judgment of the researcher without recourse to testing the "model" with alter- 

 nate tools. An empirical model is often necessary before choosing a numeri- 

 cal model. 



Beach change numerical models. Figure 50 summarizes the time ranges 

 and spatial coverage of numerical models used by CERC. Summaries of the 

 capabilities of the models follow: 



TIME RANGE 



HOURS 

 (ONE STORM) 



2co 

 OCT 

 TUJ 



MONTHS 

 (SEASON) 



PROFILE CHANGE MODELS 



3-D MODELS 



MULTI-CONTOUR 

 LINE MODELS 











i SHORELINE MODELS 

 : (GENESIS) 



1 II 



L.: 



ANALYTICAL 

 i MODELS 



BEACH CHANGE PREDICTION MODELS 



CLASSIFICATION BY SPATIAL AND TEMPORAL SCALES 



33 



Eos 

 P 



m 



Sl.8S 



> c CO 



JHi?8 



Figure 50. Classification of beach change models (Kraus 1989) 



• Analytical models of shoreline change. These are closed-form mathe- 

 matical solutions of simplified differential equations for shoreline 

 change derived under assumptions of steady wave conditions, idealized 

 initial shoreline and structure positions, and simple boundary conditions. 

 Because of the many simplifications needed to obtain closed-form 

 solutions, these models are too crude to use for design. 



Chapter 5 Analysis and Interpretation of Coastal Data 



121 



