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• Profile change/beach erosion models. These are used to calculate sand 

 loss on the upper profile caused by storm surge and waves. The models 

 are one-dimensional, assuming that longshore currents are constant. 

 Extra work needs to be done to extend their use to simulate major 

 morphological features such as bars and berms. 



• Shoreline change models. These models generalize spatial and 

 temporal changes of shorelines analytically in response to a wide 

 range of beach, wave, coastal structure, initial and boundary 

 conditions. These conditions can vary with time. Because the profile 

 shape is assumed to remain constant, onshore and offshore movement of 

 any contour can be used to represent beach change. These models are 

 sometimes referred to as "one-contour line" or "one-line" models. The 

 representative contour line is usually taken to be the shoreline (which is 

 conveniently measured or available from a variety of sources). The 

 GENESIS model has been extensively used at CERC (Hansen and 

 Kraus 1989). 



• Multi-contour line / schematic three-dimensional (3-D) models. These 

 models describe the response of the bottom to waves and currents, 

 which can vary both cross- and alongshore. The fundamental 

 assumption of constant shoreline profile, necessary for the shoreline 

 change models, is relaxed. 3-D beach change models have not yet 

 reached wide application. They have been limited by their complexity 

 and their large requirements for computer resources and user expertise. 

 In addition, they are still limited by the ability to predict sediment 

 transport processes and wave climates. 



Calibration and verification. Model calibration is the procedure of repro- 

 ducing with a model the changes in the shoreline position that were measured 

 over a certain time interval. Verification refers to the application of the 

 model to reproduce beach changes over a time interval different than the one 

 used for the model's calibration. Successful verification means that the 

 model's predictions are independent of the calibration interval. However, if 

 empirical coefficients or boundary conditions change (for example, by the 

 construction of an entrance channel which interrupts sand transport) the verifi- 

 cation is no longer valid. Therefore, a modeler must be aware of any changes 

 in the physical conditions at the study site that could affect the validity of his 

 model. 



Unfortunately, in practice, data sets are usually insufficient to perform 

 rigorous calibration and verification of a model. Wave gage data are typically 

 missing, and historical shoreline change maps are usually spotty or unsuitable. 

 In situations where data are lacking, coastal experience must be relied upon to 

 provide reasonable input parameters. This underscores that considerable 

 subjectivity is part of the modeling procedure, even if the model itself may be 

 mathematically rigorous. 



Chapter 5 Analysis and Interpretation of Coastal Data 



