4 . DISCUSSION 



4 . 1 Bathymetry 



Results of the bathymetric surveys conducted at the 

 WLIS disposal site indicate that dredged material is accumulating 

 at the designated disposal point between mounds "A" and "C". The 

 volume of deposited dredged material estimated from scow logs was 

 73,230 m 3 . The volume difference calculated from the bathymetric 

 surveys in October 1985 and August 1986 was 35,700 ± 6720 m 3 , or 

 49% of the scow log estimate. The difference in the two 

 estimates is partially due to the overestimates from scow logs 

 due to unknown amounts of water in the scow. In addition, 

 dredged material at the flanks of the mound can occur in thin 

 layers that are undetectable acoustically. Finally, compaction 

 of the material on the bottom prior to the post-disposal 

 bathymetric survey can significantly affect the estimate of the 

 volume of deposited material. 



A study was conducted by the New York District of the 

 Corps of Engineers in 1980 at the Mud Dump Site in the New York 

 Bight to determine the loss of dredged material from the initial 

 dredging to disposal (Tavalaro, 1983) . A comparison of carefully 

 determined volumes of dredged material in the scows with the 

 volume of material deposited at the disposal site, determined by 

 pre- and post-disposal bathymetric surveys, indicated a loss in 

 volume of approximately 40.7%. Of this total, a volume loss of 

 15.4% was attributed to the dispersal of interstitial water 

 during descent. It also has been estimated that approximately 7% 

 can be attributed to compaction of the material once on the 

 bottom (Bokuniewicz et al . , 1980). Bokuniewicz et al. has 

 determined that 50% of the total compaction will occur within one 

 month of disposal and 100% within one year. Of the total loss in 

 volume of 40.7% determined at the Mud Dump Site, approximately 

 18.3% (or 40.7% - 15.4% - 7%) of the loss in volume was 

 unaccountable. This loss is likely due to dredged material being 

 deposited in thin layers that can't be detected acoustically. 



4.2 REMOTS® Sediment-Profiling 



The major objectives of the present REMOTS® survey were 

 to document the distribution of dredged material in the WLIS 

 survey area and to document the process of recolonization on the 

 new and existing disposal mounds. As observed in the surveys 

 conducted in 1985, dredged material was widespread in the 

 surveyed area (Figure 3-6) . Dredged material layers were 

 distinct and relatively thick, often consisting of coarse-grained 

 sediments, in the eastern portion of the survey area and 

 apparently represent materials deposited at the present disposal 

 point since the last complete REMOTS® survey in August 1985. 

 This dredged material may extend somewhat east and northeast of 

 the area surveyed. However, because the survey area was 



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