4 . DISCUSSION 



4.1 Bathymetry 



The objective of the bathymetric survey at WLIS was to 

 delineate the extent and topography of the dredged sediment deposit 

 resulting from the past year's disposal activities. The results 

 indicated a significant accumulation of dredged material at the "B" 

 mound, where the disposal buoy had been located since 1 September 

 1986. The disposed material occurred around the buoy in a broad, 

 circular deposit up to 2.0 m thick having a radius of about 100 m. 



A discrepancy of 29,472 m 3 existed between the scow log 

 volume estimate of 52,842 m 3 and the depth difference calculation 

 of 23,370 m 3 of disposed material. The scow log volume is assumed 

 to be an overestimate due to the significant amount of interstitial 

 water associated with the dredged material in the barges and the 

 self -compaction of the material after it is disposed. In addition, 

 the new material could have caused additional compaction of the 

 material disposed in earlier years. In a mass balance study in the 

 New York Bight, Tavolaro (1984) determined an apparent decrease in 

 volume of 40.7% when comparing the scow log volume and the volume 

 estimated by comparing pre- and post-disposal bathymetric surveys. 

 Applying this factor to the present data results in a corrected scow 

 log volume estimate of approximately 31,300 m 3 of dredged material. 



A comparison of the corrected scow log estimate of 31,300 

 m 3 with the depth difference calculation of 23,370 m 3 showed a 

 difference of approximately 8,000 m 3 of dredged material which could 

 not be accounted for on the bottom. Examination of the scow logs 

 from 1987 confirmed that some disposal took place up to 360 meters 

 away from the buoy, but scow log positions can be subject to a 

 number of reporting errors and are difficult to verify with 

 certainty. Disposal at such distances from the buoy would have 

 resulted in dredged material being beyond the area used to compare 

 the November 1987 and July 1988 bathymetric surveys (a 350 x 350 m 

 area around the center of the "B" mound) and therefore not 

 represented in the depth difference volume estimate. At WLIS in 

 1987 and at other DAMOS disposal sites surveyed in recent years, the 

 corrected scow log volume estimate consistently has been higher than 

 the depth difference volume estimate. This suggests that the scow 

 log volume estimate correction factor (40.7%) may require 

 re-evaluation based on a comprehensive mass balance study. 



4.2 REMOTS® Sediment-Profile Photography 



One objective of the REMOTS® survey at WLIS was to 

 delineate, in conjunction with the precision bathymetric survey, 

 the extent of dredged material deposited during the past year at 

 the "B" disposal mound. The results indicate that 



