a. 

 _o 



CO 



CO 



$ O) 



a>-o 



CO 



a> 



CO) 

 O) 



> 

 < 



Elapsed Time (hr) 



Figure 25. Evolution of shoreward slope of main breakpoint bars 



274. In general, the average shoreward bar face slope generated in the 

 LWT experiments increased with time, and the angle of initial yield was 

 apparently not achieved (see Cases 400 and 500 in Figure 25). In particular, 

 for the finer grain sizes, steepening of the shoreward face slope appeared to 

 be slower even though the angle of initial yield should be approximately 

 independent of grain size for the range of material studied. 



275. If a second bar formed immediately shoreward of a main breakpoint 

 bar, steepening of the shoreward slope of the main bar was usually hindered, 

 and the slope sometimes decreased. The maximiom bar face slope on the shore- 

 ward side of a bar was 35 deg (Case 4-3), which is considerably less than 

 Allen's (1970) limiting value. A smaller maximum slope under wave action is 

 logical because of the turbulent fluid environment existing in the surf zone, 

 which is considerably different from the laminar flow conditions under which 

 Allen performed his experiments. The expected result of turbulent flow is 

 increased destabilization of the sand grains, thus lowering the maximum stable 

 slope, which is in agreement with the trend of the observations. Evaluation 



102 



