BOGUE BANKS 



AV„=-32 



-*► 415.8 

 — 98.3 



ATLANTIC 



B E = 317.5 



AV S = 140.9 



Figure 25. Weir-jetty construction sediment budget 

 for strategy 1. 



The values of the unknowns are 



Bg = 317.5 and A¥ g = +140.9 



Consequently, if this strategy is adopted, Shackleford Banks will accumulate 

 sand at the rate of 140,900 cubic yards per year, corresponding to a shoreline 

 advance of 4.7 feet per year if the sand were uniformly distributed along the 

 beach by wave action. The amount of sand to be bypassed is 317,500 cubic 

 yards per year, a relatively large volume. The volume of sand that must be 

 bypassed under strategy 1 may exceed the ability of the waves to redistribute 

 it along the downdrift beach, which could cause problems in identifying needed 

 disposal areas. 



b. Strategy 2 . A second strategy (Fig. 26) might be to limit downdrift 

 beach losses to those resulting from sea level rise so that A¥- is fixed at 

 -33,000 cubic yards per year. The Bogue Banks equation is then 



415.8 (gain from west) - 98.3 (loss to east) - 32 (lost offshore) 



" \ = A ^B 

 and the Shackleford Banks equation becomes 



Bg - 223.0 (loss to east) + 79.4 (gain from east) 



- 33 (lost offshore) = -33 (net volume lost) 



with the solution 



Bg = 143.6 and AV B = +141.9 



The amount of sand to be bypassed is small but the updrift beach adjacent to 

 the weir will accumulate 141,900 cubic yards of sand per year and cause a sea- 

 ward movement of the beach at a minimum rate of 3.9 feet per year if the sand 

 were spread uniformly along Bogue Banks. Localized areas of accretion could 

 advance faster. It is doubtful whether a weir jetty can operate according to 



45 



