4.6 Landslide and subsidence hazards

Landslides and subsidence pose significant threats to coastal communities and infrastructure. Understanding these hazards is crucial for effective risk management and mitigation in coastal resilience engineering. From rotational slides to debris flows, various types of landslides can impact coastal areas.

Causes of landslides include geological factors, hydrological influences, and human activities. Subsidence, both natural and anthropogenic, exacerbates coastal vulnerabilities. Assessing and monitoring these risks is essential for developing comprehensive strategies to protect coastal areas and adapt to changing conditions.

Types of landslides

• Landslides pose significant threats to coastal communities and infrastructure
• Understanding different landslide types crucial for effective risk management and mitigation in coastal resilience engineering
• Classification based on movement type and material composition informs appropriate prevention and response strategies

Rotational vs translational slides

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• Rotational slides move along a curved surface, creating a bowl-shaped depression
• Translational slides move along a planar surface, often following weak layers in the soil or rock
• Rotational slides typically occur in homogeneous materials (clay soils)
• Translational slides common in layered materials (sedimentary rocks)
• Slope angle and material strength influence slide type and potential for movement

Debris flows and mudflows

• Rapid mass movements of loose soil, rock, and organic matter mixed with water
• Debris flows contain coarser materials (rocks, logs)
• Mudflows consist primarily of fine-grained sediments (clay, silt)
• Triggered by intense rainfall, rapid snowmelt, or dam failures
• Can travel long distances at high speeds, posing severe hazards to downstream areas
• Often occur in steep, mountainous terrain or recently burned areas

Rock falls and topples

• Rock falls involve detachment and free-falling of rock masses from steep cliffs
• Topples occur when rock columns or slabs rotate forward about a pivot point
• Caused by weathering, erosion, and seismic activity
• Common in coastal areas with steep cliffs or rocky shorelines
• Can pose immediate threats to beachgoers and coastal infrastructure
• Size of falling material ranges from small pebbles to massive boulders

Causes of landslides

• Multiple factors contribute to landslide occurrence in coastal environments
• Understanding causes essential for predicting and preventing landslide events
• Interplay between natural processes and human activities often exacerbates landslide risks

Geological factors

• Rock and soil types influence slope stability (weak or fractured rocks more susceptible)
• Tectonic activity creates fault zones and areas of weakness
• Volcanic activity produces unstable deposits and alters landscape
• Weathering processes weaken rock and soil structures over time
• Bedding planes and foliation in rocks can create slip surfaces
• Presence of expansive clays increases landslide potential

Hydrological influences

• Rainfall intensity and duration affect soil saturation and pore water pressure
• Groundwater fluctuations alter effective stress in soil and rock masses
• Coastal wave action erodes toe of slopes, destabilizing upper portions
• Freeze-thaw cycles in colder regions weaken rock structures
• Snowmelt contributes to soil saturation and increased landslide risk
• Tidal fluctuations impact stability of coastal cliffs and bluffs

Human activities

• Excavation and construction on slopes alter natural stress distributions
• Deforestation reduces soil cohesion and increases erosion rates
• Improper drainage systems concentrate water flow and increase instability
• Overloading slopes with structures or fill materials
• Vibrations from traffic or construction activities can trigger landslides
• Alteration of natural waterways affects slope hydrology and stability

Subsidence mechanisms

• Subsidence poses significant challenges to coastal resilience and infrastructure stability
• Understanding mechanisms crucial for developing effective mitigation strategies
• Coastal subsidence often exacerbates flooding risks and erosion processes

Natural vs anthropogenic subsidence

• Natural subsidence occurs due to geological processes (tectonic movements, sediment compaction)
• Anthropogenic subsidence results from human activities (resource extraction, urbanization)
• Natural subsidence rates typically slower than anthropogenic rates
• Differentiating between natural and anthropogenic causes crucial for management
• Combined effects of natural and anthropogenic subsidence amplify coastal hazards
• Monitoring programs essential for distinguishing between subsidence types

Karst terrain processes

• Dissolution of soluble rocks (limestone, gypsum) creates underground voids
• Sinkholes form when surface collapses into subsurface cavities
• Karst landscapes characterized by caves, springs, and irregular topography
• Coastal karst areas particularly vulnerable to saltwater intrusion
• Subsidence in karst terrain can be sudden and catastrophic
• Urban development in karst regions requires specialized engineering approaches

Groundwater extraction effects

• Excessive pumping of aquifers leads to compaction of sediments
• Land surface subsidence occurs as pore spaces collapse
• Irreversible compaction results in permanent elevation loss
• Coastal aquifers particularly vulnerable due to saltwater intrusion risks
• Subsidence rates can reach several centimeters per year in heavily exploited areas
• Sustainable groundwater management crucial for mitigating subsidence

Coastal landslide hazards

• Coastal areas face unique landslide risks due to dynamic interactions between land and sea
• Understanding coastal processes essential for effective hazard management
• Integrating coastal landslide hazards into resilience planning crucial for long-term sustainability

Cliff erosion and retreat

• Wave action undercuts cliff bases, destabilizing upper portions
• Erosion rates vary based on rock type, wave energy, and weathering processes
• Cliff retreat threatens coastal infrastructure and property
• Sediment from eroded cliffs contributes to beach nourishment
• Climate change may accelerate erosion rates through increased storminess
• Monitoring cliff retreat essential for coastal management and hazard assessment

Sea level rise impacts

• Rising sea levels increase wave attack on coastal cliffs and bluffs
• Submergence of low-lying areas alters groundwater dynamics
• Increased pore water pressures in coastal slopes reduce stability
• Salt water intrusion weakens soil and rock structures
• Sea level rise amplifies effects of storm surge and coastal flooding
• Long-term planning must account for projected sea level rise scenarios

Storm surge influences

• Storm surges temporarily raise water levels, intensifying wave attack on cliffs
• Rapid water level fluctuations during storms create instability in coastal slopes
• Saturated soils more susceptible to failure during storm events
• Debris from landslides can exacerbate coastal flooding during storms
• Post-storm slope failures common due to weakened soil conditions
• Integrating storm surge modeling with landslide risk assessment crucial for coastal resilience

Landslide risk assessment

• Systematic evaluation of landslide hazards essential for effective risk management
• Risk assessment informs decision-making processes for coastal development and protection
• Integration of multiple factors required for comprehensive risk analysis

Susceptibility mapping

• Identifies areas prone to landslides based on geological and topographical factors
• Utilizes GIS techniques to overlay multiple data layers (slope, lithology, land use)
• Remote sensing data provides valuable input for large-scale mapping
• Historical landslide inventories improve accuracy of susceptibility maps
• Susceptibility maps guide land-use planning and development regulations
• Regular updates necessary to account for changing environmental conditions

Probability analysis

• Estimates likelihood of landslide occurrence within a given time frame
• Incorporates statistical methods and historical data to assess frequency
• Considers triggering factors (rainfall thresholds, seismic activity)
• Probabilistic approaches account for uncertainties in input parameters
• Monte Carlo simulations used to generate multiple scenarios
• Results expressed as annual exceedance probabilities or return periods

Consequence evaluation

• Assesses potential impacts of landslides on people, property, and environment
• Considers elements at risk (population density, infrastructure, economic assets)
• Vulnerability analysis determines susceptibility of elements to damage
• Economic loss estimation informs cost-benefit analysis of mitigation measures
• Social and environmental impacts (loss of life, ecosystem disruption) evaluated
• Integration of consequence evaluation with probability analysis yields overall risk assessment

Monitoring and early warning

• Effective monitoring systems crucial for reducing landslide and subsidence risks
• Early warning capabilities enable timely evacuation and emergency response
• Integration of multiple monitoring techniques provides comprehensive hazard assessment

Remote sensing techniques

• Satellite-based InSAR measures ground deformation over large areas
• LiDAR surveys provide high-resolution topographic data for change detection
• Optical satellite imagery used for landslide inventory mapping and monitoring
• UAV-based photogrammetry offers flexible, high-resolution monitoring capabilities
• Thermal imaging detects changes in ground moisture content and potential instability
• Integration of multiple remote sensing data sources improves monitoring accuracy

Ground-based instrumentation

• Inclinometers measure subsurface deformation and movement rates
• Piezometers monitor groundwater levels and pore water pressures
• Extensometers detect surface displacement and ground movement
• Tiltmeters measure changes in slope angle and orientation
• Seismometers detect microseismic activity associated with slope instability
• GPS stations provide continuous monitoring of ground surface displacement

Early warning systems

• Integrate real-time monitoring data with predictive models
• Establish alert thresholds based on historical data and expert knowledge
• Automated alert systems notify authorities and affected populations
• Tiered warning levels correspond to increasing hazard potential
• Communication protocols ensure rapid dissemination of warnings
• Regular drills and public education improve system effectiveness

Mitigation strategies

• Comprehensive approach to landslide and subsidence risk reduction
• Combination of structural and non-structural measures often most effective
• Adaptation of mitigation strategies to local conditions and risk profiles crucial

Structural measures

• Retaining walls and buttresses provide mechanical support to unstable slopes
• Drainage systems reduce pore water pressures and improve slope stability
• Soil nailing and rock bolting reinforce slopes and cliffs
• Shotcrete application protects exposed soil and rock surfaces
• Grading and benching alter slope geometry to increase stability
• Seawalls and revetments protect coastal cliffs from wave erosion

Non-structural approaches

• Vegetation management improves soil cohesion and reduces erosion
• Bioengineering techniques (live staking, brush layering) stabilize slopes
• Land-use zoning restricts development in high-risk areas
• Building codes and construction standards reduce vulnerability
• Public education and awareness programs promote risk-reducing behaviors
• Insurance and financial incentives encourage adoption of mitigation measures

Land-use planning

• Integrates landslide and subsidence hazard information into development plans
• Designates buffer zones and setbacks from high-risk areas
• Promotes cluster development to minimize disturbance of unstable slopes
• Incorporates green infrastructure to manage stormwater and reduce erosion
• Preserves natural vegetation and drainage patterns in susceptible areas
• Requires geotechnical assessments for proposed developments in hazard zones

Coastal subsidence issues

• Subsidence in coastal areas compounds risks associated with sea level rise
• Understanding specific coastal subsidence issues crucial for resilience planning
• Integrated approach to subsidence management essential for long-term sustainability

Salt marsh loss

• Subsidence causes marsh surfaces to sink relative to sea level
• Reduced sediment input limits natural accretion processes
• Marsh vegetation drowns as inundation periods increase
• Loss of salt marshes reduces natural coastal protection and habitat
• Carbon sequestration capacity diminishes with marsh degradation
• Restoration efforts (sediment nourishment, thin-layer deposition) combat marsh loss

Infrastructure damage

• Differential subsidence causes structural stress and damage to buildings
• Underground utilities (pipelines, sewers) vulnerable to misalignment and breakage
• Transportation infrastructure (roads, bridges) requires frequent maintenance and repair
• Flood control structures (levees, floodwalls) lose effectiveness as land sinks
• Port facilities face challenges with changing water depths and dock elevations
• Increased groundwater salinity affects water supply infrastructure

Flooding vulnerability

• Subsidence lowers land elevation, increasing susceptibility to inundation
• Drainage systems become less effective as outfall elevations change
• Storm surge impacts exacerbated by lowered coastal elevations
• Increased frequency and duration of nuisance flooding in low-lying areas
• Groundwater table rises closer to surface, reducing soil storage capacity
• Saltwater intrusion into coastal aquifers threatens freshwater resources

Resilience planning

• Holistic approach to addressing landslide and subsidence risks in coastal areas
• Integration of resilience concepts into long-term planning and decision-making
• Adaptive management strategies crucial for responding to changing conditions

Adaptation strategies

• Elevation of structures and infrastructure to accommodate subsidence and flooding
• Managed realignment of coastlines to create buffer zones for natural processes
• Implementation of nature-based solutions (living shorelines, artificial reefs)
• Diversification of water sources to reduce reliance on subsidence-prone aquifers
• Development of floating or amphibious structures for flood-prone areas
• Integration of green and grey infrastructure for comprehensive risk reduction

Retreat vs protect options

• Managed retreat involves relocation of assets away from high-risk areas
• Protection strategies focus on defending existing development through engineering
• Cost-benefit analysis guides decision-making between retreat and protect options
• Hybrid approaches combine elements of retreat and protection for optimal outcomes
• Consideration of long-term sustainability and ecosystem health in strategy selection
• Social and economic factors influence feasibility of retreat vs protect decisions

Community engagement

• Participatory planning processes involve stakeholders in resilience decision-making
• Risk communication strategies improve public understanding of hazards
• Citizen science initiatives engage communities in monitoring and data collection
• Local knowledge integration enhances relevance and effectiveness of resilience plans
• Capacity building programs empower communities to implement resilience measures
• Collaborative governance structures promote coordination among diverse stakeholders

Case studies

• Analysis of real-world examples provides valuable insights for coastal resilience engineering
• Lessons learned from past events inform future management and mitigation strategies
• Diverse case studies highlight range of challenges and solutions in different contexts

Notable coastal landslides

• 1993 La Conchita landslide (California) demonstrates long-term instability in coastal bluffs
• 2005 La Jolla landslide (California) illustrates impacts of urbanization on slope stability
• 2011 Cinque Terre landslides (Italy) highlight vulnerability of coastal cultural heritage sites
• 2018 Anak Krakatau landslide and tsunami (Indonesia) shows cascading hazards in volcanic islands
• 2021 Great Cliffs of Dover rockfall (UK) exemplifies ongoing coastal erosion processes

Subsidence in delta regions

• Mississippi Delta (USA) experiences high subsidence rates due to sediment compaction and fluid extraction
• Mekong Delta (Vietnam) faces challenges from groundwater pumping and reduced sediment supply
• Po Delta (Italy) demonstrates impacts of land reclamation and water management on subsidence
• Ganges-Brahmaputra Delta (Bangladesh) illustrates compound risks of subsidence and sea level rise
• Nile Delta (Egypt) shows effects of dam construction on sediment supply and coastal stability

Successful mitigation examples

• Hong Kong's slope management program demonstrates comprehensive landslide risk reduction
• Venice's MOSE project addresses subsidence and flooding through innovative engineering
• Netherlands' Room for the River program showcases nature-based solutions for flood resilience
• Japan's landslide early warning system highlights effective integration of monitoring and communication
• New Orleans' post-Katrina levee improvements illustrate adaptive management in subsiding coastal areas

Future challenges

• Anticipating and preparing for emerging issues in coastal landslide and subsidence management
• Developing innovative solutions to address complex, interconnected coastal hazards
• Adapting resilience strategies to rapidly changing environmental and societal conditions

Climate change impacts

• Increased frequency and intensity of extreme weather events exacerbate landslide risks
• Accelerated sea level rise compounds effects of coastal subsidence
• Changes in precipitation patterns alter groundwater dynamics and slope stability
• Ocean acidification may impact stability of carbonate-rich coastal cliffs
• Thawing permafrost in Arctic coastal areas creates new landslide and subsidence hazards
• Ecosystem shifts due to climate change affect natural slope stabilization processes

Population growth pressures

• Urbanization in coastal areas increases exposure to landslide and subsidence risks
• Demand for water resources exacerbates subsidence from groundwater extraction
• Informal settlements often develop in high-risk areas, increasing vulnerability
• Infrastructure expansion in coastal zones alters natural landform stability
• Economic pressures drive development in hazard-prone areas despite risks
• Growing populations require more robust early warning and evacuation systems

Emerging technologies

• Machine learning and AI enhance landslide prediction and risk assessment capabilities
• Blockchain technology improves transparency and efficiency in resilience project management
• Internet of Things (IoT) enables real-time monitoring and early warning systems
• 3D printing facilitates rapid prototyping and deployment of innovative coastal protection structures
• Augmented reality applications support visualization of hazard scenarios and mitigation options
• Advances in materials science offer new solutions for slope stabilization and subsidence mitigation