21 



disposal at MQR, the apparent retrograde recolonization at MQR could be the a result of 

 physical disturbance. It is also possible that these results indicate that the relic dredged 

 material at these stations has inhibited extensive bioturbation activity (see Section 3.2.5.2). 

 At CLIS-88 and CLIS-89, the stations closest to the active disposal locations display recent 

 dredged material while the stations to the north and west contain relic dredged material 

 (Figure 3-9). 



3.2.3 Boundary Roughness 



High boundary roughness produced by physical processes such as erosion or 

 deposition of cohesive materials is typical of newly deposited dredged material. Old or relic 

 dredged materials, particularly on the distal parts of mound flank deposits, have low 

 boundary roughness due to "smoothing" by currents, small-scale bioturbation, and filling-in 

 of relief from natural deposition (Figure 3-8). 



3.2.3.1 Active Mounds 



Over the main REMOTS® survey grid, boundary roughness values were low with 

 most values being less than 3 cm. Only two stations had boundary roughness over 3.0 cm 

 (15 and M10). These stations were located (respectively) within 100 m of the CLIS-90 buoy 

 and CS-90-1 mounds, and it is likely that this high relief is related to the recent deposition of 

 dredged materials (Figure 3-10). Boundary roughness values at the disposal site stations 

 were not significantly different from those at the reference areas (Figure 3-11; Mann- 

 Whitney U-test, p = . 824174). 



3.2.3.2 Inactive Mounds and Reference Areas 



All of the mean boundary roughness values at CS-1, CLIS-88, CLIS-89, FVP, and 

 NHAV-74 were less than 3.0 cm. This indicates that remolding processes such as 

 hydrodynamic "smoothing", deposition, and biological reworking have reduced the high 

 relief associated with cohesive fresh dredged material at these inactive disposal mounds. At 

 MQR, the boundary roughness value was 3.0 cm at 300W due to a sloping sediment water 

 interface. Boundary roughness values at the three reference areas were all less than 2 cm 

 (Figure 3-12). 



3.2.4 Apparent RPD Depth 



3.2.4.1 Active Mounds 



In the disposal area grid, five stations had mean RPDs greater than 3 cm. Most 

 stations had RPDs that fell within the class > 1 cm and <3 cm. Where RPD depths were 



Monitoring Cruise at the Central Long Island Sound Disposal Site, June 1991 



