example, may have meaning when a single pattern prevails, but have much 

 less significance when a more complex one prevails. 



Rhythmic Patterns . Hom-ma and Sonu (1963) have made a study of 

 rhythmic longshore bar patterns in Japanese coastal waters, relying 

 heavily on airphoto interpretation. According to these authors (1963, 

 p, 248), "a longshore bar may attain a rhythmic pattern consisting, of 

 echelons of arcuate (or lunate) bar units, which in entire appearance 

 resembles that of a honeycomb." They also have found that when a rhythmic 

 bar system is present, it is tied in closely with various rhythms found 

 along the littoral shore. They found (p. 255) that, in general, the foot 

 of an arcuate unit corresponds to a shoal, while the center to a deep 

 trough and a steep bottom slope in the surf zone. The rhythms were thought 

 to have their fundamental origin in the inherent undulations of the off- 

 shore bottom. (It is not believed that artificial sand pumping had any 

 effect on the topography shown on the maps of this study because the area 

 is updrift of the zone of beach nourishment in summer, and nourishment was 

 slight during the period of measurements.) 



Three maps appear to display the rhythms described above. Figure 7, 

 for May 1961, shows by shading the bar crest patterns apparent from the 

 detailed soundings. They have the two characteristics mentioned previously. 

 Somewhat similar rhythms, but without the definitive troughs, are present 

 on the map for September 1962 (Figure 12), and there is a suggestion of a 

 much larger rhythm on the October 1961 map (Figure 8), the shoreward 

 margin of the apex lying just seaward of the 15-foot depression contour. 



Rates of Modification. An idea of the expectable rates and magnitudes 

 of summer changes, at 2-month intervals, may be gained from Figures 9, 10, 

 11, and 12. Significant changes are seen from map to map. Of particular 

 interest are the maps and profiles (Figure 9) made 12 days after the great 

 storm of March 7-8, 1962. Profiles show a nearly continuous, relatively 

 deeply incised trough. Immediately seaward of the bar crest the bottom 

 descends at a fairly regular rate. The steepness of the trough sides and 

 their tendency to intersect at the bottom of the trough, suggests that the 

 trough bar configuration rather closely duplicates that formed by the waves 

 of the Ash Wednesday storm itself. Two months later (Figure 10) the trough 

 is wider and more flat bottomed; 4 months later (Figure 11) the trough has 

 been obliterated in places; and 6 months later (Figure 12) an apparent 

 rhythm pattern has developed, all but destroying the relatively simple 

 pattern imparted by waves of the great storm. 



Daily changes in bar and trough formation, evident from the profiles 

 of Figure 6, are interesting because in several cases the bars occurred 

 in depths well beyond those influenced by the prevailing breaking waves. 



