Summary

Introduction 1, 2
  Study Area
  Previous Studies
  Oceanography
  Seafloor Materials

K1-93 Survey
  Methods
  Scope of Work
  Navigation
  Sidescan Sonar
  Bathymetry
  Profiling

Results
  Bathymetry
  Sonar, 3.5kHz 1, 2, 3

Conclusions

Figures
  1   2   3   4   5
  6   7   8   9 10
11 12 13 14 15
16 17 18 19 20

Plate 1

Apx 1: Statistics 1
Apx 1: Statistics 2
Apx 2: Equipment 1
Apx 2: Equipment 2
Acknowledgments

References 1, 2, 3

METHODS
Throughout the remainder of this report shipboard operations from the 1993 USGS survey are reported in Julian Day and Greenwich Mean Time (JD/GMT). In some cases local time and date are also shown. The geophysical and navigational instrumentation and methods are explained in greater detail in Appendix 2.

SCOPE OF WORK
The original scope of work presented by the USGS, Branch of Pacific Marine Geology (PMG) to the COE and EPA stated that the principal objective and primary products of the acoustic survey are maps of the seafloor, including a sidescan sonar mosaic and bathymetric map. These goals were achieved; primary products include a detailed bathymetric map (Chase and others, 1994), and a sidescan sonar mosaic of the Mamala Bay seafloor that delimits the general extent of the acoustically-resolvable dredged material deposits (figures 5, 6, and plate 1). There are no major acoustic data gaps, and there now exists a firm foundation and basis for further studies. Also included as a product is a characterization of the seafloor substrate in and adjacent to the disposal sites, interpreted from 3.5 kHz high-resolution subbottom profiles.

NAVIGATION
Navigation is a critical element of any acoustic marine survey because the location of specific seafloor features imaged or profiled must be accurately known so that identical features on adjacent sidescan swaths coincide, and other data sets can be registered to the sonographic mosaic. Also, it is often necessary to reoccupy specific sites for sampling purposes.

The Global Positioning System (GPS) was used to navigate the ship during the survey, and provided nearly 24 hours per day coverage. When GPS was not in service, LORAN-C or transit satellites were used for positioning. Steering of the ship was aided by a trackline- following display on monitors located on the bridge and at the navigation station in the geophysics lab (Gann, 1992; Appendix 2). Nominal accuracy of the GPS system used is 100 m, but may be as good as 20 m (Appendix 2). Most lines were run east-west/west-east (figures 3 and 4), as we were unable to run any north-south lines owing to the northeasterly trade winds and the resulting sea state.

SIDESCAN SONAR
An EG&G Model SMS 960 Seafloor Mapping System and 59-kHz SMS 990 sidescan sonar towfish were used to obtain the plan-view image of the seafloor shown in figure 5. Specific details of the sonar system, data collection, processing, and interpretation are discussed in Appendix 2. The system was set at a 1-km swath, and sidescan tracklines were spaced 800 m apart, providing 20% overlap between adjacent swaths (figures 3 and 4). The processed mosaic is shown in figures 5, 6, and plate 1. Plate 1 is a Mercator projection at 1:40000 scale, and has a resolution of 1.3 m per pixel, and the bathymetry is taken from Chase and others (1994).