criterion, the following means are available for increasing energy flux into 

 the protected region. 



48. Wave overtopping. The structure cross-section can be designed to 

 allow wave transmission over the top. The transmitted wave energy prevents 

 connection of the salients to the structure and the salient tends to accrete 

 in a more spatially uniform manner. However, reformed overtopped waves have a 

 higher frequency and irregularity than the incident waves. Water level, wave 

 height and period, and structure slope and roughness all affect, in a nonlin- 

 ear manner, the amount and form of energy transmitted by overtopping. These 

 parameters are rarely constant; therefore, the rate of overtopping is quite 

 variable. The amount of energy which will pass the structure due to over- 

 topping can be estimated using the procedures of Section (7.23) of the SPM 

 (1984), Seelig (1980) or Douglass (in press). The structure cross-section can 

 be altered so that sufficient energy is transmitted by overtopping to prevent 

 tombolo or large salient formation. An existing structure that is not per- 

 forming as required could conceivably have its crest raised or lowered, but 

 this is often costly and impractical. 



49. Breakwater permeability. Another means of transmitting wave energy 

 is to make the structure permeable. Energy is transmitted at the incident 

 frequency and is generally more predictable and regular than overtopping 

 transmission. Also, wave energy that would be transmitted through a structure 

 is generally more uniform than diffracted wave energy, resulting in a more 

 uniform shoreline. However, transmission quantities are highly dependent on 

 water level and wave period. Design permeability of the structure can be 

 selected using the procedure contained in Chapter 7 of the SPM (1984) or 

 Seelig (1979) to influence the degree of wave transmission through the struc- 

 ture, if the water level and wave period are predictable within a limited 

 range. It is nearly impossible to economically adjust the permeability of an 

 existing structure as a way of modifying transmitted wave energy except for 

 sealing a permeable one to render it impermeable. 



50. Segmentation. The most predictable method at present for influ- 

 encing transmitted wave energy is by utilizing a segmented design. Segmented 

 detached breakwaters are especially useful when protecting a long section of 

 shore and tombolo development is not desired. Segmenting permits a predict- 

 able proportion of wave energy to enter the breakwater's lee and at the same 

 time allows the structure to be built in an economical water depth. Waves in 



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