PART II: OVERVIEW OF BEACH CHANGE MODELS 

 Need for Models of Shoreline Change 



18. Shore protection and beach stabilization are major responsibilities 

 in the field of coastal engineering. Beach erosion, accretion, and changes in 

 the offshore bottom topography occur naturally, and engineering in the coastal 

 zone also influences sediment movement along and across the shore, altering 

 the beach plan shape and depth contours. Beach change is controlled by wind, 

 waves, current, water level, nature of the sediment (assumed here to be 

 composed primarily of sand), and its supply. These littoral constituents 

 interact as well as adjust to perturbations introduced by coastal structures, 

 beach fills, and other engineering activities. Most coastal processes and 

 responses are nonlinear and have high variability in space and time. Although 

 it is a challenging problem to predict the course of beach change, such 

 estimations must be made to design and maintain shore-protection projects. 



19. In the planning of projects located in the nearshore zone, predic- 

 tion of beach evolution with numerical models has proven to be a powerful 

 technique to assist in the selection of the most appropriate design. Models 

 provide a framework for developing problem formulation and solution state- 

 ments, for organizing the collection and analysis of data, and, importantly, 

 for efficiently evaluating alternative designs and optimizing the selected 

 design. It should be cautioned that models are tools that can be misused and 

 their correct or incorrect results misinterpreted. Ultimately, it is the 

 modeler who has responsibility for results and actions taken, not the model. 



20. Given the complexity of beach processes, efforts to predict shore- 

 line change should be firmly grounded on coastal experience, i.e., adaptation 

 and extrapolation from other projects on coasts similar to the target site. 

 However, prediction through coastal experience alone, without the support of a 

 numerical model, suffers limitations. 



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



coast and on experience with or histories of previous projects, 

 which may be limited, inapplicable, or anachronistic. Also, 

 conflicting opinions can lead to confusion and ambiguity. 



15 



