Other Evaluations 



103. Recently, both Kriebel (1986) and Vellinga (1986) presented 

 additional evaluation data for their models. Kriebel, using an improved and 

 recalibrated version of the model tested here, evaluated 20 poststorm 

 Hurricane Eloise profiles from Walton County, Florida, which were deemed 

 representative of the 80 to 90 eroded profile lines available. Maximum 

 measured erosion above MSL was approximately 60 m-'/m. All 20 cases were 

 within a 40-percent margin of error, with 17 cases lying within 25 percent. 

 Dune recession tended to be underpredicted . 



104. In his dissertation, Vellinga (1986) presents comparisons for 

 three different events, including one profile from Hurricane Eloise. The 

 largest storm, the 1953 storm surge, caused an average of 90 m-'/m of erosion 

 and formed the basis for much of the development of the Vellinga and earlier 

 Dutch models. The Vellinga model estimated an average loss of 97 m^/m for 

 this event. The comparison containing the most data (58 cases) documented 

 the 1976 storm surge which produced an average loss of 32 m^/m. This overall 

 loss is well estimated by the model, though individual profile changes show 

 considerable scatter with differences up to 400 percent. Good agreement was 

 also obtained for the one profile from Hurricane Eloise. 



105. Chiu and Dean (1986) evaluated two Florida profiles eroded by 

 hurricanes using a highly simplified version of the Kriebel model (Chiu and 

 Dean 1984) and found that, even with a variability factor of 2.5, the pre- 

 dicted horizontal recession of the dune face was underestimated. 



Conclusions 



106. Based on the comparison in the above section, both the Vellinga 

 and Kriebel models have been shown to produce reasonable estimates of dune 

 erosion. The models are stable with respect to the input parameters if they 

 lie within reasonable physical limits. The Vellinga model requires a detail- 

 ed knowledge of the initial beach and offshore profile and the storm surge 

 level in order to predict storm erosion volumes and the associated poststorm 

 profiles. It can be seen from the governing equation of the Vellinga model 

 that both the predicted profile shape and offshore termination point are 

 highly dependent on the estimated deepwater significant wave height. 



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