the no-time-lag comparisons in Figure 33. This was also previously noted in Part VI and demonstrated by 

 Figure 29 for the comparisons with no vertical seawall. 



Vertical Seawall Summary and Conclusions 



223. Modification of the basic testing arrangement in the 6-ft flume by addition of a vertical seawall 

 provided the opportunity to examine Dean's approximate principle, which states that the volume of the 

 additional scour in front of the seawall is approximately equal to the volume of sediment denied to the 

 profile by the seawall. Comparison of regular wave tests (with and without the vertical seawall) supported 

 the approximate principle, when averaged over the cross-tank profile variations, exhibiting a ratio of 1.03 

 for eroded volume over retained volume. Comparison tests using irregular waves were more uniform in the 

 cross-tank dimension, but less erosion was observed, with a ratio of 0.83 for eroded over retained volume. 

 Both results give ratios higher than that obtained by Barnett (1987); however, the present results represent 

 only one condition, wherccis Barnett 's results stem from 11 different test cases. 



224. Comparison between vertical seawall tests using both irregular waves and regular waves support 

 the earlier conclusion that the irregular wave height parameter i/1/3 provides best correspondence to the 

 monochromatic wave height in terms of profile development. The regular wave period was represented by 

 the peak spectral period. 



225. Time for profile development under irregular wave action lagged the development caused by 

 regular waves by a factor of approximately two. This also conforms to conclusions given earlier based on 

 tests without a vertical seawall. 



92 



