At a 1989 nearshore processes workshop in St. Petersburg, Florida, 60 scientists agreed upon a general framework for nearshore fluid dynamics [ Holman, et al., 1990]. Figure 1 illustrates the spread of energy and momentum from a typical ocean wave frequency of 0.1 Hz to both higher and lower frequencies (across the page) as the waves progress from offshore (figure top) to the shoreline (figure bottom). Spectral transformation processes are generically split into two regions; shoaling processes that occur outside the surf zone (the region wherein waves dissipate energy rapidly due to depth-limited breaking), and breaking processes, that occur within the surf zone. The split is pragmatic; shoaling processes can successfully be modeled based on fundamental equations of motion with little or no empiricism, while breaking processes involve a turbulent cascade of energy that can only be parameterized. Swash, the mapping of the shallow water wave field onto a sloping beach surface, occurs across a range of frequencies and represents a component of the wave field that is reflected at the shoreline and will radiate back to the ocean. Mean flows are those that are considered zero frequency under steady (stationary) forcing; varying wave climate and tidal elevation are just two of the factors that make mean flows unsteady at long time scales.
The wave field varies in the cross-shore due to both kinematic variations with depth and dynamic variations due to nonlinear spectral evolution. For both reasons, fluid measurements taken at any particular point may not be representative of the overall wave field. Complexities in these spatial transformations have hindered progress.
Because incident waves provide the forcing for all other frequency bands, discussion will begin with the incident band and its associated higher frequency harmonics. We will then progress from low to high frequency in the description.