where K 2 and K 2 are empirical coefficients, S is the ratio of the density of 

 sand to the density of water, p is the porosity of sand on the bed, and tanfl is 

 the average bottom slope from the shoreline to the depth of active longshore 

 sand transport. The coefficients Kj and K 2 are treated as model calibration 

 parameters, with K 2 on the order of 0.5 to 1.0 times Kj . Both Kj and K 2 

 control the magnitude and rate of shoreline change in the model, although the 

 importance of K 2 is apparent in the vicinity of coastal structures, where 

 diffraction produces a substantial change in breaking wave height over a short 

 longshore distance (Gravens, Kraus, and Hanson 1991). 



Capabilities. The capabilities and limitations of GENESIS Version 2.0 are 

 detailed by Gravens, Kraus, and Hanson (1991). GENESIS can simulate 

 shoreline change due to an almost arbitrary number of engineering works, 

 alone or in combination: detached breakwaters, groins (T-shaped, Y-shaped, 

 and spur), jetties, seawalls, and beach fills. The model simulates sand 

 bypassing around groins and jetties, and has the capability to simulate 

 diffraction and wave transmission at groins, jetties, and detached breakwaters. 

 Offshore waves may be input with arbitrary height, period, and direction, and 

 may be described as multiple wave trains (as from independent sources, e.g., 

 sea and swell). Sand transport is predicted both due to oblique wave 

 incidence and longshore gradients in wave height. The model may be applied 

 to a project with wide spatial extent (from hundreds of meters to tens of 

 kilometers). 



Limitations. General shoreline change modeling assumptions as presented 

 previously limit GENESIS applicability to situations for which these 

 assumptions are reasonable representations of the project site and planned use. 

 In addition, GENESIS does not simulate wave reflection from structures. The 

 shoreline can not touch a detached breakwater; therefore, tombolo evolution at 

 detached breakwaters or a headland breakwater system can not be modeled. 

 There are minor restrictions on placement, shape, and orientation of the 

 structures, and the model does not directly provide for changing tide level. 

 GENESIS is not applicable to calculating shoreline change for situations in 

 which beach change occurs unrelated to Equation 18, such as: in the vicinity 

 of inlets or areas dominated by tidal currents; regions for which wind-driven 

 beach transport is significant; storm-induced beach change for which cross- 

 shore transport processes are dominant; and scour at structures (Hanson and 

 Kraus 1989b). 



Data requirements 



Two levels of physical data are typically required prior to conducting 

 shoreline change modeling; background information used to make an 

 assessment of coastal processes at the site on the local and regional levels, and 

 project-level information with which the model can be calibrated, verified, and 

 applied to examine future scenarios. The first level includes information 

 about regional transport rates, regional geology, water levels (typical ranges 

 and datums), and the frequency and extent of extreme events. Analysis of 



Chapter 3 Tools for Prediction of Morphologic Response 



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