4.2 REMOTS® Sediment Profiling 



The previous REMOTS® survey at this area was performed 

 in January 1986; it is interesting to note that the dispersion 

 pattern of dredged material from the February 1987 survey is 

 essentially unchanged from the areal limits detected in January 

 1986, despite the additional volume of material disposed. Table 

 4-1 presents the disposal volumes of operations conducted since 

 that survey. 



The areal extent of the dredged material detected by 

 REMOTS® images (Figure 3-2) is the result of disposal operations 

 at this disposal point from November 1985, when the disposal 

 point was established, to February 1987, when this survey was 

 conducted. Newly deposited material can be distinguished from 

 "old" dredged material in REMOTS® images by comparing imaged 

 sediment with known characteristics of sediment barged to the 

 disposal site. For example, cohesive mud clasts are readily 

 distinguished in REMOTS® images (see Figure 3-4) . In addition, 

 gradients in boundary roughness, successional stage, depth of the 

 mean apparent RPD, and Organism-Sediment Indices (OSI) can be 

 used to identify freshly deposited materials. Once deposited, 

 dredged materials experience changes in mass properties, 

 chemistry, and biology; these can collectively be termed 

 "weathering" or diagenetic changes. Our experience with REMOTS® 

 mapping of recently disposed materials in Long Island Sound 

 indicates that the "weathering" process makes recently disposed 

 materials on the flanks of the disposal mounds indistinguishable 

 from "old" disposed materials within a few months when 

 depositional layers are less than 5 cm thick. The material 

 deposited at the "DGD" buoy since the last REMOTS® survey can be 

 recognized in images from the present survey; a comparison of 

 these two surveys shows the difference in dredged material 

 thickness detected (Figure 3-3) . 



Measurements of the area of seafloor covered with 

 dredged material show approximately 792,400 m 2 of bottom are 

 covered by this deposit. The REMOTS® images from approximately 

 89% of this area show dredged material in excess of the REMOTS® 

 prism penetration (maximum penetration = 20 cm) , while the 

 remaining 11% of the area shows an average dredged material 

 thickness of approximately 8 cm. By estimating a minimum 

 thickness of 20 cm of dredged material in those areas where 

 depositional layers exceed prism penetration, a conservative 

 calculation shows the estimated volume of dredged material 

 covering this area would egual approximately 147,825 m 3 . The 

 REMOTS® estimates give minimum thicknesses of approximately 2 

 cm; the "true" thickness of newly deposited material would 

 therefore fall somewhere between 20 cm (the REMOTS® detection 

 limit) and 50 cm (bathymetric detection limit for this area and 

 depth) . According to the disposal scow logs, a total volume of 



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