34 



3.4 Side-Scan Sonar 



Side-scan sonar data were used to remotely characterize the entire southern region 

 of the PDS seafloor during the February 1996 baseline survey. The high resolution side- 

 scan sonar survey was performed concurrently with the bathy metric data collection efforts. 

 The side-scan sonar survey lanes were spaced at 100 m intervals, and the towfish altitude 

 was controlled to insure 150 percent bottom coverage over the expanded February 1996 

 survey area. Acoustic signals at a frequency of 100 kHz were emitted from two 

 transducers mounted in a Klein 422S dual-frequency (100 kHz and 500 kHz) towfish. The 

 acoustic returns were relayed to a Klein 595 side-scan sonar data recorder and thermal 

 printer to produce images of the bottom features at PDS. 



3.5 Photography 



3.5.1 REMOTS® Sediment-Profile Photography 



For the Portland Disposal Site Capping Demonstration Project, the REMOTS® 

 sediment-profile photography supplemented the bathymetric data, minimizing the 

 limitations of single-beam bathymetry over PDS. The REMOTS® camera provided 

 undisturbed profile images of the top 20 cm of sediment to obtain information on the 

 physical and biological composition at the sediment- water interface (Figure 3-3). For the 

 capping project, REMOTS® photography was primarily used to map the distribution of 

 dredged material layers over the Royal River Project Area, measuring thin sediment strata 

 as part of the baseline, pseudo-UDM, and CDM stages of mound development. 



A Benthos® Model 373 1 sediment-profile camera was used to sample the surficial 

 sediment layers and track the distribution of dredged material within the Royal River 

 Project Area. Cross-sectional photographs were collected for detailed analysis and 

 intercomparison of a variety of physical characteristics. A series of 33 REMOTS® camera 

 stations were established over the project area and occupied during three of the four PDS 

 surveys (February 1996 baseline, pseudo-UDM, and CDM). Three replicate photographs 

 were taken within a 20 m radius of each target REMOTS® camera station. 



The REMOTS® sampling grid over the Royal River Project Area was designed to 

 form a modified star-shaped pattern, radiating from the PDA 95 and PDA 96 disposal 

 buoy positions (Figure 3-4). The sampling scheme was established with respect to the 

 bathymetric features of the 800 m x 800 m project area and remained constant throughout 

 the demonstration project distributed within the likely pattern of dredged material 

 accumulation (Table 3-1). 



The Portland Disposal Site Capping Demonstration Project, 1995-1997 



