Waves are the driving force behind coastal processes, shaping shorelines and influencing marine ecosystems. Wind-driven wave formation, influenced by factors like wind strength and fetch, creates various wave types with distinct characteristics. Understanding these dynamics is crucial for grasping coastal evolution.

As waves approach the shore, they undergo transformations that impact coastal landforms and sediment transport. Wave refraction, shoaling, and breaking in the surf zone generate currents and energy patterns that sculpt beaches, headlands, and bays. These processes are key to comprehending coastal morphology and erosion.

Wave generation and characteristics

Wind-driven wave formation

• Wind transfers energy to water surface through frictional drag and pressure differences
• Wave size and energy determined by wind strength, duration, and fetch (distance wind blows over water)
• Significant wave height (H1/3) describes average height of highest one-third of waves in a given period
• Swell waves generated by distant storms travel long distances with regular, long periods
• Local wind waves (sea waves) characterized by irregular, choppy patterns and shorter periods

Wave properties and influencing factors

• Wave characteristics defined by height, length, period, and steepness
• Wave height influenced by wind speed, duration, and fetch length
• Wave period affects wavelength and propagation speed
• Wave steepness ratio of wave height to wavelength determines wave stability
• Water depth, bottom topography, and coastal geography modify wave characteristics near shore
• Shallow water causes wave shoaling decreases wavelength and increases wave height
• Wave breaking occurs when steepness exceeds critical ratio (typically when wave height is ~0.78 times water depth)

Wave types and properties

Deep and transitional waves

• Deep-water waves occur in depths greater than half wavelength
  • Orbital motion does not interact with seafloor
  • Particle movement follows circular paths
• Transitional waves exist in intermediate depths
  • Wave motion begins to be affected by bottom friction
  • Particle orbits become elliptical
• Wave base depth where wave energy no longer affects bottom sediments (approximately half wavelength)

Shallow-water waves and coastal phenomena

• Shallow-water waves occur in depths less than 1/20th of wavelength
  • Elliptical particle orbits with horizontal motion dominant
  • Potential for wave breaking as wave height increases relative to depth
• Surf zone area where waves break and dissipate energy
  • Crucial role in sediment transport and beach morphology
  • Generation of longshore currents and rip currents
• Wave setup increases mean water level within surf zone
  • Contributes to coastal flooding during storms
• Wave runup maximum vertical extent of wave uprush on beach or structure above still water level

Special wave types

• Tsunamis long-period waves generated by sudden water displacements
  • Caused by earthquakes, landslides, or volcanic eruptions
  • Can travel across entire ocean basins with minimal energy loss
• Edge waves trapped along coastlines, oscillating parallel to shore
  • Play role in nearshore circulation patterns and beach cusps formation
• Infragravity waves with periods longer than wind-generated waves
  • Important in sediment transport and coastal morphodynamics
  • Can contribute to coastal erosion during storms
• Standing waves (seiche) occur in enclosed or semi-enclosed basins
  • Characterized by nodes (minimal vertical motion) and antinodes (maximum vertical motion)
  • Can affect harbor operations and coastal infrastructure

Wave propagation and coastal interaction

Wave transformation in coastal zones

• Wave shoaling process as waves approach shallower water
  • Decreased wavelength and increased wave height
  • Conservation of energy leads to wave steepening
• Wave breaking occurs when steepness exceeds critical ratio
  • Spilling breakers on gently sloping beaches
  • Plunging breakers on steeper slopes
  • Surging breakers on very steep slopes or structures
• Surf zone dynamics and energy dissipation
  • Generation of turbulence and sediment suspension
  • Formation of longshore bars and troughs

Coastal currents and sediment transport

• Longshore currents generated by oblique wave approach to coastline
  • Responsible for longshore sediment transport (littoral drift)
  • Influence beach morphology and coastal erosion patterns
• Rip currents form when water piled up by breaking waves returns seaward
  • Narrow, fast-moving channels of water
  • Pose hazards to swimmers and contribute to offshore sediment transport
• Undertow currents near-bottom return flow compensating for onshore mass transport
  • Influence cross-shore sediment transport and beach profile evolution

Wave refraction and coastal morphology

Wave refraction processes

• Wave refraction bending of wave crests approaching shore at an angle
  • Caused by differences in wave speed in varying water depths
  • Waves tend to become parallel to depth contours near shore
• Refraction patterns influenced by bathymetry
  • Complex bottom topography creates focusing and defocusing of wave energy
• Wave diffraction occurs when waves encounter obstacles or pass through gaps
  • Spreads wave energy into shadow zones behind barriers
  • Creates complex wave patterns around coastal structures and islands

Coastal landform development

• Headlands experience wave energy concentration due to refraction
  • Increased erosion and formation of wave-cut platforms
  • Development of sea cliffs and rocky shorelines
• Bays experience wave energy dispersion through refraction
  • Promotes sediment deposition and beach formation
  • Development of embayed beaches and tombolos
• Cuspate forelands and spits form due to longshore sediment transport
  • Influenced by wave refraction patterns and sediment availability

Applications in coastal engineering

• Understanding wave refraction crucial for coastal engineering projects
  • Design of breakwaters, groins, and artificial reefs
  • Prediction of sediment transport patterns and coastal erosion
• Numerical models simulate wave refraction and diffraction
  • Used in coastal zone management and shoreline change forecasting
• Wave energy converters placement optimized based on refraction patterns
  • Maximizes energy capture in wave farm designs