and New London Lighthouse. A detailed description of the navigation 

 system and its operation can be found in DAMOS Contribution #60 

 (SAIC, 1989) . 



Depths were determined to a resolution of 3.0 cm (0.1 ft) 

 using an Odum DF3200 Echotrac Survey Recorder with a narrow beam 208 

 kHz transducer. The speed of sound used in depth calculations was 

 determined from water temperature and salinity data measured by an 

 Applied Microsystems CTD probe, model STD-12. A complete 

 description of this instrument and its operations are given in DAMOS 

 Contribution #66 (SAIC, 1990) . The speed of sound determined from 

 CTD casts and the transducer depth were entered into the fathometer 

 to adjust the depth values being transmitted to the computer. 

 During analysis, raw bathymetric data were standardized to Mean Low 

 Water by correcting for changes in tidal height occurring during the 

 survey. A detailed discussion of the bathymetric analysis technique 

 is given in DAMOS Contribution #60 (SAIC, 1989) . 



3 . RESULTS 



The contour plot from analysis of the 1989 bathymetric 

 data revealed a highly variable topography of old disposal mounds 

 resulting from dredged material disposed in previous years, as well 

 as from cap material disposed at the buoy location (Figure 1) . The 

 clearly visible north-south contours running along the western 

 border of the survey area delimited the eastern flanks of the old 

 disposal mound NL-RELIC. The NL-III mound was seen along the 

 southern border of the survey area. The western flanks of the NL-II 

 mound were also shown on the eastern limits of the survey area. 

 Changes in topography resulting from capping material deposition 

 were indicated by comparison of this contour plot with the results 

 of the October 1988 post-disposal survey (Figure 2) . 



Most of the capping material was evident in the area to 

 the southeast of the buoy. At roughly 150 m south of the buoy, the 

 cap layer showed a minimum depth of 14.8 m, in comparison to the 

 1988 minimum depth of 15.5 m at this location. Another topographic 

 high of 15.6 m was detected 140 m southeast of the buoy in the 1989 

 contour plot, 0.6 m higher than the 16.2 m shown at this location 

 in the 1988 contour plot. While this capping layer was relatively 

 steep-sided in parts, it showed several isolated topographic highs. 

 This reflected both the areal extent of the underlying disposal 

 mound as well as a spatial variation in cap thickness ranging from 

 10 to 70 cm. It should be noted that in 1988 the western part of 

 NL-II showed a minimum elevation of 15.5 m, whereas in 1989 the very 

 western part of the mound showed a minimum elevation of 15.2 m. 

 This indicated an extension of the cap layer to the edge of NL-II 

 with a thickness of approximately 30 cm in this area. 



