Moreover, the method is expected to work best with profiles similar in slope 

 to those on the Dutch coast. As pointed out by Sargent and Birkemeier 

 (1985), for much flatter slopes the predicted profile may be too steep to 

 balance the erosion and deposition. Finally, an accurate representation of 

 the offshore profile shape through the storm surf zone is required. The more 

 different the prestorm and predicted poststorm shapes are, the higher the 

 erosion. Offshore survey data, particularly through the surf zone, are 

 difficult and costly to obtain, and the dynamic nature of this zone dimin- 

 ishes the value of a single survey for long-term estimates by FEMA. Use of 

 the Vellinga model is not recommended except possibly to supplement the 

 Kriebel model for conditions suited to its range of applicability. It could 

 be particularly useful in situations where the prestorm offshore profile 

 shape is known and the surge duration is not. 



107. The Kriebel model is a more sophisticated and generalized dune 

 erosion predictive technique than the empirically based Vellinga model, 

 because it is based on a predictive transport rate formula and has a time 

 dependency. The Kriebel model requires only a schematized prestorm profile 

 (which can be obtained from measurements or calculated within the framework 

 of the model), storm surge hydrograph, and the deepwater wave height. The 

 capability to use a generalized profile shape is an advantage compatible with 

 FEMA's standardized calculation procedures because the model is relatively 

 insensitive to small changes in the beach profile that continuously occur 

 through time. In conclusion, based primarily on this ability to use a 

 schematic prestorm profile and because it is relatively insensitive to minor 

 variations in surge level, wave height, and duration, the Kriebel model is 

 recommended as being the most suitable for use by FEMA. 



64 



