wave period. If spectral wave information is given, T is taken as the peak 

 spectral wave period; otherwise, it is the period associated with the signifi- 

 cant waves. Equation 5 was introduced by Hallermeier (1983) to estimate an 

 approximate annual limit depth of the littoral zone under extreme waves. In 

 the framework of GENESIS, D LTo is calculated at each time step from the 

 deepwater wave data and is assumed to be valid over the entire longshore 

 extent of the modeled reach. Since wave characteristics vary seasonally, this 

 definition of the maximum depth of longshore transport will reflect changes in 

 average profile shape and beach slope , as described next . 



Average profile shape and slope 



120. The shoreline change equation does not require specification of 

 the bottom profile shape since it is assumed that the profile moves parallel 

 to itself. However, to determine the location of breaking waves alongshore 

 and to calculate the average nearshore bottom slope used in the longshore 

 transport equation, a profile shape must be specified. For this purpose, the 

 equilibrium profile shape deduced by Bruun (1954) and Dean (1977) is used. 

 They demonstrated that the average profile shape for a wide variety of beaches 

 can in general be represented by the simple mathematical function 



D = Ay 2/3 (6) 



in which D is the water depth, and A is an empirical scale parameter. The 

 scale parameter A has been shown by Moore (1982) to depend on the beach 

 grain size. For use in GENESIS, the design curve for A given by Moore was 

 approximated by a series of lines given as a function of the median nearshore 

 beach grain size d 50 (d 50 expressed in mm and units of A of m 1/3 ) : 



< 0.4 

 0.22 0.4 < d 50 < 10.0 



'50/ > u 50 



,0.32 



(7) 



10.0 < d. n < 40.0 



i 50 y , j-v.v ^ u 50 



A = 0.46 (d 50 ) 0U , 40.0 < d< 



56 



