of them were made very close to sea level and the waves were often so much 

 confused that it was very difficult to be sure of the direction of approach 

 of the principal wave trains,," Regarding unexplained current behaviors 

 it states| "ooothere appear to be a consideraible number of appreciable 

 cxarrents where the approach was normal and even a number of currents which 

 appeared to flow in the wrong direction so far as wave approach was con- 

 cernedo" In view of their experience it is concluded that the determination 

 of the direction of approach of principal wave trains from a point low on 

 the beach is difficulty, and that reliable observations for multiple systems 

 is practically impossible o In the subject study, the extent to which un- 

 recognized multiple wave systems may have influenced the results can never 

 be knownj but it is noted that dual wave trains from the north were not 

 given recognition in an illustration used (aerial photoc, Newport Bay,, their 

 Figure L4)o 



In connection with a study by the Beach Erosion Board at Mission Bay^, 

 Californiaj, it was found that of the several observational procedures^ a 

 satisfactory method of determining wave direction presented the greatest 

 problemo A sighting bar(4-) was devised for use with a transit and its 

 use improved the results as far as the predominant waves were concernedo 

 Observations were made from the bluff c, and no attempt was made to separate 

 wave systems o 



Every test made up to the time of writing indicates that the parallel 

 lines method is the most economical and convenient means yet devised for 

 determining directionSj and for studying general sea surface conditionsj^ 

 particularly for those who have a file of aerial photographs available. 

 Were it necessary to fly pictiires for wave study alone tte expense could 

 scarcely be justified, but since it appears that similar but limited results 

 can be obtained from photographs taken from some high point on the shore^ 

 the method comes within the reach of alio 



Figure 3 is an oblique photo showing good wave action at Jones Beach^ 

 Long Island;; New Yorko In the center and bottom prints^ the two principal 

 wave trains have been separated, and it can be seen that each train has a 

 positive direction of approach that can be measure do Note how well the two 

 systems conform to classical theory o Furthermore ^ when the camera height 

 is known;, the wave lengths can be computed and other data derivedo 



The illustration used has a fairly high oblique angle » Field tests 

 have not been made to determine how low the angle can be and still give 

 satisfactory results,, but judging from pictures taken from the pavilion on 

 the Steel Pier at Atlantic City, New Jersey, in connection with stereophoto- 

 gr^mraetric wave measurements (5) 5, which were relatively low in oblique angles, 

 the lower limit comes well within the heights of the usual vantage points 

 found on the seashore o 



(4) "A Method of Estimating Wave Direction", Do Re Forest^ Beach Erosion 

 Board Bulletin., Volo 4.5 Noo 2o 



(5) "Stereophotogrammetric Wave Measurement s"^ BEB Bulletin^ 7olo 4^ Noo 4-o 



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