— ^ ^10 single bxeakwatex (18) 



The median- depth system (structures constructed in the surf zone, 

 2- to 4-m depth) was the most common type of system observed in 

 Toyoshima's survey of Japanese breakwaters. For reduction of wave 

 energy, a continuous structure (long single breakwater) is 

 recommended, while either an island (single) or group island type 

 (segmented) breakwater is recommended for the primary purpose of 

 sediment deposition. Construction is through the use of a floating 

 plant; a rubble -mound or composite type rather than armor block 

 construction is recommended to reduce costs. As was recommended for 

 the shallow-water depth system, the structure crown height should be 

 one -half wave height above the high-water level (1 to 1.5 m above 

 high water). For single breakwaters, the following structure ratio 

 is recommended: 



— ^ = 3 to 10 {recommended L^ = 100 to 300 m) (19) 



For a segmented system, the structure lengths are decreased: 



— - = 2 to e> {recommended L, = 60 to 200 m) (20) 



L„ = L {recommended L = 20 to 50 m) (21) 



For both single and segmented systems, the following structure- 

 distance ratio is recommended as a standard: 



Il± = 1 to 3.3 (22) 



For a continuous breakwater, 

 X 



1 to 3 {recommended X = 30 to 100 m) (23) 



24. Toyoshima used the described guidance to design more than 20 



systems along the Kaike coast, Japan, and concludes that the structures were 



successful in accomplishing their intended purpose. He recommends, however, 



16 



