Wave Refraction and Diffraction . Considerable work has been done 

 on the theory of wave refraction and diffraction as a dominant factor 

 in wave action in shoal waters^^ »^»^^. The basic concepts are simple; 

 however, the application becomes very complex in an area of even 

 moderately complex hydrography. Work is now under way at the University 

 of California (Berkeley) under contract to the Beach Erosion Board to 

 establish the degree of accuracy of present concepts for predicting 

 wave refraction and diffraction over both simple and moderately complex 

 hydrography. An estimation of the accuraf'y of existing methods and 

 possibly simpler forms of their application may result from this study. 



It is to be recognized that the above discussion on refraction 

 applies to simple wave trains only; actually the complex wave trains of 

 the ocean further complicate the application of refraction methods to 

 actual problems. It is felt, however, that a quantitative understanding 

 of 'the simpler aspects must precede the understanding of the more com- 

 plex aspects. 



Wave Dissipation . Waves may loose a considerable portion of their 

 energy due to bottom friction and percolation as they move into the 

 shallow water of the Continental Shelf. Theoretical studies of this 

 have been made by Putnam and Johnson(S»9), laboratory studies have been 

 made at the Beach Erosion Board^'-'^ and field studies in the Gulf of 

 Mexico by Texas A&M Research Foundation^^-'-^ Further progress on this 

 phase of wave action will probably have to await a more comprehensive 

 set of reliable field data showing the energy loss of wave trains 

 travelling over the Continental Shelf. 



Littoral Currents. Any obliquity of wave attack on the shore re- 

 sults in the generation of a littoral current along the shore face. For 

 the most part these currents are more or less parallel to the shore but 

 occasionally flow away from the shore as rip currents. Whatever their 

 form, they have a considerable influence on shore processes. Due to 

 the combination of complexities of wave action and irregularities of 

 hydrography that are found in most areas, the attempts to correlate 

 littoral currents with the concurrent wave action have been somewhat 

 disappointing. However, simultaneous observations of waves and littoral 

 currents are being accumulated in increasing numbers, and some satisfactory 

 correlation of the two should be expected within the next 3 or 4 years. 

 Theoretical formulae are available (Putnam, Munk and Traylor^l^)) ^^hich 

 develop the alongshore littoral current velocities to be expected from 

 a simple, uniform wave train; however, the complexities of the natural 

 ocean wave trains complicate the application of the method to natural 

 conditions. Some work has been done on the gaining of a quafttitative 

 understanding of rip currents (Shepherd )(^-^\ but much remains to be 

 done. 



SHOIE PROCESSES 



Sand Movement . The movement of beach sands by wave action is poorly 

 understood at the present time. However a number of studies have 



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