Between April 1948 and February 1970, the shoreline receded from the south jetty to 

 approximately 7,000 ft south. The FDEP and present study results for this period are consistent 

 in trend and direction of shoreline change. The magnitude of advance south of 7,000 ft is less for 

 the FDEP data than determined in the present study. Overall, shoreline adjustments between the 

 February 1970 and December 1993 (FDEP) and from February 1970 and May 1996 (this study) 

 show the shoreline advanced to at least 27,000 ft south of the Harbor, demonstrating the long- 

 term effectiveness of the beach fill. Shoreline change analysis for this study shows greater 

 advance, possibly caused by seasonal differences in the survey end dates (December 1993 for the 

 FDEP analysis and May 1996 for this study). Greater shoreline advance adjacent to the south 

 jetty (as shown in Figure 3 -3c for the data taken in the present study) results from beach fills that 

 occurred between December 1993 and May 1996 (Table 2-1). 



FDEP beach-profile data were also analyzed to document shoreline response between 

 September 1972 and February 1998 (see Appendix F for description of the available USACE and 

 FDEP survey data). Because historical shoreline-position data are collected differently than 



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beach-profde data, the different data sets were compared to determine possible inconsistencies. 

 Figure 3-4 shows potential differences that can exist between shoreline position and beach- 

 profile survey. The April 1948 and February 1970 shorelines are from NOS surveys, whereas 

 September 1972 was the first FDEP beach-profile survey. The trend of erosion and accretion to 

 approximately 27,000 ft from the south Harbor jetty is consistent between the two data sets. 

 South of this position to about 34,000 ft, the beach-profile data show recession, whereas the NOS 

 map data show advance. The difference in trends may be due in part to the different season and 

 date of termination (February 1970 versus September 1972). This comparison indicates that data 

 of the same type are desirable for increasing the confidence of calculations of shoreline change. 



To maintain consistency in comparing shoreline change between shoreline-position surveys 

 and beach-profile surveys, an elevation for the HWL was estimated from beach response 

 identified in profile surveys of beaches in the study area. Through the examination of 

 morphologic features on beach profiles, an elevation of 8.0 ft NGVD was judged to represent the 

 location of the HWL (this elevation is consistent with the design berm crest for past and planned 

 USACE beach fills (USACE 1996)). For quantifying shoreline change from beach-profile 

 surveys, the 8-ft elevation served as a surrogate for the HWL. 



From September 1972 to August 1985, sand placement on the beach south of the Harbor in 

 1974/75 advanced the shoreline an average of 95 ft within about 26,000 ft of the south jetty 

 (Figure 3-5). Between August 1985 and February 1998, the shoreline receded an average of 69 ft 

 within 17,000 ft (FDEP Monument R-19) of the south jetty, while the shoreline south of this 



See Section 2.4: Shoreline-position surveys are continuous longshore measurements of the interpreted HWL; beach- 

 profile surveys are measurements of elevation across the shore on lines from which shoreline position can be referenced to 

 MHW. 



3-8 Chapter 3 Assessment of Coastal Change 



