c_. Representative grain size or fall velocity for the profile. 



d. Representative initial shape of the profile, including the 

 dune. 



e_. Onshore boundary condition(s) for dune erosion. 



f_. Phenoraenological calculation procedure for the cross-shore 



sediment transport rate or, alternatively, direct calculation 

 of the morphologic change of the profile based on a given 

 idealized form. 



g_. Calculation procedure for computing dune erosion that contains 

 a temporal dependence. 



h. Verification with field data over the range of conditions for 

 which the model will be applied. 



The conditions for defining a pragmatic dune erosion model are fewer and 

 considerably less rigorous compared to those defining an ideal beach profile 

 change model. 



Numerical Models of Cross-Shore Sediment Transport 

 and Beach Profile Change 



54. This subsection introduces several recent models which might be 

 considered as candidates for developing a "first principles" model of dune 

 erosion. It will be concluded that none of the models can be readily adapted 

 for immediate use as a dune erosion model. 



55. The models may be classified into one of two groups according to 

 whether they rely on basic sediment transport equations or on empirical 

 results. Models developed from relations for the cross-shore sediment 

 transport rate include those of Bailard (1981, 1982, 1983, and 1985), Bowen 

 (1980), Dally and Dean (1984), Leont'ev (1985), Moore (1982), and Yang 

 (1981). Empirically based models include those of Swart (1974, 1975, and 

 1977), Kajima et al. (1983), and Swain and Houston (1983, 1985). Three 

 models developed specifically for estimating dune erosion and profile change 

 are discussed in Part IV. 



Theoretical models 



56. The transport rate equations of Bowen (1980) and Bailard (1981, 

 1982, 1983, and 1985) are based on the energetics approach of Bagnold (1963, 

 1966). Both contain provisions to calculate bed load and suspended load 



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