A SIMPLIFIED METHOD FOR DETERMINING VERTICAL BREAKWATER CREST 

 ELEVATION CONSIDERING WAVE HEIGHT TRANSMITTED BY OVERTOPPING 



by 

 William N. Seetig 



I . INTRODUCTION 



The function of a breakwater is to lower wave heights in an area to 

 be protected, where the final design depends on the incident wave condi- 

 tions, protection criteria, cost, and environmental considerations. Wave 

 energy can be transmitted to the lee of a structure by regeneration of 

 waves by wave overtopping of the structure, propagation through the 

 structure if sufficiently porous, and diffraction through openings in 

 the breakwater. This design memorandum discussed wave regeneration by 

 overtopping for three types of vertical-faced impermeable breakwaters: 

 vertical thin-wall breakwaters, vertical-wall breakwaters, and composite 

 breakwaters (see Section 7.23 of the Shore Protection Manual (SPM) (U.S. 

 Army, Corps of Engineers, Coastal Engineering Research Center, 1975) -^ 

 for discussion of wave transmission) . 



II. BREAKWATER CREST HEIGHTS 



Goda, Takeda, and Moriya (1967)^ and Goda (1969)^ performed extensive 

 wave transmission by overtopping laboratory tests for a variety of struc- 

 tures. They found that wave regeneration by overtopping for vertical- 

 faced breakwaters is given by: 



H, = 0.5 Hi {l - sin[^('4^. 3)]} , 



(1) 



where H^^ is the average transmitted height (which will have different 

 wave height and period characteristics than the incident wave) , H^ is 

 the incident wave height (assumed to approach the structure normally), and 

 (h - dg) is the breakwater crest height or freeboard above the local water 

 level . 



^U.S. ARMY, CORPS OF ENGINEERS, COASTAL ENGINEERING RESEARCH CENTER, 

 Shove Protection Manual, 2d ed. , Vols. I, II, and III, Stock No. 008-022- 

 00077, U.S. Government Printing Office, Washington, D.C., 1975, 1,160 pp. 



^GODA, Y., TAKEDA, H. , and MORIYA, Y., "Laboratory Investigation of 

 Wave Transmission over Breakwaters," Report of the Port and Harbour 

 Research Institute, No. 13, Apr. 1967. 



^GODA, Y. , "Reanalysis of Laboratory Data on Wave Transmission over 

 Breakwaters," Report of the Port and Harbour Research Institute, Vol. 18. 

 No. 3, Sept. 1969. 



