Table A7 



Wave Transmission Versus Crest Height 



Storm 

 Event 



DSWL 

 (ft) mlw 



Incident 

 Wave 

 Height 

 (H (ft)) 



Wave 

 Period 

 (Tp 

 leeel) 



Transmitted Wave Heights at Various 

 Crest Heights H(ft) 



+ 4.0 mlw 



+ 5.0 mlw 



+ 6.0 mlw 



50 yr 



7 



7.2 



9.7 



5.6 



5.3 



4.9 



50 yr 



7 



6.2 



9.7 



4.9 



4.6 



4.2 



50 yr 



7 



5 



9.7 



4.0 



3.7 



3.4 



25 yr 



6.2 



6.5 



7.6 



4.8 



4.4 



4.0 



25 yr 



6.2 



5.6 



7.6 



4.2 



3.8 



3.5 



25 yr 



6.2 



4.5 



7.6 



3.4 



3.1 



2.8 



10 yr 



5.5 



5.6 



6.5 



3.9 



3.5 



3.1 



10 yr 



5.5 



4.8 



6.5 



3.4 



3.0 



2.7 



10 yr 



5.5 



3.9 



6.5 



2.8 



2.5 



2.2 



1 Vr 



4.6 



5 



4.3 



3.1 



2.7 



2.3 



1 yr 



4.6 



4.3 



4.3 



2.6 



2.3 



1.9 



1 yr 



4.6 



3.5 



4.3 



2.2 



1.8 



1.5 



wave-induced erosion control for the existing banks is the construction of 1 1 

 offshore breakwaters and the placement of beachfill. The recommended 

 breakwater segment lengths are 100 ft each, separated by 100-ft-wide gaps 

 (except for a 75-ft-wide gap immediately south of the existing pumping 

 station) and located about 140 ft bayward of the existing mean high water 

 shoreline. The recommended design crest elevation is +4.0 ft mlw. 



The recommended beachfill includes a storm berm at +6.0 ft mlw 

 extending about 30 ft bayward of the existing toe of the bank and then sloping 

 at 1V:8H until intersecting with the existing bottom. 



Project Construction 



The construction of the project was initiated in November 1990 and 

 completed in July 1991 by Coastal Design and Construction of Gloucester, 

 Virginia. The construction sequence was breakwater construction, initial 

 beach fill placement, extension of existing storm drains, grading and 

 stabilization of critical bank erosion areas, and final beach fill placement. 



The breakwaters were constructed by land-based equipment using 

 temporary sand causeways from the existing shoreline out to the breakwater 



Appendix A Case Design Example of Detached Breakwater 



A13 



