102. Bars observed in the field typically have seaward angles less than 

 10 deg, as discussed by Larson and Kraus (1989). At least four reasons can be 

 given to explain the gentleness of bar slope in the field: 



a. Waves are irregular in height, period, and direction. 



b. The water level varies with the tide. 



c. Steady wave conditions do not exist. 



d. Mechanisms other than short-period incident waves, such as 

 undertow and infragravity waves, may contribute to move sand. 



103. After examining bar angles from the aforementioned movable-bed 

 studies performed with monochromatic waves, a range of bar angles was 

 selected. The bars used in the experiment consisted of two angles, fi 1 and 

 yS 3 , which implies /? 2 equals /3 X . The secondary angle was not included 

 since it covered only a small area of the bar, and it was felt that one 

 seaward angle was sufficient for this initial study. The use of two bar 

 angles resulted in bars that were either triangular (Figure 27) or, in the 

 case of /? 3 = deg , terraced. Seaward bar angles ranged from 5 to 40 deg, 

 and shoreward bar angles ranged from to 40 deg. The greater seaward angles 

 are unrealistic for sand bars in the field; these were included because it was 

 beneficial for engineering purposes to observe breaking waves on shapes that 

 approximate those of submerged breakwaters or reefs, sills of perched beaches, 

 and similar structures. 



Figure 27. Shape of typical bar used in study 



104. The location and size of the bars were required to produce break- 

 ing waves. Sunamura (1987) found a relationship between the depth of the bar 



68 



