14 



3.0 RESULTS 



The 2100mx2100m precision bathymetric survey at CLIS was conducted to 

 monitor changes in bottom topography and long-term stability of the sediment mounds 

 occupying the most active region of the disposal site. This survey yielded a bathymetric 

 chart of the 4.41 km^ area with a minimum depth of 15.5 m over the NHAV 74 mound 

 (Figure 3-1). A total of seventeen discrete and/or coalesced dredged material disposal 

 mounds were detected within the surveyed area. 



To improve the resolution and focus on each of the subject disposal mounds (CLIS 

 95, CLIS 94, NHAV 93, and MQR), the data collected over the 2100 m x 2100 m survey 

 area was regridded into smaller analysis areas. Depth difference calculations for apparent 

 accumulation and consolidation of dredged material were performed within the analysis 

 area for each mound. 



3.1 CLIS 95 Mound 



3.1.1 Bathymetry 



The CLIS 95 mound is a capped mound composed of an estimated barge volume of 

 66,400 m3 of dredged material (16,300 m^ UDM and 50,100 m^ CDM) deposited at the 

 CD A 95 buoy from 2 October 1995 through 4 March 1996. Based on the relatively small 

 volume of dredged material disposed, a 600 m x 600 m analysis area was defined around 

 the CDA 95 buoy position. The bathymetric chart of this smaller area displays a sediment 

 mound approximately 150 m wide along its north-south axis with a minimum depth of 

 17.25 m at the apex (Figure 3-2). 



Depth difference calculations based on comparisons with bathymetric data collected 

 at CLIS during the July 1994 survey indicate the deposition of new material succeeded in 

 forming a discrete sediment mound with a height of 3.75 m (Figures 3-3 and 3-4). The 

 CLIS 95 mound appears to be irregularly shaped along the east-west axis as a lobe of 

 material extends 110 m eastward from the base of the mound. DAMOS disposal logs 

 indicate the release of approximately 12,500 m^ of CDM 80 m to 90 m east of the disposal 

 buoy in order to achieve proper cap thickness, accounting for the irregular shape. 



A total of 28 barge loads of UDM were transported to the CDA 95 buoy and 

 deposited on the CLIS seafloor followed by 86 barge loads of CDM. Detailed analysis of 

 the disposal pattern shows a slight difference between the reported disposal position and 

 the areas of accumulation (Figure 3-5). However, this 75 m to 100 m offset can be 



Monitoring Cruise at the Central Long Island Sound Disposal Site, July 1996 



