b. It is subjective and does not readily allow comparison of 

 alternative designs with quantifiable evaluations of relative 

 advantages and disadvantages. 



c. It is not systematic in that it may not include all pertinent 

 factors in an equally weighted manner. 



d. It does not allow for estimation of the functioning of novel or 

 complex designs. This is particularly true if the project is 

 built in stages separated by long time intervals. 



e. It cannot account for the time history of sand transport as 

 produced, for example, by natural variations in wave climate, 

 modifications in coastal structures, and modification in the 

 beach, as through beach nourishment or sand mining. 



f . It does not provide a methodology or criteria to optimize 

 project design. 



21. In summary, complete reliance on coastal experience means that 

 project decisions are based mainly on the judgment of the engineer and planner 

 without recourse to external and alternative evaluation procedures. Although 

 the project engineer must assume full responsibility, use of GENESIS in 

 applicable situations introduces a means to make objective assessments and 

 promotes collective analysis of the results. 



Shoreline Change Model and Capabilities 



22. Over the past decade, a powerful class of numerical models has been 

 developed that is applicable to the prediction of beach change. These models 

 are referred to as shoreline change or shoreline response models because they 

 simulate changes in position of the shoreline in response to wave action and 

 boundary conditions. The framework for shoreline change models was estab- 

 lished by Pelnard-Considere (1956), who set down the basic assumptions, 

 derived a mathematical model, and verified the solution of shoreline change at 

 a groin with laboratory experiments. Under certain assumptions (to be dis- 

 cussed) that are valid for many conditions encountered on sandy coasts, these 

 models can calculate the response of the shoreline to wave action for a wide 

 variety of engineering situations. Shoreline change models have been applied 

 in numerous projects, and their usefulness as a planning and design tool has 

 been confirmed. 



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