A METHOD OF SEPARATDIG MULTIPLE SYSTEMS OF OCEAN WAVES 

 FOR DETAILED STUDY OF DIRECTIONS AND OTHER PROPERTIES 



by 



H. A. WARD 

 Engineer, Reports and Publications iOivision 



In past studies of water -waves, primary attention has been given to the 

 measurenBnts of individual wave trains and to refraction and diffraction 

 theory for a single system of waves* Some attempts have been made to 

 determine the state of the sea for local areas through the use of stereo- 

 photogrammetric method s(l), but aside from this, little has been contributed 

 on the general make-up of the sea patterns. 



Various organizations, including the Beach Erosion Board, maintain auto- 

 matic wave -recording devices that give a record of the change in water surface 

 on a height and time scale as waves pass the gaging point, but such records 

 give no data on the direction of approach, or on the several separate wave 

 systems which may be present at the time. Obviously, the energy value of 

 different systems that pass the gaging point, and their relative directions 

 of approach are of the utmost importance, since they may either augment or 

 oppose each other whereupon "the algebraic values of the systems determine their 

 ability to transport material or produce other coastal phenomena of interest. 



Where two or more systems of waves are present and the systems are 

 running at angles with each other, the recoil from the gages is confused 

 and erratic o For a period the waves may be regular, only to be followed by 

 a very irregular series, and occasionally out of a fairly rough sea, a flat 

 of considerable diiration will appear. The study of multiple wave systems 

 has shewn that data from a single gaging point is not enough to permit 

 evaluation of the forces, and because of lateral components resulting from 

 interference by companion wave trains, clapotis effects and flats will show 

 up on a record where to all appearances only generally uniform systems of 

 waves are present. These lateral components have not been taken into con- 

 sideration in the theory of harmonic analysis for present methods of wave 

 recording. 



Because of the irregularities shown on wave gage records, some have 

 concluded what ocean vraves do not conform to classical theory. However, 

 when the separate wave trains of a multiple system are examined, it is 

 found that they do conform to a surprising degree; but the crests must be 

 considered more in the nature of an undulating line whose full behavior 



(1) Methods d'etude des Lames, M. J. Larras, Trauaux, Vol. 21, No, 58, 1937, 

 and Beach Erosion Board Bulletin, Vol. 4-, No. 4-. 



