d. Engineering applications to prototype cases based on more sophisti- 

 cated approaches such as given by the two-line theory of Bakker (1968b) 

 are not known. These more sophisticated approaches can be currently 

 considered as belonging to the realm of research rather than of engineer- 

 ing practice. 



e. - Local effects, diffraction, rip currents, wave refraction and inter- 

 action between these effects are, at present, still not so conveniently 

 formulated to be used by practicing engineers. Introduction of these 

 effects, if and when important in the mathematical formulation, is 

 feasible but will require further investigation. 



f. A simple numerical scheme that can be used by design engineers and 

 planners and which includes theoretical or empirically all important 

 effects could be developed. Effects that should be included in the 

 mathematical model are wave diffraction, loss of sand by rip currents 

 along groins, sea (lake) level variation, and beach slope variation 

 near groins. 



g. The introduction of the concept of radiation stress in the mathe- 

 matical formulation is not recommended at this time, but research 

 related to this approach should be pursued in view of the eventual 

 input that subsequent results could have on then existing operational 

 mathematical models. 



53 



