breakwater systems (217 segments total) along the Japanese coast. The 

 relationships are categorized based on the proposed depth at the structure: 

 the shoreline system, where the structure is placed at or near the waterline; 

 the shallow-water system, with a structure depth less than or equal to 1 m; 

 and the median- depth system, for structures in a depth of 2 to 4 m. Relation- 

 ships are not given for a deepwater system, which is described as being 

 located at the outside of the surf zone for the purpose of dissipating wave 

 energy rather than sediment deposition. 



a. The shoreline system is recommended for sites with either a steep 

 beach slope, where only small-scale sand deposition is required, to 

 protect an existing structure from wave attack (i.e., seawall), or 

 to maintain the existing beach width. The "group island type" 

 (segmented) breakwater is recommended, constructed of two-layer 

 pile armor blocks. A problem noted with shoreline system structures 

 is large-scale scour on the seaward face of the structure, 

 especially if the structure is exposed to significant wave attack. 



— - = 2 to 3 segmented breakwater n4') 



{recommended L„ = 40 to 6 m) 



{recommended L = 20 m) (15) 



The shallow-water depth system (constructed in depths less than 1 m) 

 is recommended for gently sloping beaches or at sites where the 

 structures are expected to be constructed from the beach using a 

 track and crane method. A "group island type" (segmented) system is 

 recommended, constructed of armor blocks with a crest elevation 

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

 1.5 m above high-water level). 



— - = 3 to 5 segmented breakwater (16) 



{recommended L„ = 60 to 100 m) 



L - L {recommended L = 20 m) (17) 



If an island breakwater is used (single breakwater) , Toyoshima 

 recommends that the following segment length ratio: 



15 



