An engineer might be required for physical or economic reasons to 

 select a borrow source that contains more fine sediment than is expected 

 to be lost during dredging and placement, and a dike and fill approach 

 might be necessary to rebuild the beach. In this case, some of the fines 

 would still be lost during dredging but much of this material would end 

 up as beach fill. In this case, the subsamples taken from the cores should 

 include "reasonable" proportions of the fine-grained layers to reflect 

 construction procedures used. A reasonable proportion would have to be 

 determined from the engineer's experience with the equipment and techniques 

 to be used rather than from a "cookbook" on beach fill. 



4. Composite Samples . 



A wide variety of size gradations across the active beach surface can 

 be expected. Fine-grained, well-sorted sediments are typical of deepwater 

 offshore areas, whereas coarse poorly sorted, and medium- grained well- 

 sorted sediments are generally found near the plunge zone and backshore, 

 respectively. A suite of samples from a densely sampled beach profile can 

 be expected to show a nearly continuous sediment-size gradation from coars- 

 est to finest, and the frequency plot of all samples combined would plot 

 close to a straight line on log probability paper. These expectations 

 have not been proven rigorously, but practical experience has shown them 

 to be essentially true. 



The beach-fill models discussed in this study indicate that beach proc- 

 esses will actively sort and transport the various size components of a 

 fill into compatible environments. Thus, fill materials initially placed 

 on the foreshore are expected to be quickly re-distributed across the 

 entire active beach profile into a pattern as similar as possible to that 

 of the native sediments. Sediments finer than the native sediments will 

 probably be transported from the system; coarser sediments will remain 

 and somewhat modify the system. Predicting the response of a particular 

 fill involves comparing the textural properties of the native beach and 

 fill sediments and requires accurate estimates of the overall or composite 

 textural properties of these sediments. 



The easiest and probably best method of determining the composite prop- 

 erties of a representative suite of beach or borrow site samples is to total 

 the percentage of sediment in each size interval for all of the samples, 

 then divide these totals by the number of samples. This gives an average- 

 size distribution which can be plotted on log probability paper to determine 

 phi mean and phi sorting. This approach is appropriate if the suites of 

 samples are collected according to an adequately designed sampling program. 



Figure 6 qualitatively shows the formation of a composite distribution 

 from four beach sand samples collected at equal elevation intervals along 

 a profile. The actual calculations for the composite are in Table 6. The 

 coarsest, most poorly sorted sediments are found near the plunge zone (Table 

 6, sample 2) and they become finer and better sorted offshore and onshore, 

 respectively. The composite gsd is represented by the dashed curve (C in 

 Fig. 6) which is more poorly sorted than any of the individual sample 



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