21. The design cross section of the Phase I model tests is presented in 

 Figure 5 with key elements which include a stepped seawall with parapet face 

 designed for reducing wave overtopping by reflecting incident waves in a sea- 

 ward direction. The design crest elevation was 15.7 ft above NGVD. As de- 

 signed for the model study, the seawall would be supported on vertical sheet 

 piles with a stone toe berm consisting of riprap. The riprap had a design 

 elevation of 3.4 ft above NGVD and a design width of approximately 5 ft. The 

 face of the riprap had a IV: 2H slope down to +1.0 NGVD. The proposed beach 

 berm, which was not incorporated in the model tests, would then be placed over 

 the toe berm to an elevation of 5.4 ft above NGVD. 



as- 



f 1.25' 



' I* *| £L 15.7- 



h*- 



EL 9.r 



EL 8.2- 



EL&7- 



225- 

















1 >v 











EL 5.2- 



u> 







"t 



EL 3.7- 





1.5 ^ 











Figure 5. Phase I cross section 



22. Selection of this design profile fronting the seawall required 

 assessment of the maximum storm-induced scour which could be expected to 

 accompany either of the design storms. Phase I GDM calculations were based on 

 scour to a depth of +3.4 ft NGVD or approximately 2 ft of erosion. Virginia 

 Beach core borings from 1948 and 1968 (pre- and post-1962) were reviewed by 

 NAO personnel who noted that the 1962 extratropical storm eroded the general 

 beach elevation to approximately 1 ft below NGVD. However, there was no 



17 



