Table B-2. Composite grain-size distribution parameters 

 and beach-fill comparisons. 





Native beach 



Middle Ground 



Yellow Banks 



Phi mean 

 Phi sorting 



V S n 



M ZT V S n 

 Pet sand 



G 

 *7 



1.90 

 0.80 



100 



1.56 

 0.98 

 1.22 



-0.42 



89 

 1.00 

 1.12 

 0.61 



1.94 

 0.72 

 0.90 

 0.05 

 95 

 1.20 

 1.26 

 1.07 



Even with adjustments, the Middle Ground sediments clearly have the 

 greatest potential as fill but as discussed earlier, other cost consider- 

 ations prevented their selection. However, the renourishment calculations 

 (Rt) predict that a fill consisting of Middle Ground sediments would last 

 nearly twice as long as Yellow Banks sediments. Thus, although a similar 

 volume of material would initially be needed from either source to obtain 

 project dimensions, the yearly renourishment requirements using the shoal 

 sediments would be significantly less (Table B-3). These relationships 

 show how the use of Middle Ground shoal sediments might become more eco- 

 nomical when renourishment considerations are included in project planning. 



Table B-3. Comparison of initial fill and 

 renourishment requirements 

 using different borrow sources, 

 Oak Island Project, North 

 Carolina. 



Source 



Initial fill 

 (yd 3 ) 



Nourishment 



per year 



(yd 3 ) 



Middle Ground 

 Yellow Banks 



10,618,946 

 11,931,400 



200,558 

 351,800 



For this particular project, the estimated mobilization-demobilization 

 expenses and cost per cubic yard of fill estimates used in the original 

 GDM favor the Yellow Banks area even when renourishment is considered. 

 However, as the use of offshore borrow sites becomes more commonplace and 

 the techniques of their exploitation better understood, the costs of off- 

 shore sediments should become more economically favorable when compared 

 with conventional sources. 



51 



