depth near the peak of the mound on the order of 25 cm. This could 
be the result of erosion and/or consolidation. 
Volume difference calculations were performed for the 
three NLON-85 surveys to estimate the amount of material involved 
in the detected changes in bathymetry. The volume of additional 
material determined by comparison of data from the November and 
January surveys was approximately 194,000 cubic meters. Scow logs 
for this period indicated that approximately 385,710 cubic meters 
of dredged material was deposited. 
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. 
Compaction of the material on the bottom prior to the post-disposal 
bathymetric survey can also 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 reduction in volume of dredged material from 
the initial dredging to disposal (Tavolaro, 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 reduction 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 and initial self-compaction. It 
also has been estimated that approximately 7% can be attributed to 
further compaction of the material once on the bottom (Bokuniewicz 
et al., 1980). Bokuniewicz et al. determined that 50% of the total 
compaction will occur within one month of disposal and 100% within 
one year. The remaining reduction in volume is likely due to 
dredged material being deposited in thin layers that can't be 
detected acoustically. 
Correcting the scow log estimates of 385,710 m by the 
40.7% factor resulted in a volume of 228,726 m, much closer to the 
194,000 m> calculated from the survey comparison of the November 
1985 and January 1986 NLON-85 bathymetric surveys. 
Comparison of the January and July surveys revealed an 
apparent reduction in volume of approximately 17,000 cubic meters 
at the NL-85 mound. NED scow logs for this period revealed that 
an additional 5720 m* (7475 yd*) of material were dumped since 
January 1986 (28 March and 30 April 1986). To determine the 
significance of this estimated reduction in volume, the statistical 
error of this calculation was determined for the NLON-85 survey 
area. The NLON-85 survey was composed of 37 survey lanes (or rows) 
spaced 25m apart. Each lane was divided into 72 cells, each 12.5 
meters wide. This configuration represented a grid of 2664 cells, 
15 
