Compare the above findings at the historic Brenton Reef 

 Disposal Site with those found during the 1978 study, to 

 determine the extent of physical change in the dredged 

 material deposit and to determine changes in biological 

 conditions. 



2 . METHODS 



2 . 1 Navigation 



The precise navigation required for all field operations 

 was provided by the SAIC Integrated Navigation and Data Acquisition 

 System (INDAS) . A detailed description of the INDAS system and its 

 operation can be found in DAMOS Contribution #60 (SAIC, 1989) . 

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

 provided by a Del Norte Trisponder® System. Shore stations were 

 established over known benchmarks at Point Judith and Beavertail 

 Lights. 



2 . 2 Bathymetry 



Precision bathymetric surveys were performed at each of 

 the four study areas using a Raytheon DE-719® Precision Survey 

 Fathometer with a 208 kHz transducer and a Raytheon SSD-100® 

 digitizer, as described in DAMOS Contribution #60 (SAIC, 1989) . 

 This system allows depth to be determined to a resolution of 3.0 

 centimeters (0.1 feet) with an accuracy of ±15 cm at the depths 

 encountered in this study. The fathometer was calibrated by 

 adjusting the speed of sound to the value observed on the 

 digitizer. The actual speed of sound was determined from the water 

 temperature and salinity data obtained using an Applied 

 Microsystems® CTD probe. These values were used during later 

 analysis of the bathymetric data. 



The Brenton-A survey was run northeast to southwest at 

 715 meter lane spacing with 8 lanes 8500 meters long (Figure 2-1) . 

 The Brenton-B survey was run west-southwest to east-northeast at 

 740 meter lane spacing with 7 lanes 6300 meters long (Figure 2-1) . 

 The Brenton Reef disposal site survey was run northeast to 

 southwest at 50 meter lane spacing with 49 lanes 2100 meters long 

 (Figure 2-1) . This narrower lane spacing was required for 

 comparison with the 1978 bathymetric survey. The Prudence survey 

 was run north-northeast to south-southwest at 300 meter lane 

 spacing with 4 lanes 3150 meters long (Figure 2-2) . 



During bathymetric data analysis, each survey area was 

 divided up into a number of rows and columns of cells in a matrix. 

 Each of these cells was centered along a survey lane, with 

 dimensions equal to the lane spacing in a perpendicular direction 



