their reliability and limitations throughout the design process. A number of 

 the relationships that were evaluated are presented herein. Rosati (1990) 

 presents additional evaluations and provides correlation coefficients for the 

 various comparisons. Parameter definitions are provided in Appendix A. 



Prediction of shoreline response. The most investigated effect of 

 detached breakwaters is the relationship between project accretion, in 

 particular morphological response, and structural parameters. An evaluation 

 of these relationships showed an apparent trend in the prototype data for 

 deposition to increase as the structure length-to-distance offshore ratio 

 increases (Rosati 1990). 



Suh and Dalrymple (1987) developed the following relationship for the 

 prediction of salient length X s by combining movable-bed laboratory results 

 with prototype data: 



>ra & 



X M = X(14.8)-*-€ 



where X is defined as the breakwater segment distance from the original 

 shoreline and L is the gap distance between adjacent breakwater segments. 



Tombolos usually formed for single prototype breakwaters when 



h. ^ i.o w 



X 

 For multiple offshore breakwaters, tombolos formed when 



f^ « 0.5 (5) 



A 



For evaluation, Equation 3 was applied to all segmented projects. The 

 relationship tends to overpredict the seaward excursion of the spit for 

 themajority of prototype data evaluated, but appears to accurately predict 

 response for pocket-beach type structures with periodic tombolo formations 

 (Figure 25). 



Prediction of gap erosion. Seiji, Uda, and Tanaka (1987) give the 

 following gap erosion relationships, where gap erosion is defined as the retreat 

 of shoreline to the lee of the gap from the initial (pre-project) shoreline 

 position: 



— - < 0.8 no erosion opposite gap 



42 



(6) 



Chapter 2 Functional Design Guidance 



