CHAPTER 5 



CONCLUSIONS AND RECOMMENDATIONS 



The following conclusions and recommendations are based on the entries 

 in the Surf Zone Currents, Annotated Bibliography," (Vol. II) and the review 

 and summary of physical processes, theory, and experimental verification 

 described in this report. 



I. CONCLUSIONS 



1. General . 



A general time-averaged coastal hydrodynamic theory now exists based 

 upon sound conservation laws pf physics and radiation stress principles. 

 It has been proven to qualitatively describe the mean water surface varia- 

 tions and currents generated by short-period surface gravity waves as shown 

 by laboratory and field data comparisons. However, to improve the quantita- 

 tive accuracy, further research and development is required. Specific con- 

 clusions on various aspects of the time-averaged theory are presented below. 

 Two inherent shortcomings of the method are: 



(a) Wave height fields must be specified by independent methods. Are 

 these methods accurate? 



(b) Closure coefficients must be determined from field data fitted to 

 the theory. The proper averaging time for the field data is not 

 known. 



Spatial and temporal variability of field data cannot be explained nor 

 studied by the method. 



The Boussinesq theory offers an alternative approach. It is founded in 

 the same conservation laws of physics but no time-averaging takes place. 

 Instantaneous water surface and current variations are considered. Conse- 

 quently, the two shortcomings listed are not present in this method. To date, 

 only conditions up to breaking have been simulated by the theory. It is 

 Goncluded that research efforts to extend the method into the surf zone 

 should be conducted. Specific conclusions on the Boussinesq theory are 

 given below. The theory will primarily serve as a research tool to further 

 understanding of the physical processes taking place in the surf zone within 

 each wave. Consequently, it will also serve to improve the time-averaged 

 method. 



Both theories rely on wave breaking and surf zone empirism that requires 

 fundamental research for improvement. 



2. Time-Averaged Radiation Stress Theory , 

 a. General . 



230 



