In May 2005, the Castle Peak Power Company
Limited submitted an application for an Environmental Impact Assessment (EIA) study
brief (No. ESB-126/2005) to be undertaken on a Liquefied Natural Gas (LNG)
Terminal and Associated Facilities at South Soko Island, and a
submarine natural gas pipeline between Black Point and South Soko (Figures 1.1 and
1.2). As the proposed development involves marine
works (see Part 2 – Section 3.2.1, 3.2.3,
3.2.4, 3.2.6, 3.3.3, 3.3.4 and 3.3.5
for details of marine works required), potential impact on marine
archaeological resources would be a concern.
Thus, a Marine
Archaeological Investigation (MAI), in accordance with Clause 3.7.8.2(ii) of
the Study Brief, was
required. This report was prepared by
Figure 1.1 LNG Layout Plan at
1.2
Objectives of the
Marine Archaeological Investigation
The objectives of the MAI were to include
a phased review/investigation of the Study Areas in accordance with the MAI
Guidelines as stated in ESB-126/2005,
which should include the following:
·
Baseline
Review on known sources of archive data as stated in Section 1.2 of the MAI
Guideline;
·
Review
of Geophysical Survey Raw Data prepared by CAPCO’s
Geophysical Contractor EGS (
·
Review
of Magnetic Survey Data prepared by CAPCO’s
Geophysical Contractor EGS (
·
Remote
Operated Vehicle Survey prepared by CAPCO’s
Geophysical Contractor EGS (
·
Establish
Archaeological Potential;
·
Provide
a Report on these aspects.
This report represents the MAI results.
Following this introductory section, the
remainder of the report has been structured as follows:
Section 2 The legislative framework for the marine
archaeological assessments in
Section 3 The methodology used in
this survey;
Section 4 The findings of the baseline conditions
(desktop and geophysical surveys) for the Study Areas;
Section 5 Establish archaeological potential of the
Study Areas; and
Section 6 Assessment of the impact on the
archaeological resources and recommendations.
The following legislation and guidelines
are applicable to the assessment of marine archaeological sites in
· Environmental Impact Assessment Ordinance
(Cap. 499) and the associated Technical Memorandum on the EIA Process
(EIAO-TM);
·
Antiquities and Monuments Ordinance (Cap.
53)(AM Ordinance);
·
Land (Miscellaneous Provisions) Ordinance
(Cap. 28);
·
·
Guidelines
for Marine Archaeological Investigation prepared by AMO.
2.1
Environmental
Impact Assessment Ordinance Technical Me
The EIAO-TM outlines the approaches
required in investigating and assessing the impacts on marine archaeological
sites. The following sections of the EIAO
– TM are applicable:
Annex 19:
“There is no quantitative standard in deciding the relative importance
of these sites, but in general, sites of unique archaeological, historical or
architectural value will be considered as highly significant. A baseline study shall be conducted: (a) to
compile a comprehensive inventory of places, buildings, sites and structures of
architectural, archaeological and historical value within the proposed project
area; and (b) to identify possible threats of, and their physical extent,
destruction in whole or in part of sites of cultural heritage arising from the
proposed project.”
The EIAO – TM also outlines the
criteria for assessment of impact on sites of cultural heritage as
follows:
Annex 10:
“The criteria for evaluating impact on sites of cultural heritage
includes: (a) The general presumption in
favour of the protection and conservation of all sites of cultural heritage
because they provide an essential, finite and irreplaceable link between the
past and the future and are points of reference and identity for
The EIAO – TM also outlines the
approach in regard to the preservation in totality; and in part to cultural
resources:
Annex
19: “Preservation in totality will be a
beneficial impact and will enhance the cultural and socio-economical
environment if suitable measures to integrate the sites of cultural heritage
into the proposed project are carried out.
If, due to site constraints and
other factors, only preservation in part is possible, this must be fully
justified with alternative proposals or layout designs, which confirm the
impracticability of total preservation.”
2.2
Antiquities and
The Antiquities
and Monuments Ordinance (Cap. 53) (AM
Ordinance) provides statutory protection against the threat of development
on
“This Ordinance provides for the preservation of objects of historical,
archaeological and palaeontological interest…”
The Ordinance
defines an antiquity as a relic (a movable object made before 1800) and a
place, building, site or structure erected, formed or built by human agency
before the year 1800. The Ordinance also states, amongst other things, that the
discovery of an antiquity shall be reported to the Authority (Secretary for
Home Affairs); that ownership of all relics discovered after 1976 shall be
vested in the Government; that the Authority can declare a place, building,
site or structure to be a monument, historical building or archaeological or palaeontological site or structure (and therefore
introducing certain additional controls for these sites); and that licences and
permits can be granted for excavation and for other work.
Over the years, surveys have been
undertaken to identify archaeological sites in
Section
11 of the AM Ordinance requires any person who discovers
an antiquity, or supposed antiquity, to report the discovery to the Antiquities
Authority. By implication, construction
projects need to ensure that the Antiquities Authority, the Antiquities
Advisory Board (AAB) ([1]), is formally notified of archaeological
resource which are discovered during the assessment or construction of a
project.
2.3
Land
(Miscellaneous Provisions) Ordinance (Cap. 28)
Under this Ordinance, it is required that a permit should be obtained for any
excavation within the Government land prior to any excavation work commencing.
2.4
The
Chapter 10, Conservation, of the HKPSG
provides general guidelines and measures for the conservation of historical
buildings, archaeological sites and other antiquities.
2.5
Marine
Archaeological Investigation (MAI) Guidelines
Guidelines for MAI which detail the
standard practice, procedures and methodology which must be undertaken in
determining the marine archaeological potential, presence of archaeological artefacts
and defining suitable mitigation measures can be found in Appendix D of
the EIA Study Brief No. ESB-126/2005. Baseline review, geophysical
survey and establishing archaeological potential are considered the first stage
of a MAI. Subject to the results of the
first stage MAI, further investigation may or may not be required.
The methodology used in this assessment
followed the Guidelines for MAIs as prepared by AMO
and experience from the marine archaeologist and comprised the following tasks.
3.1.1
Establish Baseline Conditions
·
Implement
Desktop Research, comprising a review of geotechnical survey data, historical
documents and United Kingdom Hydrographic Office
‘Wreck’ files to establish the potential for marine archaeological sites in the
Study Area (South Soko terminal, gas pipeline, watermain and submarine cable);
·
Examination
of the seabed and below seabed information using the geophysical survey
equipment, magnetic survey and remote operate video (ROV) for the preferred gas
pipeline alignment in order to locate and define any sites of archaeological
potential in the Study Areas.
3.1.2
Establish Archaeological Potential
The synthesis and analysis of the baseline
conditions were used to establish if there were any marine archaeological sites
in the Study Areas.
3.1.3
Impact Assessment
Based on the findings and analysis of the
baseline conditions, an assessment was made of the potential impact of the project
on the marine archaeological sites, and recommendations made to mitigate any
impact.
The review of the historical documents and
literature indicated that the general region was occupied and used by Chinese,
then many other foreign traders for many years.
The islands of the region contain archaeological evidence of occupation
from about 4,000 years ago, including evidence of the use of the sea, and
material from the seabed, during that time.
They became important trading centres for trading vessels from
4.1.1
Geotechnical Data
Generally, the
submarine deposits in the
The Chek Lap Kok Formations, the lowest part of the Quaternary
succession are considered to be Middle to Late Pleistocene in age and consists
of colluvium, alluvium and lacustrine
sediments Fyfe, et.al., (2000). The marine sediments on top of this formation
are sediments related to the Holocene period (from about 13,000 BP to the
present day) and referred to as the Hang Hau
Formations consisting of clayey silt sediments and some sand.
The Sham Wat
Formation, found between Chek Lap Kok
Formations and Hang Hau Formations is considered to
be the Eemian deposit with uncertain age and consists
of soft to firm silty clays with yellowish
mottling. This formation is presently
not widespread but only in subcrops beneath the Hang Hau Formation ([2]).
More modern sediments are related to the
discharge from the Pearl River, (and which would have an effect on the project
area, being located down stream from the mouth of the
Fyfe ([4])
further explains the rate of
sedimentation:
“In
general, present day sedimentation rates in
During the late Pleistocene period (18,000BP)
sea levels began to rise until about 6,000 years BP to levels similar to the
present day. “The extent of the rise
could be as great as perhaps 140 metres in parts” ([5]).
The sediments of the Late Holocene period,
considered to be relatively homogenous very soft to soft silty
clay and with high moisture content, offers the greatest potential to include
well preserved remains associated with the occupation and use of the islands in
4.1.2
Review of Historical Documents
There is lack of precise historical
document in relation to the maritime activities associated with the Study
Area. However, literature review
indicated that the water channel between South Soko
and
Marine
archaeology is still a new area in
4.1.3
The United Kingdom Hydrographic
Office (UKHO) in
Annex
12-D-A and Figure Annex A1 provide a list of these
sites, which are summarised as follows.
A total of 24 shipwrecks were found to be in
a very broad area that included the three Study Areas. Twelve of them are still ‘live’ (i.e. exist)
and the remaining have been ‘lifted’/’dead’ from the seabed and nothing remains
of them on the pipeline route (see Figure 4.24). For the ‘live’ (either chartered or unchartered but potentially still lying on the seabed)
shipwrecks, only two of them (No. 46602 and 62931) were found to be within 1 km
of the Centre Line (CL) of the pipeline route and the associated
facilities. No. 62931 located about 928
m east of the CL and at 2462177m N, 792754mE and No. 46602 located about 57 m
east of the CL of the proposed pipeline at 2481409m N, 795912m E(UTM, WGS84).
The UKHO records state that Wreck No.
46602 was a 3130 ton Japanese freighter Shirogane Maru that was sunk during World War II. Its position was last verified by a diver on
20th October 1987. Wreck No
62931 is referred to as an ‘obstruction’, its position is accurately known but
no other details recorded – it is potentially not even a shipwreck. The identity of wreck No. 46537 is also
unknown apart from it being 14 m in length.
Chart No. HK1503 has an Obstruction marked
(“Obstn”) at the location of Wreck No. 46602 and
which is recorded as a Wreck on Chart 3026 (Dated 1990). One of the other UKHO Wrecks (No. 62931) also
appears on this chart.
The Hong Kong Marine Department could not
provide any additional information beyond what was provided by the UKHO. The
geophysical survey (which was very comprehensive, as outlined below) failed to
locate either wrecks Nos. 46602 or 62931 and this would indicate that they have
been salvaged/lifted or removed for unknown reasons.
Discussions were also carried out with the
Hong Kong Marine Department about a wreck adjacent to Sha
Chau/Lung Kwu Cha that had
been lifted in March 2006 from a location about 700 m north of the pipeline
CL. The wreck is a Chinese engineering
vessel mostly damaged and approximately 10 m x 3 m x 2 m in size. It is estimated that the wreck was about 30
years old (see Figure 4.24 for location). Shipwrecks/Obstructions are continually
salvaged in
4.2.1
Introduction
The objective of the geophysical survey
was to define the areas/sites of greatest archaeological potential by
establishing the depth and nature of the seabed sediments and mapping any
seabed and sub-bottom anomalies, which may be archaeological material. This information is provided below.
4.2.2
Survey Scope
The survey scope (see Figure 4.1) of
the Geophysical Survey covers the following:
·
Proposed
Approach Channels, Turning Circles and Reclamation Areas at South Soko covering 715 km2 of seabed;
·
A 500
m wide corridor was surveyed, centred on the preferred option of the proposed
gas pipeline route from South Soko to Black Point
with route length of 39 km, a total of 1,145 km of line survey;
·
A 400
m wide corridor was surveyed, centred on the proposed power cable route survey
from Shek Pik to
·
A 504
km line of geophysical records, in a corridor stretching from the north west of
Lantau to close to the southern boundary of the Sha Chau and Lung Kwu Chau Marine Park; and
·
A
15km route length, 300-500 m wide corridor inshore of the area to the west of Lantau.
Geophyscial
Surveys were undertaken by CAPCO contractor, EGS (
4.2.4
Equipment Used
·
Multi-Beam
Echo Sounder (Seabeam 1180 multi-beam system, 180 kHz transducer and cable, Anschutz
Raytheon Gyrostar II gyrocompass, Seatronix
MRU 5, Valeport Model 600 temperature/salinity
profiler);
·
Single-Beam
EchoSounder (Knudsen Model 320 survey echo sounder,
Dual frequency transducer, Bar Check);
·
Navigation
& Positioning (C-Nav DGPS System w/ 50m cables,
C-Nav Antenna Stand, Navigation PC, Navigation
Monitor, Marine Radio, Hand Held Radio Set w/ Charger);
·
Sub-bottom
Profiler (C-Boom low voltage boomer system, EGS TVG Processor, C-Phone
hydrophone system, 120/138 Waverley Recorder);
·
Side
Scan Sonar System (Klein 3000 side scan sonar system);
·
Measurement
of Currents (RD Instruments acoustic Doppler current profiler (ADCP));
·
Magnetometer
(‘SeaSPY’, manufactured by Marine Magnetic Ltd); and
·
Other
Computer facilities (C-View Logging System & monitors, C-View Int. System,
Printers (B/W), UPS for computer systems).
4.2.5
Review of Geophysical Survey Results
The geophysical survey data obtained by
EGS were processed by in house geophysicists and reviewed by the marine archaeologist. The geophysical surveys showed how the seabed
in the different Survey Areas had been impacted by anchoring, trawling (Figure 4.5) and the dumping of materials
(Figure 4.6). Anchoring and trawling will reduce the
archaeological potential of the seabed in these areas as will the dumping of
materials, although this activity can also enhance the archaeological potential
by providing a protective covering over sites (it can also interfere/damage
sites through this activity). It makes
it very difficult, potentially impossible to assess the archaeological
potential of these parts of the seabed.
Seismic records found the underlying sediments on the route close to Lantau have been worked and reworked, caused by scouring
and deposition from the strong currents.
In addition, the surveys located a total of 255 Sonar Contacts([9])
comprising natural features,
dumped materials, shipwrecks, linear debris, anchor marks and fishing
devices. Further review of the 255 Sonar
Contacts identified 14 which are considered as wrecks, possible wrecks or sites
of archaeological potential (Table 4.1 and
Figure 4.7).
|
Figure 4.5 Geophysical
Survey Showing How The Seabed Was Impacted By
Anchoring & Trawling
|
Figure 4.6 Geophysical
Survey Showing How The Seabed Was Impacted By The
Dumping Of Materials
Table 4.1 List of the 14 Sonar Contacts
Contact number |
Latitude Longitude |
Easting Northing |
KP RPL offset |
Dimensions (m) |
Description |
SC014 |
22°
24.389' N 113° 52.407'
E |
795836.0E 2480649.0N |
34.039 198m E |
6m x
1.3m x 0.3m |
Possible
wreck |
SC020 |
22°
24.360' N 113°
52.354' E |
795745.0E 2480594.0N |
33.977 96m E |
13m x
5m x 0.25m |
Possible
wreck |
SC027 |
22°
21.253' N 113°
52.268' E |
795708.0E 2474854.0N |
28.227 33m E |
39m x
6.5m x 2m |
Wreck |
SC028 |
22°
20.235' N 113°
52.237' E |
795691.0E 2472974.0N |
26.338 5m W |
8m x 2m
x 0.2m |
Possible
wreck |
SC043 |
22°
12.320' N 113°
49.589' E |
791415.0E 2458273.0N |
10.491 176m W |
6m x 2m
x 0.5m |
Possible
wreck |
SC044 |
22°
12.304' N 113°
49.628' E |
791482.0E 2458244.0N |
10.437 126 W |
6m x 2m
x 0.5m |
Sites
of Archaeological Potential |
SC053 |
22°
10.885' N 113°
50.471' E |
792981.0E 2455651.0N |
7.384 743m SW |
3m long |
Linear
Debris |
SC055 |
22°
10.742' N 113°
51.264' E |
794350.0E 2455413.0N |
6.013 107m SW |
14m
long |
Linear
debris |
SC067 |
22°
10.546' N 113°
51.276' E |
794377.0E 2455052.0N |
5.874 373m SW |
12m x
3m x 0.5m |
Sites
of Archaeological Potential |
SC072 |
22° 10.074'
N 113°
53.422' E |
798084.0E 2454250.0N |
2.103 277m N |
8m x 3m
x nmh |
Sites
of Archaeological Potential |
SC086 ([10]) |
22°
24.388' N 113°
54.072' E |
798693.9E 2480702.4N |
39.148 1572m
SW |
10.77m
x 3.31m x 2.03m |
Possible
wreck |
SC090 |
22°
9.876' N 113°
54.338' E |
799667.0E 2453914.0N |
0.440 19m N |
5m x 2m
x 0.2m |
Sites
of Archaeological Potential |
SC091 |
22°
9.923' N 113°
54.411' E |
799791.0E 2454003.0N |
0.309 118m N |
18m x
4m x 0.9m |
Possible
wreck |
SC092 |
22°
9.991' N 113°
54.488' E |
799921.0E 2454132.0N |
0.168 236m N |
9m x 2m
x 0.5m |
Wreck |
The 241 Sonar Contacts discounted as wrecks, possible
wrecks or sites of archaeological potential were based on a combination of factors,
which included the interpretation and a comparison of the geophysical
signatures with those signatures that were clearly wrecks (and possibly
wrecks), debris and dumped materials.
Wrecks as seen in the side scan sonar images have identifiable relief
(as seen in the shadows they develop on the side scan sonar images) and
features that could be considered not-natural, such as straight lines
delineating its boundaries. In
comparison, debris could show relief but it is characterised by natural, rounded
features and boundaries. Dumped
materials and some debris were characterised by areas of a darker/black section
of the seabed on the side scan sonar images consisting of coarser
materials/sediments with little or no relief.
The assessment also included the context of the Sonar Contact with its
surrounding seabed environment, where identifiable dumped materials/debris was
found to be in the very near vicinity.
The raw data for all the Sonar Contacts was reviewed by the marine
archaeologist using the above criteria and 14 contacts were interpreted as
wrecks, possible wrecks, linear debris or sites of archaeological potential.
Sonar Contacts 079 and SC082 , while initially identified as debris/wrecks ,
upon review of the side scan sonar images by the marine archaeologist using the
above criteria were interpreted as debris/dumped materials and this is
illustrated in the SC082 case (see Figure
4.7a).
Figure 4.7a A Further
Review and Interpretation of SC082 Was
Based on Its Context with the Nearby Dumped Materials, Its Physical Appearance and Lack of Relief.
In some sections of the survey area, a
small number of ‘masked zones’ are referred to.
This applied to some of the seismic data, where gas masking affected the
interpretation of the sediments/formations but only below the Hang Hau Formations (the zone which most likely to contain
archaeological deposits). The side scan
sonar data was not masked, so there were no gaps in the geophysical surveys
from an archaeological perspective.
All of these 14 anomalies are sitting on
the seabed. A review of the boomer data
failed to identify any sub-bottom anomalies.
Based on the side scan sonar results, six
of the anomalies are problematic about their identity but were labeled as ‘linear debris’ or ‘sites of archaeological
potential’ and worthy of further investigation, including SC044 (Figure
4.8), SC053(Figure 4.9), SC055(Figure 4.10), SC067 (Figure 4.11), SC072(Figure 4.12) and SC091(Figure
4.13). While it is quite likely that
others, such as SC014 (Figure 4.14),
SC020 (Figure 4.15), SC028 (Figure 4.16), SC043 (Figure 4.17), SC086 (Figure 4.18) and SC091 (Figure 4.19) are possibly shipwrecks,
there was still a degree of doubt given the problematic side scan sonar survey
images of these anomalies. Some of the
side scan sonar results revealed without doubt shipwrecks, e.g. SC027, (Figure 4.20) and SC092 (Figure 4.21).
Figure 4.8 Site
of Archaeological Potential (SC044)
Figure 4.9 Linear Debris (SC053)
Figure 4.10 Linear Debris (SC055)
Figure 4.11 Site
of Archaeological Potential (SC067)
Figure 4.12 Site
of Archaeological Potential (SC072)
Figure 4.13 Linear Debris (SC090)
Figure 4.14 Possible
Wreck (SC014)
Figure 4.15 Possible
Wreck (SC020)
Figure 4.16 Possible
Wreck (SC028)
Figure 4.17 Possible
Wreck (SC043)
Figure 4.18 Possible
Wreck (SC091)
|
Figure 4.19 Possible
Wreck (SC086)
Figure 4.20 Wreck (SC027)
Figure 4.21 Wreck (SC092)
It was this degree of doubt in some of the sites as
well as the possibility that the recognisable shipwrecks could be modern sites,
i.e., post-1800 (the date which AM
Ordinance defines an antiquity as a relic) that prompted the recommendation
that a Magnetic Survey was conducted of the above sites to ascertain how much
ferrous material remains on the anomalies.
While pre-1800 ships would have carried ferrous equipment and used
ferrous material in their construction, post-1800 ships, particularly the
larger ships of the size of SC027 could potentially be modern ferrous barges
that are used today in and around
For the purpose of the MAI, a Magnetic
Survey covering the 14 Sonar Contacts as presented in Table 4.1 was undertaken by EGS from 2 to 4 September 2005([11]).
4.3.1
Survey Scope and Methodology
Magnetometers have been used in maritime
archaeology for about 40 years to locate and map shipwrecks, both iron
shipwrecks and non-ferrous shipwrecks (Green, 2004: 62-73)[12].
Ferrous material (such as anchors, cannons, nails, chain, etc.)
contained in a shipwreck will change the intensity of the earth’s magnetic
field and this change in intensity can be measured with a magnetometer sensor
towed behind a boat. For a typical
object (such as a shipwreck) the intensity of the magnetic anomaly varies as
the inverse of the cube of the distance from the anomaly and the unit of measurements
is known as a nano Tesla (nT).
The SeaSPY magnetometer used in this survey can
detect changes in intensity of less than 1 nT. A 5 nT change in intensity will detect a 10 tonne shipwreck at
45 metres, a 10kg cannon ball at 3 m and a 2 tonne cannon at 27 m (Green, 2004:
63). Conversely, a 10kg cannon ball will produce a change in intensity of c.2-3
nT at 5 m (distance from sensor to seabed in this
survey) and a 2 tonne cannon will be produce a change in intensity of c.600 nT at 5 m.
When searching for shipwrecks,
magnetometers use wide search lanes, perhaps 50, 100 or hundreds of metres
depending on the size of the anomaly to provide an exact location, with little
detailed information about the nature of the anomaly. In this survey, the SeaSPY magnetometer was used to implement close-plot
surveys over small areas of a number of sites, using a maximum of 5 m search
lanes and with the instrument capable of taking a reading every 0.25 second.
This enabled detailed magnetic contour plans to be developed which in
association with other surveys, such as other remote sensing surveys can assist
in ascertaining the nature of a site. These accurate contour plans can help to
locate discreet anomalies such as cannons, anchors, even iron fittings used in
wooden hull construction.[13] Large intensity anomalies without many
discreet anomalies could be single objects, such as a cannon, an anchor, an
engine, dumped materials and the ship itself if constructed of ferrous
material.
It is highly unlikely that timber vessels
of any size from small sampans to large junks would not contain some ferrous
material. Iron nails have been found in
use on Chinese ships dating back to 220BC, together with the use of iron adzes
and chisels used in their construction and maintenance ([14]). Some
pieces of iron equipment in the form of anchors, grapnels, guns, machinery have
also been used on Chinese junks for over 1000 years. The quantity and distribution of the ferrous
material (found through an analysis of the intensity of the anomaly and an
examination of the close-plot contour plans) will in association with the other
surveys help to identify the nature of the site and was the major objective of
the magnetic survey.
The survey covered the 14 Sonar Contacts
identified by the Marine Archaeologist as presented in Table 4.1. For each of the
Contacts, survey lines around 100m long were surveyed, with a line spacing of 5
m (see Figures 4.1 and 4.22a to 4.22i). The 100 m line lengths were selected to
allow time for the magnetic sensor to be deployed close to the seabed and
moving smoothly at a fixed level by the time it passed across the feature. The line interval of 5 m was selected as
magnetic anomalies decay rapidly with distance from the ferrous material
(usually an inverse cube relationship), and a wider spacing risked completely
missing a magnetic anomaly.
Turbidity and
Visibility
For each of the surveyed areas of the 14
Sonar Contacts, a vertical profile of turbidity was recorded, with closely
spaced readings close to the seabed and wider spacing close to the sea
surface. The turbidity sensor was
attached to a Secchi disc, so that the greatest depth
that visible objects could be seen from the survey boat was also recorded.
Magnetometer
The magnetometer was deployed 15 m behind
the survey vessel, to separate the magnetometer sensor from the magnetic effect
of the vessel’s steel engine. In shallow
water close to coastlines, in less than around 5 m of water, the sensor and
cable were buoyed with floatation material to keep them close to the sea
surface. In deeper waters away from the
shore, non magnetic (brass) weights were attached to the sensor so that it
would sink down close to the seabed. The
position and quantity of these weights was adjusted until the pressure sensor
attached to the magnetometer showed that the magnetometer sensor was within 5 m
of the seabed, without striking the seabed.
The magnetic field strength measured in
the sensor was transmitted up the towing cable to the survey vessel, where the
values were logged together with the navigation information on a computer
logging system.
Positioning and
Navigation
Surface positioning was provided by GcGPS during all of the work: C-Nav
provided primary positioning with a one sigma standard deviation of 0.5 m for
this project. A C-Nav
antenna provides the GcGPS position of the vessel on
a C-Nav decoder.
For each position update, an NMEA string (GGA, VTG) was sent from the C-Nav decoder directly to the computer logging the navigation
and magnetometer information.
4.3.2
Magnetic Survey Results
For each survey line, the regional
gradient and diurnal variability was subtracted from the measured values using
proprietary EGS software, leaving the background geological magnetic field; in
Some of the anomalies have significant
variations from the surrounding background which is associated with the
features containing ferrous material.
Others had no noticeable magnetic variation beyond the level of natural
variability expected in these readings, indicating little ferrous material
around these locations. The results are
summarised below in the description of the magnetic surveys.
The vertical profile of turbidity
measurements and the Secchi disc depths are presented
in Annex 12-D-B.
The turbidity readings and Secchi disc depths suggest that visibility near the seabed
will be less than 1 m for much of the route, so it is likely to be difficult
for divers to make a visual inspection of these features. The outcomes of the Magnetic Survey is
presented in Table 4.2.
Table 4.2 Outcomes of the
Magnetic Survey
Survey number |
Sonar Contact |
Intensity of anomaly |
Conclusion |
M01 |
SC092 |
500nT |
Confirms
presence of ferrous material |
M02 |
SC091 |
>1,000nT |
Confirms
presence of ferrous material |
M02 |
SC090 |
No
change with surrounding environment |
No
ferrous material |
M03 |
SC072 |
No
change with surrounding environment |
No
ferrous material |
M04 |
SC055 |
No change
with surrounding environment |
No
ferrous material |
M05 |
SC067 |
No
change with surrounding environment |
No
ferrous material |
M06 |
SC053 |
No
change with surrounding environment |
No
ferrous material |
M07 |
SC043 |
>1,000nT |
Confirms
presence of ferrous material |
M07 |
SC044 |
No
change with surrounding environment |
No
ferrous material |
M08 |
SC028 |
>1,000nT |
Confirms
presence of ferrous material |
M09 |
SC027 |
700nT |
Confirms
presence of ferrous material |
M10 |
SC020
and SC014. |
No
change with surrounding environment |
No
ferrous material |
M11 |
SC086 |
>1,000nT |
Confirms
presence of ferrous material |
4.3.3
Interpretation of the Magnetic Anomalies
Of the 14 Magnetic Anomalies part of M02 (SC090),
M03(SC072), M04 (SC055), M05(SC067), M06 (SC053), part of M07 (SC044), M10
(SC014 & SC020) contained insufficient ferrous material for the
magnetometer to record any magnetic anomaly.
The magnetic sensor was within 5 m of the seabed/sonar contact and only
a 1-4 nT magnetic variation was detected around
SC014, SC020, SC044, SC053, SC055, SC067, SC072 and SC090 and which could be
explained as ‘background noise’, related to the movement of the cable or sensor
during the magnetic survey, or the variability in the nature of the seabed([15]).
If these particular Sonar Contacts were timber vessels with no or little
ferrous fastenings, equipment, stores or cargo then they may not produce any
addition to the 1-4nT variation.
However, it is considered that a vessel of pre-1800 would contain some
ferrous fittings, equipment, stores or cargo that would provide a significant
change (greater than 1-4nT) in the earth’s magnetic field given the magnetic
sensor was within 5 m of the Sonar Contact.
Another possibility is that these anomalies are very old, pre Iron Age
vessels, but given their location, i.e., exposed on the seabed, this is not
realistic. Coupled with their problematic Side Scan Sonar results it is
concluded that Sonar Contacts 014, 020, 044, 053, 055, 067, 072
and 090 are natural features
and or debris and not of archaeological potential.
In association with the side scan sonar
results, it is concluded that SC027, SC028, SC043, SC086, SC091
and SC092 are vessels or man-made structures of some sort and potentially
pre-1800. Given the size of the magnetic
intensities at the distance of the magnetic sensor to the Sonar Contacts they
are considered not to be solely made of iron, but are of a composite material,
possibly timber and iron/steel. While they could be pre-1800, they could also
be post-1800 as many composite vessels are from this era as well. It also concluded that SC027 in particular
has the potential, through its size and the Side Scan Sonar image to be a
modern steel barge. However, the 700nT
magnetic intensity is far too low if this was the case and it is potentially an
interesting archaeological site.
In
summary, the magnetic survey results has eliminated 8 Sonar Contacts from those
identified through the side scan sonar surveys and enhanced the potential of
the remaining 6 and which require further investigation.
4.4
Remote Operated
Video (ROV)
As mentioned above, six Sonar Contacts
were identified as possible sites of archaeological potential (see Table 4.3 and Figure 4.24 for
details). In order to identify their nature and age, an
inspection of the sites was undertaken on the 15th February 2006,
carried out by EGS using their Remote Operated Vehicle (ROV) from their work-boat and employing EGS
staff (six in total) to operate the ROV, the positioning equipment (DGPS) and
boats. The ROV is
a small piece of equipment that contains a video with lights and is controlled
by an operator on the boat. It can be
propelled (using a surface generator attached with a cable to the ROV) to move
about in the water. However this model
(Titan) cannot operate against much current and needs to be used as a ‘drop
camera’, i.e., to be simply dropped onto the site to be inspected and to be
moved by operators with ropes from the surface (see Figures 4.25(i) & 4.25(ii)). The ROV was dropped on some of the sites from
the work-boat (Figure 4.25(iii)) and the
sampan depending on current and site location (Figures 4.25(iv)).
Table 4.3 List of the Six Sites
of Archaeological Potential
Contact
number |
Latitude Longitude |
Easting Northing |
KP RPL
offset |
Dimensions
(m) |
Description |
SC027 |
22° 21.253' N 113° 52.268' E |
795708.0E 2474854.0N |
28.227 33m E |
39m x 6.5m x 2m |
Wreck |
SC028 |
22° 20.235' N 113° 52.237' E |
795691.0E 2472974.0N |
26.338 5m W |
8m x 2m x 0.2m |
Possible Wreck |
SC043 |
22° 12.320' N 113° 49.589' E |
791415.0E 2458273.0N |
10.491 176m W |
6m x 2m x 0.5m |
Possible Wreck |
SC086 |
22° 24.388' N 113° 54.072' E |
798693.9E 2480702.4N |
39.148 1572m SW |
10.77m x 3.31m x 2.03m |
Possible wreck |
SC091 |
22° 9.923' N 113° 54.411' E |
799791.0E 2454003.0N |
0.309 118m N |
18m x 4m x 0.9m |
Possible Wreck |
SC092 |
22° 9.991' N 113° 54.488' E |
799921.0E 2454132.0N |
0.168 236m N |
9m x 2m x 0.5m |
Wreck |
Most
videos will work in low lux (amount of luminosity)
values of 5-15 lux (10 lux is early twilight or light from 60 watt bulb from 3 m
away; 1 lux is late twilight; and 0.1 lux is light from a full moon). It was anticipated that the water in the
vicinity of the sites would be turbid (from suspended sediments) and most
likely with a very low lux value.
Tides during the day were 0.5 m at 0505; 1.5
m at 1117; 1.0 m at 1607; and 2.1 m at 2239. The weather was overcast, either
fog, pollution or a combination and which would have only contributed slightly
to the gloomy underwater visibility.
4.4.1
ROV Results
1. SC092
(10:30am) (Figure 4.26(i))
This site is located adjacent to
2. SC091
(12 noon)
This site is also located adjacent to
|
|
Figure 4.27 Video Clips Showing SC091
3. SC043
(1:40pm)
This site is located adjacent to western
end of Lantau island in 23m of water and was not
found during the ROV survey. Sea conditions were calm with little breeze. The visibility
was zero, the water had a very muddy appearance on the surface, unlike SC091
and SC092 (see water colour in Figure 4.26(ii)). Some
current (c. 1/2 knot) was experienced.
4. SC028
(3:20pm)
This site is located adjacent to the
existing marine park in 6-7 m of water and was not found during the ROV survey.
Sea conditions were calm with little breeze. The visibility was zero, the water
had a very muddy appearance on the surface. Some current (c. 1/2 knot) was
experienced.
5. SC027
(4:15pm)
This site is located adjacent to the
existing
6. SC086
(5:35pm) (Figure 4.26(iii))
This site is located about 20m from the
rocks at Black Point in 7 m of water and was not found during the ROV survey.
The visibility was zero, the water had a very muddy appearance on the surface,
the same as SC043, SC028 and SC027. There was a slight breeze and given the
busy shipping activity in the vicinity, there was at times a choppy sea. The
ROV Video camera did show what was most likely rocks (or possibly wreckage) and
the remains of some fishing nets (see Figure
4.28 for the clip of video record).
Figure 4.28 Video Clips Showing SC086
4.4.2
ROV Conclusions
There are a number of issues to address in
terms of the impact of the project on the sites.
SC91 was shown from the ROV to contain
rope and due to its exposed condition would not be expected to be found on a
site that was 206 years old in these waters, i.e. pre-1800. A visual survey requires some visibility and
the 20-30 cm visibility found on SC091 was adequate given the lights on the
ROV. It is considered that SC091 is of
no or low archaeological potential, however, due to the poor visibility in the
sea, the wreck cannot be clearly seen.
For the rest of the sites (SC027, SC028, SC043 and SC086), as there was
a lack of visibility, the nature of the sites could not be determined. For SC092, the site could not be located from
the survey due to poor visibility.
Given the lack of visibility for most of
the sites (and most likely to be encountered all the time on these sites) and
low visibility of two sites, it was not possible to conduct a visual survey of
these sites with the current ROV or divers.
The presence of fishing nets found on SC086 also makes diver surveys
hazardous for this and the other sites that could contain nets, given their
prominence on the seabed and the likelihood of trapping nets.
It was recommended that a more detailed
remote sensing work incorporating multi beam sonar and side scan sonar data be
undertaken for the sites so that the sonar data could be used to develop three
dimensional models that could be rotated and viewed at different angles. These very accurate virtual models are the
closest thing to viewing the real site and are currently the best system that
can be used in nil visibility situations.
In combination with more detailed side scan sonar surveys and the
existing magnetometer data (or closer plot magnetometer survey data) it may be
possible to identify rope or other modern artefact/equipment that will confirm
the nature and age of the sites.
It is problematic if diver surveys would
be more useful in determining the nature of the sites. The ROV with its low lux values can ‘see’ better than human eyes and while a
diver can feel objects, he/she may not be able to produce objective results in
the form of drawings as they would be reliant on their memory or the
translation of their surface, diving supervisor when noting their descriptions.
It was considered more useful to implement a multi beam survey which produces
objective and recordable results and in combination with the other remote
sensing surveys provides for more comprehensive and independent assessments.
4.5
Side Scan Sonar and Multi Beam Sonar Survey
Further
to the ROV result, a further detailed Side Scan Sonar and Multi Beam Sonar
Surveys was undertaken by EGS on the 6th and 7th April
2006 covering the six Sonar Contact numbers including SC027, SC028, SC043, SC086, SC91 and SC92. Survey track plots are shown in Figures 4.29 to 4.34.
The main equipment used for the survey is
shown in Table 4.3.
Table 4.3 Equipment
Used for the Side Scan Sonar and Multi Beam Sonar Surveys
Survey System |
Manufacturer |
Model Number |
Swath
Bathymetry |
Reson A.s. |
400 kHz
8125 |
Side
Scan Sonar |
Klein
Associates Inc |
System
3000 |
Positioning |
C&C
Technologies Inc |
C-Nav GcDGPS |
Navigation |
C-Products
Ltd |
C-View Nav |
The navigation receiver was placed
vertically above the swath transducer mounted on the side of the survey
vessel. As the vessel travelled along
the survey traverses, the system transmitted a fan of echo sounder beams down
into the water column to map the shape of the sea bed in great detail. The geometry is illustrated in Figure 4.35.
Figure 4.35 Illustrations of
Swath Bathymetry Systems
At each location, the survey vessel sailed
along four traverses around the artefact, “boxing in” and isonifying
the sonar contact from each side. The measurements from each side were combined
into a single image using the QinSys processing
software supplied with the swath system.
The level of each sounding has been colour coded, using a spectrum of
colours to represent the range of levels found at each location. To give the impression of looking at the
sonar contact from different directions, the image has been rotated in three
dimensions before capturing the image. The images are presented in the results.
At each location, the survey boat sailed
along four traverses to box in the sonar contact and isonify
it from each direction, as for the swath measurements. The side scan sonar fish
was towed behind the survey vessel a few metres above the sea bed. As it
travelled along the survey traverse, the transducers emitted sound pulses to
either side and measured the echoes from features on the sea bed. The arrangement is illustrated in Figure 4.36.
|
Figure 4.36 Schematic Illustration of Side Scan Sonar
System Operation
A dual frequency (100 kHz and 500 kHz)
system was used. The echoes for each
frequency were recorded separately using the C-View acquisition system. Amplifier gains were applied to compensate
for geometrical dispersion of the wave intensity with distance: no other
processing was applied.
The images for each pass were examined and
the clearest images for each contact were selected for printing in the results.
4.5.4
Side Scan Sonar and Multi Beam Sonar Surveys
Findings
After
EGS completed the Side Scan Sonar and Multi Beam Sonar Surveys, an analysis of
this new data in context with the earlier survey work (side scan sonar survey
and magnetometer data) was carried out by the marine archaeologist. The results are presented below under each
Sonar Contact.
SC027
The
site was identified as a shipwreck and the most obvious of all the sites being
about 39 m (length) x 6.5 m (breadth) x 2 m (height) as can be seen in the side
scan image (see Figure 4.37), surveyed
in 2005.
Figure 4.37 Side
Scan Sonar Image of SC027
The
magnetometer survey carried out between the 2nd to 4th
September 2005 found the anomaly to contain about 700 Nanotesla
(nt) more than the surrounding seabed/sub-bottom
material. This was estimated to be about
1-2 tons of iron/steel. Given the
relatively large size of the shipwreck, one ton of ferrous material is
indicative of this shipwreck being a wooden vessel containing a number of
ferrous fittings (perhaps fastenings, chain, water tank, etc.)
The
further side scan sonar survey carried out on the 6th and 7th
April 2006 failed to locate the anomaly.
This was not a result of poor navigation as grid coordinates within a few
metres of the 2005 location were reproduced in the outcomes of this further
survey (see Figure 4.38). The shipwreck has either been intentionally
removed or unintentionally moved (from storms/currents) as is verified by
examining the side scan sonar image (see Figure
4.39); the multi beam sonar image (see Figure
4.40) and C-view bathymetric data (see Figure
4.38). The disturbed area of seabed
as seen in these images is a shallow depression of about ½ m, where it once had
nearly 2m elevation.
Figure 4.38 Bathymetric
Data of the Same Area (The Yellow Region is the Same Depression as in Figure
4.40 and Coloured Blue) and Showing the Coordinates of the Position; 795703E,
2474862N.
Figure 4.39 Showing Area where Shipwreck had been Located
Figure 4.40 Multi
Beam Sonar Image with the Area in Darker Blue, Being a Depression of About 0.5m
Deep and With Only a Very Small Fragment with Any Elevation in the Middle of
the Image.
Conclusions
This shipwreck was moved prior to the
April 2006 remote sensing surveys. The
ROV survey in February 2006 failed to locate this shipwreck and it was
concluded at that time, that the nil visibility was the factor it could no be
seen, but it is highly likely to have been moved before the date of this
survey. Its new location is unknown and
a further survey undertake confirmed that it is not found in the proposed
pipeline route.
SC028
The
side scan sonar survey implemented in 2005 found an anomaly located at
795691.10E, 2472975.41N. The site was identified as SC028 and had the
dimensions, 8m x 2m x 0.2m as shown in Figure
4.41. It had the appearance of some
type of man-made object possibly a small sampan.
Figure 4.41 The
Small Anomaly (Left of Centre in this Image)
The
magnetometer survey found this anomaly to contain in excess of 1,000nt more
that the surrounding area. This was
estimated to be about 2-3 tons of ferrous material and given the size of the
anomaly, the Sonar Contact could be interpreted as a wooden vessel containing a
reasonable amount of iron/steel, or some other type of man-made object,
possible even some type of dumped materials consisting of ferrous materials.
During
the side scan sonar survey of the 6th and 7th April 2006,
no similar side scan image could be obtained (see Figure 4.42) suggesting that these remains have also been
removed/moved and which was verified through the multi beam sonar survey which
only showed a depression in the seabed (see Figure
4.43).
Figure 4.42 SC028 Remains in the Centre (under the text
30m) of this Image
Figure 4.43 A Multi
Beam Sonar Survey Image of a Black Hole (Depression) which Indicates the
Position of SC028. A Small Sand Bar Lies
Next to the Hole (White Mass to the Left of the Hole)
Conclusions
It
also appears that this wreckage has been removed or moved. The combination of the shadow (from something
proud of the seabed) on the initial side scan sonar image and the 1000nt
magnetic anomaly would tend to indicate something more than the present
depression and small raised sand bar was located in this position. While it is a possibility, from the sonar and
magnetic data, that this shipwreck could be interpreted to be a small motor
vessel similar to the one shown in SC086, it could also have been some other
type of man-made object, possible even some type of dumped materials containing
ferrous materials.
SC043
The
side scan sonar survey implemented in 2005 found a 6m x 2m x 0.5m “possible
wreck” at 791415E, 2458273N (see Figure
4.44).
Figure 4.44 The
Initial Side Scan Sonar Image of SC043
The
magnetometer survey found this anomaly to contain in excess of 1,000nt more
that the surrounding area. This was
estimated to be about 2-3 tons of ferrous material and given the size of the
anomaly, the possible wreck could be interpreted as a wooden vessel containing
a reasonable amount of iron/steel or some other type of man-made object,
possible even some type of dumped object consisting of ferrous materials.
During
the 6th and 7th April side scan sonar and multi beam
surveys, the anomaly was re-located.
Figure 4.45
is a high resolution scan but with slightly different orientations provide
different and inconclusive results as to the nature of the anomaly.
|
|
Figure 4.45 SC043
Image from two different angle (Left: in the Centre, Right: Centre )
The
multi beam sonar survey also provided inconclusive results as to the nature of
SC043 (see Figures 4.46 and 4.47).
Figure 4.46 Only a
Small Section is Proud of the Seabed (Shown as
Figure 4.47 Another
View of the Small Anomaly (SC043)
Conclusions
The
relatively small physical size of the anomaly, the comparatively large amount
of ferrous material and the possible sampan shape and collapsed nature is suggestive
indicative of a small motorised wooden sampan.
On the other hand this anomaly could be some other type of man-made
object, possibly even a dumped object.
SC086
In
the side scan sonar survey in 2005, the following assessment was made of this
anomaly. A vessel of about 10.77m x
3.31m x 2.03m and located at 798694E, 2480702N (see Figure 4.48).
Figure 4.48 A
Vessel Located in the Middle of the Image, Located close to the Rocks at Black
Point
The
magnetometer survey found this anomaly to contain in excess of 1,000nt more
that the surrounding area. This was estimated to be about two to three tons of
ferrous material and given the size of the anomaly, this site was interpreted
as a wooden vessel containing a reasonable amount of iron/steel.
On
the 6th and 7th April 2006 the area was surveyed with the
multi beam sonar and the side scan sonar and better images of the vessel were
obtained (See Figures 4.49 to 4.52.
Figure 4.49 Side
Scan Sonar Image of SCO86 UNDERTAKEN in April 2006 (Centre)
Figure 4.50 General
View of the Vessel by the Multi Beam Sonar
Figure 4.51 Sampan
with What Looks Like a Hole Towards One End of the Vessel
Figure 4.52 Plan
View of Sampan Confirming Damage in the
Conclusions
The
vessel and its location has all the appearances of a ‘recent’ motorised wooden
sampan (see Figure 4.52). Located close to the rocks at Black Point and
effected by the swells breaking over it, and the continual sea traffic, the
vessel could not be expected to maintain its integrity for very long (perhaps
months or just a year or so). Seats can
be seen in the vessel and it shows damage to its hull which is considered to
have been caused from its continual movement underwater and/or sinking. A vessel of pre-1800 age would not be in this
condition in this location but a modern vessel illustrated in Figure 4.53 could be. The Marine
Department salvaged a similar looking sampan on the 22 March 2006 (see Figure 4.24 for its
location and Figure 4.54) which they reported was about 30 years old. SC086 is probably of a similar vintage.
Figure 4.53 A
Motorised Sampan of about the Size of SC086
Figure 4.54 Recently
Recovered (by Marine Department) Sampan with Dimensions very similar to SC086
(Source: Marine Department )
SC091
The
side scan sonar survey of 2005 classified this sonar contact as a wreck of 18m
x 4m x 0.9m and located at 799794E, 2454000N (see Figure 4.55).
Figure 4.55 Bottom
Right Hand Corner of Image with ‘Shadow’ Providing the Height of the Vessel
The
magnetometer survey found this anomaly to contain in excess of 1,000nt more
than the surrounding area. This was
estimated to be 2-3 tons of ferrous material and given the size of the anomaly,
this site was interpreted as a wooden vessel containing a reasonable amount of
iron/steel.
On
the 15th February 2006, the ROV video survey provided images of this
vessel. Coils of rope, or cable could be
seen lying within the vessel and what could have been iron/steel fittings.
On
the 6th and 7th April 2006 the area was surveyed with the
multi beam sonar and the side scan sonar and better images of the vessel were
obtained (See Figures 4.56 to 4.58).
Figure 4.56 Side
Scan Sonar Image of Vessel and Debris Field
Figure 4.57 Modern
Work Vessel and Scattered Debris
Figure 4.58 A
Possible Propeller Shaft and Propeller Located a the Lower Right End of the
Image/Boat
Conclusions
The
shape and nature of this vessel is indicative of a modern working vessel. It
appears to contain an engine (as shown by the propeller) and the size of the
magnetic anomaly is also indicative of this.
The rope/rigging that was seen during the ROV survey is indicative of a
vessel of only a few years in age, rather than something that is pre 1800.
SC092
The
side scan sonar survey of 2005 concluded this sonar contact to be a wreck of
about 13m x 1.1m x 0.6m and located at 799910E, 2454136N (see Figure 4.59). In another side scan sonar
view of the site the dimensions were provided as: 9m x 2m x 0.5m.
Figure
4.59 The Sampan Looking Vessel Designated
SC092
The
magnetometer survey found this anomaly to contain about 500nt more that the
surrounding area. This was estimated to be about one ton of ferrous material
and given the size of the anomaly, the wreck was interpreted as a wooden vessel
containing a reasonable amount of iron/steel.
On
the 6th and 7th April 2006 the area was surveyed with the
multi beam sonar and the side scan sonar and further images of the vessel were
obtained (See Figures 4.60 to 4.63).
Figure 4.60 Side Scan
Sonar View of the Sampan undertaken in April 2006
Figure 4.61 The Raised and Squared Bow or Stern
Figure 4.62 The Site
is Possibly Another Sampan of Poor Condition
Figure 4.63 The
Anchor Scar Adjacent to the Site
Conclusions
The
vessel appears in April 2006 to be in much the same condition as in the 2005
side scan sonar survey. It is similar in
size and shape (although narrower, from one set of measurements) to the sampan
at Black Point (SC086) and in slightly worse condition. The nature of the
remains is suggestive of a more modern vessel and not something that is pre
1800.
If
the larger length/narrow beam set of measurements are more accurate and given
the narrow breadth (beam) of the vessel, it is possible that the boat is a
dragon boat. Dragon boats can vary in size, an International Racing Standard
Dragon Boat is 12.5m (length) x 1.16m (breadth). The other possibility is that
the vessel is something like the longer vessel shown in see Figure 4.64. Either of these possibilities don’t fit well
with the amount of ferrous material found on the site as they would possibly
not have contained much iron or steel.
Figure 4.64 Model
of a Vessel Used in Hong Kong Waters, Similar in Size to SC092 (
The
2006 survey shows a line (scar) on the seabed adjacent to the vessel which was
not apparent in 2005. It is most likely
this is from an anchor being dragged along the seabed, indicating an anchor was
dropped nearby and dragged away from the site, or an anchor was dragged adjacent
to the site and then raised. There is
the likelihood that the vessel has been damaged in this process. It is also possible that the scar is the
result of the vessel being dragged to its present location.
4.5.5
Further Side Scan Sonar and Multi Beam
Sonar Surveys Findings for SC027 and SC028
As SC027 and SC028 were not identified
from the April 2006 survey, if the two wrecks are still surviving within the
proposed gas pipeline route, potential impact on these two contacts due to the
installation of the gas pipeline would be a concern. Marine Department was consulted to check if
any vessels had been removed recently adjacent to SC027 and SC28. It is confirmed that apart from the vessel
recovered in March 2006 (see Figure 4.54),
no other vessels were recovered by the Marine Department. Therefore, it is considered necessary to
undertake further survey to confirm if they are still within the proposed gas
pipeline route. On the 2nd
June 2006, EGS implemented a further survey of a more extensive area surrounding
the original locations of SC027 and SC028 and within the pipeline route. Using the same multi beam sonar and side scan
sonar equipment and processes as in the 6th and 7th April
surveys, four vessel tracks spaced 20 m apart covered an area of 4,300m x 100m
(Figures 4.1 and 4.65).
The surveys confirmed the disappearance of
SCO27 finding a large shallow depression where the shipwreck was once located (see Figure 4.66).
Figure 4.66 Side
Scan Sonar View of SC027
The surveys also confirmed a depression containing
different sediments in the original location of SC028, but no feature
containing any elevation indicative of a shipwreck sitting proud of the seabed,
as was originally found (see Figure 4.67).
Figure 4.67 Side Scan
Sonar View of Original Location of SC028
The surveys failed to locate any feature
that could be construed to be either SC027 or SC028.
Review
of the UKHO data identified two ‘live’ shipwrecks within 1 km of the centre line of the pipeline route and the
associated facilities (nos. 46602 and 62931).
The comprehensive Geophysical Surveys undertaken for this study covering
the area where shipwreck nos. 46602 and 62931 indicated no such shipwrecks exist
within the marine area of the proposed development where seabed disturbance may
occur. Since the geophysical survey
covered comprehensively the potential impacted area, the shipwrecks may have
been removed for unknown reasons. The
geophysical survey data (which included magnetometer data along the CL)
covering the locations of these two shipwrecks were thoroughly checked. Wreck no. 46602 (which is within 20 m of the
CL) was a 3130 ton Japanese frighter (length 318 m x
beam 45 m x draught 24m) and with a superstructure of many more meters in
height. The depth of water for its
location is 4-5 m. If it was still in
the location recorded by the UKHO at the time of the geophysical surveys, it
would not have been unobserved. It must
have been removed – it could not have deteriorated to an extent where is is not evident. The
only other possibility is that its location is incorrect, but a similar coordiate location is recorded in the UKHO files for
several years and it is the only “obstruction” recorded in this location. Therefore, its incorrect location is not a possibity for being unobserved in the survey data.
While no information is available about
wreck no. 62931 that would assist in its interpretation (apart from it being
recorded by the UKHO as an obstruction, and therefore it is possible that it is
not a shipwreck). It was not observed
during the review of the geophysical data.
The most obvious conclusions to be drawn from it not appearing on the
survey data, is that it has been removed or it was of a nature that could have
deteriorated to such an extent that makes it unobservable in the survey data.
Nevertheless, the Geophysical
Survey and Magnetic Survey identified six Sonar Contacts comprising SC027, SC028, SC043, SC086, SC91 and SC92
to have marine archaeological potential. They were
considered to be possible wrecks. In
order to investigate their nature and age, further surveys comprising a Remote
Operated Video Survey and a further detailed side scan sonar survey and multi
beam sonar survey were undertaken.
The
results indicate that SC043 was some type of man-made object, possibly the
remains of a motorised sampan and even a recently dumped object. The
combination of its physical size and shape (from the multi beam and side scan
sonar surveys) and its magnetic intensity does suggest a site of post-1800 in
origin. It is not suggestive of a cannon or anchor related to a pre-1800 site
given its physical size, shape and magnetic intensity. Sonar Contacts 086 and
092 were concluded to be motorised sampans and SC091 was concluded to be a
motorised work boat. In the context with the Antiquities and Monuments Ordinance (Cap. 53), these four sites are
not considered an antiquity or relic and of no archaeological value. Thus, due to the lack of archaeological value
of the sites, impact to them is considered acceptable.
Sonar
Contacts 027 and 028 could not be re-located with the subsequent detailed side
scan sonar survey and multi beam survey. Further investigative surveys to
confirm their whereabouts failed to relocate them within the immediate
surrounds. It is therefore concluded
that SC027 and 028 have been intentionally or unintentionally moved out of the
pipeline route and the pipeline poses no threat to these sites.
Review
of the UKHO shipwreck record identified two shipwrecks (no. 46602 and no.
62931) adjacent to the proposed pipeline route and the associated facilities. However, the comprehensive Geophysical
Surveys undertaken for the study indicated that these shipwrecks no longer
exist within the marine area of the proposed development where seabed
disturbance may occur. It is highly
likely that these shipwrecks/obstructions may have been removed for unknown
reasons. Nevertheless, Geophysical
Survey, Magnetic Survey, Remote Operated Video Survey and a further detailed
side scan sonar survey and multi beam sonar survey were undertaken to identify
marine archaeological potential sites within the marine area of the proposed
development where seabed disturbance may occur.
Six
sites considered to be shipwrecks were identified from the survey. It is
concluded that three of them are motorised sampans or work boats and another
possibly the remains of a sampan or possible some other type of recent man-made
object. They are not considered to be an
antiquity or relic in the context of the AM
Ordinance.
Two
other sites, while initially located in the pipeline route were removed before
subsequent surveys and the opportunity to provide a more comprehensive
assessment. Further surveys failed to relocate these shipwrecks in the pipeline
route it is concluded that the pipeline project poses no threat to these sites.
[15] EGS geophysicists concluded that the
1-2nT was ‘natural variability expected in these readings’