31 

 4.0 DISCUSSION 



The objective of the combined REMOTS® and precision bathymetric surveys was to 

 delineate the areal extent and the height of dredged material deposits resulting from the 

 release of dredged material at CLIS since the 1988 survey. The bathymetric survey showed 

 accumulations of dredged material in the vicinity of the disposal buoys used during the 

 1988/89 and 1989/90 disposal seasons (CLIS-88, CLIS-89, and CS-90-1). The disposal 

 buoy in 1988/1989 was located approximately 100 m southwest of the CLIS-87 disposal 

 mound. As dredged material was deposited at the CLIS-88 location, it formed a mound with 

 a radius of 150 to 200 m that merged with the CLIS-87 mound. When disposal was 

 completed, a distinct peak of 4.4 m had formed at the CLIS-88 buoy location. The CLIS-87 

 disposal mound retained its 4.6 m peak. The disposal mound formed in 1989/1990 at CLIS- 

 89, northeast of CLIS-87 and CLIS-88, had a height of 3.0 m and a radius of 200 m. 



The capping operation at the CS-90-1 mound involved releasing material from the 

 Harbor Village project at the CS-90-1 buoy and capping it with material from the Branford 

 River project. The postdisposal, precapping survey in January 1990 found aim high 

 mound approximately 50 m east of the disposal buoy (Figure 4-1). Based on the distribution 

 of the Harbor Village sediments, as identified from REMOTS® photographs and bathymetry, 

 eight LORAN-C locations, A through H, were chosen as release points for cap material. 

 When the pre- and postcapping bathymetric surveys at CS-90-1 were compared, points F and 

 H were covered with a minimum of 60 cm of cap material. Between points C and D, the 

 location of the thickest dredged material base deposit, the cap thickness was also at least 

 60 cm. The remaining cap material release points appeared to have less than 20 cm of 

 accumulation (Figure 4-2). The final height of the mound formed by all disposal activity at 

 the CS-90-1 buoy was a minimum of 80 cm (Figure 3-3). The decrease in the height of the 

 mound since it was capped can be attributed to consolidation of the base and mound 

 sediments, which also contributed to underestimating cap thickness. 



With each survey, 1986, 1988, and 1990, there were depth changes of >0.20 m on 

 the flanks of the disposal mounds (Figures 3-5 and 3-6). Small, 0.20 to 0.40 m decreases in 

 water depth from 1988 to 1990 corresponded to dredged material located by the REMOTS® 

 survey south of the CLIS-88 disposal mound. Similar depth decreases between 1986 and 

 1990 may also be due to the presence of dredged material forming the flanks of the disposal 

 mound. The depth difference chart based on a comparison of 1988 and 1990 bathymetric 

 surveys had negative contours, i.e., an increase in depth of 0.20 m to greater than 0.60 m. 

 Observed depth changes greater than 0.60 m were on the edges of the CLIS-87 mound. 

 However, the rapidly sloping topography in these areas could result in inaccurate estimates of 

 differences in depth due to the actual locations of the depth transducer during the 1988 and 

 1990 surveys. Less dramatic changes in topography between 1988 and 1990 over more 

 gradually sloping bottom could be due to erosion, consolidation, and/or errors in navigation. 



Monitoring Cruise at the Central Long Island Sound Disposal Site, July 1990 



