2012_CCU_Hardbottom_&_Cultural_Resource_Survey.pdf

Hardottom an Cultural Resources of the Post 45 Charleston Harbor Project Study Area

Hardbottom and Cultural Resource Surveys of the Post 45 Charleston Harbor

Project Study Area, Charleston, South Carolina

Paul Gayes, Cheryl Ward, Jenna Hill, Shinobu Okano, Jeff Marshall, Brian Johnson, Jamie Phillips, Bradley Craig, Richard Viso

Burroughs and Chapin Center for Marine and Wetland Studies

Coastal Carolina University

Conway, SC 29526

Submitted to:

United States Army Corps of Engineers

Charleston, SC District

January 2013 http://images.google.com/imgres?imgurl=http://content.answers.com/main/content/wp/en-commons/thumb/1/14/275px-United_States_Army_Corps_of_Engineers_logo.svg.png&imgrefurl=http://www.answers.com/topic/corps-castle&h=209&w=275&sz=6&hl=en&start=1&tbnid=RsQyJNM8eHDerM:&tbnh=87&tbnw=114&prev=/images?q=usace+logo&gbv=2&hl=en

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 2

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 3

TABLE OF CONTENTS

ABSTRACT

1.0 INTRODUCTION

2.0 METHODS

2.1 SIDE SCAN SONAR

2.1.1 Side Scan Data Processing

2.2 MAGNETICS

2.2.1 Magnetic Data Processing

2.3 SUB-BOTTOM PROFILING

2.3.1 Sub-bottom Data Processing

2.3.2 Subsurface Layer and Isopach Map Creation

2.3.3 3-D Visualization

2.4 HYDROGRAPHIC SURVEYING

2.4.1 Data Procesing

2.5 GROUNDTRUTHING

2.5.1 Video

2.5.2 Sediment Grabs

3.0 GENERAL DISCUSSION AND HABITAT ASSESSMENT

3.1 OVERVIEW OF DATA AND HABITAT CHARACTERIZATION

3.2 GEOPHYSICAL INTERPRETATION OF SURFICIAL HABITAT

3.3 GROUNDTRUTHING GEOPHYSICAL DATA AND INTERPRETATIONS

3.3.1 Habitat interpretation and groundtruth site selection procedures

3.4 HARDBOTTOM HABITAT CLASSIFICATION MAPPING

4.0 GENERAL DISCUSSION AND INTERPRETATION OF SUB-BOTTOM PROFILES

4.1 GEOLOGIC FRAMEWORK

4.2 SEDIMENT THICKNESS AND SUB-BOTTOM SURFACES

4.3 MAIN ENTRANCE CHANNEL AND EXTENSION SURVEY AREA

4.4 ODMDS SURVEY AREA

4.5 HARDBOTTOM HABITAT SUMMARY

5.0 CULTURAL RESOURCES ANALYSIS

5.1 INTRODUCTION AND PROJECT BACKGROUND

5.2 PREHISTORIC AND HISTORIC OVERVIEW

5.3 DOCUMENTATION OF VESSEL LOSSES

5.4 PAST INVESTIGATIONS

5.5 FIELD AND ANALYTICAL METHODS

5.6 ANALYSIS AND RESULTS

ACKNOWLEDGEMENTS

REFERENCES

BENCHMARK INFORMATION

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 4

LIST OF FIGURES

FIGURE 1. VICINITY MAP OF MAPPING CORRIDORS FOR HARDBOTTOM HABITAT AND CULTURAL RESOURCES

ASSESSMENT IN THE PROPOSED CHARLESTON HARBOR ENTRANCE CHANNEL EXTENSION AND

IMPROVEMENT AREAS OF THE NAVIGATION CHANNEL

FIGURE 2. TOP: PHOTOGRAPH OF KLEIN 3000 DUAL FREQUENCY SIDE SCAN SONAR. BOTTOM: GEOMETRICS

G-882 MARINE MAGNETOMETER (LEFT) AND CCU’S VIDEO TOW SYSTEM

FIGURE 3. SIDE SCAN SONAR DATA ACQUISITION AND PROCESSING WORKFLOW

FIGURE 4. MAGNETOMETRY DATA ACQUISITION AND PROCESSING WORKFLOW

FIGURE 5. PHOTO SHOWING THE EDGETECH SB512I CHIRP SUB-BOTTOM REFLECTION SONAR

FIGURE 6. ILLUSTRATION OF TOWFISH GEOMETRY RELATIVE TO SEA SURFACE SHOWING SEAFLOOR AND

MULTIPLE RAY PATHS

FIGURE 7. CHIRP SUB-BOTTOM DATA ACQUISITION AND PROCESSING WORKFLOW

FIGURE 8. SINGLE BEAM ACQUISITION AND DATA PROCESSING WORKFLOW DIAGRAM

FIGURE 9. SIDE SCAN SONAR (BACKSCATTER INTENSITY) MOSAIC IN POST 45 ODMDS AND ENTRANCE

CHANNEL

FIGURE 10. SUB-BOTTOM PROFILE (LINE 94) SHOWING EXAMPLES WHERE OLDER, TILTED REFLECTORS ARE

EVIDENT AT OR NEAR THE SEA FLOOR WITH LITTLE OR NO OVERLYING SURFICIAL SEDIMENT COVER.

HARD GROUND HABITATS ARE HIGHLY LIKELY TO BE FOUND IN SUCH AREAS

FIGURE 11. SUB-BOTTOM PROFILE (LINE 41) SHOWING EXAMPLES WHERE A DEFINABLE THICKNESS (>4

METERS) OF SEDIMENT INFILLING WITHIN A DEFINABLE AND LATERALLY CONTINUOUS CHANNEL AND

ABOVE A FLAT LYING RAVINEMENT SURFACE. IN SUCH AREAS OLDER, TILTED AND POTENTIALLY

INDURATED SUBSTRATE THAT COULD FORM HARD GROUNDS IS SEPARATED FROM THE SEA FLOOR AND

PRESENCE OF HARD GROUNDS IS HIGHLY UNLIKELY

FIGURE 12. SIDE SCAN SONAR (BACKSCATTER INTENSITY) MOSAIC AND CHIRP (SEDIMENT THICKNESS) IN

POST 45 ODMDS AND ENTRANCE CHANNEL

FIGURE 13. SIDE SCAN SONAR (BACKSCATTER INTENSITY) MOSAIC OVERLAIN WITH INDIVIDUAL TARGETS

FROM FULL RESOLUTION SONAR FILES IN POST 45 ODMDS AND ENTRANCE CHANNEL

FIGURE 14. MOSAIC OF SIDE SCAN SONAR COLLECTED AT THE ODMDS SITE. TARGET CLASSIFICATIONS

FROM INDIVIDUAL SIDE SCAN LINES IS ALSO SHOWN. NOTE CLUSTERING OF HIGH CONFIDENCE PICKS

(RED AND PINK CIRCLES) AS WELL AS CLUSTERING OR MORE UNCERTAIN SIGNALS (GREEN QUESTION

MARKS). LINES FOR VIDEO TOW VERIFICATION/GROUNDTRUTHING ARE ALSO SHOWN (YELLOW)

FIGURE 15. SIDE SCAN SONAR (BACKSCATTER INTENSITY) MOSAIC OVERLAIN WITH GEOCODED VIDEO

OBSERVATIONS (GROUNDTRUTH) IN POST 45 ODMDS AND ENTRANCE CHANNEL

FIGURE 16. AREAS OF HARDBOTTOM HABITAT FROM SIDE SCAN SONAR (BACKSCATTER INTENSITY), SEDIMENT THICKNESS (CHIRP), AND GEOCODED VIDEO (GROUNDTRUTH) IN POST 45 ODMDS AND

ENTRANCE CHANNEL

FIGURE 17. AREAS OF HARDBOTTOM HABITAT AND PROBABLE HARDBOTTOM HABITAT FROM SIDE SCAN

SONAR (BACKSCATTER INTENSITY), SEDIMENT THICKNESS (CHIRP), AND GEOCODED VIDEO

(GROUNDTRUTH) IN POST 45 ODMDS AND ENTRANCE CHANNEL

FIGURE 18. AREAS OF HARDBOTTOM HABITAT, PROBABLE HARDBOTTOM HABITAT, AND POSSIBLE

HARDBOTTOM HABITAT FROM SIDE SCAN SONAR (BACKSCATTER INTENSITY), SEDIMENT THICKNESS

(CHIRP), AND GEOCODED VIDEO (GROUNDTRUTH) IN POST 45 ODMDS AND ENTRANCE CHANNEL

FIGURE 19. AREAS OF HARDBOTTOM HABITAT, PROBABLE HARDBOTTOM HABITAT, AND POSSIBLE

HARDBOTTOM HABITAT FROM SIDE SCAN SONAR (BACKSCATTER INTENSITY), SEDIMENT THICKNESS

(CHIRP), AND GEOCODED VIDEO (GROUNDTRUTH) OVERLAIN ON SIDE SCAN MOSAIC IN POST 45

ODMDS AND ENTRANCE CHANNEL

FIGURE 20. DATA LAYERS FOR HABITAT INTERPRETATION ARE SHOWN IN HABITAT APPENDIX AT A SCALE OF

1:16000 FOR THE AREAS DEFINED BELOW (ODMDS AREAS 1-7, AND CHANNEL/EXTENSION AREAS

C1-C-8 CAN BE FOUND IN APPENDIX 2)

FIGURE 21. DEPTH TO TRANSGRESSIVE SURFACE (BASE OF MODERN SEDIMENT) GRID DERIVED FROM CHIRP

SUB-BOTTOM PROFILES FOR ALL SURVEY AREAS. CONTOURS ARE EVERY 5 FEET

FIGURE 22. THICKNESS OF MODERN SEDIMENT ABOVE THE TRANSGRESSIVE SURFACE (MINIMUM MAPPABLE

SEDIMENT THICKNESS) DERIVED FROM CHIRP SUB-BOTTOM PROFILES FOR ALL SURVEY AREAS.

CONTOURS ARE EVERY 5 FEET

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 5

FIGURE 23. DEPTH TO TOP OF ROCK (BASE OF MODERN AND RELICT SEDIMENT) GRID DERIVED FROM CHIRP

SUB-BOTTOM PROFILES FOR ALL SURVEY AREAS. CONTOURS ARE EVERY 5 FEET

FIGURE 24. MAXIMUM THICKNESS OF MODERN AND RELICT SEDIMENT DERIVED FROM CHIRP SUB-BOTTOM

PROFILES FOR ALL SURVEY AREAS

FIGURE 25. DEPTH TO TRANSGRESSIVE SURFACE (BASE OF MODERN SEDIMENT) GRID DERIVED FROM CHIRP

SUB-BOTTOM PROFILES FOR THE MAIN ENTRANCE CHANNEL SURVEY AREA. CONTOURS ARE EVERY 5

FEET

FIGURE 26. THICKNESS OF MODERN SEDIMENT ABOVE THE TRANSGRESSIVE SURFACE (MINIMUM MAPPABLE

SEDIMENT THICKNESS) DERIVED FROM CHIRP SUB-BOTTOM PROFILES FOR THE MAIN ENTRANCE

CHANNEL SURVEY AREA. CONTOURS ARE EVERY 5 FEET

FIGURE 27. DEPTH TO TOP OF ROCK (BASE OF MODERN AND RELICT SEDIMENT) GRID DERIVED FROM CHIRP

SUB-BOTTOM PROFILES FOR THE MAIN ENTRANCE CHANNEL SURVEY AREA. CONTOURS ARE EVERY 5

FEET

FIGURE 28. MAXIMUM THICKNESS OF MODERN AND RELICT SEDIMENT DERIVED FROM CHIRP SUB-BOTTOM

PROFILES FOR THE MAIN ENTRANCE CHANNEL SURVEY AREA. CONTOURS ARE EVERY 5 FEET

FIGURE 29. DEPTH TO TRANSGRESSIVE SURFACE (BASE OF MODERN SEDIMENT) GRID DERIVED FROM CHIRP

SUB-BOTTOM PROFILES FOR THE ENTRANCE CHANNEL EXTENSION SURVEY AREA. CONTOURS ARE

EVERY 5 FEET

FIGURE 30. THICKNESS OF MODERN SEDIMENT ABOVE THE TRANSGRESSIVE SURFACE (MINIMUM MAPPABLE

SEDIMENT THICKNESS) DERIVED FROM CHIRP SUB-BOTTOM PROFILES FOR THE ENTRANCE CHANNEL

EXTENSION SURVEY AREA. CONTOURS ARE EVERY 5 FEET

FIGURE 31. DEPTH TO TOP OF ROCK (BASE OF MODERN AND RELICT SEDIMENT) GRID DERIVED FROM CHIRP

SUB-BOTTOM PROFILES FOR THE ENTRANCE CHANNEL EXTENSION SURVEY AREA. CONTOURS ARE

EVERY 5 FEET

FIGURE 32. MAXIMUM THICKNESS OF MODERN AND RELICT SEDIMENT DERIVED FROM CHIRP SUB-BOTTOM

PROFILES FOR THE ENTRANCE CHANNEL EXTENSION SURVEY AREA. CONTOURS ARE EVERY 5 FEET. .. 60 FIGURE 33. MORTIER PORTION OF PIERRE MORTIER’S “CARTE PARTICULIERE DE LA CAROLINE” FIRST

PUBLISHED IN AMSTERDAM IN 1696. THE MAP ILLUSTRATES THE CHARLESTON HARBOR WITH ITS

ANCHORAGES, CHANNEL DEPTH, AND NAMES OF PROPERTY OWNERS THROUGHOUT THE AREA

FIGURE 34. 1776 SKETCHES DRAWN BY BRITISH FORCES WERE COMBINED INTO THIS 1776 MAP

ILLUSTRATING THE DISPOSITION OF AMERICAN DEFENSES INCLUDE ILLUSTRATIONS OF THE BRITISH

SQUADRON, INCLUDING HMS ACTEON, WHICH SANK AND HAS NOT BEEN RELOCATED

FIGURE 35. CIVIL CHARLESTON HARBOR AND ITS SHIFTING SHOALS, TIDAL FLOWS, AND ESPECIALLY THE

BATTERIES AND FORTS RANGED AGAINST UNION FORCES WERE OF INTEREST TO THE PUBLIC AS WELL

AS TO COMBATANTS (REPRODUCED IN HART, 1907: 244)

FIGURE 36. COE CHARLESTON’S CORPS OF ENGINEERS CHART FROM 1918 SHOWS THE WETLANDS THAT

STILL SURROUNDED THE CITY IN 1918 AND THE IMPROVEMENTS TO THE HARBOR MADE UNDER THE

DIRECTION OF COLONEL GILLMORE

FIGURE 37. STONEY A.T. STONEY MAP SHOWING PLANTATIONS ALONG THE COOPER RIVER AS THEY

APPEARED IN THE YEAR 1842 (REPRODUCED IN IRVING, 1932)

FIGURE 38. MODERNS EXAMPLES OF SONOGRAMS ILLUSTRATING MODERN CRAB POTS, PIPES, CABLE, PIPELINE, ROCKS FROM THE END OF A GROIN, AND A PONTOON

FIGURE 39. MAGNETIC ANOMALY COLOR CONTOUR MAP OF LH1

FIGURE 40. MAGNETIC (L) AND SIDE SCAN SONAR (R) SIGNATURES OF TARGET LH1-009 IN THE LOWER

HARBOR AREA. VISUAL INSPECTION OF THIS TARGET IS RECOMMENDED

FIGURE 41. ANOMALY LH1-001 SONOGRAM SHOWING BURIED PIPES (TOP). ANOMALY LH1-001 MAGNETIC

CONTOUR MAP (NEXT PAGE)

FIGURE 42. ANOMALY LH1-008 SONOGRAM SHOWING POSTS AND DEBRIS (TOP). ANOMALY LH1-008

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 43. ANOMALY LH1-018 SONOGRAM SHOWING SCATTERED ROCK (TOP). ANOMALY LH1-018

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 44. MAGNETIC ANOMALY COLOR CONTOUR MAP OF LH2

FIGURE 45. MAGNETIC ANOMALY COLOR CONTOUR MAPS OF LH4 AND LH5

FIGURE 46. ANOMALY LH4-006 SONOGRAM SHOWING BOTTOM DEPOSIT (TOP). ANOMALY LH4-006

MAGNETIC CONTOUR MAP (BOTTOM)

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 6

FIGURE 47. ANOMALY LH4-011 SONOGRAM SHOWING SMALL SCATTERED DEBRIS (TOP). ANOMALY LH4-

011 MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 48. MAGNETIC (L) AND SIDE SCAN SONAR (R) SIGNATURES OF TARGET LH5-013 IN THE LOWER

HARBOR AREA. VISUAL INSPECTION OF THIS TARGET IS RECOMMENDED

FIGURE 49. ANOMALY LH5-011 SONOGRAM SHOWING TIRES AND OTHER MODERN DEBRIS (TOP). ANOMALY

LH5-011 MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 50. ANOMALY LH5-024 SONOGRAM SHOWING SCATTERED DEBRIS(TOP). ANOMALY LH5-024

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 51. ANOMALY LH5-034 SONOGRAM SHOWING SCATTERED DEBRIS (TOP). ANOMALY LH5-034

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 52. ANOMALY LH5-042 SONOGRAM SHOWING MODERN DEBRIS (TOP). ANOMALY LH5-042

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 53. MAGNETIC ANOMALY COLOR CONTOUR MAP OF WR1

FIGURE 54. THIS AREA IS MARKED AS "SUBMERGED PILES" ON NAVAL CHARTS; PREVIOUS UNDERWATER

SURVEYS JUST NORTH OF THIS SURVEY AREA LOCATED TARGETS LIKE WR1-031 PICTURED ABOVE (TOP

A) AND IDENTIFIED THEM AS THE TOP OF AN I-BEAM, OFTEN WITH A STUD-LINK CHAIN ATTACHED, LIKELY TO HAVE BEEN USED AS A MOORING DOLPHIN AFTER WORLD WAR II (WILBANKS 2009)

FIGURE 55. MAGNETIC ANOMALY COLOR CONTOUR MAP OF WR2

FIGURE 56. ANOMALY WR2-004 SONOGRAM SHOWING NO FEATURES (TOP). ANOMALY WR2-004

MAGNETIC CONTOUR MAP

FIGURE 57. ANOMALY WR2-008 SONOGRAM SHOWING SCATTERED SMALL DEBRIS (TOP). ANOMALY WR2-

008 MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 58. ANOMALY WR2-010 SONOGRAM SHOWING A WIRE OR CABLE (TOP). ANOMALY WR2-010

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 59. MAGNETIC ANOMALY COLOR CONTOUR MAPS OF MB1 AND MB2

FIGURE 60. ANOMALY MB1-003 SONOGRAM SHOWING ROCKS (TOP). ANOMALY MB1-003 MAGNETIC

CONTOUR MAP (BOTTOM)

FIGURE 61. MAGNETIC ANOMALY COLOR CONTOUR MAPS OF MB1 AND MB2

FIGURE 62. ANOMALY MB2-003 SONOGRAM SHOWING MODERN PIER STRUCTURE FOUNDATIONS (TOP).

ANOMALY MB2-003 MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 63. ANOMALY MB2-006 SONOGRAM SHOWING CRAB POTS (TOP). ANOMALY MB2-006 MAGNETIC

CONTOUR MAP (BOTTOM)

FIGURE 64. ANOMALY MB2-013 SONOGRAMS SHOWING NO FEATURES (TOP). ANOMALY MB2-013

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 65. MAGNETIC ANOMALY COLOR CONTOUR MAP OF CR1

FIGURE 66. MAGNETIC ANOMALY COLOR CONTOUR MAP OF CR2

FIGURE 67. MAGNETIC ANOMALY COLOR CONTOUR MAP OF CR2 CONTINUED

FIGURE 68. ANOMALY CR2-010 SONOGRAM SHOWING SCATTERED SMALL DEBRIS (TOP). ANOMALY CR2-

010 MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 69. ANOMALY CR2-023 SONOGRAM SHOWING VARIOUS HARD RETURN SMALL DEBRIS (TOP).

ANOMALY CR2-023 MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 70. ANOMALY CR2-046 SONOGRAM SHOWING A CABLE OR WIRE AND SCATTERED DEBRIS AND

ANOMALY CR2-047 SONOGRAM SHOWING A PIPE AND OTHER SCATTERED DEBRIS (TOP). ANOMALIES

CR2-046 AND CR2-047 MAGNETIC CONTOUR MAP (NEXT PAGE)

FIGURE 71. ANOMALY CR2-062 SONOGRAM SHOWING A BUNDLE OF TIMBERS OR A BARRICADE (TOP).

ANOMALY CR2-062 MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 72. ANOMALY CR2-067 SONOGRAM SHOWING A SCATTER OF ROCKS (TOP). ANOMALY CR2-067

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 73. MAGNETIC ANOMALY COLOR CONTOUR MAP OF CR3

FIGURE 74. MAGNETIC ANOMALY COLOR CONTOUR MAP OF CR3 CONTINUED

FIGURE 75. ANOMALY CR3-006 SONOGRAM SHOWING A DEBRIS SCATTER AND A CRAB POT (TOP). ANOMALY

CR3-006 MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 76. ANOMALY CR3-012 SONOGRAM SHOWING A DEBRIS SCATTER AND TIRES (TOP). ANOMALY CR3-

012 MAGNETIC CONTOUR MAP (BOTTOM)

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 7

FIGURE 77. ANOMALY CR3-028 SONOGRAM SHOWING A PIPE, CRAB POTS AND A SCATTER OF DEBRIS AND

ANOMALY CR3-029 SONOGRAM SHOWING A SCATTER OF ROCKS (TOP). ANOMALIES CR3-028 AND

CR3-029 MAGNETIC CONTOUR MAP (NEXT PAGE)

FIGURE 78. ANOMALY CR3-039 SONOGRAM SHOWING A SCATTER OF DEBRIS AND ANOMALY CR3-044

SONOGRAM SHOWING A SCATTER OF DEBRIS (TOP). ANOMALIES CR3-039 AND CR3-044 MAGNETIC

CONTOUR MAP (NEXT PAGE)

FIGURE 79. ANOMALY CR3-066 SONOGRAM SHOWING CRAB POTS AND RIPRAP AND ANOMALY CR3-067

SONOGRAM SHOWING BRIDGE AFFILIATED RIPRAP (TOP). ANOMALIES CR3-066 AND CR3-067

MAGNETIC CONTOUR MAP (NEXT PAGE)

FIGURE 80. ANOMALY CR3-071 SONOGRAM SHOWING A SCATTER OF DEBRIS (TOP). ANOMALY CR3-071

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 81. ANOMALY CR3-076 SONOGRAM SHOWING A SCATTER OF ROCKS AND A CRAB POT (TOP).

ANOMALY CR3-076 MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 82. MAGNETIC ANOMALY COLOR CONTOUR MAPS OF EC1 AND EC2

FIGURE 83. MAGNETIC ANOMALY COLOR CONTOUR MAPS OF EC1 AND EC2 CONTINUED

FIGURE 84. MAGNETIC ANOMALY COLOR CONTOUR MAPS OF EC1 AND EC2 CONTINUED

FIGURE 85. MAGNETIC ANOMALY COLOR CONTOUR MAPS OF EC1 AND EC2 CONTINUED

FIGURE 86. MAGNETIC ANOMALY COLOR CONTOUR MAPS OF EC1 AND EC2 CONTINUED

FIGURE 87. MAGNETIC ANOMALY COLOR CONTOUR MAPS OF EC1 AND EC2 CONTINUED

FIGURE 88. MAGNETIC ANOMALY COLOR CONTOUR MAPS OF EC1 AND EC2 CONTINUED

FIGURE 89. ANOMALY EC1-001 SONOGRAM SHOWING DISPERSED DEBRIS (TOP). ANOMALY EC1-001

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 90. ANOMALY EC1-002 SONOGRAM SHOWING DISPERSED DEBRIS (TOP). ANOMALY EC1-002

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 91. ANOMALY EC1-006 SONOGRAM SHOWING DISPERSED DEBRIS (TOP). ANOMALY EC1-006

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 92. ANOMALY EC1-008 SONOGRAM SHOWING ISOLATED DEBRIS AND ANOMALY EC1-009

SONOGRAM SHOWING DISPERSED DEBRIS (TOP). ANOMALIES EC1-008 AND EC1-009 MAGNETIC

CONTOUR MAP (NEXT PAGE)

FIGURE 93. ANOMALY EC1-017 SONOGRAM SHOWING SCATTERED DEBRIS (TOP). ANOMALY EC1-017

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 94. ANOMALY EC1-022 SONOGRAM SHOWING SCATTERED DEBRIS (TOP). ANOMALY EC1-022

MAGNETIC CONTOUR MAP (BOTTOM)

FIGURE 95. ANOMALY EC2-009 SONOGRAM SHOWING LARGE DEBRIS (TOP). ANOMALY EC2-009 MAGNETIC

CONTOUR MAP (BOTTOM)

FIGURE 96. MAGNETIC ANOMALY COLOR CONTOUR MAP OF OD1

FIGURE 97. MAGNETIC ANOMALY COLOR CONTOUR MAP OF OD2

FIGURE 98. MAGNETIC ANOMALY COLOR CONTOUR MAP OF OD2 CONTINUED

FIGURE 99. ANOMALY OD2-024 SONOGRAM SHOWING DISPERSED ROCKS (TOP). ANOMALY OD2-024

MAGNETIC CONTOUR MAP (BOTTOM)

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 8

LIST OF TABLES

TABLE 1. SEDIMENT GRAB DESCRIPTIONS, CORRESPONDING VIDEO TOW LINES, AND GRAB POSITIONS TABLE 2. THIS LIST OF SHIP LOSSES REFLECTS CONSULTATION WITH ARCHAEOLOGICAL AND HISTORICAL

WORKS AND INDIVIDUALS (SPIREK & AMER EDS. 2004, WATTS 1986, GAINES 2008, SPIREK 2012). THE

STONE FLEETS ARE COMPOSED OF 14 AND 16 SHIPS; SPIREK (2012) HAS IDENTIFIED THE FIRST STONE

FLEET, BUT THE SECOND HAS NOT BEEN LOCATED PRECISELY

TABLE 3. CHARACTERISTICS OF LOWER HARBOR 1 (LH1) MAGNETIC ANOMALIES

TABLE 4. CHARACTERISTICS OF LOWER HARBOR 2 (LH2) MAGNETIC ANOMALIES

TABLE 5. CHARACTERISTICS OF LOWER HARBOR 4 (LH4) MAGNETIC ANOMALIES

TABLE 6. CHARACTERISTICS OF LOWER HARBOR 5 (LH5) MAGNETIC ANOMALIES

TABLE 7. CHARACTERISTICS OF WANDO RIVER 1 (WR1) MAGNETIC ANOMALIES

TABLE 8. CHARACTERISTICS OF WANDO RIVER 2 (WR2) MAGNETIC ANOMALIES

TABLE 9. CHARACTERISTICS OF MYERS BEND 1 (MB1) MAGNETIC ANOMALIES

TABLE 10. CHARACTERISTICS OF MYERS BEND 2 (MB2) MAGNETIC ANOMALIES

TABLE 11. CHARACTERISTICS OF COOPER RIVER 1 (CR1) MAGNETIC ANOMALIES

TABLE 12. CHARACTERISTICS OF COOPER RIVER 2 (CR2) MAGNETIC ANOMALIES

TABLE 13. CHARACTERISTICS OF COOPER RIVER 3 (CR3) MAGNETIC ANOMALIES

TABLE 14. CHARACTERISTICS OF ENTRANCE CHANNEL 1 (EC1) MAGNETIC ANOMALIES

TABLE 15. CHARACTERISTICS OF ENTRANCE CHANNEL 2 (EC2) MAGNETIC ANOMALIES

TABLE 16. CHARACTERISTICS OF OCEAN DREDGED MATERIAL DISPOSAL SITE 1 (OD1) MAGNETIC

ANOMALIES

TABLE 17. CHARACTERISTICS OF OCEAN DREDGED MATERIAL DISPOSAL SITE 2 (OD2) MAGNETIC

ANOMALIES

TABLE 18. DATE, LOCATION, AND FIELDWORK COMPLETED BY CCU FOR POST 45 STUDY

Abstract

The Center for Marine and Wetland Studies (CMWS) at Coastal Carolina

University (CCU) has conducted geophysical mapping to delineate hardbottom areas and to identify possible cultural resources in the proposed Charleston Harbor entrance channel extension and improvement areas of the navigation channel. Data consisting of side scan sonar, sub-bottom profiles, magnetics, and single beam bathymetry were collected between October and December, 2012. Following initial examination of the geophysical data records, groundtruthing was conducted in late 2012 and early 2013. A combination of geophysical data, sediment grabs, and video tows revealed areas of known, probable, and possible hard bottom throughout the study area. In addition, 421 magnetic anomalies were identified and examined. Two anomalies in the lower harbor area (sites LH1-009 and LH5-013) were identified as possibly containing culturally significant material. While no further investigation is recommended for the vast majority of the magnetic anomalies, LH1-009 and LH5-013 are recommended for visual inspection. All raw and processed geophysical data, maps, and interpretations are contained in a digital volume accompanying this report.

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 10

1.0 INTRODUCTION

The Center for Marine and Wetland Studies (CMWS) at Coastal Carolina

University (CCU) has conducted geophysical mapping to delineate hardbottom areas and to identify possible cultural resources in the proposed Charleston Harbor entrance channel extension and improvement areas of the navigation channel (figure 1). Mapping efforts were also completed, with the same objectives, in the proposed Ocean Dredged

Material Disposal Site (ODMDS) expansion area as well as hardbottom habitat only in the South Carolina Department of Natural Resources and EPA coordinated monitoring zones. The geophysical efforts consisted of side scan sonar, sub-bottom profiling, and magnetic mapping within identified survey limits (appendix 1). In addition mapping efforts extended 75 m either side of the proposed outer channel extension toe offshore and 50 m outside the proposed ODMDS expansion area. Hydrographic surveys were conducted to supplement bathymetric surveying previously undertaken by the United

States Army Corps of Engineers, Charleston, SC. The goals of this geophysical study are specifically to 1) identify hardbottom throughout the entire study area, 2) identify cultural resources throughout the entire study area with the exception of the ODMDS monitoring zones, and 3) to characterize sub-bottom reflectors in the entrance channel. Magnetic and side scan sonar data were evaluated to identify anomalies consistent with cultural resources in accordance with provisions of Section 106 of the National Historic

Preservation Act of 1966 and the Abandoned Shipwreck Act of 1987. Groundtruthing of the geophysical data consisted of video transects and sediment grabs.

For the hardbottom identification objective, the side scan sonar revealed areas of high backscatter intensity in several areas within the ODMDS and proposed channel extension. Video groundtruthing, comparison with sub-bottom profiles, and sediment grabs help to further characterize areas of high backscatter intensity. Generally speaking, changes in backscatter intensity owed to either changes in sediment composition and texture, or presence of hardbottom/ledges. A combination of geophysical and groundtruthing data were used to delineate areas of seafloor exhibiting quality habitat.

Sub-bottom profiles were used to contour seafloor, top of modern sediment, and top of rock surfaces. These contour maps were then used to construct sediment thickness isopachs. The study area contains variable sediment thickness of 0-4.5 m. Sub-bottom profiles varied throughout the study area, sometimes revealing several obvious reflectors and other times appearing homogeneous. In some cases, sediments were very thin or absent in the sub-bottom records while other data records indicated thick sediments.

These observations were useful for corroboration of side scan records and delineation of hardbottom as areas of thick sediment accumulations will not have hardbottom exposed at the sea floor.

Magnetic anomaly maps were constructed and reveal 421 anomalies greater than

5 nanoTeslas (nT). These targets were evaluated and found to be largely consistent with pipelines, channel markers, bridges, and other modern features or debris. Anomalies vary widely in duration and intensity and were interpreted in combination with raw (full resolution) side scan records and/or video for the most complete characterization.

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 11

Historical research, consultation with South Carolina Institute of Archaeology &

Anthropology (SCIAA), and examination of prior cultural resource studies were also used to constrain these data (Watts, 1984, 1995; Spirek, 2012).

Field work was conducted during the fall and winter of 2012-2013. The work was divided into two phases. Phase one included geophysical mapping and data reduction. Phase two included video and sediment grab groundtruthing and a small amount of additional geophysical mapping. Preliminary interpretations from phase one and an approach for phase two were described to various state and federal agencies in the

Nov 29, 2012 Post 45 Habitat/Cultural Resources Assessment meeting at the Charleston

District Corps of Engineers offices a meeting with the United States Army Corps of

Engineers (USACE) Charleston District. Data were provided to this Interagency

Coordination Team with descriptions and plans for locations of groundtruthing efforts prior to commencement of phase two. Following a reasonable review period, responses from the Interagency Coordination Team was used to refine and maximize the phase two effort.

In this report, we present descriptions of methods, rational for identification and mapping of select hardbottom features, and images of data collected. Appendix 4 includes all field notes. These notes contain dates, times, and weather conditions during all survey/mapping activities. The accompanying external hard drive includes the full volume of raw digital data, ESRI geodatabases, metadata records, and a copy of this report. The accompanying DVD set includes all video data.

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 12

Figure 1. Vicinity map of mapping corridors for hardbottom habitat and cultural resources assessment in the proposed Charleston Harbor entrance channel extension and improvement areas of the navigation channel.

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 13

2.0 METHODS

Geophysical mapping was conducted during October, 2012 – January, 2013.

Areas within the harbor were mapped using CCU’s 24 foot Privateer. In the main channel leading through the jetties, the proposed extension area, and the ODMDS, the

R/V Cape Fear was used in order to accommodate 24-hour operations during weather windows suitable for data collection. Groundtruthing was completed aboard the R/V

Silver Crescent. Data are reported relative to State Plane NAD 1983 SC International

Feet and NAVD 88 datum.

2.1 Side Scan Sonar

Side scan sonar surveys were completed with CCU’s Klein 3000 (500 kHz) side scan sonar (figure 2). On the CCU Privateer, the sonar towfish was rigged on the port side davit with variable layback as required by depth to maintain a constant altitude from seafloor. On the R/V/ Cape Fear the side scan was rigged through the starboard side of the A frame with layback adjusted to maintain constant towfish altitude. All laybacks and other rigging adjustments were documented in field notes and applied in post processing. The side scan was towed in tandem with the magnetometer as often as conditions allowed. Lane spacing, defined by cultural resources requirements for the magnetometry, was 20 m. The beam pattern was narrowed for maximum resolution in raw records, but still provided greater than 50% overlap.

2.1.1 Side Scan Data Processing

Post processing included navigation merging, demultiplexing, slant range correction, destriping, beam pattern correction, and mosaic construction with Xsonar and

ShowImage software packages developed by the USGS Woods Hole Science Center

(Danforth, 1997). The nadir was removed from each line of data prior to mosaicing, allowing port and starboard channels to be merged, thus removing the water column portion of the data record. Mosaics were output as 25 cm pixel resolution geotiffs for import to ESRI ArcGIS. Raw records at full resolution were used for cultural resources interpretation. The complete workflow is shown in figure 3.

2.2 Magnetics

A Geometrics G-882 marine magnetometer was used to measure total magnetic field intensity (figure 4). The instrument consists of a cesium vapor magnetometer in a towfish, 100 m of cable to tow the instrument and transmit data, and a topside computer with acquisition software. Total field intensity is controlled in part by distance between sensor and target among other factors. Towfish altitude above seafloor was therefore maintained as constant as mapping conditions allowed. Vessel position was integrated with the magnetic signal through the MagLog Lite software interface. This acquisition software also allows for monitoring of signal intensity in real time to ensure data quality.

On the CCU Privateer, the towfish was configured on the starboard side from a tow extension pipe. The towfish was configured with variable layback, tow point, and depressor weight configuration as conditions and depths required. On the R/V/ Cape

Fear the towfish was deployed from port side with the tow extension pipe with 50 m of

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 14

Figure 2. Top: Photograph of Klein 3000 dual frequency side scan sonar. Bottom:

Geometrics G-882 marine magnetometer (left) and CCU’s video tow system.

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 15

Figure 3. Side scan sonar data acquisition and processing workflow.

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 16 layback, using the nosecone tow point and depressor weight. All laybacks and other rigging adjustments were documented in field notes and applied in post processing. The magnetometer was towed in tandem with the side scan sonar as often as conditions allowed at a lane spacing of 20 m and ship speed maximum of 5-7 knots.

2.2.1 Magnetic Data Processing

The magnetometer data files (.int) were processed with MagPick v3.22 and QPS

Dmagic v7.3.2. Magnetometer profile data were first imported into MagPick to remove diurnal variations. In order to use smoothed profile data as diurnal variations, raw profile data were smoothed using the Robust smoothing method with a spline smoothing parameter of 1.00e-4, smooth window of 100m, and smooth order of 1. Raw magnetometer data were then corrected for diurnal variations and were normalized by subtracting the smoothed profile data. Corrected data were gridded using spline interpolation with an X and Y interval of 2m and a tension of 0.25 for 250 iterations with a convergence limit of 0, and max and min data values as data limits. Data were filtered during the gridding process using the median value. The grids were clipped to remove areas not covered by data with a clip radius of 30m from each data point. Gridded data were then imported into Fledermaus Dmagic v7.3.2 to re-grid (.sd) for import to ESRI

ArcGIS.

The ESRI Spatial Analyst Surface Analysis tools were used to produce 5nT interval contour lines from the 5m spatial resolution magnetometry grids. The complete workflow is shown in figure 4.

2.3 Sub-bottom Profiling

CHIRP sub-bottom data were acquired aboard the UNC-Wilmington’s R/V Cape

Fear in November 2012, using an EdgeTech sb512i CHIRP sub-bottom reflection sonar with Edgetech Discover acquisition software (figure 5). Data were acquired at a ship speed of ~2-3 knots. Towfish navigation was obtained by a topside NorthStar 965 DGPS receiver. The sub-bottom reflection profiles were acquired using a .5-8 kHz CHIRP signal with a 5 ms sweep. All surveys are georeferenced in NAD 1983 South Carolina

State Plane Feet unless otherwise noted.

2.3.1 Sub-bottom Data Processing

The CHIRP sub-bottom data were processed using SIOSEIS and Seismic Unix seismic processing software packages. The final processed data have been heave corrected and trace balanced for noise reduction. The data were also depth corrected to account for tidal variations in water depth and the depth of the fish in the water column

(figure 6, 7). Since fish depth is not directly recorded in the CHIRP data, the approximate fish depth was determined by correlating seafloor depth in the CHIRP data with measurements made by a georeferenced multibeam survey of the channel area provided by the Army Corps of Engineers. CHIRP sub-bottom data is recorded in two-way-travel time (TWT) in seconds, or the time it takes for a sound wave to travel down to the seafloor and be reflected back to the instrument. In general, an average sound velocity in seawater of 1525 m/s is used to convert TWT to depth, keeping in mind that TWT represents twice the reflector depth (e.g., Depth = {TWT * 1525 m/s}/2). Seafloor

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 17

Figure 4. Magnetometry data acquisition and processing workflow.

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 18

Figure 5. Photo showing the EdgeTech sb512i CHIRP sub-bottom reflection sonar.

Figure 6. Illustration of towfish geometry relative to sea surface showing seafloor and multiple ray paths.

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 19

Figure 7. CHIRP sub-bottom data acquisition and processing workflow.

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 20 multiple and “ghost” reflectors (illustrated below) occur below ~.035 s (TWT) in most of the CHIRP profiles.

2.3.2 Subsurface Layer and Isopach Map Creation

Three horizons (seafloor, base of surficial modern sediment [minimum depth to top of rock], and base of relict sediment [maximum depth to top of rock] were digitized from the CHIRP sub-bottom profiles using The Kingdom Suite (Seismic Micro

Technology, Inc.) seismic interpretation software. All of these horizons were gridded using an inverse distance weighting algorithm and then used to compute modern sediment thickness, relict sediment thickness and paleo-channel depth isopach grids, which were then imported to ESRI ArcGIS 9.3. In the main entrance channel and survey extension areas, the data is divided into 4 segments: center of the main channel, southern flank of the main channel, northern flank of the main channel and channel extension.

Bounding boxes around these segments were used to constrain the surface interpolation and provide a more realistic and better surface fit for the shape of the channel.

2.3.3 3-D Visualization

CHIRP sub-bottom profile imagery was imported into IVS Fledermaus as georeferenced vertical “curtains”. The digitized horizons (base of surficial modern sediment and base of relict sediment) were imported as xyz point objects for interpretation overlay.

2.4 Hydrographic Surveying

Single beam surveys were conducted with a Real-Time Kinematic Global

Positioning System (RTK-GPS). A virtual base station using the South Carolina

Geodetic Survey’s real time virtual network was used to broadcast real-time corrected

GPS data to the roving unit collecting single beam data. Virtual base station point was moved accordingly to ensure distance to suvey area did not exceed 5km. Positional accuracy was determined by comparison of established benchmark values versus collected data. For the offshore sections of the entrance channel and the ODMDS, data were collected aboard the R/V Cape Fear and tidal data were applied to the DGPS poisiton using a tide file from a NOAA tidal station located in Charleston SC.

Single beam data acquisition was conducted aboard a 20 ft Carolina Skiff outfitted with a Knudsen Mini-Sounder (210 kHz) , TSS DMS-05 motion reference unit, Ashtech Z-Xtreme GPS receiver, and dual frequency GPS antenna. Sound velocity profiles conducted at the beginning and end of surveying each day were used to determine sound velocity. All instrument and water level offsets were measured and entered into HYPACK. HYPACK software was used for navigation and data acquisition.

A diagram illustrating single beam data acquisition and processing workflow is provided in (figure 8). All raw and processed data can be found in the digital files accompanying this report.

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 21

Figure 8. Single beam acquisition and data processing workflow diagram.

Virtual base station using SCGS network

Single beam fathometer

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 22

2.4.1 Data Procesing

Raw depth and position data were merged, heave/pitch/roll and tide corrections were applied, and data were processed to produce a corrected, RTK-positioned depth with HYPACK software. Initial outlier points were removed using the HYPACK Single

Beam editor and exported as a text file.

2.5 Groundtruthing

2.5.1 Video

Video was collected with a submersible camera mounted on a three-wheel cart

(figure 2). The camera was positioned to look downward and slightly in front of the cart.

Video data were time-synchronized with the GPS time stamp and recorded to DVDs.

After data collection, all video was reviewed and changes in bottom type were noted by time (position). Bottom type was coded by sediment type, bathymetry, and biological features. For example, changes between flat, sandy bottom and rocky ledges were coded.

High-relief bottom (ledges) were coded and distinctions were made between ledges possibly associated with drowned marsh deposit and rocky ledges sometimes covered with heavy emergent growth.

2.5.2 Sediment Grabs

A Ponar type grab sampler was used to collect sediment grabs aboard the South

Carolina Department of Natural Resource’s R/V Silver Crescent. Two sediment grabs were collected along each video transect. Samples were placed in labeled plastic bags for subsequent analysis. At CCU, sediment samples were subsampled, dried, and sieved at one-phi increments. Visual classification according to the Unified Soil Classification

System was used to qualitatively describe the range of sediment textures throughout the study area.

Sediments largely consist of fine-coarse sands. Some areas contained extensive coarse grains and shell hash. Fines were typically less than 10%. Basic sediment descriptions by video line number and position are listed in Table 1. Full detail of the sediment analysis including sieve size fractions are located in Appendix 3.

Table 1. Sediment grab descriptions, corresponding video tow lines, and grab positions.

Sample # Tow line lat long Verbal Description

01_1922 1A 32.625764° -79.791150° <5% shell hash, Moderately sorted, medium grained sand

01_2_1929 1A 32.629782° -79.795204° ~30% shell hash, Poorly sorted, medium grained sand

02_1934 2A 32.629843° -79.788740° ~5% shell hash, Moderately well sorted sand, fine to medium grained sands

02_2_1941 2A 32.631368° -79.789618° ~25% broken shell, Poorly sorted, fine-medium grained sands

03_1906 3A 32.615234° -79.778505° ~30% shell hash, sand

03_2_1911 3A 32.616589° -79.779729° See appendix 3

04_1849 4A 32.603251° -79.766642° ~20% shell hash

04_2_1855 4A 32.601652° -79.767674° ~50% shell hash, Poorly sorted, fine-medium grained sand

05_1838 5A 32.603252° -79.757880° ~35% shell hash, sand

05_2_1842 5A 32.603200° -79.761424° ~10-15% shell hash, Moderately well sorted sand, medium grained sand

06_1912 6A 32.644146° -79.694641° ~40% shell hash, Poorly sorted sand

06_2_1925 6A 32.645796° -79.698146° ~70% shell hash, Poorly sorted, medium grained sand

07_1935 7A 32.651277° -79.696851° ~5% shell hash, very fine grained sand

07_2_1940 7A 32.650639° -79.699922° <5% shell hash, Moderately-well sorted, fine-medium grained sand

08_1956 8A 32.655565° -79.717573° ~70% shell hash, Poorly sorted, medium grained sand

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 24

Table 1 continued

08_2_2001 8A 32.653738° -79.715569° ~50% shell hash, Moderately well sorted sand, coarse to medium grained sands

09_1947 9A 32.658015° -79.710077° ~5% shell hash, Moderately well sorted sand, fine to medium grained sands

09_2_1951 9A 32.657833° -79.712776° <5% shell hash, Moderately well sorted, fine-medium grained sand

10_1725 10A 32.658990° -79.729846° ~25% shell hash, Poorly sorted sand, coarse to medium grained sands

10_2_1732 10A 32.659475° -79.732036° ~70% shell hash, Poorly sorted, medium grained sand

11_1949 11A 32.665420° -79.740092° ~25% shell, Moderately-well sorted, medium grained sand

11_2_1951 11A 32.665760° -79.742846° <5% shell hash, Moderately-well sorted, fine-medium grained sand

12_1740 12A 32.669031° -79.737169° ~45 shell hash

12_2_1745 12A 32.671788° -79.738388° ~80% shell hash, Poorly sorted, medium-coarse grained sand

13_1749 13A 32.674446° -79.742074° ~60% shell hash, Poorly sorted, medium-coarse grained sand

13_2_1752 13A 32.675029° -79.744430° ~65% shell hash, fine grained sand

14_1800 14A 32.669579° -79.748625° ~50% shell hash, Poorly sorted sand, fine to medium grained sands

14_2_1811 14A 32.668869° -79.751102° ~60% shell hash, Poorly sorted, medium grained sand

15a_2_214

15A 32.686817° -79.766494° ~50% shell hash, Poorly sorted, medium-coarse grained sand

15a_2139 15A 32.685600° -79.764589° ~60% shell hash, Poorly sorted, medium-coarse grained sand

16_1744 16A 32.616226° -79.592034° See appendix 3

16_2_1748 16A 32.616576° -79.594074° ~70% shell hash, Poorly sorted, medium-coarse grained sand

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 25

17_1825 17A 32.652399° -79.659892° ~10% shell hash, Moderately-well sorted, medium grained sand

17_2_1828 17A 32.652857° -79.661035° ~40% shell hash, Poorly sorted, medium-fine sand

18_1921 18A 32.663721° -79.683516° ~10-15% shell hash, Moderately well sorted sand, medium grained sands

18_2_1927 18A 32.661097° -79.678008° ~25% shell hash, Moderately-well sorted, medium grained sand

19_32_184

19A_32A 32.677905° -79.712385° ~10% shell hash, Poorly sorted, medium grained sand

19_32_2_1

19A_32A 32.678913° -79.716503° ~5% shell hash, Moderately sorted, medium grained sane

1a_2207 1A 32.629080° -79.794945° ~10% shell hash, Moderately-well sorted, fine-medium grained sand

20_1846 20A 32.615954° -79.708702° ~25% shell hash, Poorly sorted, fine-medium grained sand

20_2_1849 20A 32.615218° -79.712702° ~40% shell hash, Poorly sorted, medium grained sand

22_1941 22A 32.588096° -79.728879° ~10-15% shell hash, Moderately-well sorted, medium grained sand

22_2_1944 22A 32.590621° -79.728421° ~50% shell hash, Poorly sorted, medium-coarse grained sand

23_2_2013 23A 32.647926° -79.722712° ~60% shell hash, Poorly sorted, medium grained sand

23_2008 23A 32.649451° -79.716459° See appendix 3

24_1803 24A 32.619008° -79.758372° <5% shell hash, Moderately-well sorted, fine-medium grained sand

24_1813 24A 32.615998° -79.754661° ~70% shell hash, Poorly sorted sand, coarse to medium grained sands

25_2_2027 25A 32.657423° -79.741926° ~5% shell hash, Moderately well sorted sand, fine-medium grained sands

25_2024 25A 32.659110° -79.739444° ~20% shell hash, Moderately-well sorted, fine-medium grained sand

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 26

26_1821 26A 32.612392° -79.748083° ~60% shell hash, Poorly sorted, medium grained sand

26_2_1826 26A 32.610921° -79.744847° Moderately well sorted sand no noticeable shell hash, fine-medium grained sands

26_2228 26A 32.611765° -79.746993° ~40% shell hash, Poorly sorted, medium grained sand

27_1702 27A 32.594384° -79.540670° ~45% shell hash

27_2_1710 27A 32.592733° -79.536705° ~15% shell, Poorly sorted, medium grained sand

27_2027 27A 32.594280° -79.538979° ~50% shell hash, Moderately-well sorted, medium grained sand

28_1721 28A 32.606210° -79.568020° ~35% shell hash

28_2_1731 28A 32.607874° -79.571808° ~50% shell hash, Poorly sorted, medium grained sand

28-2014 28A 32.605948° -79.566914° 10-15% shell hash, Moderately well sorted, fine-medium grained sand

29_1735 29A 32.613319° -79.582146° ~40% shell hash, Moderately-well sorted, fine-medium grained sand

29_2_1741 29A 32.614354° -79.584947° See appendix 3

30_1754 30A 32.622759° -79.606089° ~60% shell hash, Moderately-well sorted, coarse-medium grained sand

30_2_1758 30A 32.625871° -79.612479° <50% shell hash, Poorly sorted, medium grained sand

31_1822 31A 32.693919° -79.745881° ~10% shell hash, Moderately-well sorted, fine-medium grained sand

31_2_1827 31A 32.695091° -79.748554° ~25% shell hash, Poorly sorted sand, coarse to medium grained sands

33_1805 33A 32.631905° -79.624550° ~50% shell hash, Poorly sorted, medium grained sand

33_2_1808 33A 32.633485° -79.627715° ~15% shell hash, Poorly sorted, fine-medium grained sand

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 27

34_1815 34A 32.642439° -79.646194° ~60% shell hash, Poorly sorted, medium-coarse grained sand

34_2_1819 34A 32.643442° -79.648155° See appendix 3

5_2221 5A 32.603135° -79.648155° ~50% shell hash, Poorly sorted, medium grained sand

3.0 GENERAL DISCUSSION AND HABITAT ASSESSMENT

3.1 Overview of Data and Habitat Characterization

The side scan sonar data varied throughout the study area in backscatter intensity

(figure 9). Areas of high backscatter intensity are generally characterized as either hardbottom or coarse, sometimes shelly sediments swept into bedforms. The survey and interpretation methods for habitat characterization in the ODMDS and Entrance Channel extension were presented at the Nov 29, 2012 Post 45 Habitat/Cultural Resources

Assessment meeting at the Charleston District Corps of Engineers offices. These are summarized below for ease of evaluation of the groundtruth targets and priorities selected and proposed within this interim report.

Similar geophysical methods were used in mapping and delineating potential hardbottom habitat areas in the previous ODMDS expansion in the 1990s and initial results are consistent with previous work in the vicinity of the ODMDS (Gayes and Viso, 2006).

3.2 Geophysical Interpretation of Surficial Habitat

Side scan and sub-bottom records were analyzed to characterize sea floor habitat into three classes of mappable geophysical units.

These are:

1. areas of clear hardbottom habitat (Probable Hardbottom)

2. areas where hardbottom substrate existing at the sea floor is highly unlikely

(Absence of Hardbottom)

3. areas where localized outcrop of hardbottom substrate are exposed the sea floor is possible but limited and patchy in aerial extent. (Possible Hardbottom).

Probable Hard Ground

Sub-bottom profiling of these areas typically shows very thin (less than 50 cm) or no surficial sediment cover overlying older potentially indurated substrate. Occasionally, strong subsurface reflectors can be traced from depth to where they intersect the sea floor, often forming a surficial expression such as change in slope or standing relief on the sea floor. The sea floor is often coincident or nearly coincident with the transgressive ravinement. Hard ground areas in the region tend to exhibit strong acoustic impedance

(reflectivity) in sub-bottom records at or very near the sea floor (figure 10, 11).

Penetration of the acoustic signal is impeded at the sea floor as evidenced by absence of coherent reflectors with depth; sometimes also expressed as strong “ringing” of multiples of the acoustic signal between the sea floor and surface of the ocean.

Broad areas of generally high backscatter on side scan sonar records typically characterize probable hard ground areas. Indurated material standing exposed in relief on the sea floor as ledges or mounds frequently form mappable linear or curvilinear ledges in the side scan record. Occasionally, such ledges may stand in relief sufficient to cast

“shadows” in the sonar record allowing an estimate of relief of the ledge. Coarse shell

Figure 9. Side scan sonar (backscatter intensity) mosaic in Post 45 ODMDS and entrance channel.

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 30

Figure 10. Sub-bottom profile (Line 94) showing examples where older, tilted reflectors are evident at or near the sea floor with little or no overlying surficial sediment cover. Hard ground habitats are highly likely to be found in such areas.

No definable surficial sediment veneer Reflector exposed at sea floor

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 31

Figure 11. Sub-bottom profile (Line 41) showing examples where a definable thickness (>4 meters) of sediment infilling within a definable and laterally continuous channel and above a flat lying ravinement surface. In such areas older, tilted and potentially indurated substrate that could form hard grounds is separated from the sea floor and presence of hard grounds is highly unlikely.

Channel Infill Sediment Layer Above Ravinement Older Tilted Reflectors hash lags (also high backscatter) frequently heavily rippled are common within the ledge areas. Locally, patches of lower backscatter (fine sand) are often present within the broader field of outcrop.

This type of habitat is known to be present within the region and has been previously identified in the Southwest corner ODMDS (Gayes and Viso, 2006).

Absence of Hard Ground

In other areas, there is clear geophysical evidence of the absence of hardbottom habitat exposed at the sea floor. Such areas are typically characterized by varying thicknesses of recent sediment cover (usually sand) overlying a well-defined and laterally mappable “ravinement” surface in sub-bottom profile data. Locally, relatively thick sections of sediment coincide with seismically-defined relict fluvial and/or tidal channel incisions. Theses channel features, now backfilled with thick sediments, result from paleo-drainage networks incised into a more thoroughly indurated, potentially hardbottom habitat forming substrate. In addition, sand ridges and other large-scale sedimentary bed forms, may overlie hard substrate separating potential hard grounds and the sea floor by several meters of unconsolidated sand.

In these areas, side scan sonar records typically exhibit lower overall backscatter and variability. Wave and current driven sedimentary bedforms are also commonly apparent in side scan records of these areas.

Possible Hard Grounds

On the inner continental shelf in the vicinity of the ODMDS there are known areas of “low relief” hard grounds. In these areas a very thin, and potentially mobile, veneer of sand typically covers hard substrate with relatively low physical relief. Such areas are often expressed as patchy high backscatter areas in side scan sonar interspersed with coarse shell hash rippled lenses and patches of bedforms starved of finer (low backscatter) sand. Chirp records show very thin veneers of surficial sediment above a definable strong, largely flat lying near surface reflector. Such areas can be locally found either as transition between extensive hard ground areas and increasing percentage cover and thickness of sediment or as patches of low lying partially sand covered areas independent of easily defined (high relief) hard grounds. As a result the character of acoustic signatures is often a hybrid between extensive hard grounds and more extensive sand sheets.

3.3 Groundtruthing Geophysical Data and Interpretations

Geophysical survey methods such as side scan and chirp are remote sensing mapping tools that report responses of the system to an active pulse of acoustic signal.

The character and spatial geometries of the response are valuable in interpretation of sea floor and shallow subsea habitats and deposits.

For many settings, such as areas of extensive high relief hard grounds or incised channel fills, a very high degree of confidence can be placed on interpretation of the

Hardbottom and Cultural Resources of the Post 45 Charleston Harbor Project Study Area 33 remote sensing of the area (figures 10, 11).