prior to this (1960 to 1978), approximately 1.03 million cubic 

 meters of dredged material has been deposited at Cornfield Shoals. 



2 . METHODS 



The precise navigation required for the bathymetric 

 survey was provided by the SAIC Integrated Navigation and Data 

 Acquisition System (INDAS) . A detailed description of INDAS and 

 its operation can be found in Contribution #60 (SAIC, 1986) . 

 Positions were determined to an accuracy of ±3 meters from ranges 

 provided by a Del Norte Trisponder System. Shore stations were 

 established over benchmarks at Cornfield Point and Lynde Point in 

 Old Saybrook, Connecticut. 



The depth was determined to a resolution of 0.1 feet (3.0 

 cm) using a Raytheon DE-719 Precision Survey Fathometer with a 208 

 kHz transducer. The fathometer was calibrated with a bar check at 

 fixed depths below the transducer before the survey began. A 

 Raytheon SSD-100 Digitizer was used to transmit the depth values 

 to the SAIC computer system. Forty-one survey lanes were run east 

 and west at a 25 meter lane spacing over an 1000 by 1000 meter area 

 positioned around the center of the disposal site. (The center of 

 the site serves as the target for all disposal operations.) This 

 lane spacing provides good resolution for subsequent data analysis 

 and the production of detailed depth contour charts. During 

 analysis of the bathymetric data, the raw depth values are 

 standardized to Mean Low Water by correcting for ship draft and for 

 tidal changes for the duration of the survey. 



3.0 RESULTS and DISCUSSION 



The majority of the site resides in an irregularly shaped 

 depression where depths range from approximately 49 meters in the 

 northeast corner to a maximum of 57 . 5 meters in the south central 

 area (Figure 3-1) . Visual comparison of the July 1987 survey with 

 surveys conducted on 30 July 1978 (Figures 3-2a,b) and on 27 

 January 1979 (Figure 3-3) suggests that no significant changes in 

 depth (greater than 0.5 meters) have occurred at the site. It is 

 important to note that these earlier surveys were conducted at a 

 50 meter lane spacing and with different computer and fathometer 

 systems. Because of the different foirmats used to store the 

 position and depth data for the three surveys, a direct comparison 

 could not be made. By overlaying copies of the suirvey plots that 

 were enlarged or reduced to a uniform scale, the shape and depth 

 of the contours were compared. As expected, some inconsistencies 

 did exist but the three survey plots were in good overall 

 agreement . 



A combination of factors control the accumulation of 

 dredged material at Cornfield Shoals. Because no disposal buoy is 

 deployed, dredging contractors are required to dispose at a set of 



