28 



although they were collected during the first two weeks of disposal at B, were not reported 

 (Bohlen et al. 1992), and possible water column transport of this material could not be 

 determined. 



The REMOTS® survey conducted at the completion of the North Cove dredging 

 project substantiated the accumulation of fine-grained dredged material near buoy B (Figure 

 3-8), and provided additional evidence for active bedload transport of sands near buoy A. 

 As in previous REMOTS® surveys at dredged material disposal mounds (e.g., Germano et 

 al. 1994) the areal extent of dredged material detected by REMOTS® was greater than that 

 detected acoustically. Unlike more quiescent disposal sites, the REMOTS® stations at CSDS 

 detected a layer of sand over the dredged material that, in general, increased in thickness 

 with increasing distance from the mound center (Figure 3-12). The detection of fresh fine- 

 grained dredged material with no sand layer at the buoy location, surrounded by REMOTS® 

 stations where a layer of sand was over the mud, indicated that the sand had moved over the 

 finer grained dredged material after the dredged material was deposited. This process would 

 tend to reduce the rate of dispersion of fine-grained materials deposited at the site. 



The sand seen in the REMOTS® photographs, whether dredged material was detected 

 beneath it or not, was either fine-grained with sand ripples or coarser grained with shell 

 fragments. The stations with fine-grained sand were concentrated in the south central or 

 deeper areas of the REMOTS® grid and showed well-developed sand ripples approximately 

 1.5 to 3.0 cm high. The coarser grained sands with shell fragments and pebbles on the 

 surface were located on the shallower slope in the northern portion of the survey area. The 

 areas covered by shell fragments and pebbles are examples of lag deposits where the fine 

 material has been winnowed away. Once the shell fragments and pebbles are left behind, 

 biota, particularly hydroids, begin to grow in the area (Fenster et al. 1990). The presence of 

 these two sedimentary types is indicative of areas that are accumulating or transporting 

 sediment (where there is sand over mud and/or sand ripples) and areas that have been 

 winnowed or eroded (where there are shell fragments and pebbles). 



This visual information, combined with measured current and suspended sediment 

 records, supports the conclusion that CSDS experiences active bedload transport that is 

 apparently dependent on local topography and the nature of materials introduced to the site. 

 Further investigations could clarify whether the accumulation of materials is dependent on the 

 type of dredging (mechanical or hydraulic) or grain size. These results could then be 

 incorporated into future monitoring plans for CSDS. 



Synthesis of Monitoring Surveys at the Cornfield Shoals Disposal Site, July 1991 to May 1992 



