SURF ZONE CURRENTS 



Volume I. State of Knowledge 



by 

 David R. Basoo 



CHAPTER 1 



INTRODUCTION 



For more than 60 years, investigations of coastal currents have been 

 conducted worldwide with the primary motivation of understanding sediment 

 transport, shoreline migration (erosion and accretion) processes, and the 

 transport and dispersion of pollutants. This report (Vol. I) and its com- 

 panion report entitled "Bibliography of Longshore and Nearshore Currents" 

 (Vol.11) are part of a major new study of nearshore currents initiated by 

 the Coastal Engineering Research Center (CERC) in 1979. 



Those currents generated by short-period surface gravity waves in water 

 depths generally less than 10 meters are particularly important. These cur- 

 rents are longshore currents, nearshore circulation cells, rip currents, on- 

 shore-offshore flows caused by winds, and wind-driven alongshore currents. 

 Articles and reports on the physical processes, theories, field and laboratory 

 experiments, and numerical models of these coastal flows were reviewed for 

 this study, along with the measurement technology and instruments used to 

 conduct the experiments. In addition, the following related topics were re- 

 viewed: wave thrust (radiation stress) principles, wave setdown and setup, 

 bed shear in oscillatory flow, edge waves, wave breaking, and surf zone hydro- 

 dynamics. Coastal currents induced by tides were excluded. Also, the vast 

 body of literature on fundamental, oscillatory, water wave theory, wave-current 

 interaction, and analytical theories for waves propagating over variable depth 

 bathymetry has been purposely left out. Sediment transport literature is 

 omitted except where coastal hydrodynamic investigations were a major part of 

 the effort. 



Previous state-of-the-art studies and reviews were important contribu- 

 tions to this report. Calvin's (1967) analysis and conclusions were, no doubt, 

 in some way responsible for the emergence of the wave thrust theory of the 

 of the 1970's. Many explicit summaries of theoretical interest in longshore, 

 nearshore, and rip currents have ensued, including Longuet-Higgins (1972a, b), 

 Meyer and Taylor (1972), Jonsson, Skovgaard, and Jacobsen (1974), Miller and 

 Barcilon (1978), Dalrymple (1978), Komar (1976 a,b), Fisher and Dolan (1977), 

 and Horikawa (1978) . Other valuable reviews of the literature can be found in 

 the doctoral dissertations of Bowen (1969a, b) , Thornton (1969), Battjes (1974a, 

 b), Sasaki (1974-1975), Meadows (1977), and Gourlay (1978). Researchers con- 

 tinue to investigate various weak links in the field (e.g.. Dean, 1976; Collins 

 1977). The ongoing Nearshore Sediment Transport Study (NSTS) , sponsored by the 

 National Oceanic and Atmospheric Administration, will undoubtedly result in 

 future reassessments of current knowledge. In Europe, a recent mechanics con- 

 ference, Euromech 102 (1978) , concentrated on new research efforts in coastal 

 hydrodynamics. And finally, many researchers who have developed numerical 



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