potential beach, fill. The Lockwood's Folly Inlet sediments are not in- 

 cluded here because of the small volume available. 

 2. Composite Distributions . 



The procedure for obtaining the composite gsd for sediments from the 

 native beach and for the two potential borrow sites consisted of: (a) 

 obtaining averaged frequency distributions for the set of samples from each 

 profile or core (Table B-l); (b) calculating the three composite distribu- 

 tions by averaging the distributions from Table B-l (a, b, and c, respec- 

 tively); (c) plotting these composite averages as cumulative frequencies 

 on phi probability paper (Fig. B-2); and (d) using equations (3) and (4) 

 from the text for calculating the phi mean and phi sorting values and using 

 percentile data obtained directly from the plots. 



a. Native Beach . Seventeen surface samples were collected from across 

 each of 10 profiles spaced at approximately 6,000-foot (1,829 meters) inter- 

 vals along the study beach (Fig. B-l). Profiles 120 and 180 were located 

 west of the project area in order to include sediments being introduced 

 into the area from updrift sources. Samples were collected at specific 

 elevations across the profiles starting from the berm out to an offshore 

 depth of -32 feet (-9.8 meters) MSL. For this example, the -24-foot 



(-7.3 meters) depth is used to define the margin of the active profile; 

 thus, 130 sample-size distributions were averaged to obtain the native 

 beach composite distribution (Table B-l, a). 



b. Middle Ground Shoal . This area contains the coarsest materials of 

 all potential borrow sites investigated. Six cores from within the area 

 plus four cores obtained nearby (Fig. B-l) were used to collect 98 samples 

 to determine the composite-size distribution (Table B-l,b). 



c. Yellow Banks . This area (Fig. B-l, area A) has high topographic 

 relief (+30 to 50 feet MSL) and consists of ancient beach deposits and 

 spoil material dredged from the Atlantic Intracoastal Waterway (AIWW) . 



The composite distribution (Fig. B-2) was calculated by averaging the sized 

 data from 108 samples (Tables B-l,c) taken from 11 cores. 



3. Beach-Fill Calculations and Discussion . 



Table B-2 summarizes the comparison of native beach sediments with 

 the composite grain-size characteristics of the two potential borrow sites, 

 using the adjusted SPM fill factor (R^) and the renourishment (FU) models 

 as determined graphically from Figures 9 and 10. A third factor, G, is 

 also given where, 



G = ^Sd XR ^ • ^ 



This factor is used in the original GDM to adjust for the proportion of 

 clay contained in the sediments at each borrow site. These fine sediments 

 were judged dynamically unstable in the beach environment and would be lost 

 during dredging and placement or soon after placement. 



48 



