all beach change occurs in the cross-shore direction. These models are 

 primarily employed to design and evaluate beach fill projects, in conjunction 

 with the shoreline change models. Shoreline response models assume that 

 longshore sediment transport is the primary long-term contributor to planform 

 response. The underlying postulation is that cross-shore movement of 

 sediment during storms equilibrates over the long term. Shoreline response 

 models are best applied to sites for which there is a clear trend in beach 

 change. Thus, shoreline change models are well-suited to predict morphologic 

 response of the beach as a function of detached breakwater design. However, 

 for those detached breakwater projects with beach fill that are intended to 

 provide storm protection, storm-induced profile change models may also be 

 applied in the design process to provide a worst-case evaluation of beach fill 

 response to extreme events. For more information on the S_torm-Induced 

 BEA ch CJHange (SBEACH) model available from CERC, see CERC (1993), 

 Larson and Kraus (1989), and Larson, Kraus, and Byrnes (1990). 



One-line or shoreline response models idealize the beach profile with an 

 average shape, which moves seaward or landward as the beach accretes or 

 erodes, respectively. The shoreline response model available from CERC, 

 GENESIS (Hanson and Kraus 1989b; Gravens, Kraus, and Hanson 1991) will 

 be discussed herein because of its wide availability and previous application to 

 detached breakwater projects. GENESIS may be obtained as an executable 

 file for personal computer (PC) use (Gravens 1992), or applied within the 

 Coastal Modeling System (CMS) documented by Cialone et al. (1992). 



By making simplifying assumptions to one-line modeling theory, analytical 

 or closed-form solutions to the mathematical models may be derived. Larson, 

 Hanson, and Kraus (1987) present more than 25 closed-form solutions for 

 predicting beach evolution and structure interaction. Included are solutions 

 for salient evolution behind a detached breakwater, and the final equilibrium 

 shoreline position. These solutions can provide a simple and economical 

 means of making a rapid qualitative evaluation of shoreline response. 



Another class of numerical model that has assisted in detached breakwater 

 design is the multi-contour line model. This type of model can describe the 

 evolution of a number of beach contours to varying waves and currents, both 

 in the longshore and cross-shore directions. These models have not yet been 

 widely applied; they require considerable modeling expertise and 

 computational capability. Of note was an application of the "N-Line Model" 

 (Perlin and Dean 1983, Scheffner and Rosati 1987, Scheffner 1988) to provide 

 qualitative results for use in functional design of the Redington Shores, 

 Florida, detached breakwater project (USAED, Jacksonville 1984). Three- 

 dimensional models are at the forefront of beach change simulation research, 

 and will eventually allow the most detailed description of nearshore evolution. 

 These models calculate sediment transport rates as a function of waves, 

 currents, and resulting changes in bathymetry at many points defined by a 

 horizontal grid. Because of their complexity, these models require detailed 

 input and calibration data sets, powerful computers for application, and 

 extensive verification and sensitivity testing (Kraus 1990). 



Chapter 3 Tools for Prediction of Morphologic Response 



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