3.0 RESULTS 



3.1 Bathymetry 



3.1.1 Cape Cod Canal Disposal Site 



Analysis of the predisposal bathymetry at the CCDS revealed a portion of 

 what appeared to be an historical disposal mound in the northeast corner of the 

 survey grid (Figure 3-1). The postdisposal CCDS survey was extended 300 m 

 eastward in order to delineate more clearly the boundary of this mound (Figure 3-2). 

 Postdisposal analysis indicated the minimum depth of this mound was 19.3 m, 

 approximately 4 m in height compared to ambient water depths of 23 m. 



All analyses of depth differences between pre- and postdisposal surveys were 

 calculated using only that 1200 x 1200 m region which was included in both pre- 

 and postdisposal survey grids. The depth difference contour plot (Figure 3-3) 

 indicated that the majority of the dredged material was deposited within a 300 m 

 radius of the "CCD" buoy, with the greatest change in depth occurring approximately 

 150 m southwest of the buoy. At this point, predisposal survey depths of 22.8 m 

 were reduced to a depth of 21.8 m in the postdisposal survey, indicating a maximum 

 detected thickness of deposited material of 1.0 m. The broadest region of 

 accumulation was evident within 100 m north of the buoy. Depth decreased 0.7 m, 

 from 23.3 m in the predisposal survey to 22.6 m in the postdisposal survey. 



Comparison of the depth matrices from the pre- and postdisposal bathymetric 

 surveys resulted in a volume calculation of 21,823 m s with 95% confidence limits of 

 10,739 and 32,908 m ! . Examination of barge logs indicated that an estimated 15,296 

 m 5 of material were deposited at this site during the time between the two surveys. 



3.1.2 Springhill Beach Site 



Analyses of pre- and postdisposal depth contour plots of the Springhill Beach 

 Site (Figures 3-4 and 3-5, respectively) indicated a natural shoaling within the survey 

 area from 12.0 m offshore to 1.0 m near-shore. The postdisposal contour plot 

 revealed several areas where disposal activities created shoals. In these areas the 

 depth was reduced from 5.5 m to 3.5 m after disposal. Most of these shoal areas 

 occurred along lanes 16 and 19 of the bathymetric survey grid, north of the buoy 

 positions (Figure 3-6). 



These discrete shoals appear clearly on the depth difference plot (Figure 3-7). 

 The shallowest area resulting from disposal occurred approximately 600 meters from 

 the western end of lane 16 (Figure 3-6) where the depth was 2.8 m (MLW). This 

 represents a depth difference of 2.2 meters from the pre- to postdisposal survey. The 

 other significant depth differences were 2.3, 2.1, and 2.2 m (Figure 3-7). 



Monitoring Cruise at the Cape Cod Canal Disposal Site and Springhill Beach Site 



