or family groupings are constantly changing position, though in general, 

 the wave systems maintain their organization remarkably well. When a 

 short-crested appearance is found, invariably two or more wave trains are 

 present, 



■While studying the aerial photographs some very interesting result s were 

 obtained through the use of a nBchanical aid in the form of a transparent 

 sheet on which parallel lines had been ruled, spaced about ten to the inch. 

 This was used to separate the individual wave systems appearing in the 

 picture and oftimes to the astonishment of the viewer, order appeared out 

 of a turbulent state of the sea that seemed devoid of orderly arrangement » 



In making the aid, fairly thin lines were ruled on clear cellophane 

 spaced as previously mentionedo In lieu of the above, a sheet of Noo 79 

 Zip-A-Tone will give good results. In use, the sheet is rotated until one 

 train of waves appear, then aligned generally with the system viewed to 

 disclose the other. The same procedure is used with secondary systems 

 that are running with the primary systems. In some areas, such as the west 

 coast of the United States, long period swells may be running with the lesser 

 systems, but these will usually be obvious without an aid. 



Photographs in ii^ich waves have only minor irregularities and the image 

 has the appearance of a single system should not be discounted. The smaller 

 the angle the crests make with each other, the more the wave pattern will 

 appear as a single unit, nevertheless, as long as the tell-tale interruption 

 of crests is present, multi-directional groups are indicated. 



The accompanying photographs will illustrate the application of the 

 principles. Figure 1-A has two obvious wave trains, one a minor system 

 approadiing from the upper left corner, and the other the more prominent 

 system which has the broken-crest characteristics. Figures 1-B and 1-C 

 show the latter to be two trains, each conforming to classical theory re- 

 markably well, Figxire 2-A is an example of a turbulent condition of the 

 sea in which, although no wave patterns are clearly shown in the offshore 

 area, two wave systems can be traced into the surf zone as shown in Figures 

 2-Q and 2-C, Note particularly that each maintains its separate identity 

 through the surf, and that each produces littoral currents. In one portion 

 of the picture these currents oppose each other and in another portion they 

 augment each other. 



Based on the many pictures examined, the conclusions are reached that 

 single wave trains are rarely found in the nearshore area and that multiple 

 systems are the rule. On the west coast of the United States the secondary 

 systems are often greatly overshadowed by the heavy swells which, of course, 

 are the more significant waves as far as coastal engineering is concerned. 

 Of the heavier swells, some approach from the northwest and concurrently 

 the southerly swells may be running, whereupon the condition is no different 

 than that of other coastal regions, and if net littoral forces are to be 

 determined the result must be the algebraic sum of the various systems. On 

 the east coast many of the pictures show waves that appear similar, iiriiich 



