🌊Coastal Resilience Engineering Unit 1 – Coastal Processes and Dynamics

Coastal Landforms and Features

• Coastal landforms shaped by the interaction of land, sea, and air include beaches, dunes, cliffs, and estuaries
• Beaches are accumulations of sediment along the shoreline that form through the action of waves and currents (sandy beaches, pebble beaches)
• Dunes are mounds of sand formed by wind action and stabilized by vegetation, providing a buffer against coastal erosion and flooding (foredunes, backdunes)
• Cliffs are steep, vertical faces of rock or sediment that form due to erosion by waves and weathering processes (sea cliffs, bluffs)
  • Cliffs can experience mass wasting events, such as rockfalls and landslides, which contribute to coastal retreat
• Estuaries are partially enclosed coastal bodies of water where freshwater from rivers mixes with saltwater from the ocean, creating unique habitats (deltas, lagoons)
• Barrier islands are elongated, narrow islands that run parallel to the mainland coast, protecting the mainland from waves and storms (Outer Banks, North Carolina)
• Spits are elongated ridges of sand or gravel that extend from the mainland into the sea, formed by longshore drift (Hurst Castle Spit, England)
• Tombolos are sand or gravel bars that connect an island to the mainland or another island, formed by wave refraction and deposition (Mont Saint-Michel, France)

Waves and Tides

• Waves are oscillations of the ocean surface caused by wind, with energy transferred across the ocean surface
• Wave characteristics include height, wavelength, period, and speed, which influence their impact on coastal processes
• Wind waves are generated by wind blowing over the ocean surface, with their size dependent on wind speed, duration, and fetch (distance over which the wind blows)
• Swell waves are long-period waves that have traveled far from their area of generation, with a more regular and organized pattern compared to wind waves
• Tides are the rise and fall of sea levels caused by the gravitational pull of the moon and sun, with a semi-diurnal (twice daily) or diurnal (once daily) pattern
  • Tidal range is the vertical difference between high and low tide, varying from a few centimeters to over 15 meters in some locations (Bay of Fundy, Canada)
• Tidal currents are horizontal movements of water associated with the rise and fall of tides, influencing sediment transport and coastal morphology
• Storm surges are temporary increases in sea level caused by low atmospheric pressure and strong winds during storms, leading to coastal flooding and erosion (Hurricane Katrina, 2005)

Sediment Transport Mechanisms

• Sediment transport is the movement of solid particles (sand, gravel, silt, clay) by water, wind, or gravity in the coastal environment
• Longshore drift (littoral drift) is the movement of sediment parallel to the shoreline, driven by waves approaching the coast at an angle
  • Longshore drift can lead to the formation of spits, barrier islands, and the accumulation of sediment on the downdrift side of structures (jetties, groins)
• Cross-shore transport is the movement of sediment perpendicular to the shoreline, driven by wave action and currents
• Bed load transport involves the rolling, sliding, or hopping of sediment particles along the seabed, typically larger particles like sand and gravel
• Suspended load transport involves the movement of finer sediment particles (silt, clay) within the water column, kept in suspension by turbulence
• Aeolian transport is the movement of sediment by wind, playing a crucial role in the formation and evolution of coastal dunes
• Fluvial transport is the movement of sediment by rivers and streams, delivering sediment to the coast and influencing coastal morphology (river deltas, estuaries)
• Gravity-driven transport, such as mass wasting events (landslides, rockfalls), can move large volumes of sediment from cliffs and slopes to the coastal zone

Erosion and Deposition Processes

• Erosion is the removal and transport of sediment by waves, currents, wind, or gravity, leading to the loss of land and the retreat of the coastline
• Abrasion is the mechanical wearing away of rocks and sediments by the impact of water-borne particles, often occurring at the base of cliffs and rocky shores
• Attrition is the reduction in size and smoothing of sediment particles through collision and grinding during transport
• Hydraulic action is the force exerted by waves and currents on coastal features, leading to the loosening and removal of sediment particles
• Deposition is the settling and accumulation of sediment particles when the energy of waves, currents, or wind decreases
  • Deposition can occur in various coastal environments, such as beaches, dunes, estuaries, and deltas
• Accretion is the gradual buildup of sediment along the shoreline, leading to the seaward advance of the coastline (progradation)
• Longshore drift can result in the deposition of sediment on the downdrift side of coastal structures, such as jetties and groins, leading to accretion
• Sea-level rise can lead to increased erosion and landward migration of the shoreline (coastal squeeze), as well as increased deposition in low-lying areas (coastal wetlands, estuaries)

Coastal Ecosystems and Their Role

• Coastal ecosystems are diverse and dynamic environments that support a wide range of plant and animal species adapted to the unique conditions of the land-sea interface
• Salt marshes are intertidal wetlands dominated by salt-tolerant vegetation (cordgrass, glasswort) that provide habitat for fish, birds, and invertebrates
  • Salt marshes act as natural buffers against coastal erosion and flooding by attenuating wave energy and stabilizing sediments
• Mangrove forests are tropical and subtropical wetlands characterized by salt-tolerant trees and shrubs (red mangrove, black mangrove) that grow in the intertidal zone
  • Mangroves provide nursery grounds for fish and shellfish, protect the coast from erosion and storms, and sequester large amounts of carbon
• Seagrass beds are submerged meadows of marine flowering plants (eelgrass, turtle grass) that grow in shallow, clear waters
  • Seagrass beds stabilize sediments, improve water quality, and provide habitat and food for a variety of marine organisms (manatees, sea turtles, fish)
• Coral reefs are underwater structures built by colonies of coral polyps that secrete calcium carbonate skeletons
  • Coral reefs support high biodiversity, protect the coast from waves and storms, and provide economic benefits through tourism and fisheries (Great Barrier Reef, Australia)
• Coastal dunes are formed by wind-blown sand and stabilized by vegetation (beach grass, sea oats), providing a buffer against coastal erosion and flooding
• Estuaries are highly productive ecosystems that support a diverse array of plant and animal life adapted to the mixing of fresh and saltwater (oysters, crabs, waterfowl)
• Coastal ecosystems play a vital role in coastal resilience by attenuating wave energy, stabilizing sediments, and providing natural flood protection

Human Impacts on Coastal Dynamics

• Coastal development, such as the construction of buildings, roads, and infrastructure, can alter natural coastal processes and increase the risk of erosion and flooding
• Hardening of the shoreline through the construction of seawalls, revetments, and bulkheads can lead to increased erosion downdrift and the loss of natural habitats
• Beach nourishment involves the addition of sand to the shoreline to combat erosion and maintain beach width, but can have ecological impacts and require ongoing maintenance
• Dredging of navigation channels and ports can alter sediment transport patterns and lead to erosion or accretion in adjacent areas
• Damming of rivers reduces the supply of sediment to the coast, leading to increased erosion and the loss of coastal habitats (Nile Delta, Egypt)
• Groundwater extraction can cause land subsidence, increasing the risk of coastal flooding and saltwater intrusion into aquifers
• Climate change-induced sea-level rise and changes in storm intensity and frequency can exacerbate coastal erosion, flooding, and ecosystem loss
• Pollution from land-based sources (agricultural runoff, sewage, industrial waste) can degrade coastal water quality and harm marine life
  • Eutrophication caused by excess nutrients can lead to algal blooms, oxygen depletion, and fish kills in coastal waters
• Overfishing and destructive fishing practices (bottom trawling, dynamite fishing) can disrupt marine food webs and damage coastal habitats
• Invasive species introduced through ballast water or aquaculture can outcompete native species and alter coastal ecosystem dynamics (European green crab, lionfish)

Coastal Hazards and Risks

• Coastal flooding is the inundation of low-lying areas by seawater due to high tides, storm surges, or sea-level rise, causing damage to infrastructure and ecosystems
• Coastal erosion is the loss of land along the shoreline due to the action of waves, currents, and wind, leading to the retreat of the coastline and the loss of property and habitats
• Tsunamis are large, powerful waves generated by undersea earthquakes, landslides, or volcanic eruptions that can cause severe coastal flooding and destruction (Indian Ocean tsunami, 2004)
• Hurricanes and cyclones are intense tropical storms with high winds, heavy rainfall, and storm surges that can cause extensive coastal damage and loss of life (Hurricane Katrina, 2005)
• Sea-level rise, caused by global warming-induced thermal expansion of seawater and melting of land-based ice, can lead to increased coastal flooding, erosion, and saltwater intrusion
  • Low-lying coastal areas, such as small island states and delta regions, are particularly vulnerable to the impacts of sea-level rise (Maldives, Bangladesh)
• Saltwater intrusion is the movement of saline water into freshwater aquifers and surface waters, caused by sea-level rise, overextraction of groundwater, or reduced river flows
  • Saltwater intrusion can compromise the quality of drinking water sources and impact agricultural productivity in coastal areas
• Harmful algal blooms (HABs) are rapid growths of algae that can produce toxins harmful to marine life and human health, often triggered by nutrient pollution and warming waters (red tides, cyanobacteria blooms)
• Coastal subsidence, or the gradual sinking of land, can be caused by natural processes (sediment compaction, tectonic activity) or human activities (groundwater extraction, oil and gas production), increasing the risk of flooding and erosion

Monitoring and Assessment Techniques

• Remote sensing techniques, such as satellite imagery and aerial photography, are used to monitor changes in coastal landforms, land use, and vegetation cover over large areas
  • Multispectral and hyperspectral sensors can provide information on coastal water quality, bathymetry, and habitat distribution
• LiDAR (Light Detection and Ranging) is an active remote sensing technology that uses laser pulses to create high-resolution digital elevation models (DEMs) of coastal topography and bathymetry
• Unmanned Aerial Vehicles (UAVs) or drones equipped with cameras and sensors can provide high-resolution imagery and data for coastal monitoring and mapping at a local scale
• In-situ measurements, such as beach profiles and sediment sampling, provide detailed information on coastal morphology and sediment characteristics
  • Beach profiles are cross-shore surveys that measure the elevation of the beach and nearshore seabed, used to monitor changes in beach shape and volume over time
• Tide gauges and water level sensors measure changes in sea level and tidal range, providing data for coastal flood risk assessment and sea-level rise monitoring
• Wave buoys and acoustic Doppler current profilers (ADCPs) measure wave height, period, direction, and current velocity, providing data for wave and hydrodynamic modeling
• Ecological surveys, such as transect sampling and quadrat sampling, are used to assess the distribution, abundance, and health of coastal habitats and species
• Geospatial analysis and modeling techniques, such as Geographic Information Systems (GIS) and numerical models, integrate various data sources to assess coastal vulnerability, predict future changes, and inform management decisions
  • Coastal vulnerability indices (CVIs) combine multiple variables (elevation, geology, wave exposure, etc.) to map the relative vulnerability of coastal areas to erosion and flooding