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State-of-the-art summary of theories and experiments investigated since 1967. 

 The theories before 1967 have been included in previous summaries (e.g., 

 Galvin, 1967). 



Currents generated by short-period surface gravity waves both within and 

 just beyond the breakers are of particular concern. The major types are 

 longshore currents, nearshore circulations, rip currents, and wind-driven 

 currents. Tidal currents are excluded. The study included the review of 

 physical processes, theories, field and laboratory experiments, numerical 

 models, and the measurement technology and instruments used to conduct the 

 experiments. Related topics included are wave thrust (radiation stress) 

 principles, wave setdown and setup, boundary and lateral mixing stress models, 

 edge waves, wave breaking, and surf zone energy dissipation. 



There are currently two major theoretical approaches to coastal hydro- 

 dynamics, each in a different stage of development. Both approaches assume 

 uniform currents with depth, require numerical computer methods for general 

 solutions, and both suffer from a limited data base for verification. The 

 older, time-averaged radiation stress theory is in the final refinement stage 

 and is now generally accepted. The new Boussinesq theory, which is just being 

 implemented, follows the instantaneous water surface and current variations to 

 essentially go beyond the time-averaged mean to observe the physics occurring 

 within each wave period. 



The drawbacks and limitations of both approaches are different. The radi- 

 ation stress approach requires a priori specification of wave height fields 

 by separate means and closure coefficients obtained from time-averaged field 

 data. The proper averaging time is unknown. A major limitation of the 

 Boussinesq theory is the size and speed of computers needed to handle the vast 

 grids and large number of time steps required for a meaningful simulation. 

 Both methods rely on wave breaking and surf zone empiricism that needs con- 

 siderable improvement. 



Detailed state-of-the-art summaries are presented for both methods. For 

 practical applications in coastal engineering, it is concluded that the knowl- 

 edge gained from future research with the Boussinesq method will best serve to 

 improve the time-averaged radiation stress approach and its eventual coupling 

 to coastal sediment and pollutant transport simulations. 



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