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3.2.1 Dredged Material Distribution and Physical Sediment Characteristics 



Dredged material was detected in the REMOTS® images at 15 of 22 borrow pit 

 stations (Table 3-1; Figure 3-3). The dredged material layer extended from the sediment 

 surface to below the imaging depth of the REMOTS® camera at all of these stations (i.e., 

 dredged material greater than penetration, denoted by a "greater than" sign in Table 3-1 and 

 Figure 3-3). Surface sediments considered to be ambient bottom (i.e., unaffected by 

 dredged material disposal) were observed in the replicate images at Stations lOONW, 150E, 

 150SW, 150W, and 150WN located outside or on the presumed edges of the pit (Table 3-1; 

 Figure 3-3). At Stations 150NE and 150SE, it could not be clearly determined from the 

 images whether the material present was dredged material or ambient sediment (INDET = 

 indeterminate in Table 3-1 and Figure 3-3). 



The dredged material comprising the surface sediment within the borrow pit was fine- 

 grained, composed mainly of sandy silt having a grain size major mode of >4 phi (Table 3-1; 

 Figure 3-4). At Station 150NE, a hard bottom prevented sufficient penetration of the 

 sediment profile camera. Replicate-averaged camera penetration depths for the borrow pit 

 stations ranged from 3.2 cm at Station 150E to 20.8 cm at Station 150SE, with an overall 

 average of 13.2 cm (Table 3-1). The majority of the penetration depth values were greater 

 than 10 cm, suggesting the dredged material within the pit was relatively soft. As previously 

 indicated, the soft nature of the sediment caused the replicate images at some stations to be 

 overpenetrated, obscuring the sediment-water interface and preventing the measurement of 

 key parameters (e.g., RPD, successional status, OSI, and boundary roughness). 



The average boundary roughness value for the borrow pit stations was 2.33 cm, 

 indicating a moderate amount of small-scale surface relief (Table 3-1). The irregular and/or 

 sloping small-scale topography observed at many stations was deemed to be physical in 

 nature, due to the presence of cohesive clay clumps resulting from the dredging and 

 subsequent disposal operations (Figure 3-4). There was no obvious spatial pattern in the 

 boundary roughness values across the surveyed area. A single occurrence of biogenic 

 surface roughness was due to the presence of a dense mat of tubicolous amphipods 

 {Ampelisca sp; see Figure 3-4) at station 25NE. Shells and shell hash were observed at the 

 sediment surface at several stations. 



Sediments at the reference area stations were similar to those within the borrow pit in 

 being predominantly fine-grained (major modal grain size of >4; Table 3-2 and Figure 3-5). 

 Dredged material was not observed in any of the images at the reference area stations. Mean 

 camera penetration depths ranged from 10.76 cm at Station REF4 to 14.06 cm at Station 

 REFl, with an overall average of 13 cm (Table 3-2). This is moderately deep penetration, 

 comparable to that at the borrow pit stations, which is considered typical for the soft, fine- 

 grained ambient sediment present at the reference areas. 



Monitoring Cruise at the Morris Cove Borrow Pit 



