During the calculation of volumetric change between two subsequent 

 profiles, based upon the application of the volumetric equivalent factor 

 to the MLW-MHW contour excursions of those profiles, an assumption of 

 self similarity in profile shape was employed. In other words, 

 volumetric changes were assumed to occur only as a result of horizontal 

 displacement of the profile and not to the redistribution of material 

 from the upper beach face offshore, a phenomenon which occurs during the 

 slope readjustment phase of the beach-fill response. Consequently, the 

 total initial volumetric loss for the fill may be slightly less than the 

 80 percent value; however, the average initial loss in beach face 

 position is still 80 percent of the fill excursion. 



The adjustment during the design phase of the project for the 

 expected sorting losses was accomplished by applying a factor known as 

 the critical ratio (or beach-fill factor) to the required volume of 

 beach fill. The critical ratio is simply an estimate of the quantity of 

 borrow material required to yield 1 cubic meter of beach material having 

 granulometric characteristics similar to the native beach. The value 

 calculated for the Banks Channel borrow site, and which was applied to 

 the Shell Island borrow material, was 2.5 (U.S. Army Engineer District, 

 Wilmington 1977). This means that 2.5 cubic meters of fill material was 

 required to produce 1 cubic meter of fill material on the beach after 

 sorting; i.e., a 60-percent sorting loss was expected. 



A modification to the original fill-factor formulation was developed 

 by James (1965) and has now been incorporated into modern beach-fill 

 design practices (U.S. Army, Corps of Engineers, Coastal Engineering 

 Research Center, 1977). Granulometric data from profiles taken in July 

 1969 just before the fill and samples taken from profiles along the fill 

 just after placement are shown in Table 20. These values were used to 

 calculate the adjusted fill factor, R^, from Figure 5.3 of the SPM. 

 The value of the adjusted fill factor was R^=3.0, which implies that 

 66 percent of the initial fill was lost to sorting. The new adjusted 

 fill factor predicted larger sorting losses than did the older formu- 

 lation; however, both methods predicted losses that were lower than that 

 measured. Assuming that these formulations are correct, then losses in 

 addition to sorting (slope readjustment, lateral spreading, etc.), are 

 significant and must be included in the beach-fill design. 



Table 20. Granulometric data for Wrightsville Beach 1970 beach fill. 



Granulometric 

 conditions 



Date 



Profile 



Composite 



mean grain 



size M 



(in phi units) 



Composite 



standard 



deviation s 



(in phiunits) 



Jefore fill 



July 1969 



WB16 

 WB29 



Prefill composite values 



1.53 

 1.52 

 1.52 



0.41 

 0.83 

 0.87 



After fill 



Aug. 19 70 



Prefill composite values 



WB13 

 WB19 

 WB25 



2.23 

 1.64 

 1.78 

 1.88 



0.49 

 0.76 

 0.83 

 0.69 



84 



