offshore, at elevations above approximately 4 ft NGVD. The difference between the two 

 calculations is small, with the maximum departure being at one grid cell on the dune face. 



Experience with the SBEACH model, including a recent validation with a large data set (Wise, 

 Smith, and Larson 1996), indicates that calibrated model calculations have a typical accuracy of 

 about ±15% in estimating erosion volume above mean water level (in the present study, storm- 

 induced erosion landward of the MHW line was tabulated). To account for uncertainties in the 

 input data and lack of knowledge of the exact profile shape on specific dates for which information 

 is needed in this study, a total uncertainty to the erosion-model calculations of ±25% of the 

 calculated (best-estimate) value was assigned. 



20 

 15 

 10 



=^o^ 





Initial Meas. 



- 



* A 



^— — Final Meas. 





- 



{A 



M 





_ 



\\. 





: 



"*%V... 





': 







- 







1,1,1,1, 



200 



400 600 



Distance Offshore, ft 



800 



1000 



Figure 3-6. Reproduction of calibration calculation at R-124 for Tropical Storm Gordon 

 in the Feasibility Report (USACE 1996). 



Chapter 3 Assessment of Coastal Change 



3-15 



