41 



4.0 DISCUSSION 



The New London Disposal Site region is in close proximity to the "dispersive" 

 Cornfield Shoals Disposal Site. A study of bottom currents in the area suggests that the 

 region near NLON has high bottom currents, averaging about 30 cm-s" 1 (DAMOS 1979). 

 Evidence of significant bottom currents initiating sediment transport at NLON was also 

 present in REMOTS® photographs. REMOTS® photographs from the reference area WREF 

 indicated that coarse/medium grained rippled sands (0-2 phi) were prevalent on the surface at 

 almost all stations (Figure 3-8). This was probably the result of active bedload transport by 

 bottom currents. The coarseness of clastic and biogenic particles in this region resulted in 

 shallow REMOTS® camera penetrations. Active bedforms (ripples) were readily apparent in 

 the eastern section of the disposal site and in a few replicate photographs obtained at NLON- 

 REF. 



4.1 Disposal Mound Topography 



An objective of the 1991 survey was to delineate the topographic relief and footprint 

 of dredged material deposited at the New London Disposal Site during 1990-1991. The 

 bathy metric survey showed a mound approximately 160 m in diameter and a minimum water 

 depth of 14.5 m (Figure 3-3). The depth difference calculation showed an increase in height 

 of 2.4 m at NL-TR over the past year (Figure 3-4). Also apparent was a smaller mound that 

 developed around the buoy and was adjacent to the NL-TR mound. This mound was 0.6 m 

 in height and approximately 110 m in diameter. The predicted height (2 m) and radius of the 

 mound (150 m) was based on a disposal simulation model for one mound. The combined 

 radius of these two mounds was approximately 150 m. However, the observed heights of the 

 two mounds from the depth difference plot were 0.6 m and 2.4 m, significantly more than 

 the predicted height of 2 m for one mound. 



Following the original deposit of material dredged from the Thames Shipyard and 

 Repair Company (TSR) in October 1988, cap material was placed from October 1988 

 through June 1990 (98,983 m 3 ), and from September 1990 through June 1991 (31,475 m 3 ), 

 prior to this survey. Cap material was placed at six separate LORAN-C locations (A-F); in 

 order to gauge the total accumulation of two years of capping, a depth difference was 

 calculated between the 1991 and the 1988 bathymetric survey conducted after disposal of 

 TSR material (Figure 4-1). This figure shows that there is at least 50 cm of cap at all 

 disposal points except for point C. Point C was selected originally as a precaution because 

 possible TSR material was detected at this location during the post-disposal survey, although 

 relatively far from the disposal buoy (150 m; Kullberg and Fredette, 1993). The calculated 

 contours of cap material are minimum thicknesses because of consolidation; actual cap 

 thicknesses are potentially 15 to 25 cm thicker because of consolidation of TSR material 

 (Brandesetal., 1991). 



Monitoring Cruise at the New London Disposal Site, June 1991 



