Figure 



17. Volume change in the offshore zone for the disposal 

 area and flanking northeast and southwest areas. 



occurred [^^ 690 cubic meters) . The time-sequence plots of individual profile 

 ranges showed a negligible change along the northeastwardmost range (-1+00) with 

 only a slight buildup along the adjacent range (-2+00) (Fig. 14; App. A). 



The southwest offshore zone showed a greater volume increase than the up- 

 coast zone (Fig. 17). This volume trend was partially a result of mechanical 

 placement of disposal sediment slightly beyond range -9+00. However, natural 

 buildup in this part of the offshore zone was also indicated by continued ac- 

 cretion during the postdisposal period. Although no sediment was mechanically 

 placed along range -10+00, the southwestern limit of the study area, time-se- 

 quence profiles and area calculations for those profiles showed offshore accre- 

 tion. The greater amount of offshore accretion in the southwest direction 

 rather than the northeast direction corresponds with a predominance of waves and 

 longshore currents toward the southwest during the postdisposal period. 



The offshore disposal zone was also partitioned into 30-meter-wide shore- 

 parallel subzones (Fig. 18, F to I) . As in the case of volume change for the 

 entire offshore zone (Fig. 16), all of the offshore subzones showed accretion 

 during the disposal period (mechanically placed sand), and erosion during the 

 first half of the postdisposal period and accretion in the second half of the 

 postdisposal period (natural processes). In addition, following disposal and 

 prior to the overall erosion trends, continued accretion occurred within some 

 subzones. This accretion trend continued longer for the landward subzones than 

 for the adjacent seaward subzones, resulting in a sequential offset of accretion 

 peaks (maximums) in the volume trends for adjacent subzones (Fig. 18, F to H, 

 time period 26 to 42 days). In general, the volume peaks shifted in the direc- 

 tion of increasing time for adjacent landward subzones indicating that a volume 

 of sediment, or rather, the position of maximum buildup, migrated landward with 

 time. Such a trend corresponds with onshore migration of the disposal bar form. 

 The landwardmost subzone (Fig. 18F, 30 to 42 days) showed a longer duration of 

 accretion than other subzones and was followed by a lower erosion rate. 



(3) Inshore . Volume changes for the inshore zone were similar in trend 

 to those of the offshore zone, but were of much lower magnitude and were totally 

 a response to the natural redistribution of sand (Fig. 16) . 



31 



