What makes the waves at the beach?
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Understanding the Formation of Waves at the Beach
Wave Generation and Propagation
Ocean Wave Formation
Waves at the beach are primarily generated by wind blowing across the surface of the ocean. The energy from the wind is transferred to the water, creating waves that travel across the ocean until they reach the shore. These waves can vary greatly in size and energy depending on the wind speed, duration, and the distance over which the wind blows (fetch)5.
Wave Refraction and Transformation
As waves approach the shore, they undergo a process called wave refraction. This occurs because the part of the wave in shallower water slows down more than the part in deeper water, causing the wave to bend and align more parallel to the shore. This refraction is influenced by the underwater topography, such as the presence of submarine canyons, ridges, and the slope of the beach4. The refraction process can lead to significant variations in wave height along the shore, contributing to the complex patterns of waves observed at the beach4.
Wave Breaking and Beach Interaction
Wave Breaking Mechanisms
When waves move into shallower water near the shore, they increase in height and eventually break. This breaking occurs when the wave's crest becomes too steep and unstable, often when the horizontal particle velocity at the wave crest matches or exceeds the wave celerity1. The type of breaking wave—plunging, spilling, or surging—depends on the slope of the beach and the wave's characteristics1.
Energy Dissipation and Sediment Transport
Upon breaking, waves dissipate a significant amount of their energy through processes such as friction, turbulence, and the movement of sediments. The energy dissipation is influenced by the beach slope and the wave height, with steeper slopes generally leading to higher energy dissipation2 3. This energy loss is crucial for the transport and redistribution of sediments along the beach, contributing to beach erosion and the formation of various coastal features4 8.
Infragravity Waves and Their Impact
Generation and Characteristics
Infragravity (IG) waves are long-period waves with frequencies lower than those of wind-generated waves. They are typically generated by groups of shorter waves and can be modulated by the breaking of these shorter waves5. IG waves play a significant role in coastal dynamics, especially on gently sloping beaches where they can dominate sediment transport and influence groundwater flows5.
Effects on Coastal Environments
IG waves can have profound impacts on coastal environments. They can enhance longshore and cross-shore mixing, modulate current velocities in rip channels, and contribute to dune erosion and barrier breaching during storm conditions5. Additionally, IG waves can propagate into tidal inlets and back-barrier lagoons, affecting sediment transport and current patterns5.
Conclusion
The waves at the beach are a result of complex interactions between wind energy, underwater topography, and coastal features. From their generation in the open ocean to their transformation and breaking near the shore, waves undergo various processes that shape the coastal environment. Understanding these processes is essential for predicting and managing coastal erosion, sediment transport, and the overall dynamics of beach ecosystems.
Sources and full results
Most relevant research papers on this topic
Evolution of breaking waves on sloping beaches
The Lagrangian solution and experiment data for breaking waves on sloping beaches agree reasonably well, with the Lagrangian solution predicting wave breaking criteria and experiments confirming experimental data.
Beaches Produced by Waves of Low Phase Difference
Beach slope and distance from shore to breakers correlate with breaker height, wave period, and grain diameter, with energy lost in breaking, friction, turbulence, and moving material accounting for 25% to 50% of incident wave energy.
Wave reflexion from beaches
Bottom friction can significantly contribute to wave absorption on beaches, even without breaking, if the parameter (3)1212g2 is not too small.
Refraction of Ocean Waves: A Process Linking Underwater Topography to Beach Erosion
Wave refraction is the primary mechanism controlling changes in wave height along beaches, and sediment transport is influenced by the existing refraction pattern.
Highly CitedInfragravity waves: From driving mechanisms to impacts
Infragravity waves, driven by groupings in incident short waves, can significantly impact coastal hydro-sedimentary dynamics, affecting currents, sediment transport, and dune erosion.
Highly CitedReflection of Ocean Surface Gravity Waves from a Natural Beach
The ratio of seaward to shoreward propagating energy in ocean surface gravity waves on a natural beach decreases with wave frequency and height, and increases with beach-face slope, with significant reflection occurring at steep beach faces and low-energy, low-frequency swell.
Highly CitedA Scale Comparison of Waves Breaking on a Beach
Scale effects in wave heights, set-up, and vertical profiles are virtually absent in the range of 0.1 m to 1.5 m, when measuring waves breaking on a beach.
Depth of Disturbance of Sand on Sea Beaches by Waves
The depth of sand disturbance on beaches increases with wave height and energy, and is greatest in shallow water near the break-point, with coarser sand causing greater disturbance.
Highly CitedLong waves on a beach
The study provides equations for small amplitude waves in varying depth water, and numerical solutions for a solitary wave on a beach with uniform slope.
Highly CitedIncompressible SPH simulation of solitary wave propagation on permeable beaches
Permeability of beaches, influenced by particle diameter, can significantly reduce the impact of tsunami-like waves on coastal structures.
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