10 20 30 40 50 60 70 80 

 Distance from South Jetty, ft (thousands) 



110 



Figure 3-2. Change in historical shoreline position (HWL) prior to Harbor construction. 



3.3.2. Shoreline Change after Harbor Construction (1948 to 1996) 



After Harbor construction, greater shoreline advance occurred north of the Harbor because of 

 impoundment at the north jetty. The shoreline for about 7,000 ft of coast directly south of the 

 Harbor receded as a result of this impoundment and deposition into the entrance channel. 



Change in shoreline position for the period 1948 to 1970 was evaluated using NOS data sets, 

 which were also compiled and analyzed by the FDEP. A reevaluation of the FDEP historical 

 data set was completed in the present study as a quality control and assurance procedure because 

 these data are central for determining alleged losses. A May 1996 GPS ground survey was also 

 performed in this study to evaluate cumulative shoreline changes to that date, representing the 

 "present," for regional geomorphic analysis. Figure 3-3 shows post-construction shoreline 

 response prior to and after the beach fill in 1974/75. Between April 1948 and February 1970, 

 downdrift shoreline recession occurred along a reach extending to about 7,000 ft south of the 

 Harbor. For the same period, south of this 7,000-ft reach to approximately 34,000 ft south of the 

 Harbor, the shoreline advanced about 50 ft. The change from net shoreline recession to net 

 shoreline advance determines the boundary of Harbor-induced erosion to be located within 

 7,000 ft south of the jetty. South of this location, no net adverse impacts to the beach can be 

 attributed to the Harbor for the period 1948 to 1996, because the shoreline advanced. 



The FDEP historical shoreline-position data from the 1948 and 1970 NOS data sets were obtained from the FDEP 

 Internet web site at http://www.dep.state.fl.us/. 



3-6 



Chapter 3 Assessment of Coastal Change 



