Bogue Sound 

 BOGUE BANKS 



: At I on 1 1 c B e 6 c h'.:-.' V\ ? .'- 



28,000 ft- 



ATLANTIC OCEAN 



Cape Lookout 



Figure 22. Conceptual layout of Bogue Banks, Beaufort 



Inlet, and Shackleford Banks, North Carolina. 



site) indicates that a volume change of about 35 cubic feet of sand on the 

 profile is needed to cause a 1-square-foot change in beach area (1-foot 

 recession along 1 foot of beach). This value will vary from site to site but 

 can be obtained from the average depth of closure of beach profiles taken at 

 various times at a given site. The shoreline recession on Shackleford Banks 

 was -8.2 feet per year, corresponding to a volume loss of -245,000 cubic yards 

 per year along the 23,000 feet of shoreline. 



Changes in sand volume on the ocean bar between 1936 and 1974 determined 

 from hydrographic surveys amounted to a total sand loss of 11,750,000 cubic 

 yards or an annual rate of -309,000 cubic yards per year. Records indicate 

 that hopper dredging removed 23,920,000 cubic yards of sand from the inlet 

 between 1936 and 1974, giving an annual loss rate of -629,000 cubic yards per 

 year. From hydrographic surveys, accumulations in the bay area behind the 

 inlet amounted to 58,000 cubic yards per year in Back Sound and 134,000 cubic 

 yards per year in Bogue Sound for a combined rate of -192,000 cubic yards per 

 year. 



Two beach nourishment projects were completed on Bogue Banks between 1936 

 and 1974; 92,800 cubic yards was placed in 1965 and 105,000 cubic yards in 

 1969. If the nourishment had been placed at a uniform rate over the 1936-74 

 period it would have averaged 5,000 cubic yards per year. Sand losses off- 

 shore are assumed to result from sea level rise and can be estimated using 

 Bruun's (1962) method (see also Weggel, 1979). For Bogue Banks, 32,000 cubic 

 yards per year is lost offshore; Shackleford Banks loses 33,000 cubic yards 

 per year. 



The amount of sand in transport along the beaches driven by wave-induced 

 longshore currents was estimated from SSMO wave data (ship observations) 

 brought from deep water to shore using a refraction analysis. The coefficient 

 of proportionality relating longshore sand transport, Q^, with longshore 

 wave energy flux factor, I '» , can be taken as one of the three unknowns 

 in the system of three simultaneous equations that result from the sediment 

 budget. All values of longshore transport can be expressed as a fraction of 

 the eastward longshore transport at the east end of Bogue Banks. A schematic 

 of the Inflow and outflow of sediments from the three elements of the sediment 

 budget is presented in Figure 23. The three unknowns defined in the figure 

 are: Q E , the eastward longshore sand transport rate at the east end of Bogue 



42 



