0.5 m relative to the surge level. The model does not predict 

 berm recovery. 



f. Because the model is based on an assumed equilibrium of the 

 poststorm shape, the rate of transport is not directly 

 specified. Conservation of sediment is satisfied by requiring 

 that deposition balance erosion. 



g_. An equilibrium profile is computed under the assumption of a 

 5-hr storm surge duration. Longer durations are treated 

 indirectly. This approach correctly assumes that most of the 

 upper beach and dune erosion takes place during the time of 

 peak surge. 



h. The shape of the poststorm profile has been verified by model 

 tests at a number of different scales and for field profiles 

 recorded after the Dutch storm surge of 1953 (Vellinga 1983b). 

 Sargent and Birkemeier (1985) have also demonstrated 

 applicability of the model for modeling erosion caused by 

 minor storms in the United States. 



74. Although the Vellinga model lacks a detailed description of 

 sediment transport and is limited to cross-shore transport on sandy beaches 

 with dunes, as will be shown in Part V, it is easy to apply and does provide 

 reasonable estimates of dune erosion. Its major disadvantage for use on 

 United States' beaches is the lack of a duration factor. The method is 

 expected to underestimate dune erosion caused by long duration northeasters. 

 In addition, a poststorm profile shape of almost fixed form limits the 

 applicability of the procedure since it prevents the method from working on 

 mildly sloping (flat) beaches. (It was found to be impossible to balance the 

 erosion and deposition.) 



The Kriebel Model 



75. The Kriebel model is based on the equilibrium profile concept 

 originated by Bruun (1954) and further investigated, extended, and verified 

 by Dean (1977), Hughes (1978), Hughes and Chiu (1981), and others. The 

 equilibrium beach profile concept is discussed in Part II. The fundamental 

 assumption of the model is that the profile is shaped by uniform energy 

 dissipation per unit volume of breaking and broken waves in the surf zone. 

 By this principle, the model is limited to describing the evolution of the 

 subaqueous beach profile from the swash zone to the breaker zone (Figure 2). 



38 



