(2) If the wave conditions and water level are held constant, 

 the model should allow spatially and temporally accurate 

 calculation of both erosional and depositional profiles 

 and produce an equilibrium profile shape. 



(3) The model must be verified to produce accurate results 

 for the range of conditions for which it is expected to 

 be applied. 



d. Extendability . 



(1) Since a deterministic model is not expected to be 

 practicable for field use, the developed model must be 

 compatible with stochastic or probabilistic prediction 

 procedures . 



(2) Although as a first step a monochromatic wave input is 

 expected to be adequate, refinements should include the 

 randomness of wave height, direction, and period. 



48. The deepwater wave height and wave period are usually available or 

 may be estimated with acceptable accuracy (item a(l)). It is difficult to 

 specify the beach material grain size along the profile as required by a(2). 

 The minimum requirement is knowledge of an average grain size or fall 

 velocity for the target beach. For a(3), in principle, the exact initial 

 profile is required. This information will not be available in a practical 

 situation. Either a historic profile or a representative profile shape will 

 have to be used in applications. 



49. For the offshore sediment transport boundary condition (item 

 a(4)), the work of Hallermeier (1979), as modified by Birkemeier (1985b), is 

 probably acceptable at the first stage of modeling. At present, little 

 knowledge exists to formulate a first-principles onshore boundary condition 

 (item a(5)). A rigorous onshore boundary condition will probably incorporate 

 a number of boundary conditions for the foreshore, for the berm, and for the 

 dune. For the present, simple geometrical arguments may have to be used. 



50. For item b(l), at present, accurate calculation of the 

 cross-shore current flow through the water column in the surf zone and 

 seaward of the breakers is not possible. Water levels (item b(2)) can be 

 estimated with sufficient accuracy for the purpose of a dune erosion model. 

 The requirement of valid cross-shore sediment transport rate relationships 

 for all regions along the profile (item b(3)) cannot be satisfied by any 

 single formulation or combination thereof presently available. Beach profile 

 change and the sediment transport rate are connected through a continuity 



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