the clearly modem deposits. Whether this is a relict, possibly hyper- 

 saline lagoon, deposit or a facies of the modem sediment is unclear. 



In summary, it appears that modem and relict deposits in the study 

 area can be differentiated in most cases by bulk properties (i.e., shear 

 strength, water content, density), glauconite content, the presence or 

 absence of fauna, and in some cases by the nature of the faunal assem- 

 blage. More precise sediment age determinations will be available when 

 the results from seven radiocarbon-14 analyses are made on shells and 

 wood fragments in cores 1, 2, 4, 7, 14, and 28. 



4. Suitability of Sandfill for Beach Nourishment . 



The suitability of sand as fill material in the restoration and 

 maintenance of beaches depends on such factors as mineralogic composition, 

 transport distance from the project site, percentage of fine-grained sedi- 

 ments, means of dredging, methods of transport and placement, grain size, 

 and total grain-size distribution (degree of sorting) . The relation of 

 these factors to the total design of beach fills is discussed in Krumbein 

 and James (1965), James (1974, 1975), Dean (1974), Hobson (1977), and in 

 pages 5-9 to 5-18 of the SPM (U.S. Army, Corps of Engineers, Coastal Engi- 

 neering Research Center, 1977) . 



Borrow material should be at least the same size or, preferably, 

 slightly coarser than native material on the beach to be nourished. 

 Borrow material that is significantly finer in grain size than native 

 sand will probably be less stable than the natural material and hence 

 more easily eroded. The net effect would be an accelerated retreat of 

 the beach in an attempt to readjust nearshore profiles which would require 

 considerably larger volumes of initial fill as well as more frequent nour- 

 ishment. If the borrow sand does not have the same grain-size character- 

 istics as the native beach sand, the grain-size population of the borrow 

 sand should have a greater variation in grain size than the native beach 

 sand. However, the borrow sand should not contain large amounts of fine- 

 grained silts and clays (< 0.063 millimeter or > 4 phi) which, if placed 

 on the beach, would soon be introducted to the nearshore zone. Turbidity 

 caused by the solids could have a detrimental impact on native marine 

 fauna and also be esthetically displeasing. Borrow material should also 

 be composed of hard, chemically and physically resistant minerals (e.g., 

 quartz) which will not readily degrade in the high-energy nearshore beach- 

 dune environment . 



The grain size of native beach sand decreases from High Island west 

 to Surf side (Fig. 14), but all the beach sand is in the very fine to fine 

 grain-size range (0.063 to 0.25 millimeter, 4 to 2 phi). Most beach sand 

 is moderately sorted (0.71 to 1.0 millimeter) to very well sorted (< 0.35 

 millimeter) . Borrow material should ideally meet or exceed these size and 

 sorting criteria. 



5. Dredging Effects on the Shore . 



Another factor to be carefully evaluated when considering offshore 

 sand as a source of fill in beach nourishment is the possible effects of 



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