10 deg occurred when bars moved onshore during the profile recovery process 

 after a high wave event, not when bars moved offshore. Seaward bar faces 

 rarely exceeded 10 deg. 



280. Within the context of this study, the difference between present 

 and field results for bar face slopes can be attributed in great part to the 

 action of random waves and varying water level , which would widen the breaker 

 zone and smooth profile features in the field. Another factor is that steady 

 wave conditions are usually not of sufficient duration in the field for bars 

 to reach equilibrium form. 



Step and terrace slope 



281. In the LWT experiments, when erosion occurred the beach profile 

 retreated to produce a characteristic scarp or step immediately landward of 

 the still -water level. This scarp developed concurrently with a gentle 

 terrace slope that was milder than the slope of the initial profile. The 

 slope of the step increased with time and sometimes reached the angle of 

 initial yield, exhibiting the same tendency of alternating maxima and minima, 

 similar to the behavior of the shoreward slope of breakpoint bars as discussed 

 above. If the initial slope was mild, the retreat of the shoreline was small; 

 and the shoreline sometimes advanced somewhat even if a breakpoint bar formed 

 offshore. In this latter case most of the material in the bar was taken from 

 the surf zone rather than from the foreshore. If the waves were not too 

 severe (erosive) in these cases, the bar may have also received a net contri- 

 bution of material by onshore transport from the area located seaward of it. 

 However, if the waves were severe, a step formed even if the slope were 

 relatively gentle since the surf zone was not wide enough to dissipate all of 

 the incident wave energy, thereby resulting in strong wave attack and erosion 

 of the foreshore. 



282. Figure 27 illustrates the average slope of the step fi^ as a 

 function of time for selected cases in which considerable erosion of the 

 foreshore took place. Time development of the average terrace slope /S^, 

 immediately seaward of the step is also presented. For a coarser grain size, 

 steepening of the step slope proceeded more slowly (Case 401) and may have 

 achieved an equilibrium value before the angle of initial yield was reached. 

 The slower response of the coarser grains is probably due to their greater 



105 



