Review Of Wave Breaking In Shallow Water

Wave breaking IS the most obvious and spectacular of all the physical processes that affect surface water waves It is also the most complex, and any thorough attempt to understand the physical processes involved needs to address many different aspects of the phenomenon Amongst the most Important are

• Transformation of Waves during Breaking

  • Flow field under nearly-breaking and broken waves

  • Factors influencing the initiation of breaking

  • Formation and propagation of a roller and broken wave

  • Reformation of unbroken waves after breaking over banks or bars

  • Energy exchange between spectral components

• Generation of Surf Zone Phenomena

  • Production and dissipation of turbulence

  • Water level set-up

  • Longshore currents

  • Cross-shore currents (undertow) Nearshore current circulation patterns

  • Low-frequency waves

• Effects on Solid Material

  • Erosion and deposition of seabed sediment

  • Erosion of dunes and cliffs

  • Forces on breakwaters and seawalls

Wave breaking is an essential consideration In most coastal engineering design studies This paper contains a critical review of two aspects of wave breaking necessary for such studies the prediction of wave height and water depth at which waves start to break, and the rate of energy losses from waves once they have broken This review contains both simple methods suitable for hand calculations and more detailed methods for inclusion in computational models of wave propagation In shallow water

Before breaking, waves have a relatively smooth water surface After breaking the wave fronts are usually white and foamy often with a lot of spray and bubbles Complex processes take place during breaking, involving a rapid change of wave shape and the conversion of wave energy to turbulence and subsequently heat After a short distance, roughly several times the depth at breaking, the breaking-induced turbulence becomes fully developed and the wave adopts a steady, well-organised profile which is more-or-less independent of the initial breaking behaviour, but still often with white water at the crest face In this paper the term "broken wave" will be used to describe this steady phase, and "breaking wave" to describe the initial breaking process The term "transition zone" is often applied to the region where the initial breaking phase occurs Svendsen et al (1978) also use the terms "inner region" and "outer region respectively for the regions of steady broken and initial breaking behavior

The most visually apparent phase occurs when waves initially break and the wave crest overturns, or comes as close as possible to overturning, and generates white water The different visual characteristics of breaking waves provide a classification of breaker types (Galvin (1 968)), described below

• Spilling Breakers Spilling breakers occur when white water initially appears at the wave crest and spreads down the front face An overturning jet of water is either very small or absent altogether Spilling breakers usually occur on flat or gently sloping beaches