Table 5. Beach 



-fill model comparisons. 



Source 



M(j) 



S<i> 



^a' 



^j' 



Native 1 - Beach 



1.83 



1.20 







(core samples) 

 Borrow 1 - Trap 



2.37 



0.93 



2.502 



1.80 



(core samples) 











Native 2 - Beach 



2.34 



0.83 







(grab samples) 

 Borrow 2 - Trap 



2.47 



0.84 



1.103 



1.20 



(grap samples) 











Native 3 - Beach 



2.34 



0,83 







(grab samples) 

 Borrow 3 - Trap 



2.37 



0.93 



1.05'+ 



0.80 



(core samples) 











^Adjusted SPM (R^) and renourishment (Rj) 

 fill factors (James, 1975). 



^Suggesting a 150-percent overfill require- 

 ment. 



^Suggesting a 10-percent overfill require- 

 ment. 



^Suggesting a 5-percent overfill require- 

 ment. 



becoming progressively finer and better sorted along the profiles from the 

 beach toward the offshore. Other significant textural patterns such as shore- 

 parallel trends or trends that vary with depth within the trapped sand were 

 not present. 



There are several ways that the textural trends described above might be 

 used. For example, the finer sands located offshore could be dredged first to 

 serve as the core of a beach fill which could then be covered and protected by 

 the coarser and more stable nearshore sands. To achieve this configuration, 

 the dredge would be moved through the trap, parallel to the beach with each 

 new cut located shoreward of the previous cut. Another dredging scheme might 

 call for shore-normal cuts in order to achieve a more homogeneous beach-fill 

 sediment by mixing offshore (finer) and nearshore (coarser) trapped sediments. 

 Or, a selective dredge and fill plan might be used so that coarser sand is 

 placed where erosion has been greatest on the downcoast beach and the finer 

 sand where the beach has been more stable. The points to be repeated here are 

 that textural patterns within this trap are both simple and significant, and 

 that these patterns could be easily exploited to plan an efficient and success- 

 ful dredge and bypass operation. 



VII, 



CONCLUSIONS 



1. The Channel Islands sediment trap functioned as designed by trapping 

 the bulk of littoral drift sediments. 



32 



