suggests that they are crossed trains resulting from refraction of a single 

 deep water Trave o 



The use of this simple method of sorting the wave systems opens up 

 possibilities for greater use of aerial photographs as a basis for the study 

 of local areas. It will be noted that once separated, the wave lengths are 

 more measurable and therefore provide a good basis for various computations. 

 In such matters as the investigation of the formation of "finger shoals" 

 or the unusual concentration of wave action at one point, the contributing 

 factors can be traced from known conditions in the shore vicinity. 



As a natural consequence of two or three trains running at an angle 

 with each other j they must at intervals synchronize and assume some harmonic 

 arrangements Disregarding lateral components for the moment, the determina- 

 tion of this arrangement from a single gage record woiild require a slow, 

 costly analysis of the harmonic contents, which when completed would still 

 give no information on the angle of impingement on the shore. Where aerial 

 photographs are available or perhaps where the wave train directions and 

 length or period can be established by direct observations, or by recording 

 instruments developed for the purpose, a basis will have been provided for 

 a more sinplified analysis, for then the major conponents of the record will 

 have already been set apart. Remembering that the appearance of the 

 individual system is such that a record of any one alone would be fairly 

 regular, the harmonic analysis of the group would be greatly simplified. 



More definite knowledge of the complexities of wave patterns points up 

 some of the difficulties that have been encountered in attempts to develop 

 wave direction lecoiders, in particular, the attempt by the Beach Erosion Board 

 to use the Rayleigh Disk for that purpose (2). Under the influence of multiple 

 forces the disk attempted to align to momentary predominance or resultants, 

 therefore the desired result was not obtained. 



At the pi^sent time no adequate method exists for the determination of 

 wave directions. It is even questioned whether present visual methods are 

 reliable, for in most cases they are made in connection with dye tests, 

 float runs, or some other activity, and are usually taken from some point 

 low on the beach. Scripps Institution of Oceanography made a study of long- 

 shore currents (3) which disclosed unexplained behaviors that may have been 

 due to difficulties in determining the composition of the sea and the 

 direction of approach of the various systems. Commenting on the direction 

 observations the report states, "The field assistants who made most of the 

 observations, did not feel confident in all these observations since many 



(2) "The Rayleigh Disk as a Wave Direction Indicator", Beach Erosion Board 

 Technical Memorandum Wo. '18. 



(3) "Longshore Current Observations in Southern California", Beach Erosion 

 Board Technical Memorandum No, 13. 



