and risk assessment

Uncertainty in erosion forecasts

• Erosion predictions inherently involve uncertainties due to complex, interacting processes
• Sources include data limitations, model assumptions, and future climate scenarios
• Probabilistic approaches and ensemble modeling help quantify and communicate uncertainties
• Understanding uncertainties is crucial for developing robust coastal management strategies

Erosion and coastal ecosystems

• Coastal erosion significantly impacts ecosystems, altering habitats and biodiversity
• Understanding these impacts is crucial for developing ecologically sensitive management strategies
• Erosion can both create and destroy habitats, leading to complex ecosystem responses

Impact on coastal habitats

• Erosion can lead to loss of beaches, dunes, and coastal wetlands
• Creates new habitats through the formation of cliffs, platforms, and intertidal areas
• Alters the distribution and connectivity of coastal ecosystems
• Affects species composition and biodiversity in coastal zones

Sediment dynamics in estuaries

• Erosion influences sediment supply and transport in estuarine systems
• Changes in sediment dynamics affect estuarine morphology and habitat distribution
• Impacts water quality, nutrient cycling, and primary productivity
• Alters the balance between erosion and accretion in tidal flats and salt marshes

Erosion effects on marine life

• Increased turbidity from erosion can impact light penetration and photosynthesis
• Changes in substrate composition affect benthic communities and fish habitats
• Erosion of nesting beaches threatens sea turtles and shorebirds
• Alteration of coastal landforms affects species migration and dispersal patterns

Coastal wetland loss

• Erosion, combined with sea level rise, leads to loss of coastal wetlands
• Affects important ecosystem services (flood protection, carbon sequestration, water filtration)
• Impacts nursery habitats for fish and shellfish species
• Loss of wetlands can lead to a feedback loop of increased coastal erosion

Socioeconomic aspects of erosion

• Coastal erosion has significant social and economic implications for coastal communities
• Understanding these aspects is crucial for developing equitable and effective management strategies
• Erosion impacts interact with broader socioeconomic trends and vulnerabilities

Coastal community vulnerability

• Erosion threatens homes, livelihoods, and cultural heritage in coastal areas
• Vulnerability varies based on factors like income, education, and adaptive capacity
• Disproportionate impacts on marginalized communities and indigenous populations
• Erosion can lead to displacement and loss of community cohesion

Tourism industry impacts

• Beaches and coastal landscapes are key assets for many tourism-dependent economies
• Erosion can reduce the attractiveness of coastal destinations
• May require increased investment in beach maintenance and coastal protection
• Can lead to shifts in tourism patterns and economic impacts on local communities

Insurance and property values

• Increased erosion risk can lead to higher insurance premiums or loss of coverage
• Property values in erosion-prone areas may decrease due to perceived risks
• Creates challenges for homeowners and local governments reliant on property taxes
• May lead to disinvestment in vulnerable coastal areas

Legal implications of erosion

• Raises questions about property rights and responsibilities in eroding areas
• Challenges in determining boundaries between public and private land as shorelines change
• Potential for litigation related to coastal protection measures and their impacts
• Influences the development and implementation of coastal management policies

Future trends in erosion research

• Coastal erosion research is evolving to address emerging challenges and opportunities
• Interdisciplinary approaches are increasingly important for understanding complex coastal systems
• Advances in technology and data analysis are opening new avenues for erosion research and management

Advanced monitoring technologies

• Development of high-resolution satellite and airborne remote sensing systems
• Use of autonomous underwater vehicles (AUVs) for seafloor and nearshore mapping
• Integration of Internet of Things (IoT) sensors for real-time coastal monitoring
• Application of artificial intelligence for automated feature detection and change analysis

Erosion-resistant materials

• Research into novel materials for coastal protection structures
• Development of bio-inspired designs for erosion control (mussel-inspired adhesives)
• Exploration of self-healing materials for coastal infrastructure
• Investigation of sustainable, locally-sourced materials for erosion management

Nature-based solutions

• Increased focus on working with natural processes to manage erosion
• Research on the effectiveness of living shorelines and hybrid approaches
• Exploration of ecosystem engineering species for coastal protection (oyster reefs, mangroves)
• Development of quantitative methods for assessing the performance of nature-based solutions

Adaptive management strategies

• Integration of climate change projections into coastal erosion management plans
• Development of flexible, adaptive approaches to deal with uncertainty
• Exploration of novel governance structures for managing dynamic coastal systems
• Research on socio-ecological resilience in the context of coastal erosion