. Shore processes and shoreline development . up the entire wave form, the deficiency manifesting itselfas a hollowing of the front of the wave. The water availableendeavors to curve around through the entire orbit, but on reach-ing the top of the circle finds itself unsupported and collapses. The form of a breaking wave is not that which should existif friction were the principal cause of the surf. If the observercan secure a position where the wave profile is discernible, hewill find that there is a steepening of the wave front, to be sure,but the form does not suggest a steepening due to fo

. Shore processes and shoreline development . up the entire wave form, the deficiency manifesting itselfas a hollowing of the front of the wave. The water availableendeavors to curve around through the entire orbit, but on reach-ing the top of the circle finds itself unsupported and collapses. The form of a breaking wave is not that which should existif friction were the principal cause of the surf. If the observercan secure a position where the wave profile is discernible, hewill find that there is a steepening of the wave front, to be sure,but the form does not suggest a steepening due to fo

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. Shore processes and shoreline development . up the entire wave form, the deficiency manifesting itselfas a hollowing of the front of the wave. The water availableendeavors to curve around through the entire orbit, but on reach-ing the top of the circle finds itself unsupported and collapses. The form of a breaking wave is not that which should existif friction were the principal cause of the surf. If the observercan secure a position where the wave profile is discernible, hewill find that there is a steepening of the wave front, to be sure,but the form does not suggest a steepening due to forward in-clination of the whole wave mass resulting from bottom drag/so much as it does a steepening due to the absence of water on,and consequent hollowing of the front side of the wave. Whenthe wave finally breaks, masses of foam floating on the watersurface appear to describe an orbit that is more symmetricalthan one should expect in a wave deformed by great bottomfriction, while the forward arching crest tries to complete a WAVE FORM 17. :3 fcJD a o 18 WATER WAVES wave form which, if achieved, would not show excessive steepen-ing on the front. (Plate II.) The credit for first stating theabove explanation of surf action belongs to Hagen^^. Depth at Which Waves Break. — The depth of water in whichthe oscillatory wave assumes the form of a breaker is a mat-ter of some interest. As in the case of the wave of translation,described below, Russell^- found that breaking occurred whenthe depth of the water equalled the height of the wave, a rule notwholly confirmed b}^ the experiments of Bazin*^, who found thatbreaking occurred more frequently when the height of the waveexceeded two-thirds of the total depth. Russell states that his rulealso holds good for oscillatory waves, but unfortunately he isneither clear nor consistent in his method of calculating waveheight and water depth in the case of these waves. In one placewe rea.d that every wave broke exactly when its height above