3.3.3. Coastal Sand-Volume Change 



Previous studies have estimated sand-volume change in the littoral zone through analysis of 

 shoreline and beach-profile change. The present study quantified regional changes in sand 

 volume by analysis of historical bathymetric data for the years 1929, 1956, and 1996, coupled 

 with shoreline-position data for 1928, 1948, and 1996. The NOS hydrographic survey of 1956 is 

 the closest survey data set available to distinguish bathymetric change before and after Harbor 

 construction (construction of the Harbor entrance was completed 1954, see Table 2-1). 



Bathymetric surfaces were generated for each time period to calculate net volume changes by 

 comparing surfaces (see Byrnes and Hiland 1995 for methods). Pre-construction (1929-1956) 

 and post-construction (1956-1996) bathymetric surveys were compared to quantify differences in 

 sand-volume change and to identify sediment transport patterns in the vicinity of Canaveral 

 Harbor. Data from the post-construction time interval provided detailed information on sand- 

 volume adjustments in the littoral zone to assess net longshore transport rates and sand-bypassing 

 requirements (from north to south at the entrance channel). Volume change for the interval 1929 

 to 1956 served as a baseline estimate of pre-construction sediment transport patterns within the 

 vicinity of the Harbor. 



Initial evaluation of volume changes from the HWL seaward to the 17-ft depth contour 

 (NGVD) south of the Harbor was complicated by beach-nourishment activities that occurred 

 between 1956 and 1996, introducing some uncertainty in formulating a sediment budget and 

 associated transport rates. A central issue of this analysis was to quantify the amount of 

 southward sand transport to estimate beach change before the Harbor was constructed. For this 

 purpose, it was determined that analysis of volume changes north of the entrance channel jetty, 

 combined with estimates of sand volumes dredged from the north side of the entrance channel, 

 would provide a direct estimate of net longshore transport rates and sand-bypassing requirements. 



Two assumptions were made in this analysis: (1) the Harbor is a total littoral barrier, and 

 (2) the rate of beach-volume adjustment prior to Harbor construction is representative of changes 

 that would have continued to beaches north of the Harbor if the Harbor had not been built. Both 



21 



assumptions are supported by long-term trends in shoreline- and bathymetric-change data sets 

 (1875/78 to 1929 and 1929 to 1956). Comparison of bathymetric surfaces for the period 1956 to 

 1996 reveals a well-defined area of accretion north of the entrance channel jetty that extends 

 about 12,000 ft to the north and offshore from the high-water shoreline to the 17-ft depth 

 contour. Total sand accumulation for this zone is 8.36 ±1.46 Mcy (the potential vertical 

 measurement error for the surface model comparison is ±1.6 ft), which includes naturally 



Analysis of historical shoreline and bathymetry data sets, as well as USACE dredging records for Port Canaveral, show 

 that the Harbor has trapped all sand transported from the north that would otherwise have reached beaches south of the 

 south Harbor entrance jetty. If the Harbor were not present, it is believed that beaches in the vicinity of the Harbor would be 

 changing similar to that found for historical trends. 



Chapter 3 Assessment of Coastal Change 3_*| -\ 



