transport may not be as significant a concern when using breakwaters for 

 wetlands purposes, many of the design concerns and data requirements, such 

 as wave and current climate, are the same as those necessary for traditional 

 breakwater design. The following sections discuss concerns that must be 

 addressed and evaluated during functional design of a detached breakwater 

 system. The effects of a structure on various coastal processes as well as the 

 effects of coastal parameters on shoreline response are discussed. 



Structural considerations 



Structural configuration is the extent of protection provided by the structure 

 plan and is defined by several design parameters; segment length, gap width, 

 project length, number of segments, cross-sectional design (transmission), and 

 distance offshore (Pope and Dean 1986). These design parameters should be 

 considered relative to the wave climate and potential effects on coastal 

 processes as described in the following sections. 



Single versus multiple segmented system. Use of single offshore 

 breakwaters in the United States is not a new concept; however, most have 

 been built with the objective of providing safe navigation and not as shore 

 protection or stabilization devices. One of the first single rubble-mound 

 breakwater projects was constructed at Venice, California, in 1905 for the 

 initial purpose of protecting an amusement pier. A tombolo eventually formed 

 in the lee of the Venice breakwater (Figure 17). Use of segmented systems in 

 the United States has been limited in general, but has increased substantially in 

 the past two decades (for example, see Figures 2, 7, 8, and 18). The use of 

 segmented systems as shore protection devices has been more extensive in 

 other countries such as Japan, Israel, and Singapore (see Figures 3 and 4) than 

 in the United States. 



The decision to use a single versus a multiple system is essentially based 

 on the length of shoreline to be protected. If a relatively long length of 

 shoreline needs to be protected and tombolo development is not desired, a 

 multiple segmented system with gaps should be designed. Construction of a 

 single long breakwater will result in the formation of a single or double 

 tombolo configuration. As discussed previously, tombolo formation in a 

 continuous littoral system may adversely impact downdrift beaches by 

 blocking their sediment supply. A properly designed multiple system will 

 promote the formation of salients, but will continue to allow a percentage of 

 the longshore transport to pass through the project area, thus minimizing 

 erosion along the downdrift shorelines. 



The number of breakwaters, their length, and gap width are dependent on 

 the wave climate and desired beach planform. Several long breakwaters with 

 wide gaps will result in a sinuous shoreline with large amplitude salients and a 

 spatial periodicity equal to the spacing of the structures; that is, there will be a 



Chapter 2 Functional Design Guidance 



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