Finally, complete reliance on coastal experience places full responsi- 

 bility of project decisions on the judgment of the engineer and planner 

 without recourse to external and alternative procedures. 

 Beach Change Numerical Models 



The capabilities of the various types of beach change numerical models are 

 compared in this section. Fig. 1 extends and updates the classification 

 scheme of Kraus (1983) for comparing models of beach evolution by their 

 spatial and temporal domains of applicability. The domains were estimated by 

 consideration of model characteristics, accuracy, and computation costs. The 

 ranges of these domains will expand as knowledge of coastal sediment processes 

 improves, models are improved and refined, wave and beach topography data 

 become more abundant, numerical schemes become optimized, and computer costs 

 decrease. The remainder of this section will discuss the capabilities and 

 limitations of the classes of models compared in Fig. 1. 

 Analytical models of shoreline change 



Analytical models are closed-form mathematical solutions of a simplified 

 differential equation for shoreline change derived under assumptions of steady 

 wave conditions, idealized initial shoreline and structure positions, and 

 simplified boundary conditions. Longshore sand transport is represented, 

 whereas cross-shore transport is omitted, yielding a 1-dimensional (ID) model. 

 Because of the many simplifications needed to obtain closed-form solutions, 

 particularly the assumption of constant waves, analytical models are usually 

 too crude for use in design. Analytical solutions serve as a means to examine 

 trends in shoreline change and to investigate basic dependencies of the change 

 on waves and initial and boundary conditions. Larson, Hanson, and Kraus 

 (1987) give a survey of more than 25 new and previously derived analytical 

 solutions of the shoreline change equation. 

 Profile change / beach erosion models 



Beach erosion models calculate sand loss on the upper profile resulting 

 from storm surge and waves (Kriebel 1982, Kriebel and Dean 1985, Larson 1988, 

 Scheffner 1988, 1989). This ID model is simplified by omitting longshore sand 

 transport processes, i.e., constancy in longshore processes is assumed, so 

 that only one profile at a time along the coast is treated. Although such 



