In summary, storm-induced erosion on the coast south of Canaveral Harbor is a predominantly 

 unidirectional process of beach and dune-face recession and sand volume loss, independent of 

 the Harbor. Beach erosion exposes dunes to erosion by milder storms and, if the beach narrows 

 greatly, it reduces dune buildup by wind-blown sand. The main cause of dune erosion is the 

 combined elevated water levels and higher, longer period waves accompanying storms. 



The following sections describe calculations performed to estimate erosion of beaches and 

 dunes produced by three severe storms documented to have severely impacted the Brevard 

 County coast (see Table 2-1 and Appendix C). Potential beach and dune erosion is estimated by 



25 26 



application of a numerical simulation model. ' 



3.4.1. Model Calibration 



The SBEACH model had been previously calibrated and verified in the Feasibility Report 

 (US ACE 1996) for profile lines R-124 and R-31, respectively. Pre-storm and post-storm profile- 

 survey data were available for Tropical Storm (TS) Gordon, which struck the Brevard County 

 coast in November 1994 (Table 3-4). The available data are discussed in the Feasibility Report. 

 Because periodic upgrades to SBEACH may produce slightly different final profile shapes for the 

 same input conditions, the calibration run for Profile R-124 was repeated with the newer version 

 of SBEACH (version 2.0) available for the present study. Also, the present study employed time 

 series of hourly water-level measurements made at a USACE-NOS tide gauge located at 

 St. Augustine (approximately 110 miles north of Canaveral Harbor), whereas the Feasibility 

 Report made use of an estimated water-level time series. The estimated hydrograph was based 

 on the measured peak surge elevation, surge duration, and tidal-cycle characteristics of Brevard 

 County. 



Confirmation of model operation for TS Gordon is shown in Figure 3-6, with the difference 

 between calculated profiles in the present work and the Feasibility Report. The central area of 

 interest is removal of sand and recession of the dune in the region between about 100 and 200 ft 



The terminology "potential" in the present situation refers to a beach and dune that are not armored on the dune face or at 

 the top of the dune. Armoring would reduce the actual erosion to less than the potential. The numerical model applied is 

 called SBEACH, an acronym for Storm-induced BEA ch CHanqe (Larson and Kraus 1989; Larson, Kraus, and Byrnes 

 1990). SBEACH is applied by the USACE, as well as by State agencies and private consulting companies, to estimate 

 storm-induced dune erosion for shore-protection design. 



26 



SBEACH has recently been demonstrated to perform well through comparisons of calculations against a comprehensive 

 database of measurements in the field and laboratory (Wise, Smith, and Larson 1996). Details about the model can be 

 found in the related references and in a number of other publications. The model calculates storm-induced dune and beach 

 erosion produced by elevated water levels and energetic waves. Basic inputs to the model are time series (over the 

 duration of the storm) of water level; wave height and period; initial beach profile shape; representative grain size for the 

 beach; and various coefficients controlling calibration of the model. The principal calibration parameter is called K, and it 

 and other input parameters were set to values determined in the Feasibility Report (USACE 1996). The value of K 

 determined is also the default or typical value recommended for situations where calibration data are lacking, indicating the 

 calculations were not biased. 



3-14 Chapter 3 Assessment of Coastal Change 



