In Case II (Table 5-1), the borrow material is also more poorly 

 sorted than the native material, but the larger part of borrow material 

 is coarser than the average grain size of the native material. Since 

 the sorting processes that modify the grain size distribution of the fill 

 material are most active on the finer size classes, much of the excess 

 coarse material included in the initial fill will remain in the stabi- 

 lized beach profile. In this case, the grain size distribution of the 

 stabilized fill is not expected to completely match that of the original 

 native sand. It is expected that part of borrow material lost from the 

 fill will be less than that calculated from R± Qy>-ij^- The computed value 

 of the critical ratio can be assumed to represent an upper bound. 



In Case IV (Table 5-1), the borrow material is finer and better sorted 

 than the native material. The equation for Ra o^^-f^ does not apply in Case 

 IV, because the equation denotes a minimum rather than a maximum in the 

 ratio of native to borrow weight proportion at the critical phi value. 

 This indicates that borrow material of this type is unsuitable as fill 

 material o The native and borrow size distributions cannot be matched 

 through selective sorting processes. The mathematics imply that none of 

 the original fill material will remain as stable fill after the initial 

 sorting. This implication is not totally realistic, and the instability 

 of borrow material of this type in a fill depends on the degree of differ- 

 ence between the average grain size of the stable and borrow materials. 

 If borrow material of this type is selected, large initial losses should 

 be expected, but no method in current use provides even a crude estimate 

 of loss. 



In Case III, borrow material is coarser and better sorted than the 

 native material. The equation for Ra cp-it does not apply for the same 

 reason it does not apply to borrow material in Case IV. Practical impli- 

 cations in Case III are the opposite of those for IV. In III, there is 

 a marked deficiency of material in the finer size classes which are more 

 responsive to the sorting processes. Hence the borrow material is stable 

 from the outset, and no significant losses are to be expected. The over- 

 fill ratio may be assvimed to be unity. If the material has a large coarse 

 fraction, foreshore slopes may be steepened enough to alter wave runup 

 and reflection and induce scour and loss of existing native material 

 fronting the toe of the coarse fill. It may also result in a beach fill 

 having profile slopes and textural properties not well suited for recrea- 

 tion. 



The engineering application of the techniques discussed above require 

 that basic sediment size data be collected in both the potential borrow 

 zones and in the project area. Estimation of the composite grain size 

 characteristics of native material should follow the guidelines set forth 

 by Krumbein (1957). The estimation of composite distribution of properties 

 of material in the borrow zone depends upon the heterogeneity of the tex- 

 tural properties in the zone. If material in the borrow zone exhibits 

 large vertical or horizontal gradients in textural properties, extensive 

 coring may be required to obtain reliable estimates of the composite 

 properties of the borrow material. Practical guidelines for reliable 



5-14 



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