steepened during wave condition a, then flattened during wave conditions 

 c and d. The front slope of structure IV flattened radically, but the 

 back slope changed only slightly, resulting in a narrowed crest width. 



b. Methods of Measurement . Breakwater heights, crest elevations, 

 crest widths, and front-face slopes in Table 4 were measured from the 

 average profiles of each breakwater structure in Figures 12, 24, 33, and 

 48. Listed in the table for each average profile are the structure height, 

 defined as the "highest point" from the average profile, and the crest 

 elevation, defined as the "average" of elevations across the width of the 

 average profile's crest. Compared to the highest point elevation, the 

 average crest elevation is more responsive to changes in the crest width 

 and face slopes and, hence, more representative of the crest configuration. 

 The average elevation of the crest area is used for the analysis of struc- 

 ture configuration changes in this study. The crest width was measured 



1 foot below the highest point on the crest, at approximately the base of 

 the top layer of bags. The front-face slope for each average profile was 

 difficult to measure since the plot of the face was usually curved. If 

 the entire face was too curved or irregular to fit a straight line, the 

 slope of the upper two-thirds of the face was measured. The front-face 

 slope is plotted in Figure 55 as a function of the corresponding crest 

 elevation and the ratio of that elevation to the water depth. 



Although qualitative changes in the backface were noted, the slope of 

 the backface was not measured. In tests on the structures of maximum 

 effectiveness and major interest (structures III and IV), the effect of 

 wave impact on the front-face slope was the primary emphasis; therefore, 

 less care was taken to construct the backface to conform to the design 

 slope. In addition, the lower part of the backfaces of structures III 

 and IV was the stabilized remains of structures II and III, respectively, 

 providing a stable base for the upper part and keeping the backfaces intact 

 except for bags displaced onto the faces from the crest. In field con- 

 struction, the backface and the front face of a breakwater would have to 

 be carefully designed and constructed to withstand wave attack. Also, it 

 is assumed that the structure would be completed before any part of the 

 structure had time to stabilize. Since the backfaces of the four struc- 

 tures did not consistently represent prototype conditions, the backface 

 slope was not measured. 



c. Interaction with Waves. From the incident wave height and period. 



dent wave 



steepness 



has be 



;eij 



calcu; 



Lated 



as 



follows: 



Condition 



Height 



(ft) 

 4.0 



, Hi 



(m) 

 (1.22) 



- ■ 



Period, 

 (s) 



, T 



Dimensionless 

 steepness H^/gT^ 



a 



6 







0.00345 



b 



3.9 



(1.19) 





10 







0.00121 



c 



5.8 



(1.77) 





6 







0.00500 



d 



5.7 



(1.74) 





10 







0.00177 



59 



