SUMMARY AND CONCLUDING DISCUSSION 



The use of detached breakwaters is expected to increase as a shore protec- 

 tion measure because of their desirable characteristics of (1) reducing wave 

 energy, (2) increasing the beach width, even under conditions favoring off- 

 shore sand transport, (3) allowing longshore movement of sand, and (4) main- 

 taining water circulation. A shore protection project involving detached 

 breakwaters necessarily requires consideration of a large number of parame- 

 ters. These factors must be identified and their relationship to the functio- 

 ning of a detached breakwater design understood to properly examine break- 

 waters as one of the alternatives in the planning process for shore protec- 

 tion. Numerical models developed to simulate shoreline change have proven to 

 be a powerful tool for planning in the coastal zone, in particular, for 

 evaluating the functioning of alternative designs of protective coastal 

 structures and beach nourishment (Kraus 1989). Inclusion of wave transmission 

 further enhances usefulness of these models. 



Detached breakwaters do have disadvantages which must be considered in the 

 evaluation of alternative shore protection plans. These are mainly (1) the 

 relatively high construction cost, (2) loss of beach area to direct wave 

 action, as required for surfing (although the shadow zone does provide a calm 

 bathing area for weak swimmers, such as children), (3) to some, the unaesthet- 

 ic interruption of the ocean view, and (4) the complexity of determining the 

 appropriate design to obtain a properly functioning breakwater system. To 

 reduce construction costs and to control shoreline impacts, detached break- 

 waters can be built with low crest heights and permeable cores. Other advan- 

 tages accrue from use of low and porous breakwaters, including reduction of 

 wave force on the structure (implying lower maintenance cost) and improved 

 water circulation. 



In order to estimate the impacts of detached breakwaters, wave transmis- 

 sion must be taken into account in most situations of practical interest. 

 This paper has demonstrated the newly developed capability to model the 

 effects of wave transmission together with the other major factors necessary 

 to arrive at comprehensive and quantitative estimates of the functioning of 

 detached breakwaters for shore protection. Tests of the transmission 

 algorithm gave intuitively reasonable results, and the shoreline change model 



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