analysis and, importantly, for efficiently evaluating alternative designs and 

 optimizing the selected design. Most of the physical factors mentioned above 

 and their interaction can be represented in numerical simulation models. 



This paper describes the use of numerical models in the planning process 

 for shore protection. It also introduces general concepts and capabilities 

 expanded upon in companion papers (Gravens 1989, Hanson, Kraus , and Nakashima 

 1989, Scheffner 1989, Larson and Kraus 1989) on models given in a special 

 session of the Coastal Zone '89 conference entitled "Shoreline Change and 

 Storm- Induced Erosion Modeling." 



TYPES OF MODELS 



Coastal Experience / Empirical Models 



The best "model" is to know the optimal project design from experience. 

 Because of the complexity of beach change, design decisions should be grounded 

 on "empirical modeling," i.e., adaptation and extrapolation from other pro- 

 jects on coasts similar to the target site. Coastal experience and under- 

 standing of coastal processes (waves, currents, sediment transport) and 

 geomorphology are essential. However, prediction through coastal experience 

 without the support of an objective, quantitative tool, such as a numerical 

 model, has limitations: 



a. It relies on the judgment of specialists familiar with specific 

 regions of the coast and on experience with previous projects, which 

 may be limited, inapplicable, or anachronistic. 



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

 designs with quantifiable evaluations of relative advantages and 

 disadvantages. Also, conflicting opinions can lead to confusion and 

 ambiguity. 



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

 in an equitable manner. 



d. It does not allow for estimation of the functioning of new, 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 variations in wave climate, modifications to coastal 

 structures, and modification of the beach. 



f . It does not provide a methodology and criteria to optimize project 

 design. 



