2.0 METHODS 



2.1 NLDS Survey Areas 



Field operations at the New London Disposal Site were conducted aboard the M/V 

 Beavertail from 10 to 13 August 2000. An 800 x 800 m bathymetric survey centered on the 

 NL-91 and D/S Mound Complex was completed to document changes in seafloor topography 

 resulting from the recent deposition of supplemental CDM (Figure 2-1). A total of 33 lanes, 

 oriented east-west and spaced 25 m apart, were occupied over the bottom feature. In order to 

 improve the accuracy of depth difference comparisons, the August 2000 survey lanes 

 overlaid segments of the lanes established for the 1997 master survey of the site. A second, 

 independent bathymetric survey was perfomied over the Seawolf Mound using the same 

 1000 X 1000 m grid as in previous surveys (1995 through 1998; Figure 2-1). The Seawolf 

 Mound survey consisted of 41 lanes oriented north-south and spaced 25 m apart. 



Sediment-profile photography surveys were conducted to map the distribution of 

 dredged material and to evaluate benthic recolonization over the NL-91 and D/S Mound 

 Complex, as well as the Seawolf and USCGA disposal moimds, relative to three surrounding 

 reference areas (NE REF, NLON REF, and WEST REF; see Figure 1-1). Three replicate 

 images were obtained at each station to monitor long-term benthic recovery at all three mounds 

 and the distribution of recently-placed CDM at the NL-91 and D/S Mound Complex. Separate 

 sampling grids were estabhshed over each project mound (Figure 2-1; Table 2-1). 



2.2 Navigation 



During the field operations, a Trimble 4000 RSi Global Positioning System (GPS) 

 receiver interfaced with a Trimble NavBeacon XL differential receiver provided precise 

 navigation data. Becaiise of its proximity to the survey area, the U.S. Coast Guard differential 

 beacon broadcasting from Montauk Point, NY (293 kHz) was used for generating the real- 

 time differential corrections. During all survey operations, the Trimble DGPS system output 

 real-time navigation data in the horizontal control of North American Datum of 1983 (NAD 

 83; Latitude and Longitude) at a rate of once per second to an accuracy of ±3 m. 



Coastal Oceanographic's HYP ACK® survey and data acquisition software was used to 

 provide real-time interface, display, and logging of the DGPS data. Prior to field operations, 

 HYP ACK® was used to define a Universal Transverse Mercator (UTM-Zone 1 8) grid around 

 the survey area, to establish the planned sediment-profile photography stations, and to 

 construct the planned bathymetric survey lanes. During the survey operations, the incoming 

 DGPS navigation data were translated into UTM coordinates, time-tagged, and stored within 

 HYP ACK®. Depending on the type of field operation being conducted, the real-time 

 navigation information was displayed in a variety of user-defined modes within HYP ACK®. 



Monitoring Cruise at the New London Disposal Site, August 2000 



