of the 14 cases where the angle of initial yield appeared to have been 

 attained indicated that the maximum slope on the shoreward bar face was in the 

 range of 20-35 deg, with an average of 28 deg. In each of the cases, the 

 angle of initial yield should be somewhat larger than the value determined as 

 the maximum slope. An estimate of bar face slope after avalanching occurred 

 may be obtained by examining the minimum shoreward bar face slope after the 

 angle of initial yield had apparently been exceeded. The slope thus calcu- 

 lated (10 cases showing clear minima) was in the range of 20-25 deg, with an 

 average of 22 deg. These values should be somewhat higher than the actual 

 residual angle after shearing since some steepening of the slope probably 

 occurred between the times of avalanching and the profile survey. 



276. The average seaward bar face slope was fairly constant through 

 time, sometimes exhibiting a slight increase during the first hours of the 

 run. Figure 26 shows the seaward bar face slope as a function of time for 

 representative cases. The average slope was typically in the range of 8-12 

 deg, although local slopes reached 20 deg. The variation in average seaward 

 bar face slope was small and appeared to be independent of grain size, but 

 weakly related to wave period, with longer periods giving a more gentle slope. 



277. The seaward face of the bar was in many cases well approximated by 

 two or three planes having distinctly different slopes. The upper part of the 

 bar face seaward from the crest had a slope ^2 i^^^ging from 4-8 deg, whereas 

 the slope of the lower part of the bar fi-^ was in the range of 8-18 deg. In 

 some cases, the very end of the bar could be approximated by a third line of 

 constant slope, often with a magnitude smaller than that of the two shoreward 

 slopes. The location of the intersection between the upper and lower seaward 

 face slopes approximately coincided with the location of the break point in 

 many cases (see Figure 14). This triplaned nature of bars formed under 

 regular waves does not seem to have been noted before. Although such a 

 configuration would probably not be exhibited in the field because of varying 

 waves and water level, its manifestation under regular waves indicates the 

 existence of a small and subtle regime of hydrodynamic forces in the region 

 under prebreaking waves which acts on a wave -by-wave basis whether or not it 

 is observed in macroscale profile surveys in the field. 



103 



