111. The first term in Equation 2 corresponds to the "CERC formula" 

 described in the SPM (1984) and accounts for longshore sand transport produced 

 by obliquely incident breaking waves. A value of K x = 0.77 was originally 

 determined by Komar and Inman (1970) from their sand tracer experiments, using 

 rms wave height in the calculations. Kraus et al . (1982) recommended a 

 decrease from 0.77 to 0.58 on the basis of their tracer experiments. As this 

 order of magnitude for K x is well known in the literature, the standard 

 engineering quantity of significant wave height is converted to an rms value 

 by the factor 1.416 to compare values of K x determined by calibration of the 

 model. The design value of K typically lies within the range of 0.58 to 

 0.77. 



112. The second term in Equation 2 is not part of the CERC formula and 

 is used to describe the effect of another generating mechanism for longshore 

 sand transport, the longshore gradient in breaking wave height 3H b /3x . This 

 contribution to the longshore transport rate was introduced into shoreline 

 change modeling by Ozasa and Brampton (1980). The contribution arising from 

 the longshore gradient in wave height is usually much smaller than that from 

 oblique wave incidence in an open-coast situation. However, in the vicinity 

 of structures, where diffraction produces a substantial change in breaking 

 wave height over a considerable length of beach, inclusion of the second term 

 provides an improved modeling result (Kraus 1983; Kraus and Harikai 1983; 

 Mimura, Shimizu, and Horikawa 1983), accounting for the diffraction current. 



113. Although the values of K x and K 2 have been empirically esti- 

 mated, these coefficients are treated as parameters in calibration of the 

 model and will be called "transport parameters" hereafter. The transport 

 parameter K x controls the time scale of the simulated shoreline change, as 

 well as the magnitude of the longshore sand transport rate. This control of 

 the time scale and magnitude of the longshore sand transport rate is performed 

 in concert with the factor 1/(D B + D c ) appearing in Equation 1, as discussed 

 in a later section. The value of K 2 is typically 0.5 to 1.0 times that of 

 K x . It is not recommended to vary K 2 much beyond 1.0^ , as exaggerated 

 shoreline change may be calculated in the vicinity of structures and numerical 

 instability may occur. 



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