Qinsy & Fledermaus used in a project for USACE(Savannah District), by Panamerican Consultants, Inc.

Contract No. W912HN-12-D-0016 Delivery Order No. 0014 U.S. Army Corps of Engineers Savannah District

HIGH RESOLUTION MULTIBEAM SONAR SURVEY INNER HARBOR, SAVANNAH HARBOR EXPANSION PROJECT, CHATHAM COUNTY, GEORGIA AND JASPER COUNTY, SOUTH CAROLINA

PREPARED FOR:

UNDER CONTRACT TO:

U.S. Army Corps of Engineers Savannah District

DCA/GEC A Joint Venture, LLC Jacksonville Beach, Florida

SUBMITTED BY: Panamerican Consultants, Inc. Memphis, Tennessee

REPORT OF FINDINGS MAY 2013

REPORT OF FINDINGS

HIGH RESOLUTION MULTIBEAM SONAR SURVEY INNER HARBOR, SAVANNAH HARBOR EXPANSION PROJECT, CHATHAM COUNTY, GEORGIA AND JASPER COUNTY, SOUTH CAROLINA CONTRACT NO. W912HN-12-D-0016 DELIVERY ORDER NO. 0014

PREPARED FOR:

UNDER CONTRACT TO:

U.S. Army Corps of Engineers Savannah District 100 West Oglethorpe Avenue Savannah, Georgia 31402

DCA/GEC A Joint Venture, LLC 490 Osceola Avenue Jacksonville Beach, Florida 32250

PREPARED BY:

Panamerican Consultants, Inc. 91 Tillman Street Memphis, Tennessee 38111 Panamerican Project No. 33038.MAR

AUTHORED BY: Martin Dean, Mark Lawrence, Stephen James Jr., Gordon Watts, and Mike Rice

Stephen R. James, Jr., M.A., RPA Principal Investigator

MAY 2013

ABSTRACT The U.S. Army Corps of Engineers, Savannah District is proposing to expand the Savannah Harbor Navigation Project. The expansion project will consist of deepening the existing navigation channel including Kings Island Turning Basin, eight berths at Garden City Terminal, two proposed meeting areas, and three proposed bend wideners. Consultation with the Georgia and South Carolina State Historic Preservation Offices has determined that the proposed undertaking will adversely impact the CSS Georgia shipwreck site, a National Register of Historic Places listed resource located in the Savannah River opposite Fort Jackson just downriver from the City of Savannah.

A Programmatic Agreement has been signed by U.S. Army Corps of Engineers, respective State Historic Preservation Offices, and the U.S. Navy to mitigate the impacts to the resource. To this effect, and to form a major basis for future mitigation planning of the National Register of Historic Places listed site, the U.S. Army Corps of Engineers requested that a high resolution, geo-referenced, three-dimensional plan of the wreck remains of the CSS Georgia and the surrounding environment of the Savannah River be obtained through a state-of-the-art high resolution multibeam and sidescan sonar survey. Subsequently, Panamerican Consultants, Inc. of Memphis, Tennessee, under subcontract to DCA/GEC A Joint Venture, LLC, of Jacksonville, Florida, conducted the investigation in response to the U.S. Army Corps of Engineers’ Scope of Work entitled High Resolution Multibeam Sonar Survey, Inner Harbor, Savannah Harbor Expansion Project, Chatham County, Georgia and Jasper County, South Carolina. Advanced Underwater Surveys Ltd., a Scottish-based company specializing in the survey and study of shipwrecks, performed the high-resolution multibeam sonar survey with Tidewater Atlantic Research, Inc. as subcontractors to and along with Panamerican Consultants, Inc. Dial Cordy, Inc. performed the high-resolution sidescan sonar survey.

Conducted between February 25 and March 1, 2013, the two surveys were undertaken at the same time. The two sets of data that were gathered as a result of the investigation are complimentary, both enhancing the usefulness of the other. One key aspect of the multibeam survey is the ability to use it to identify exactly where significant objects and features are on the bottom of the Savannah River, within an accuracy of a few inches (even less in some instances) and an absolute accuracy of less than 1 foot. The sidescan data, while not as accurate, allows a different view of an object not seen with the multibeam, thereby enhancing our understanding of a specific component in question.

The resultant geo-referenced site plans produced by this investigation (both the 2D Digital Terrain Model site maps and the 3D WreckSight map), as well as positioning data, afford maximum effectiveness in future mitigation planning and actual field operations. The data will be instrumental in designing the future placement of work plants on site as it relates to both functional placement, safety, and site protection (i.e., mooring, vessels, barges, and their anchors), and offers necessary information required for engineering aspects such as the size and exact location of large vessel components (i.e., Casemates) and artifacts (i.e., cannon) that will be recovered by crane. Furthermore, the maps and resultant positioning data now safely allow the mapping, recordation, and relocation by archaeological diver of any object on the riverbed, regardless of size, particularly as future diving operations on the site intend to exploit the advantages of industry-standard acoustic tracking systems for divers interfaced with the maps in real-time.

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ACKNOWLEDGEMENTS The successful completion of this project is the direct result of the input and hard work of numerous individuals. The authors would first like to thank Ms. Julie Morgan of the Savannah District U.S. Army Corps of Engineers, and Mr. Steve Dial with Dial Cordy, Inc., for allowing Panamerican Consultants, Inc. the opportunity to conduct this investigation.

The authors would also like to thank the archaeological crew who partook in this investigation.

Mr. Stephen R. James, Jr., served as the Project Manager and Principal Investigator. Dr. Gordon Watts acted as Marine Archaeologist. Mark Lawrence and Martin Dean, both with Advanced Underwater Surveys Ltd. of Scotland, directed the multibeam survey and operated all instrumentation. Mr. James Duff served to steer the boat along the survey lines during the times of multibeam data collection. David Burchard skippered the Offshore Retriever to and from the site and provided lunch during the multibeam survey days. Chris Rowland with Advanced Underwater Surveys Ltd. was responsible for the post-processing of the point cloud survey data transforming it into a 3D metrical visualization. John Anderson, also with Advanced Underwater Surveys Ltd., was responsible for embedding the 3D digital model into WreckSight software. Robert “Duke� Hunsaker with Dial Cordy, Inc. served as the boat captain for sidescan survey operations. He was assisted by Mike Rice, who, after the survey, processed the sidescan data. All are thanked for the hard work and effort that made for an extremely successful operation.

In-house Panamerican Consultants, Inc. personnel, who must be thanked for their assistance with this report production, include Kate Gilow, Office Manager, and Anna Hinnenkamp-Faulk, Editor.

Finally, the good people of Coastal Georgia are thanked for the hospitality shown to the field crew during our stay. We hope to return in the future to sample that hospitality once again.

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TABLE OF CONTENTS ABSTRACT....................................................................................................................................................................i ACKNOWLEDGEMENTS ........................................................................................................................................ ii LIST OF FIGURES .....................................................................................................................................................iv LIST OF TABLES ........................................................................................................................................................v I. INTRODUCTION ....................................................................................................................................................1 II. THE SURVEYS ......................................................................................................................................................3 HIGH-RESOLUTION MULTIBEAM SONAR SURVEY ..................................................................................................... 3 Multibeam Survey Methodology........................................................................................................................... 3 Base Station ........................................................................................................................................................................ 6 Calibration........................................................................................................................................................................... 7 Geodetics............................................................................................................................................................................. 7 Deployment......................................................................................................................................................................... 7 Coverage ........................................................................................................................................................................... 10 Post-Processing ................................................................................................................................................................. 10

Results................................................................................................................................................................. 18 Riverbed Disturbance........................................................................................................................................................ 18 Ship Structure.................................................................................................................................................................... 22 West Casemate ............................................................................................................................................................ 22 East Casemate.............................................................................................................................................................. 23 Smaller Casemate Fragment........................................................................................................................................ 23 Hawse Throat............................................................................................................................................................... 24 Propulsion ......................................................................................................................................................................... 24 Boilers.......................................................................................................................................................................... 24 Condenser .................................................................................................................................................................... 24 Steam cylinders ........................................................................................................................................................... 24 Propeller ...................................................................................................................................................................... 24 Ordnance ........................................................................................................................................................................... 25 Datum Points..................................................................................................................................................................... 25 Guide Ropes...................................................................................................................................................................... 25 Unidentified Features........................................................................................................................................................ 27

Differences Between the 2003 and 2013 Surveys............................................................................................... 27 HIGH-RESOLUTION SIDESCAN SONAR SURVEY ....................................................................................................... 30 Sidescan Sonar Survey Methodology ................................................................................................................. 30 Results................................................................................................................................................................. 35 III. CONCLUSIONS..................................................................................................................................................47 IV. REFERENCES CITED.......................................................................................................................................49 APPENDIX A: TARGET COORDINATES APPENDIX B: SURVEY LINE INFORMATION APPENDIX C: SURVEY CONTROL POINT, FORT JACKSON APPENDIX D: CALCULATED BASE STATION POSITION APPENDIX E: TOTAL PROPAGATION ERROR

iii

LIST OF FIGURES Figure 1-01. Location of the CSS Georgia wreck site.................................................................................................. 1 Figure 2-01. Diagram of equipment installation ........................................................................................................... 4 Figure 2-03. Mounting the twin GPS Novatel antennae on a cross bar at the top of the ISHAPS deployment framework............................................................................................................................................................. 4 Figure 2-04. Construction of ADUS’ ISHAPS deployment framework ........................................................................ 5 Figure 2-05. The Trimble R8 base station set up on “Fort Jackson 2000” survey control point.................................. 6 Figure 2-06. The ISHAPS deployment framework swung to the horizontal transportation position on the Offshore Retriever ............................................................................................................................................................... 8 Figure 2-07. The ISHAP deployment framework in the vertical position tied back to the vessel’s aft A-frame with ratchet cargo straps................................................................................................................................................ 8 Figure 2-08. ISHAPS deployment framework in the vertical operational/survey position .......................................... 9 Figure 2-09. Planned multibeam survey lines at the CSS Georgia wreck site and surrounding environment, overlaid on 2-D site map................................................................................................................................................... 11 Figure 2-10. Actual multibeam survey lines run at the CSS Georgia wreck site and surrounding environment, overlaid on 2-D site map .................................................................................................................................... 12 Figure 2-11. Survey visualization showing the scattered remains of CSS Georgia and numerous dredge scars....... 13 Figure 2-12. Survey visualization of a closer view of the site with color variations remains of CSS Georgia and numerous dredge scars........................................................................................................................................ 14 Figures 2-13. DTM Site map in relation to the channel location................................................................................ 15 Figures 2-14. Gridded DTM Site map ........................................................................................................................ 16 Figures 2-15. 2D screen grab of the 3D WreckSight of the total site area ................................................................. 17 Figure 2-16. Archaeological features with datum posts circled in black together with areas of post-2003 wreck damage and riverbed disturbance outlined by dotted white lines....................................................................... 19 Figure 2-17. 2003 CSS Georgia site plan ................................................................................................................... 20 Figure 2-18. Parallel grooves cutting through dredging furrows in the channel as seen in the 3D WreckSight data 21 Figure 2-19. Seabed disturbance caused by buoy ground tackle around the wreck of HMS Royal Oak in Scotland that is similar to the riverbed disturbance close to the CSS Georgia ................................................................. 21 Figure 2-20. West Casemate showing damage on its downriver end at right............................................................. 22 Figure 2-21. East Casemate showing missing section on its southern side ................................................................ 23 Figure 2-22: Propeller blade sticking up out of the riverbed as seen in the 3D WreckSight data .............................. 24 Figure 2-23: Cannon 2 as seen in the 3D WreckSight data ........................................................................................ 25 Figure 2-24. Cannon 4, a large gun tube unknown until now, was not apparent in the old or newly acquired sidescan data, only in the 3D WreckSight data................................................................................................................. 26 Figure 2-25. Guide rope between the bent Datum Pole 5 and the propeller blade as seen in the 3D WreckSight data . 27 Figure 2-26. Actual sidescan survey lines run at the CSS Georgia wreck site and surrounding environment, overlaid on aerial photograph ........................................................................................................................................... 31 Figure 2-27. Dial Cordy’s 25-foot Haley Ann employed for the sidescan sonar survey ............................................ 32 Figure 2-28. Sonar and winch array............................................................................................................................ 32 Figure 2-29. Excerpt from sonar trackline without the water column removed. Right Channel shows the West Casemate, while the Port Channel shows Cannons 2 and 3 ............................................................................... 33

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Figure 2-30. Sonar mosaic showing coverage by actual sidescan survey lines run at the CSS Georgia wreck site and surrounding environment, overlaid on aerial photograph .................................................................................. 34 Figure 2-31. Acoustic image of what is thought to represent the majority of the site ................................................ 37 Figure 2-32. Acoustic image of the West Casemate and Cannons 2 and 3 area......................................................... 38 Figure 2-33. Acoustic image of the East Casemate into the channel and just downriver........................................... 39 Figure 2-34. Acoustic image of Channel Buoy anchor area showing concentration of what appears to be railroad iron...................................................................................................................................................................... 40 Figure 2-35. Acoustic image of unknown “cylinders� in the channel just upstream from the Buoy anchor ............. 41 Figure 2-36. Acoustic image of objects on the downriver end of the site .................................................................. 42 Figure 2-37. Acoustic image of objects in the channel well on the downriver end of the site ................................... 43 Figure 2-38. A combination of the 2003 and 2013 acoustic images of the West and East Casemate portions of the site for comparative purposes ............................................................................................................................. 44 Figure 2-39. Located between the West Casemate and the Buoy anchors, Cannons 2 and 3 with their trunnions and cascabels clearly evident .................................................................................................................................... 45

LIST OF TABLES Table 2-01. Datum Coordinate Differences Recorded in 2003 and 2013................................................................... 28 Table 2-02. Comparison of 2003 and 2013 Survey Web Measurements ................................................................... 28

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Introduction

I. INTRODUCTION The U.S. Army Corps of Engineers (USACE), Savannah District is proposing to expand the Savannah Harbor Navigation Project (SHEP). The expansion project will consist of deepening the existing navigation channel including Kings Island Turning Basin, eight berths at Garden City Terminal, two proposed meeting areas, and three proposed bend wideners. Consultation with the Georgia and South Carolina State Historic Preservation Offices (SHPOs) has determined that the proposed undertaking will adversely impact the CSS Georgia shipwreck site, a National Register of Historic Places (NRHP) listed resource located in the Savannah River opposite Fort Jackson just downriver from the City of Savannah (Figure 1-01).

A Programmatic Agreement has been signed by USACE, respective state SHPOs and the U.S. Navy to mitigate the impacts to the resource. To this effect, and to form a major basis for future mitigation planning of the NRHP listed site, USACE requested that a high resolution, georeferenced, three-dimensional plan of the wreck remains of the CSS Georgia and the surrounding environment of the Savannah River be obtained through a state-of-the-art high resolution multibeam and sidescan sonar survey. The basis for future planning, information gathered as a result of this survey will help the USACE, Savannah District meet its compliance requirements in accordance with Section 106 of the National Historic Preservation Act of 1966, as amended (PL 89-665); the National Environmental Policy Act of 1969; the Archaeological Resources Protection Act of 1987 as amended; the Advisory Council on Historic Preservation Procedures for the Protection of Historic and Cultural Properties (36 CFR Part 800); and the Abandoned Shipwreck Act of 1987; USACE Regulations as identified in 33 CFR 325; and other applicable federal regulations.

Figure 1-01. Location of the CSS Georgia wreck site (base map courtesy of Google Earth).

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CSS Georgia Multibeam Survey

In order to assist the USACE, Savannah District with meeting the compliance requirements associated with the laws and regulations cited above, Panamerican Consultants, Inc. of Memphis, Tennessee (Panamerican), under subcontract to DCA/GEC A Joint Venture, LLC, of Jacksonville, Florida (DCA/GEC), conducted the investigation in response to the USACE’s Scope of Work (SOW) entitled High Resolution Multibeam Sonar Survey, Inner Harbor, Savannah Harbor Expansion Project, Chatham County, Georgia and Jasper County, South Carolina. Advanced Underwater Surveys Ltd. (ADUS), a Scottish-based company specializing in the survey and study of shipwrecks, performed the high-resolution multibeam sonar survey with Tidewater Atlantic Research, Inc. (TAR) as subcontractors to and along with Panamerican Consultants, Inc. Dial Cordy, Inc. performed the high-resolution sidescan sonar survey.

Conducted between February 25 and March 1, 2013, the two surveys were undertaken at the same time. The two sets of data that were gathered as a result of the investigation are complimentary, both enhancing the usefulness of the other. One key aspect of the multibeam survey is the ability to use it to identify exactly where significant objects and features are on the bottom of the Savannah River, within an accuracy of a few inches (even less in some instances) and an absolute accuracy of less than 1 foot. The sidescan data, while not as accurate, allows a different view of an object not seen with the multibeam, thereby enhancing our understanding of a specific component in question.

The resultant geo-referenced site plans produced by this investigation (both the 2D Digital Terrain Model [DTM] site maps and the 3D WreckSight map produced by ADUS), as well as positioning data, afford maximum effectiveness in future mitigation planning and actual field operations. The data will be instrumental in designing the future placement of work plants on site as it relates to both functional placement, safety, and site protection (i.e., mooring, vessels, barges, and their anchors), and offers necessary information required for engineering aspects such as the size and exact location of large vessel components (i.e., Casemates) and artifacts (i.e., cannon) that will be recovered by crane. Furthermore, the maps and resultant positioning data now safely allow the mapping, recordation, and relocation by archaeological diver of any object on the riverbed, regardless of size, particularly as future diving operations on the site intend to exploit the advantages of industry-standard acoustic tracking systems for divers interfaced with the maps in real-time.

The methods and findings from the investigation are presented in the following chapter. The electronic 3D WreckSight map has been submitted under separate cover.

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The Surveys

II. THE SURVEYS HIGH-RESOLUTION MULTIBEAM SONAR SURVEY ADUS undertook the high-resolution multibeam sonar survey as a subcontractor to Panamerican.

Panamerican’s marine archaeologists also participated in the ADUS survey. ADUS is a Scottishbased company specializing in the survey and study of shipwrecks using techniques developed originally to improve the effectiveness of diving operations on historic wrecks.

The company was set up by two universities and three staff members (two maritime archaeologists/geophysicists and a specialist in digital imaging) after an increasing number of requests to use their joint expertise to investigate both modern and historic wrecks. The techniques were developed through collaborative research at the University of St. Andrews and the University of Dundee for exploiting the potential of multibeam sonar to make accurate twodimensional surveys of wrecks, which could also be visualized as three-dimensional digital models. In addition to numerous historic wrecks, ADUS has also surveyed modern wrecks ranging from those that sit partially out of the water, such as the Costa Concordia in Italy, to those at depths of 5,000 feet or more, such as the Deepwater Horizon in the Gulf of Mexico.

Through experience ADUS has identified the best combination of equipment that provides the finest results, but is constantly pressuring multibeam sonar manufacturers to produce higher frequency systems to provide resolution similar to those of the high-frequency sidescan systems which only provide a visual image and not metrical data from which accurate site plans and 3D models can be made.

In conjunction with the high frequency sidescan sonar survey that was undertaken at the same time as the multibeam survey, the visualization of the two sets of data are complimentary, both enhancing the usefulness of the other. One key aspect of the multibeam survey is the ability to use it to identify exactly where significant objects and features are on the bottom of the Savannah River, within an accuracy of a few inches (even less in some instances) and an absolute accuracy of less than 1 foot. The resultant geo-referenced site plan will allow the relocation of any object on the riverbed, regardless of size, particularly if future diving operations on the site exploit the advantages of industry-standard acoustic tracking systems for divers, as planned.

The following multibeam discussion is complimented by the 3D interactive WreckSight visualization that ADUS has produced of the CSS Georgia site and that has been submitted as a separate deliverable (see below).

MULTIBEAM SURVEY METHODOLOGY A Reson SeaBat 7125 SV2 multibeam sonar with a 71p processor was employed for the survey of the CSS Georgia and was operated at a frequency of 400 kilohertz. Data were acquired on a separate acquisition PC using QPS QINSy v.8 software. Figure 2-01 shows a schematic diagram of the equipment set up. The 7125 sonar head was located on the bottom of ADUS’ Independent Sonar Head Attitude and Positioning System (ISHAPS) deployment framework. The framework, comprised of four 10-foot, 18-square-inch, aluminum space-frame trusses plus the multibeam mounting bracket, totaled 41 feet in length (Figures 2-02 and 2-03).

A tightly coupled inertial/global positioning system (GPS) system (Trimble POS-MV 320) was mounted on the submersible end with an Inertial Measurement Unit (IMU) housed in an IP68 submersible housing directly above the sonar head. Twin GPS Novatel antennae were mounted on a cross bar at the top of the ISHAPS (Figure 2-02). When in operation mode, the truss is positioned vertically along side the survey vessel with approximately half the truss submerged.

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CSS Georgia Multibeam Survey

This allows for the sonar sensor to be as close to the wreck as possible, which in turn results in higher quality data.

Figure 2-01. Diagram of equipment installation.

Figure 2-03. Mounting the twin GPS Novatel antennae on a cross bar at the top of the ISHAPS deployment framework; the truss framework is in transport position.

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The Surveys

Figure 2-04. Construction of ADUS’ ISHAPS deployment framework. Sonar head is attached in foreground.

The IMU housed in an IP68 submersible housing directly above the sonar head is not visible. Note two head ropes that alleviate hydrodynamic forces acting on the structure as the vessel moved through the water.

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CSS Georgia Multibeam Survey

Base Station Real time positioning accuracy was provided by the use of Real Time Kinematics (RTKs) with a Trimble R8 base station set up in line of sight about 700 feet away on a survey control point labeled “Fort Jackson 2000” located on the moat wall of the Fort (Figure 2-05; Appendix C: Survey Control Point, Fort Jackson).

The position supplied to ADUS for the survey control point position was keyed into the base station as 1006246.89 (feet) Easting, 759271.55 (feet) Northing and +10.58 (feet) Height.

ADUS separately calculated the base station position (using Trimble’s post-processing service) as a check (Appendix D: Calculated Base Station Position). The difference between the two base station positions is not considered to be significant.

The R8 base station was configured to transmit CMR+ positional corrections utilizing its internal radio and also to log raw satellite information (as RINEX files). The CMR+ corrections were received onboard the survey vessel using a TDL 450L radio receiver and sent straight to the POS-MV as binary data to aid the positional solution derived by the POS-MV. Typically during the survey the accuracy in three dimensions provided by the POS-MV was rarely greater than 3 centimeters.

Figure 2-05. The Trimble R8 base station set up on “Fort Jackson 2000” survey control point. ADUS’ Mark Lawrence is programming the unit. Note lead weight belts employed to anchor the base station in place.

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The Surveys

Calibration Some specific survey lines over the wreck were undertaken for calibration purposes. Given the nature of the ADUS ISHAPS system and its construction, there is limited scope for sensor misalignment with respect to the IMU in terms of roll and pitch. There is, however, a greater chance that yaw (i.e., heading) is apparent after installation of the sonar head and IMU. Selected survey lines over the CSS Georgia were used during post-processing to assess roll, pitch, and, most importantly, yaw. Lines covering the same targets, but undertaken in different directions and offsets, allowed calibration to be achieved with the following applied to all data collected: • • •

Roll: + 0.1 degrees Pitch: 0.0 degrees Yaw: -1.5 degrees

In addition a full GPS Azimuth Measurement Subsystem (GAMS), calibration was undertaken for the POS-MV. GAMS is a unique feature of the POS-MV that allows the system to achieve exceptional accuracy in the measurement of heading. The GAMS uses the two GPS receivers on the top cross bar of the ISHAPS to determine a GPS-based heading that is accurate to 0.02° or better using the 2-meter cross bar as the antenna baseline, when blended with the inertial navigation solution. POS-MV uses this heading information as aiding data together with the position, velocity, and raw observation information supplied by the primary GPS receiver.

Geodetics In the Qinsy database setup for the survey, all data was acquired utilizing NAD 83 State Plane (Georgia East) with units set as US Survey Feet for Eastings, Northings, and Heights. Heights acquired during the survey were relative to the GRS 80 Ellipsoid (foundation for NAD 83); these heights were then offset during post-processing by 96.44 feet to bring them in line with the MLLW Epoch 1983–2001.

Deployment The ISHAPS framework was deployed from the starboard quarter of the 40-foot survey vessel Offshore Retriever. It was pivoted on a thwart-ship steel pipe extended out beyond the gunnel so that the ISHAPS could be rotated to a horizontal position for transport (Figure 2-06) and to vertical for survey (Figure 2-07).

Once in the vertical position it was tied back to the vessel with ratchet cargo straps while the strain from hydrodynamic forces acting on the structure as the vessel moved through the water was alleviated by two head ropes, one running from close to the sonar head and another 10 feet higher, both forward to the bow (Figures 2-07 and 2-08).

Sound velocity was constantly monitored at the sonar head with a Valeport MiniSVS sound velocity probe, while additional measurements were taken through the water column with a DigiBar Pro SVP system at appropriate times during the survey. As the sonar was deep in the water column, the sound velocity measured at the head was more important and more reliable than the full water column measurements where there were significant sound speed differences were between the upper and lower levels on every cast.

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CSS Georgia Multibeam Survey

Figure 2-06. The ISHAPS deployment framework swung to the horizontal transportation position on the Offshore Retriever. Seen on the end of the truss system is the multibeam sonar head.

Figure 2-07. The ISHAP deployment framework in the vertical position tied back to the vessel’s aft A-frame with ratchet cargo straps. Wood block served to keep framework vertical. This system worked exceedingly well with no truss movement even in the swiftly flowing current against the forward motion of the vessel.

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The Surveys

Figure 2-08. ISHAPS deployment framework in the vertical operational/survey position. Shown are the twin Novatel antennae mounted at the top of the 40-foot framework. They are approximately 22 feet above the river surface and above all upper deck structures that might interfere with antenna reception. Sonar head is on the opposite end of the truss 18 feet below water surface, which equates to approximately 14 to 22 feet above the wreck site depending on tide. Note steel pipe that framework pivots on, as well as tightening ratchet straps. Head rope tie-off is bottom center.

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CSS Georgia Multibeam Survey

Coverage Planned survey transects were produced and a 700-x-300-foot area of riverbed was systematically covered (Figures 2-09 and 2-10) with more or less parallel and overlapping lines running roughly ESE–WNW, running into current wherever possible to reduce the speed over the ground to increase data density and so improve data resolution. Two sets of survey lines in this general direction were undertaken with both the maximum 140O swath angle and then a narrow 90O angle to increase data density. A single set of survey lines were also undertaken aligned approximately WNW–ESE at a 120O swath angle (Appendix B: Survey Line Information).

The port channel (wreck) marker buoy was close to the wreck (70 feet south of the West Casemate) and within the distribution of material that runs south from it. The strong currents that often prevailed over the site made maneuvering the vessel close to the buoy problematic and so additional short survey tracks had to be undertaken to fill areas were data could not safely be collected during the systematic parallel runs.

Post-Processing Although some initial removal of ‘fliers’ and other unwanted sonar responses within the data was acquired on site with Qinsy software, most editing was carried out by ADUS staff in Scotland using Fledermaus software. The edited files were then manually inspected using Trimble Terramodel software to identify the most useful survey files for 3D visualization and also to identify all the important targets visible in the data. A list of significant targets was then produced together with their key attributes (Appendix A: Target Coordinates). Simultaneously, all the survey lines were assessed for suitability for 3D visualization of the site using AutoDesk Maya software and a core of the most useful of these were chosen for use in the final 3D visualization. Parts of additional lines were then used to fill in shadows or other areas that needed clarification or additional detail.

The next stage was the color ramping of the various features in the combined data set. Targets at different orientations were ramped with appropriate orientations rather than the conventional horizontal ramping used in bathymetric surveys. Significant targets were also colored differently to make them stand out from the background riverbed. At this stage, a complex of occlusion objects were inserted in some of the larger targets and also beneath the riverbed so that the data set, as a point cloud, was no longer transparent. This technique makes the visualized data look more solid without recourse to the normal gridding process that provides the digital terrain models (DTMs) conventionally used for seabed depiction.

Some DTM map sheets were produced of the whole site using Fledermaus v.7 because, although this software is of limited use in depicting wreck material, it is excellent for topographic detail and shows the dredging scars particularly well (Figures 2-11 and 2-12). It also allows for the plotting of other data such as grid lines and the actual channel location (i.e., toe, centerline) and District Station Points, as well as the ability to zoom in (Figures 2-13 and 2-14).

The final post-processing operation was the incorporation of the identified components of the data, together with color ramping and occlusion objects, into ADUS’ WreckSight software.

Once this was complete, it allowed forensic analysis of the final 3D data set, which provided additional and valuable information for the written report. This is underscored by the location of Cannon No. 4., a large gun tube unknown until now, it was not apparent in old sidescan data. A 2D screen grab of the 3D WreckSight of the total wreck area is shown Figure 2-15.

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Figure 2-09. Planned multibeam survey lines at the CSS Georgia wreck site and surrounding environment, overlaid on 2-D site map.

The Surveys

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Figure 2-10. Actual multibeam survey lines run at the CSS Georgia wreck site and surrounding environment, overlaid on 2-D site map. Note “hole� in center that marks location of Channel Marker buoy.

CSS Georgia Multibeam Survey

12

The Surveys

Figure 2-11. Survey visualization showing the scattered remains of CSS Georgia and numerous dredge scars. White line marks the steepest edge of the channel; the red line marks the toe or edge of the bottom cut.

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CSS Georgia Multibeam Survey

Figure 2-12. Survey visualization of a closer view of the site with color variations remains of CSS Georgia and numerous dredge scars.

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Figures 2-13. DTM Site map in relation to the channel location (i.e., toe, centerline).

The Surveys

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Figures 2-14. Gridded DTM Site map.

CSS Georgia Multibeam Survey

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Figures 2-15. 2D screen grab of the 3D WreckSight of the total site area.

The Surveys

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CSS Georgia Multibeam Survey

RESULTS Riverbed Disturbance Distinctive cutter-suction dredge scars are characterized by areas of overlapping furrows in the riverbed up to 130 feet long by about 5 feet wide and roughly 3 feet deep, with each furrow gently curving and based on a radius of approximately 400 feet. The depth differences at the edge of the channel bottom cut ranged between approximately 2 and 3 feet, except where it coincided with more aggressive dredging as indicated by the white dashed line in Figure 2-11.

The rounded ends of the furrows tend to be cut deeper at the top of the Channel with, in places, a height difference of up to 10 feet over a horizontal distance of 10 feet. This suggests considerably more sediment is removed at the end of each swing of the arc, presumably because the dredge head is more or less stationary as it slows to a stop, is moved upstream by about 5 feet before being swung in the opposite direction.

The pattern of scarring shows that some phases of dredging have severely impacted the wreck.

The most obvious shows dredge furrows butting up to the West Casemate and covering the area of unmapped debris scatter (Figure 2-16). This appears to be closer to the wreck in places than indicated on the 2003 site plan (Figure 2-17), but that is probably due to the difficulty of even observant divers noticing such features in poor visibility and strong currents. This phase of dredging probably predates the 1986 sidescan image reproduced in the 2003 report (Watts and James 2007:21 Figure 16), which shows a well-defined northern edge of the channel running close to the Casemates.

Running roughly along the line of the channel about 35 feet south of the north edge, two parallel and intermittent grooves up to 3 feet deep and about 14 feet apart run erratically for at least 280 feet, disappearing out of the eastern edge of the surveyed area (Figures 2-11 and 2-18).

These look as if they have been caused by objects being dragged across the riverbed. There are similar looking single line features elsewhere in the dredged area, so these furrows may be related to a particular activity that happens after dredging operations have taken place, such as the dragging of anchors or the ends of dredge pipes, singly or in pairs, across the bottom.

Although the dredging damage was observed in 1986 and 2003, further damage to the East and West Casemates, together with displacement of a number of substantial objects and the bending of four of the seven datum posts, all indicate that the wreck has suffered further physical interference between 2003 and 2013. In addition, there are also two distinct areas, outlined with white pecked lines in Figure 2-11, where the bottom of old dredging scars show irregular pock marks, suggesting further riverbed disturbance.

As far as we can judge there appears to be no new direct dredging damage to the site, but we suggest that there could be other possible alternative sources for post-2003 damage. Although there is no evidence from the area immediately over the wreck, it is possible that anchor or dredge-pipe drag could account for the damage. It would have to be more than one event to impact over a relatively wide area and so it would be worth investigating if the dredging operators use anchors on a short scope, or trail the ends of dredge pipes, perhaps in pairs and barely touching the bottom, when drifting down current during changes in dredging location.

Another potential source of damage is the abandonment of unwanted dredge pipes, a number of which appear to be scattered around the site. It is possible that discarded pipes could be carried in the current and cause damage to the wreck.

18

The Surveys

Figure 2-16. Archaeological features with datum posts circled in black (red if bent) together with areas of post-2003 wreck damage and riverbed disturbance outlined by dotted white lines.

19

CSS Georgia Multibeam Survey

Figure 2-17. 2003 CSS Georgia site plan (from Watts and James 2007).

20

The Surveys

Figure 2-18. Parallel grooves cutting through dredging furrows in the channel as seen in the 3D WreckSight data.

The strongest candidate for causing the recent damage is deployment and recovery of mooring blocks and/or anchors for navigation buoys. The buoy positions are not in the same locations as they were in 2003 and ADUS has seen similar seabed features where regular buoy maintenance involving the lifting and replacing of buoys has left evidence on the seabed (Figure 2-19).

Archaeological material close to where a buoy has been placed is susceptible to damage as the riser arcs around the riverbed at every change in direction of the tidal flow.

An assessment of the published buoy positions for the immediate area over the last ten years might show a correlation with the two areas of riverbed disturbance immediately to the south of the CSS Georgia wreckage. Although those responsible are unlikely to admit it, buoy recovery and deployment is not always as accurate as it should be. The evidence suggests that some of the physical damage to the wreck may well be due to anchors and/or mooring blocks being bounced over the bottom and hitting things during recovery, or being dragged into the required position during deployment.

Figure 2-19. Seabed disturbance caused by buoy ground tackle around the wreck of HMS Royal Oak in Scotland that is similar to the riverbed disturbance close to the CSS Georgia.

21

CSS Georgia Multibeam Survey

Ship Structure West Casemate A 66-foot length of coherent structure seems to include at least one gun port. It is partially overlain by dislodged railroad iron, some bent, which spread to the south, east, and north (Figures 2-16 and 2-20; Appendix A: Item 18).

Comparison with the 2003 site plan suggests that there have been changes at the extreme eastern, or downriver, end of the structure and the gun port, which is now wider, indicating that some physical damage has taken place over the last ten years. The number and orientation of the railroad iron overlying the Casemate and surrounding riverbed has also changed, but some of that may be due to the difficulty of accurately recording such information with techniques used at the time.

Figure 2-20. West Casemate showing damage on its downriver end at right. Compare to Figure 2-17 above.

22

The Surveys

East Casemate A 25-x-24-foot coherent section of Casemate survives, but a 50-square-foot triangular section that was recorded in 2003 as being adjacent to its southern edge is no longer obvious, probably due to recent damage. There are also differences in the distribution of debris, probably railroad iron, to the north and southeast. These could be due to damage, but also might reflect the different recording techniques used in 2003 and 2013 (Figures 2-16 and 2-21; Appendix A: Item 19).

Figure 2-21. East Casemate showing missing section on its southern (bottom) side. Compare to Figure 2-17 above.

Smaller Casemate Fragment A 24-x-14-foot trapezoidal section of Casemate rests at an angle of about 10O against a 4-foot high slope at the edge of the dredged channel. Although this section does not appear to have been impacted by man-made activities since 2003, there has been some slumping of sediment onto its upper surface from the bank against which it is resting (Figure 2-16, Appendix A: Item 20).

23

CSS Georgia Multibeam Survey

Hawse Throat The hawse throat, or pipe, appears to be at the location recorded in 2003, but is now lying horizontally on the seabed with the flange end to the east and not standing vertically as originally recorded (Appendix A: Item 21).

Propulsion Boilers The possible boiler (Appendix A: Item 12) indicated on the 2003 plan to the east of the small Casemate fragment is identifiable in the 2013 multibeam data in approximately the same location, but with a slightly different orientation (Figure 2-16; Appendix A: Items 12 and 13).

The large-diameter boiler indicated on the 2003 site plan within the “Unmapped Debris Scatter” is no longer there. There is now a boiler-shaped object (Appendix A: Item 13) of lesser diameter approximately 250 feet down stream of the 2003 location, roughly 100 feet due east of the small Casemate fragment. This could be the same item if the sketch measurements in 2003 were not exact. An object such as this with a large surface area could presumably have been moved by strong currents until coming to rest in a slightly deeper and more sheltered situation.

Condenser This item was recorded in the 2003 report as being next to Cannon 2 where there is now no such object. However, there is an object of roughly similar dimensions, which could be the same possible condenser, in a similar relative position to the north of Cannon 3 (Appendix A: Item 14).

Steam cylinders Two steam cylinders were recorded in the “Unmapped Debris Scatter” in 2003, but signs of them have yet to be found within the 2013 multibeam data. This suggests that they have been broken into smaller pieces, buried under disturbed sediment, or displaced some distance from their reported position. The setting and recovery of channel marker buoys is a likely candidate for their loss.

Propeller One propeller blade is clearly visible in the data sitting upright and apparently at the end of a less obvious shaft running north south (Figure 2-22; Appendix A: Items15 and 16). Although the blade appears in the sonar record to be slightly wider than that measured by divers, its shape has similarities with the drawing in the 2003 report (Watts and James 2007:43, Figure 6).

Figure 2-22: Propeller blade sticking up out of the riverbed as seen in the 3D WreckSight data.

24

The Surveys

Ordnance Cannons 1, 2, and 3 are visible in the multibeam data with trunnions discernable on Cannons 2 and 3, and the characteristic thick breech banding on Cannon 3 and the newly located Cannon 4 (Figures 2-23 and 2-24; Appendix A: Items 5, 6, 7, and 8). Cannon 1 is less distinct and appears to be partially buried at what is probably the muzzle end; it also appears to have accumulated a substantial amount of sediment along both sides.

We think the missing heavy gun referred to by Watts and James (2007) is the object 100 feet due south of the East Casemate on the edge—but in—the channel, which we have labeled Cannon 4 (Figure 2-24). It appears to be the about the right size with an identifiable cascabel shape and a wide breech band. The gun carriage head identified in the 2003 site plan has not been located in the 2013 multibeam data set.

Datum Points Three of the datum posts are still upright, but four lean between 10O and 45O, either to the east, southeast, or west. The East Casemate Datum is partially supported by the Casemate structure, above which it extends by about 3 feet (Figures 2-12, 2-16, 2-20, 2-21, and 2-37; Tables 2-01 and 2-02; Appendix A: Items 22 through 28).

Guide Ropes A guide rope (Appendix A: Item 29) left on site after the 2003 survey work can be plainly seen in the multibeam sonar record for a minimum of 108 feet running on top of the riverbed between the East Casemate, through Datum 2, to near Cannon 2. Although the rope was approximately 0.25 inches in diameter, it shows as a larger feature probably because it has accumulated sediment on either side forming a low linear mound stretching across much of the site (Figures 225 and 2-31; Appendix A: Items 29 and 30).

Another guide rope (Appendix A: Item 30) is clear of the riverbed and runs from Datum 5 to the propeller blade (Appendix A: Item 15) 8 feet away to the south.

There is another possible rope running across the seabed from close to the West Casemate Section toward the west, but it is uncertain whether this is directly related to the work on the site.

Figure 2-23: Cannon 2 as seen in the 3D WreckSight data.

25

CSS Georgia Multibeam Survey

Figure 2-24. Cannon 4, a large gun tube unknown until now, was not apparent in the old or newly acquired sidescan data, only in the 3D WreckSight data. As seen in Figure 2-15 and 2-16 above, it sits in the channel.

26

The Surveys

Figure 2-25. Guide rope between the bent Datum Pole 5 and the propeller blade as seen in the 3D WreckSight data.

Unidentified Features There are many unidentified objects and riverbed features in the vicinity of the wreck and not all have been listed in Appendix A, particularly those immediately on top or associated with the two major Casemate sections. Many look to be railroad iron either sticking out of, or resting on, the riverbed. Some of the smaller objects could be unexploded ordnances and similar items, but the resolution of the multibeam survey was not good enough for such small-scale identification.

Comparison of the unidentified objects with the 2013 very-high-resolution sidescan sonar survey would probably assist with positive identifications of targets, which now all have accurate positions.

DIFFERENCES BETWEEN THE 2003 AND 2013 SURVEYS The numerous differences between the surveys undertaken ten years apart that relied on different methodologies are not surprising. The variations can be attributed to three factors: 1) The inherent accuracy of different methodologies 2) Physical interference with site in the time between the two surveys 3) Human error It is probable that all three have some part to play and even the latest “hi-tech� method can be just as prone to human error as earlier ones, particularly in the transcription of distances and identification of features within the sonar record.

There is reasonable correlation between the coordinate positions (rounded to the nearest foot) given for seven datum positions on the site in 2003 compared to 2013, it is just that the 2003 positions trend approximately 11 feet further south east (Table 2-01). Without high end acoustic positioning it would have been very difficult in 2003 to transfer an accurate GPS position down through 50 feet of water column to a precise location underwater. The most likely explanation for the differences is that in 2013 there was the opportunity to obtain NAD 83 positions consistently and repeatedly with a significantly more accurate system of identifying coordinates of items on the riverbed.

27

CSS Georgia Multibeam Survey

Table 2-01. Datum Coordinate Differences Recorded in 2003 and 2013.* 2003 2003 2013 2013 Easting Northing Easting Northing 1 1005 764 759 853 1005 768 759 878 2 1005 798 759 794 1005 794 759 804 3 1005 735 759 798 1005 733 759 810 4 1005 651 759 810 1005 643 759 815 5 1005 646 759 725 1005 648 759 739 West 1005 674 759 776 1005 670 759 784 East 1005 835 759 833 1005 833 759 843 *Both US Survey Feet, NAD 83 State Plane (Georgia East) Datum

Approximate 2003 Difference 25’ S 10’ SES 12’ SES 9’ SE 14’ S 9’ SSE 10’ SES

There are differences in horizontal measurements between those datum positions that could be identified in the sonar record (Table 2-02). Intuitively we would have expected the tape measurements to be longer because of the problem of tape bowing in currents and inadvertent deviations around snagged obstructions, yet over half are shorter than those measured in the multibeam point cloud data. It is possible that some of these shorter measurements were obtained using the Aqua Meter in 2003, which, although an acoustic distance measuring device, is not always easy to use accurately in poor visibility. We know this from ADUS trials with the instrument in 2001.

Another difficulty with tape measurement is that for convenience, reinforced plastic tapes are normally used by divers because they are light, easy to handle, and relatively inexpensive.

Unfortunately they are also prone to stretching, both temporarily and permanently, and cannot be consider sufficiently accurate over distances in excess of about 20 feet. The inaccuracy of tape surveys on larger sites where long measurements need to be taken is one of the reasons why ADUS began to explore the advantages of using multibeam sonar for site surveying, and why these methods were applied to the CSS Georgia site.

Table 2-02. Comparison of 2003 and 2013 Survey Web Measurements.

Datum 1 Datum 1 Datum 2 East East East East

Datum 2 Datum 3 Datum 3 Datum 1 Datum 2 Datum 3 Small Casemate

2003 Distance 68’ 8” 63’ 3” 62’ 10” 73’ 10” 51’ 4” 106’ 47’ 11”

East West West West West Datum 2 Datum 5 Steam cylinder 1 Steam cylinder 1 Steam cylinder 1

West Datum 3 Datum 4 Datum 5 Gun 2 Cascabel Gun 2 Cascabel Gun 2 Cascabel Gun 2 Cascabel Steam cylinder 2 Manifold pipe

64’ 1” 41’ 1” 58’ 4” 62’ 5” 109’ 10” 64’ 7” 29’ 10” 20’ 11” 7’ 6”

Datum

Datum

2013 Distance 77’ 11” 75’ 3” 61’ 11” 74’ 10” 55’ 9” 106’ 5” c.55’ (Unknown location on structure) 174’ 2” 68’ 4” 40’ 9” 51’ 6” 62’ 8” 106’ 6” 61’ 9” n/a n/a n/a

28

2003 Difference From 2013 - 9’ 3” - 13’ + 11” - 1’ 0” - 4’ 5” + 5” c. 7’ 1”

- 3’ 3” + 4” + 6’ 10” - 3” + 3’ 4” + 2’ 10” n/a n/a n/a

The Surveys

There will inevitably be some errors in the 2013 multibeam survey, but fewer than with most other site survey techniques. Although multibeam sonar is probably the most accurate method of surveying the overall layout of a site, and undoubtedly the quickest, it cannot yet match the effectiveness of diving archaeologists with tape measures for recording fine detail, although that time may come soon as sonar technology and operational methodologies continue to develop.

There are slight differences in orientation of a number of the major components of the site, including the East Casemate (Appendix A: Item 19) and the possible boiler (Appendix A: Item 12) as well as differences in detail of displaced railroad iron on and around the Casemates. Some of this could be the result of physical interference over the last ten years, but some of it will be due to the difficulty of recording orientation of objects underwater in 2003 in poor visibility where subjective judgments have to be made. This problem is compounded when trying to orientate objects of iron and steel when the principal tool is the magnetic compass.

One of the major advantages of multibeam survey is that visualization of the data produces objective metrical images where alignment of individual items becomes self evident, rarely requiring interpretation, and the process has not been subject to magnetic deviation.

Both the northern and southern extremities of the East Casemate show differences between 2003 and 2013. The square-shaped southern outlier with a linear object overlying it is on a different alignment, but analysis of the multibeam data suggests that the linear feature is possibly a discarded dredge pipe. If there had been physical damage to this area the object would undoubtedly have been displaced and the alignment of the rope guideline running close by would have probably been disrupted also.

The northern end of the East Casemate and the triangular outlier looks very different to that reported in 2003; there is also a marked difference in the disposition of railroad iron that overlaid it. There is a similar situation at the West Casemate where the western extremity and the width of the gun port through the Casemate section shows differences between the two surveys. The 2003 diver survey is confirmed by the 2003 sidescan images (Watts and James 2007:Figures 28 and 29) and so it is reasonable to conclude that that there has been some physical impact in these three areas.

The differences between the 2003 and 2013 surveys can be attributed to both differences in methods of recording and to physical changes to the site. The former can simply be recognized as a result of access to better equipment, improved data collection techniques, and the increased capacity of computers and software. The areas for concern are those attributable to mechanical damage.

Up until 2003, dredging was obviously the major cause of damage to the site. The dredging scars intruding on to the wreck site butting up against structures was clear evidence that dredging had caused serious damage to the site by 2003, and probably before 1986. The 2013 survey suggests that there was no obvious dredging impact to the site between 2003 and 2013, but there has been distinct physical damage caused by other activities in that period.

The changes observed include: elements that were recorded in 2003 and are now missing; bent datum poles; significant changes to structural elements; and the number and disposition of railroad iron on and around the Casemates. These together with the localized disturbance of the riverbed (e.g., to the south and west of Cannons 2 and 3) all suggest the impact of external forces.

There are a number of possible causes for the recent damage to the site, including the movement of anchors or dredge pipes along the riverbed as part of dredging operations. The multibeam

29

CSS Georgia Multibeam Survey

sonar evidence suggests that a more likely candidate for post-2003 damage to the site is the setting and recovery of navigation buoys, if that has occurred.

HIGH-RESOLUTION SIDESCAN SONAR SURVEY SIDESCAN SONAR SURVEY METHODOLOGY Dial Cordy and Associates, Inc. collected high-resolution sidescan sonar data during the week of 25 February 2013 using a digital, dual frequency (900 to 1800 kilohertz) Sea Scan high definition sonar (HDS) sidescan sonar system from Marine Sonic Technology, Ltd. The survey was conducted using a range of 20 meters and 25 meters, both with trackline spacing of 15 meters (Figure 2-26). The digital data was recorded in real time with Sea Scan Survey software and saved as native *.SDS sidescan sonar data files. This combination of range and trackline spacing provided over 100% overlap coverage.

A RTK GPS system was selected for navigation and to set sidescan sonar alignment. The survey accuracy performance standards, quality control, and quality assurance requirements were followed during this survey in accordance with latest USACE hydrographic survey manual as well as the Minimum Technical Standards (MTS) as set forth by the Board of Professional Surveyors. The project datum is based on NAVD 1988 referenced to National Oceanic and Atmospheric Administration (NOAA) Mean Sea Level (MSL) on State Plane coordinate system, East Zone (Savannah, Georgia), Transverse Mercator Projection, North American Datum 1983 (NAD83). The hydrographic survey data were collected and processed using HYPACK Pro 2012, an Odom Hydrotrac with a 200 kilohertz (high frequency) hull-mounted survey-grade Teledyne Odom transducer and a RTK GPS positioning system to provide coordinate correct accuracy within less than 0.1 feet +/-. Published Department of Transportation (DOT) and NOAA landside control monuments were used to calibrate the vertical and horizontal throughout the data collection process. This was accomplished using a Trimble R8 Model 3 Rover/Base setup clocking on U.S. and Global Navigation Satellite System (GLONASS) satellites. The final accuracy produced 0.01 feet +/- on the horizontal and 0.1 feet +/- on the vertical. Customized software and hardware were used to interface GGA/GLL NMEA stream data directly into the sonar equipment while simultaneously running the hydrographic survey. The survey was conducted aboard Dial Cordy’s 25-foot Parker 2520-XL Haley Ann, a modified V-hulled motor vessel powered by twin 125 horsepower Yamaha outboards (Figure 2-27).

Positioning of the sidescan sonar tow fish was achieved by mounting the RTK GPS antennae directly on the cable-out sheave and then counting the length of cable payed out. The digital sidescan record was post-processed using SonarWiz5 (Chesapeake Technology, Inc.) applying the appropriate amount of horizontal setback from the antennae for each individual towed survey line based on calculations from known measurements in the field for cable-out and depth of the tow fish (Figure 2-28).

Sidescan images were further processed in SonarWiz5 to remove the water column (bottom track), perform signal processing, and construct a sidescan mosaic. The water column, which is the portion of the raw sidescan image that represents the altitude of the tow fish above the benthic surface, must be removed before signal processing can properly be done (Figure 2-29).

Signal processing is conducted to apply gain control to compensate for non-linear response characteristics and equalize the backscatter of the sonar signal. With the water column removed and the appropriate gain control applied, the sonar images were then mosaiced into single cohesive images that best illustrate specific features of the wreck site (Figure 2-30).

30

Figure 2-26. Actual sidescan survey lines run at the CSS Georgia wreck site and surrounding environment, overlaid on aerial photograph. Note red Channel Marker buoy to the lower right of the green wreck location dot.

The Surveys

31

CSS Georgia Multibeam Survey

Figure 2-27. Dial Cordy’s 25-foot Haley Ann employed for the sidescan sonar survey.

Figure 2-28. Sonar and winch array.

32

Figure 2-29. Excerpt from sonar trackline without the water column removed. Right Channel (top) shows the West Casemate, while the Port Channel shows Cannons 2 and 3. The water column with black center line is between channel swaths.

The Surveys

33

Figure 2-30. Sonar mosaic showing coverage by actual sidescan survey lines run at the CSS Georgia wreck site and surrounding environment, overlaid on aerial photograph.

CSS Georgia Multibeam Survey

34

The Surveys

RESULTS Complimenting the multibeam site data, high-resolution sidescan images of the site are presented in Figures 2-31 through 2-38, which are discussed in detail below. These images point out some of the major components of the site and show their respective locations within the larger site area. They have been—and will continue to be—analyzed and compared with the multibeam data for a full understanding of the site.

Figure 2-31 shows the majority of the site components. Clearly seen are the damaged downriver end of the West Casemate and the missing section on the East Casemate. The channel toe is clearly indicated showing Cannon 4 well within the channel. Cannons 2 and 3 are just out of the channel near the channel buoy anchors.

Figure 2-32 shows the West Casemate area along with Cannons 2 and 3. Clearly evident, and seen on multibeam data as well, are two datum poles. Also seen projecting from the right, or downstream, side of the Casemate is what appears to be the main baseline from the 2003 investigation. The baseline from the East Casemate lies between the West Casemate and cannons.

Figure 2-33 illustrates the area from the East Casemate downriver and into the channel. From this view it appears that the missing Casemate section may still, in fact, be present but not as high off the bottom as in 2003. Identified on this image is the newly found Cannon 4 and large cylindrical objects that may be associated with the wreck or they may be dredge pipe. A section of small Casemate fragments and the hawse pipe are also visible (throat).

Figure 2-34 is the area upstream and in the channel adjacent to the channel buoy anchors. Note the large concentrated area of what is most likely railroad iron sections from the ram’s cladding.

Figure 2-35 depicts similarly sized cylindrical objects that are well in the channel upstream from the buoy anchors. They appear to trend down slope and are in a somewhat linear path.

Figure 2-36 is an image showing large cylindrical objects that may be associated with the wreck or they may be dredge pipe.

Figure 2-37 is an image of small objects well downstream from the site. It is unknown if they are associated with the wreck.

Figure 2-38 is a combination of the 2003 and 2013 acoustic images of the West and East Casemate portions of the site for comparative purposes. Several differences are readily apparent and are not thought to be due to angle or turn of the towfish, while many items are mirror images in the ten years that have passed. Similar to that observed with the multibeam, comparison with the 2003 site plan suggests that there have been changes to the West Casemate at the extreme eastern, or downriver, end of the structure and the gun port, which is now wider, indicating that some physical damage has taken place over the last ten years. The East Casemate shows little change, although Cannon 1 is in a different orientation, most likely an imaging issue from the 2003 survey. Cannons 2 and 3, while shown in the 2003 image, are not shown in the 2013 as they were on the port channel. These are illustrated in Figure 2-39 below and clearly indicate their orientation to one another as well as their trunnions and cascabels.

A review of the above acoustic images indicates generally the same findings as the multibeam review with respect to present wreck site components (i.e., smaller Casemate fragment, hawse throat, condenser, datum points and guide ropes). However, some differences between the two data sets are apparent, especially with the unidentified features that are well into the channel both up and down river from the main site area.

35

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36

The Surveys

Figure 2-31. Acoustic image of what is thought to represent the majority of the site.

37

CSS Georgia Multibeam Survey

Figure 2-32. Acoustic image of the West Casemate and Cannons 2 and 3 area.

38

The Surveys

Figure 2-33. Acoustic image of the East Casemate into the channel and just downriver; Cannons 1 and 4 are present.

39

CSS Georgia Multibeam Survey

Figure 2-34. Acoustic image of Channel Buoy anchor area showing concentration of what appears to be railroad iron.

40

The Surveys

Figure 2-35. Acoustic image of unknown “cylinders� in the channel just upstream from the Buoy anchor.

41

CSS Georgia Multibeam Survey

Figure 2-36. Acoustic image of objects on the downriver end of the site; it is unknown if they are associated.

42

The Surveys

Figure 2-37. Acoustic image of objects in the channel well on the downriver end of the site; it is unknown if they are associated.

43

CSS Georgia Multibeam Survey

Figure 2-38. A combination of the 2003 and 2013 acoustic images of the West and East Casemate portions of the site for comparative purposes.

44

The Surveys

Figure 2-39. Located between the West Casemate (top) and the Buoy anchors (bottom), Cannons 2 and 3 with their trunnions and cascabels clearly evident.

45

CSS Georgia Multibeam Survey

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46

Conclusions

III. CONCLUSIONS The USACE, Savannah District requested a high resolution, geo-referenced, three-dimensional plan of the wreck remains of the CSS Georgia and the surrounding environment of the Savannah River be obtained through a state-of-the-art high resolution multibeam and sidescan sonar survey. To form a major basis for future mitigation planning of the NRHP listed site, a team composed of Panamerican, Dial Cordy, Inc., ADUS, and Tidewater Atlantic Research conducted the survey, the end product of which are 2D and 3D site maps, and associated locational data in tabular format.

In conjunction with the high frequency sidescan sonar survey that was undertaken at the same time as the multibeam survey, the visualization of the two sets of data are complimentary, both enhancing the usefulness of the other. One key aspect of the multibeam survey is the ability to use it to identify exactly where significant objects and features are on the bottom of the Savannah River, to a relative accuracy of a few inches (even less in some instances) and an absolute accuracy of less than 1 foot. The sidescan data, while not as accurate, allows a different view of an object not seen with the multibeam, thereby enhancing our understanding of a specific component in question. The resultant geo-referenced site plans that have been produced by this investigation, both the 2D DTM maps and the 3D WreckSight map, as well as positioning data afford maximum effectiveness in future mitigation planning and actual field operations. The data will be instrumental in designing the future placement of work plants on site as it relates to both functional placement, safety, and site protection (i.e., mooring, vessels, barges, and their anchors), and offers necessary information required for engineering issues such as the size and exact location of large vessel components and artifacts that will be recovered by crane, not to mention identifying ordnance that will affect planning aspects. Furthermore, the maps and resultant positioning data now allow the mapping, recordation, and relocation of any object on the riverbed, regardless of size, particularly as future diving operations on the site intend to exploit the advantages of industry-standard acoustic tracking systems for divers interfaced with the maps in real-time. Additionally, the data will also allow archaeologists to ascertain the condition of the Casemate and other vessel remains, which will help make decisions on which pieces can feasibly be conserved and curated.

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References Cited

IV. REFERENCES CITED Watts, Gordon P. and Stephen R. James, Jr. 2007 In Situ Archaeological Evaluation of the CSS Georgia, Savannah Harbor, Georgia.

Prepared for the U.S. Army Corps of Engineers, Savannah District by Panamerican Consultants, Inc., Memphis, Tennessee under subcontract to Gulf South Research Corporation, Baton Rouge, Louisiana.

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APPENDIX A: TARGET COORDINATES

CSS Georgia Multibeam Survey

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Appendix A: Target Coordinates

Item

Identification

1

Buoy sinker

2 3

Anchor fluke Riser

4

Buoy sinker 2

5 6

Cannon 1 Cannon 2

7

Cannon 3

8

Cannon 4

9 10 11 12

Boiler?

13 14 15

Condenser?

Propeller blade

16 17 18

West casemate

19

East casemate

Description Square with chain (?) connecting top to riser via anchor Distinct triangular palm Rising to west in file15 and to the east 34 Square with chain (?) connecting top to riser via anchor Sediment build up either side Cascabel, thick first reinforce and trunnion visible Characteristic thick banding at first reinforce & trunnion visible Gun with distinct cascabel & thickened reinforce Gun like taper - hint of cascabel Gun-like tapered object Gun-like tapered object On 2003 site plan at a slightly different orientation Boiler like object - appears damaged at both ends This feature is parallel to cannon 3 Blade shape similar to the 2003 report drawing Probable shaft with propeller blade at south end Cylindrical object - 7' east of above Overlain by rails, others to north, south and east

Rail and other debris to north and south

File No.

East

North

ORIENTA TION

Height Length

Depth BCD

34, 15

1005

725

759

694

3'

34 34, 15

1005 1005

711 723

759 759

704 709

2'

34, 15

1005

739

759

712

3'

4' 6"

4' 6"

19 10, 32, 16, 15 10, 32, 16, 15 19, 35, 31 35 22 11 19. 35

1005 1005

844 715

759 759

837 736

N-S WNW-ESE

c.1'

>7' 10' 3"

c.1' 3" 2' 6" dia

1005

738

759

739

SE-NW

10'

2' 9" dia

1005

832

759

720

NNE-SSW

2'

11'

2' 9" dia

1005 1005 1005 1005

961 598 905 914

759 759 759 759

770 771 838 753

SWW-NEE E-W E-W NNW-SSE

2' >1' 2'

11' 10' 16' 20'

2' 6' dia 2' 6" dia 2' 6" dia 5' 9" dia

22

1005

943

759

844

NWW-SEE

c.25'

4' dia

10, 1005 32, 9, 11 1005

736 649

759 759

741 730

9, 11, 32 1005

649

759

735

E-W BLADE EW N-S

11 17, 10, 12, 30, 16, 28, 29, 9 36, 15, 12, 32, 30, 9

1005 1005

661 823

759 759

734 834

E-W WSWWNW

9' 66'

>1' 24'

19'

1005

707

759

786

N-S, E-W

24'

25'

17'

A-1

4' 6"

Width 4' 6"

23'

10' 3'

2'9" 7'

CSS Georgia Multibeam Survey

Item 20

Identification

East

North

1005

872

759

793

Horizontal on riverbed, flange to east Upright Leans c.45 degrees to west Upright Leans c. 20 degrees to the west Leans c.10 degrees to the east Leans c. 10 degrees to the south east

1005 1005 1005 1005 1005 1005 1005

881 768 794 733 643 648 670

759 759 759 759 759 759 759

789 878 804 810 815 739 784

Upright, supported by casemate

27

1005

833

759

843

9

31 32 33 34 35 36

On riverbed between East Casemate and near Cannon 3 From top of Datum 5 to Propeller Area of riverbed disturbance to south of West Casemate Area of riverbed disturbance to south of East Casemate Small objects between buoy sinkers Small objects between buoy sinkers Small objects between buoy sinkers Small objects between buoy sinkers Tire?

Tire?

37 38 39 40 41 42 43 44 45

Tire?

Tire?

Upstanding linear object Upstanding object Upstanding object Upstanding linear object Upstanding object Upstanding linear object Two upstanding linear objects

28 29 30 35 36

Guide rope

Trapezoidal fragment

File No. 11, 9, 19, 10, 20 20 19, 36 19, 9 9 9. 36 9 9, 11

21 22 23 24 25 26 27

Casemate section Hawse pipe Datum 1 Datum 2 Datum 3 Datum 4 Datum 5 W. Casemate Datum E. Casemate Datum Guide rope

Description

32 10

1005

660

759

700

10

1005

825

759

785

10 10 10 10 31 25, 10, 34 9 36, 9 35, 31 31 32 32 11 30 20, 30

1005 1005 1005 1005 1005 1005

723 740 741 748 874 621

759 759 759 759 759 759

705 701 703 701 776 763

1005 1005 1005 1005 1005 1005 1005 1005 1005

667 735 833 798 738 685 737 793 850

759 759 759 759 759 759 759 759 759

792 842 737 736 784 741 783 804 785

A-2

ORIENTA Height Length Width TION NNE-SSW 2' 24' 14' WNW

c. 5'

1' 3"

2' 3' 3' 6" 3' 6" 3' 4" 2' c.3' NE-SW

>108'

N-S

8'

c.6" c.6" c.6" c.6" 3' dia 3' 9" dia 3' 6" dia 5' 2' 3' 6" 1' 3' 2' 3'

Depth BCD 26'

Appendix A: Target Coordinates

Item 46

Identification

Description

File No.

East

North

ORIENTA TION

Height Length

Two upstanding objects, one slender, the other 1' wide Floating rope?

Linear object Linear object Linear object Linear object Linear object Linear object Linear object Linear object Linear object Linear object Linear object Linear object Linear object Dredge pipe?

30

1005

650

759

739

3'

690 722 722 731 905 942 668 039 802 961 905 945 802 773 811

759 759 759 759 759 759 759 759 759 759 759 759 759 759 759

687 735 750 748 837 844 674 912 810 770 858 842 578 49 812

3' 6"

10 10 10 10 10 31 11 30 21 21 21 14 25 9

1005 1005 1005 1005 1005 1005 1005 1006 1005 1005 1005 1005 1005 1005 1005

NWN

9

1005

590

759

800

WNW

63 64 65 66 67 68 69 70

Dredge pipe? Seems to disappear at west end into the sediment Dredge pipe?

Possible group of dredge pipes?

Dredge pipes or dredge features?

Dredge pipe?

Dredge pipe?

Dredge pipes?

Dredge pipes?

Upstanding object

1005 1006 1005 1005 1005 1005 1005 1005

944 089 950 672 961 954 629 848

759 759 759 759 759 759 759 759

843 906 819 629 803 815 677 785

3'

71 72 73 74 75

Upstanding object Upstanding object Unidentified object Unidentified object Unidentified object

11 11 11 13, 14 21 22 24 30, 31, 11 34 34 31, 35 31 31

1005 1005 1005 1005 1005

650 650 799 708 679

759 759 759 759 759

738 730 736 649 672

3' 6" 2' 2' 2' 2'

47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62

A-3

Width

9'

1' 6" 1' 6" 10' 16' 25' 43' 17' 24' 1'

>42' 22'

26'

3'

c. 1' 6"' dia

Depth BCD

CSS Georgia Multibeam Survey

Item

Identification

Description

76 77 78 79 80 81 82

Unidentified object Unidentified object Unidentified object Unidentified object Unidentified object Unidentified object Upstanding object

83 84 85 86 87 88 89 90 91 92

Upstanding object Upstanding object Unidentified object Unidentified object Unidentified object Unidentified object Unidentified object Unidentified object Unidentified L-shaped object Pair of parallel grooves in the riverbed

File No. 32 31 31 10 10 10 30, 31, 12 34 34 31, 36

32 32 32 34

East

North

1005 1005 1005 1005 1005 1005 1005

679 637 850 649 649 684 666

759 759 759 759 759 759 759

747 699 783 739 729 741 728

1005 1005 1005 1005 1005 1005 1005 1005 1005

660 654 648 642 635 629 707 706 691

759 759 759 759 759 759 759 759 759

728 728 728 727 727 727 767 756 761

ORIENTA TION

Height Length 1' 6" <2' 3'

3' 3' 6" 2' 2' 2' 2' 1' 1' 6" 2' <3’

A-4

Width

3'

2' 6' 3' >280’

2' 6" 14’

Depth BCD

APPENDIX B: SURVEY LINE INFORMATION

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Appendix B: Survey Line Information

E - W Survey Line Latitude Average1 File No.

North

Points/m

2

Swath Angle

26

759590

280

140

34

759653

700

140

35

759656

800

125

12

759762

470

120

31

759660

1600

90

10

759765

300

120

32

759767

760

90

11

759794

430

120

30

759796

1600

90

16

759800

390

120

28

759802

2000

90

29

759802

1000

90

9

759804

250

130

27

759821

1740

90

36

759870

900

140

24

759934

890

135

25

760026

600

140

N - S Survey Line Longitude Average1 File No.

East

Points/m2

Swath Angle

13

1005564

440

120

14

1005593

290

120

15

1005686

360

120

17

1005750

400

120

19

1005830

440

120

20

1005889

270

120

21

1005940

360

120

23

1005971

360

120

22

1005976

290

120

Please note that not all survey lines are straightâ&#x20AC;&#x201D;some had to curve around a channel marker buoy or infill gaps.

1

Approximate average number of surveyed points in 1 square meter on the riverbed in the center of the survey line.

B-1

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APPENDIX C: SURVEY CONTROL POINT, FORT JACKSON

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Appendix C: Survey Control Point, Fort Jackson

SAVANNAH HARBOR - SURVEY CONTROL POINT “FORT JACKSON 2000” STA. 58+497.45, OFFSET 371.96’ LEFT, PID# AI8599

View to the south of Survey Control Monument “FORT JACKSON 2000” located on the moat of historic Fort Jackson.

NOTE: This moat wall is unstable.

Vertical Datum Information Vertical Datum

Units of Feet

Units of Meters

MLLW epoch 1983 - 2001

+10.58

+3.224

GRS 80 Ellipsoid GEOID 03 (NGS) NAVD 88 NGVD 29 MLLW epoch 1960 - 1978 MLW epoch 1960 - 1978

-96.44 -102.69 +6.28 +7.21 +10.82 +10.58

-29.394 -31.301 +1.914 +2.198 +3.298 +3.224

Compare NGS Data Sheet ELEVATION NAVD 88

6.3

1.92

Horizontal Datum Information for NAD 83 (1994) Georgia HARN and SPC NAD 83 Georgia East HORZ ORDER - FIRST Latitude Longitude Northing Easting d.m.s. d.m.s. (feet) (feet) N 32 04 57.10296 W 081 02 10.82590 759271.55 1006246.89 d.m. d.m. meters meters N 32 04.9517160 W 081 02.1804317 231426.426 306704.656 SURVEY DISK SET IN CONCRETE MONUMENT STAMPING: FORT JACKSON 2000 Control Sheet 2A, Section 6

C-1

JACKSON.doc

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APPENDIX D: CALCULATED BASE STATION POSITION

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Appendix D: Calculated Base Station Position

D-1

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APPENDIX E: TOTAL PROPAGATION ERROR

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Appendix E: Total Propagation Error

ERROR MODEL OF INTEGRATED SURVEY SYSTEM TOTAL PROPAGATED ERROR Calculating the Total Propagated Error (TPE) of soundings generated from an integrated multibeam survey system requires knowledge of each contributing sensor’s accuracy.

Each sensor in the integrated survey system has an estimated, or a priori, accuracy associated with it. For the sake of the terminology in use it may be useful to think of this as the estimated error of each sensor. Propagating, or combining the effects of the errors of all sensors through a statistical model, results in an estimation of the total error of each sounding: the TPE, which is an estimation of how close to the truth we may consider the sounding to be. We never in fact know what the error of a sounding is and may only estimate it, thus commonly the alternative term “uncertainty” is used instead, meaning the estimate of the magnitude of error.

SYSTEM ACCURACY PARAMETERS The following table details the a priori standard deviations required for TPE calculation from a typical survey system comprising positioning system, motion and heading sensor, sonar, and sound velocity sensor.

For the results presented in this document the specific survey sensors and parameters used are those as specified by ADUS. Table E-01. Required Standard Deviations.

TPE Requirement SDEV of XYZ Offset of Positioning System SDEV of Heading Sensor SDEV of XYZ Offset of Motion Sensor SDEV of Roll and Pitch Alignment SDEV of Heading Alignment SDEV of Fixed Heave % of Heave Variable Error SDEV of Roll SDEV of Pitch Model of Multibeam System SDEV of Sonar Pitch Stabilization SDEV of Water Level (if not RTK) SDEV of Full SVP Profile SDEV of SV at Sonar Head

System Type POS MV RTK POS MV RTK POS MV RTK POS MV RTK POS MV RTK POS MV RTK POS MV RTK POS MV RTK POS MV RTK SeaBat 7125

RESON SVP-15 MiniSVS

E-1

Accuracy Value 0.03m Position, 0.05m Height 0.02° 0.01m 0.05° (Includes Patch Test Results) 0.10° (Includes Patch Test Results) 0.05m 5% of Heave Value 0.01° 0.01° 0.5cm Bottom Detection Resolution Not Applicable Not Applicable 0.25m/s 0.25m/s

CSS Georgia Multibeam Survey

RESULTS SUMMARY Table E-02. Minimum/Maximum Total Propagated Error Results.* Vertical Component

Computed TPE 95%

Minimum Vertical Error (Nadir Beam) 0.06m Maximum Vertical Error (Outer Beam) 0.07m Horizontal Component Computed TPE 95% Minimum Horizontal Error (Nadir Beam) 0.04m Maximum Horizontal Error (Outer Beam) 0.08m *Demonstrates compliance with IHO Special Order.

IHO Special Order Tolerance 0.26m IHO Special Order Tolerance 2.0m

TOTAL PROPAGATED ERROR RESULTS – 15 METERS WATER DEPTH The results are computed by simulation in RESON PDS2000 multibeam acquisition software using the parameters in Table E-01. The graphs show vertical and horizontal TPE results.

Figure E-01. Total Propagated Error – 15 meters Water Depth Total Propagated Error Results – IHO Special Order.

E-2

Appendix E: Total Propagation Error

The results are presented below with respect to IHO Special Order with blue dots representing TPE values and yellow dots representing the calculated IHO tolerance for the depth of 10 meters.

The graphs show vertical and horizontal.

Figure E-02. Total Propagated Error With Respect to IHO Special Order.

E-3

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E-4