Hydrodynamics of the Surf Zone

Abstract

Surf zone dynamics is a highly complicated topic in hydrodynamics which deals with the waves and wave generated phenomena in the region between the breaker line on a beach and the shoreline. When waves break on a gently sloping beach, large amounts of energy are released and turned into turbulence. As the waves keep breaking and interacting with the bottom topography, the momentum flux of the waves also decreases along with the decrease in wave height. The forcing this represents causes the generation of both currents and longer waves. The proper analysis of the dynamics of the surf zone requires a detailed knowledge of the breaking waves and the turbulence they create. This knowledge is not yet available. However, significant progress has been made over the last decade or two, in particular, in the area of understanding wave generated phenomena such as wave set-up, cross-shore and longshore currents and their stability, turbulence and mixing, and the generation of long wave phenomena (surf beats, edge waves), also termed infragravity waves. The present chapter gives a brief account of the basic mechanisms involved in these phenomena. Since the topic of surf zone hydrodynamics is very extensive, some of the subjects are merely covered in a brief descriptive way which primarily aims at referring the reader to relevant literature. The following topics are discussed: - Basic equations of nearshore circulation - The wave motion - 2-D wave and set-up models - Nearshore circulation - Infragravity waves - Very long period waves, shear waves