O = (0.10 A + 20) m 3 /m (8) 



This relationship indicates that the model was developed and is most useful 

 for large storms producing above-surge level erosion quantities in excess of 

 100 m 3 /m, a relatively large quantity if compared to published data on eroded 

 volumes along United States' coasts. For example, using above-MSL 

 quantities, only one of the storms given in Table 1 caused in excess of 100 

 m 3 /m of erosion. Similarly, in reports by Balsillie (1985c, 1985d) which 

 document the effect of Hurricane Elena and a severe northeaster on the State 

 of Florida, the largest single profile change, above MSL, was 119 m^/m. Most 

 changes were considerably less, as were the above-surge changes. 

 Properties of the Vellinga model 



73. In this section the specific properties of the Vellinga model, as 

 they relate to the requirements of a dune erosion model given in Part III, 

 are addressed. 



a. Deepwater wave height is included both in the equation of the 

 predicted profile and in the offshore termination point. On 

 the basis of the model tests, wave steepness had limited 

 effect on the erosion quantity. The model is applicable for 

 wave steepnesses between 0.02 and 0.04 (Vellinga 1983). 



b. The model requires specification only of the peak surge level. 

 The time-history of the water level is not required. Wave 

 runup and setup are not included. The duration of the storm 

 is indirectly simulated. 



c_. The shape of the predicted profile is dependent on the fall 

 velocity of the median grain size; the native slope is not 

 directly included. 



d. The actual prestorm profile shape is used. This profile 



allows features such as berms and bars to be accounted for in 

 the balance between erosion and deposition. However, the 

 required specification of the true prestorm profile is a 

 disadvantage because the shape of the profile prior to the 

 100-year storm will not be known. 



e_. A realistic 1:1 slope is assumed for the eroded dune from the 

 surge level up. This slope is consistent with field measure- 

 ments of nearly vertical beach and dune scarping. The dune 

 foot is specified at the surge level, which is consistent with 

 data from Balsillie (1985a). Vellinga (1983b) indicates that 

 field data have shown variation of the dune foot from 0.5 to - 



37 



