c. Volume Change . 



(1) General . Volume changes were examined for the offshore, inshore, 

 and beach subzones, as well as for subdivisions of each of those zones. All vol- 

 ume trends reflect sediment redistribution by natural processes with exception 

 of those for the offshore zone during the disposal period. 



(2) Offshore Subzone . Overall sediment volume in the offshore zone 

 showed a strong net increase during the disposal period, a direct result of dis- 

 posal in that zone (Fig. 16). Between 19 August and 16 September (28 days), 

 there was a large volume decrease. Placement of sediment by mechanical means 

 had ceased before that time and net volume change was entirely a result of re- 

 moval by natural processes. By 16 September, 75 percent of the 26,750-cubic 

 meter excess had been removed. As previously stated, between mid-September and 

 the end of the postdisposal period (mid-October) , there was renewed buildup in 

 the offshore zone. 



18,000 



24,000 

 22,000 



r Disposal 



I \ /■ 



\j ^ OFFSHORE / 



' \ / 



16,000 



Period 





20,000 



\ 

 1 



1 



i 

 i 

 i 



■ / 

 1/ 



14,000 

 12,000 



^10,000 



E 



a, 8,000 



E 



O 



=* 6,000 



18,000 



. 16,000 



14,000 



"^12.000 



" 10,000 



> 8,000 



4,000 



6,000 

 4,000 



^^,^^^^_^BEACH 



2,000 



2,000 



H'/^ 



. 









 -2 000 



V'' 



1 1 



— -^^.^^__ INSHORE _,,-- 



1 1 1 1 1 1 > T 



-2,000 



10 20 30 40 50 60 70 80 90 I0( 









Time (doys) 



Figure 16. Cumulative volume change through time for beach, inshore, and 



offshore zones. Each data point for Figures 17 and 18 represents 

 the "difference" in volume between the predisposal survey (19 

 July 1976) and the successive survey. 



Although the general volume trend during the disposal period was accretion, 

 the second survey within the disposal period (24 July) showed a 3,500-cubic meter 

 loss from the offshore zone and a 1,200-cubic meter loss from the inshore zone. 

 An examination of profile shapes indicated that measurement error for several 

 profiles may have been the cause of the calculated volume decrease. 



To determine the direction of net disposal sediment movement during the post- 

 disposal period, the volume change for subdivisions of the offshore zone was 

 examined. Volume change for the actual disposal zone (ranges -2+00 to -9+00) 

 versus those of the flanking northeast offshore (-1+00 and -2+00) and southwest 

 offshore (-9+00 and -10+00) zones are shown in Figure 17. The northeast offshore 

 zone showed little overall change until after 16 September when slight accretion 



30 



