of wave transmission by overtopping since investigators have noted that over- 

 topping tends to generate waves of much shorter period than the incident wave 

 (Jensen and Sorensen 1979 and Jensen 1984). Investigations of wave transmis- 

 sion over a natural reef and associated laboratory experiments by Gerritsen 

 (198I) resulted in development of a theoretical approach to the redistribution 

 of energy that occurs with wave breaking on, and spilling over, a low-crested 

 or submerged reef. The transmitted waves were found to be fairly well repre- 

 sented as a collection of "solitons" or wave energy packets generated by inci- 

 dent breaking waves represented as long waves or bores (analogous to hydraulic 

 jumps). The phenomenon of "surf beat" or wave grouping was found to be criti- 

 cal to higher levels of energy transfer. The methods of Gerritsen (1981) 

 might yield useful results if applied to wave transmission by rubble-mound 

 breakwaters. 



Wave Transmission Through Permeable Breakwaters 



77. The tendency of wave energy to permeate through the interior of 

 rubble-mound breakwaters can be important for structures with relatively 

 coarse core material. Keulegan (1973) performed laboratory experiments of 

 this phenomenon which led several others to further theoretical and laboratory 

 investigations. Sollitt and Cross (1976) and Madsen and White (1976) devel- 

 oped semiempirical techniques to predict wave transmission through permeable 

 rubble-mound breakwaters. Wave transmission by this mode was assumed by these 

 authors to be a function of wave steepness H/L , structure permeability, 

 structure width, and the capacity of the structure to reflect wave energy or 

 to dissipate it in turbulence. The theory of long waves was applied to formu- 

 late expressions for wave transmission since it was assumed that the waves of 

 significant consequence would be much longer than the width of the structure. 

 Laboratory experiments indicate this as a practical assumption for most break- 

 water sites. 



78. Madsen and White (1976) also developed a computer program for 

 predicting wave transmission through multilayered rubble-mound breakwaters. 

 This program was refined by Seelig (1980b) who successfully tested its pre- 

 dictions against an extensive set of laboratory results to account for com- 

 bined wave transmission from overtopping and permeation. It was further 

 modified for interactive use (US Army Engineer Waterways Experiment Station, 



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