1                                            introduction

1.1                                      Introduction

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 Black Point (Figure 1.1).  As the proposed development involves marine works (see Part 2 – Section 3.2.1, 3.2.2, 3.2.4, 3.2.5, 3.2.6 and 3.3.3 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 of the Study Brief, a Marine Archaeological Investigation (MAI) was required during the Review Phase of the Project.  This report was prepared by Bill Jeffery, a qualified marine archaeologist, detailing the MAI findings.

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 (Asia) Limited (EGS);

·       Review of Magnetic Survey Data prepared by CAPCO’s Geophysical Contractor EGS (Asia) Limited (EGS);

·       Remote Operated Vehicle Survey prepared by CAPCO’s Geophysical Contractor EGS (Asia) Limited (EGS);

·       Establish Archaeological Potential; and

·       Provide a Report on these aspects.

This report represents the MAI results.

1.3                                      Report Structure

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 Hong Kong;

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.


2                                            Legislative Requirements and Evaluation Criteria

The following legislation and guidelines are applicable to the assessment of marine archaeological sites in Hong Kong:

·      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);

·       Hong Kong Planning Standards and Guidelines; and

·       Guidelines for Marine Archaeological Investigation prepared by AMO.

2.1                                      Environmental Impact Assessment Ordinance Technical Memorandum on the EIA Process

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 culture and tradition; (b) Adverse impacts on sites of cultural heritage shall be kept to the absolute minimum.”

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 Monuments Ordinance, Cap. 53

The Antiquities and Monuments Ordinance (Cap. 53) (AM Ordinance) provides statutory protection against the threat of development on Declared Monuments, historical buildings and archaeological sites to enable their preservation for posterity.  The AM Ordinance also establishes the statutory procedures to be followed in making such a declaration.

“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 Hong Kong.  The AMO has established boundaries for the identified sites and a set of administrative procedures for the protection of the known archaeological sites.  However, the present record of archaeological sites is known to be incomplete as many areas have not yet been surveyed.  There is a need therefore to ensure that the procedures and mechanisms, which enable the preservation or formal notification of previously unknown archaeological resources that may be revealed or discovered during project assessment or construction, are identified and implemented at an early stage of the planning of a project.

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                                      Hong Kong Planning Standards and Guidelines

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 were provided 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.

3                                            Assessment Methodology & Scope of work

3.1                                      Methodology

The methodology used in this assessment followed the Guidelines for MAIs as prepared by AMO 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 (Black Point terminal, gas pipeline, watermain and submarine cable);

·      Examination of the seabed and below seabed using geophysical survey equipment 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.

4                                            Baseline Conditions

4.1                                      Desktop Research

4.1.1                                Geotechnical Data

Generally, the submarine deposits in the Hong Kong region are subdivided into two formations, Chek Lap Kok Formations and the overlying Hang Hau Formations.

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.  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 Pearl River) having a seasonal discharge of about 370,000 million cubic metres each year([3]).  They consist of sand, mud and some gravel.

Fyfe([4]) further explains the rate of sedimentation:

“In general, present day sedimentation rates in Hong Kong waters are low, though they were undoubtedly greater earlier in the Holocene when sea level was rising rapidly. … Without tidal flushing, the sediment entering Victoria Harbour from the Pearl River, sewage solids and losses from dredging and reclamation might be expected to raise the seabed level by 40mm per year.  However, comparison of Hydrographic charts of Victoria Harbour from 1903 to 1980 revealed no conclusive evidence of net sedimentation, implying that the seabed is a state of dynamic equilibrium.  Assuming that sedimentation in Hong Kong waters began about 8 000 years ago, deposition of the 10 to 20 m of marine mud must have occurred at an average sedimentation rate of between 1.25 and 2.5 mm per year.  Available evidence indicates that the rate of Holocene sedimentation has not been steady.  Radiocarbon dating suggests that the majority of sedimentation has taken place over the past 4 000 to 5 000 years.”

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 Hong Kong waters.  This is in contrast to the surface of the seabed, which is often found to have been disturbed by fishing and other shipping related activities.  These remains could include shipwrecks.

4.1.2                                Review of Historical Documents

The water between Shekou (situated in Shenzhen) and Black Point was in use as a war junk anchorage since the 8th century.  In the 8th century (Tang Dynasty), Black Point was within the military division area of Tunmen Bing Zhen (屯門兵鎮) where 2,000 soldiers were under the command of one Defence Commissioner.  The headquarters of this division was situated in the present Nantou (南頭) walled city of Shenzhen and its military division area also covered the HKSAR, as well as the Huizhou (惠州) and Chaozhou (潮州) areas ([6]).  The military division was serving the same area until the Yuan Dynasty (A.D.1279-1368). 

In the late 16th century (Ming Dynasty), China was facing more frequent disturbance from coastal invaders and more forts and beacon towers were set up to protect the key locations from Japanese pirates.  The Nantou Military Division (南頭寨) was set up in 1565.  It commanded 53 war junks and 1,486 soldiers ([7]) .  The military force was increased to 1,659 soldiers in 1645.

During this period, the Portuguese explorer, Jorge Alvares was permitted to land on Lintin Island (Neilingding 內伶仃) in 1513 ([8]), he then built a fort and erected a stone column with a carving of the Portuguese national symbol.  The Chinese navy attacked and demolished the Portuguese fort in 1518 ([9]).  In 1522, it was also recorded that a sea battle between the Chinese navy and Portuguese ships was fought in the water between Lantau Island and Tuen Mun.  The Chinese navy won the battle.

A review of a historical chart of the mouth of the Pearl River dated 1658 ([10]), also indicated that the waters between Black Point and Lintin Island were part of the main voyaging route from the East to the Westof the river.  

During the Ming to Qing Dynasties (A.D.1368 -1911), Imperial Junks sailing from Guangdong to Southeast Asian countries were required to anchor at a bay known as Chiwan (赤灣) of Nantou peninsula, located to the west of Shenzhen City (located some 9km north of Black Point).  A Tin Hau Temple was established in this Bay, probably in 1410 according to an inscription of the Temple where sailors worshipped Tin Hau for sea travelling safety ([11]).  During the early Qing dynasty in the 1660s, although the Nantou Military Division was replaced by Xin’an Camp (新安營), it was still situated in the Nantou Walled City ([12]).  Two stone forts were also built near the Tin Hau Temple during the Qing Dynasty and the remains of the forts can still be found.

Based on the historical development review, it is considered that Black Point is located in the vicinity of a busy marine sea route.  The water area at Black Point, Deep Bay and Neilingding Island was the main voyaging channel between Guangdong and the Southern China Sea and Southeast Asian countries as well as East and West for centuries.  On this basis, the waters at Black Point are considered in general to have marine archaeological potential. 

Marine archaeology is still a new area in Hong Kong.  In 1998, a study was undertaken on the potential, assessment, management and preservation of maritime archaeological sites in Hong Kong and to explore all aspects of the subject to ensure that the scope of all future work is feasible.  Review of the report identified a number of shipwrecks recorded some 3.5 km to the northwest outside the proposed project area but no shipwreck was identified within proposed marine works areas([13]).

4.1.3                                United Kingdom Hydrographic Office "Wreck" Files 

The United Kingdom Hydrographic Office (UKHO) in Taunton maintains a database of known shipwrecks in the HKSAR.  The aim of the UKHO in keeping the database is to maintain a list of shipwrecks/obstructions that could be navigation hazards, wrecks through deterioration/corrosion over time become less of a navigation hazard but still remain on their database and if not removed could potentially become significant archaeological sites.  The UKHO database is only one source of data, albeit an important source of historical data on shipwrecks, that combined with other historical sources on other types of sites (as well as some types of shipwrecks) and the geophysical surveys, it provides a significant contribution in ascertaining if a region encompasses submerged archaeological deposits.  The review indicated that no shipwrecks were found to be within 1 km of the proposed Black Point facilities. 

The Hong Kong Marine Department could not provide any additional information beyond what was provided by the UKHO.  However, discussion with the Marine Department noted that a wreck adjacent to Sha Chau/Lung Kwu Cha had been lifted in March 2006.  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 4.10 for location and Figure 4.19 for a description).

4.2                                      Geophysical Surveys

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 1.1) of the Geophysical Survey covers the proposed Approach Channel, Turning Circle and Reclamation Area and additional areas at Black Point covering a survey line length of 167 km. 

4.2.3                                Survey Methodology

Geophysical Surveys were undertaken by CAPCO contractor, EGS (Asia) Limited (EGS), between May and September 2005; February 2006; April 2006.  Side Scan Sonar and Boomer surveys were implemented of all the potentially impacted areas off Black Point.  The data were collected from either 20 m or 25 m traverses.  The vessel track plots of the surveys are presented Figure 4.1.  Later, multi-beam and magnetometer surveys were implemented on some specific sonar contacts.  These surveys allowed for a comprehensive investigation of the seabed, and below the seabed.

4.2.4                                Equipment Used

·       Multi-Beam EchoSounder (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);

·       Subbottom 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 survey showed how the seabed in the Survey Area had been impacted by anchoring, trawling (Figure 4.2) and the dumping of materials (Figure 4.3).  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.  In addition, it located Sonar Contacts comprising natural features, dumped materials, shipwrecks, linear debris, anchor marks and fishing devices.  In a further review of the Sonar Contacts identified a site (Figure 4.4) as possible wrecks off Black Point area (Table 4.1).  The Sonar Contact discounted as possible wreck 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.

Figure 4.2       Geophysical Survey Showing How the Seabed Was Impacted By Anchoring & Trawling

Figure 4.3       Geophysical Survey Showing How the Seabed Was Impacted By The Dumping Of Materials

Table 4.1        Sonar Contact Located off Black Point

Contact number






RPL offset

Dimensions (m)



22° 24.388' N

113° 54.072' E




1572m SW

10.77m x 3.31m x 2.03m

Possible wreck







The above anomaly is sitting on the seabed.  A review of the boomer data failed to identify any sub-bottom anomalies.

Based on the side scan sonar image there was a degree of doubt if SC086 was a shipwrecks (see Figures 4.4 and 4.5).

Figure 4.5       Possible Wreck (SC086)

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 Antiquities and Monuments Ordinance defines an antiquity as a relic) that prompted the recommendation that a Magnetic Survey be conducted on 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, later ships could potentially be modern ferrous barges or timber vessels with larger amounts of ferrous material and used today in and around Hong Kong.  It was considered that the amount of ferrous material detected during a Magnetic Survey and in association with the site descriptions already obtained during the side scan sonar survey, an indication on the age (through the nature of the remains) of the sites could be obtained. 

4.3                                      Magnetic Survey

4.3.1                                Survey Scope and Methodology

For the purpose of the MAI, a Magnetic Survey covering the 3 Sonar Contacts as presented in Table 4.1 was undertaken by EGS from 2 to 4 September 2005([14]).  Survey lines around 100m long were surveyed for the Contact, with a line spacing of 5 m (see Figure 4.6).  The 100m 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 5m 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.

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)([15]). 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.([16]) 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 ([17]).  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.

4.3.2                                Turbidity and Visibility Readings

A vertical profile of turbidity was recorded for the Sonar Contact, 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.

4.3.3                                Magnetometer

The magnetometer was deployed 15m 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 5m 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 5m 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.

4.3.4                                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 0.5m 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.

4.3.5                                Magnetic Survey Results

The regional gradient and diurnal variability was subtracted from the measured values using proprietary EGS software, leaving the background geological magnetic field; in Hong Kong, this is mostly around 44,500nT to 45,000nT.  The remaining magnetic anomalies associated with ferrous material at the seabed or buried at shallow depth were contoured at a scale of 1:500.  The drawing also show the location of seabed features (see Figure 4.7).

The results are summarised in Section 4.3.6 below in the description of the magnetic surveys and in Figures 4.8 and 4.9.

The vertical profile of turbidity measurements and the Secchi disc depths are presented in Annex 12-B-A.

The turbidity readings and Secchi disc depths suggest that visibility near the seabed will be less than 1m for much of the route, so it is likely to be difficult for divers to make a visual inspection of these features.

4.3.6                                Description of the Magnetic Surveys

M11        West of Black Point. >1,000nT anomaly associated with sonar contact SC086 (11m long wreck) confirms presence of ferrous material.

4.3.7                                Interpretation of the Magnetic Anomalies

The magnetic sensor was within 5 m of the seabed/sonar contact.  If a Sonar Contact was timber vessel with no or little ferrous fastenings, equipment, stores or cargo then they may not produce any addition to the 1-2nT 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 1-2nT) in the earth’s magnetic field given the magnetic sensor was within 5 metres 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.  SC086 is considered to be a vessel of some sort.  Given the relatively low magnetic signals for the size of the anomaly and at the distance of the magnetic sensor to the anomaly that it is not solely made of iron, but is of a composite material, possibly timber and iron/steel. 

4.4                                      Remote Operated Video (ROV)

One possible wreck (SC086) was identified and has been presented in Table 4.2 and Figure 4.4.  In order to identify its 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 Figures 4.8(i) and 4.8(ii)).  The ROV was dropped on some of the sites from the work-boat (Figure 4.8(iii)) and the sampan depending on current and site location (Figures 4.8(iv)).

Table 4.2        Identified Archaeological Potential Site

Contact number






RPL offset

Dimensions (m)



22° 24.388' N

113° 54.072' E




1572m SW

10.77m x 3.31m x 2.03m

Possible 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 metres 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 0.5m at 0505; 1.5m at 1117; 1.0m at 1607; and 2.1m at 2239. The weather was overcast, either fog, pollution or a combination and which would have only contributed slightly to the underwater visibility.

4.4.1                                ROV Results

SC086 (5:35pm) (Figure 4.9)

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. 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 4.10 for the clip of video record). 

Due to the lack of visibility, the nature and age of SC086 could not be determined.  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 entrapment.

It was recommended that more detailed remote sensing work incorporating multibeam sonar and side scan sonar data be undertaken for the site so that the sonar data can be used to develop three dimensional models that can 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.


Figure 4.9       Area at SC086

Figure 4.10   Video Clips Showing SC086

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 in April 2006 for the Sonar Contact SC086.  The survey track plot is shown in Figures 4.11.  

4.5.1                                Survey Methodology

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


Model Number

Swath Bathymetry

Reson A.s.

400 kHz 8125

Side Scan Sonar

Klein Associates Inc

System 3000


C&C Technologies Inc



C-Products Ltd

C-View Nav

4.5.2                                Swath Bathymetry

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 4.12.

Figure 4.12   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.

4.5.3                                Side Scan Sonar

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 4.13.

Figure 4.13   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 result is presented below. 


In the side scan sonar survey in 2005, the following assessment was made of this anomaly.  A vessel 10.77m x 3.31m x 2.03m in dimensions and located at 798694E, 2480702N (see Figure 4.5).

The magnetometer survey found this anomaly to contain in excess of 1,000nt more that the surrounding area. This was estimated to be in excess of 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 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 Figure 4.14.


Figure 4.14     Top Left: Side Scan Sonar Image of SC086 UNDERTAKEN in April 2006 (Centre)

                        Top Right :General View of the Vessel by the Multi Beam Sonar

                        Bottom Left: Sampan with What Looks Like a Hole Towards One End of the Vessel

                        Bottom Right: Plan View of Sampan Confirming Damage in the Hull

The vessel and its location has all the appearances of a ‘recent’ motorised wooden sampan (see Figure 4.15).  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.  A vessel of pre-1800 age would not be in this condition in this location.  The Marine Department salvaged a similar looking sampan on the 22 March 2006 (see Figures 4.4 and 16) which they reported was about 30 years old.  SC086 is probably of a similar vintage.

Figure 4.15     A Motorised Sampan of about the Size of SC086

Figure 4.16     Recently Recovered by Marine Department with Dimensions Similar to SC086 (Source: Marine Department)


5                                            Impact Assessment

Literature review supplemented by Geophysical Survey, Magnetic Survey and further detailed side scan sonar and multi beam sonar survey identified one shipwreck (SC086) within the Study area.  However, based on the survey data, the result indicated that SC086 is considered to be a motorised sampan.  In the context with the AM Ordinance (Cap. 53), the site is not an antiquity or relic and of no archaeological value.  Thus, due to the lack of archaeological value of the site, impact to it is considered acceptable.


6                                            Conclusions and Recommendations

Literature review supplemented by Geophysical Survey, Magnetic Survey and further detailed side scan sonar and multi beam sonar survey identified one shipwreck (SC086) within the Study area.  However, based on the survey data, the result indicated that SC086 is considered to be a motorised sampan.  In the context with the A M Ordinance (Cap. 53), the site is not an antiquity or relic and of no archaeological value.  Thus, due to the lack of archaeological value of the site, impact to it is considered acceptable.  No mitigation measure is considered necessary.



([1])      The Antiquities and Monuments Office is the entry point to pass information to the AAB.   The AAB is a statutory body consisting of expertise in relevant fields to advise on any matters relating to antiquities and monuments.

([2])     Fyfe, J.A., R. Shaw et al. 2002. The Quaternary Geology of Hong Kong, Hong Kong: Civil Engineering Department.

([3])     Ibid.

([4])     Ibid..

([5])     Fyfe, J.A., R. Shaw and et al. 2002. The Quaternary Geology of Hong Kong, Hong Kong: Civil Engineering Department.

([6])      Siu, K.K 1997 Forts and Batteries: Coastal Defence in Guangdong During Ming to Qing Dynasties, Hong Kong, Urban Counil.

([7])     蕭國健 1994 〈明代粵東海防中路之南願頭寨〉,《香港歷史與社會》,香港教育圖書公司。

([8])      Brage, J.M. 1965  China Landfall 1513, Jorge Alvares Voyage to China, Macau, Imprensa Nacional.

([9])     Cortesão, A 1944, The Suma Oriental of Tome Pires and the Book of Francisco Rodrigues. London, Hakluyt Society. 龍思泰 (Anders Ljungstedt) 1832, 1997 《早期澳門史》,北京,東方出版社。 

([10])    Nessel , Johan 1658 Tngqvin, in 格斯‧冉福立 (Kees Zenlvliet) 江樹生  1997 《十七世紀荷蘭人繪製的台灣老地圖》,台北,漢聲出版社。

([11])    王應華 1660年代,2000〈赤灣天妃廟記〉,《明清兩朝深圳檔案文獻演繹》,廣州,花城出版社蔡學元 18142000 〈重修赤灣天后廟記〉,《明清兩朝深圳檔案文獻演繹》,廣州,花城出版社。 

([12])    靳文謨 1688 《新安縣志》,新安縣衙。

([13])       Ali, Sarah 1998 Study on the Potential, Assessment, Management and Preservation of Maritime Archaeological Sites in Hong Kong. Hong Kong: Lord Wilson Heritage Trust

([14])    The numbering in the plans do not reflect the numbers shown in the above table

[15]      Green, J.G., 2004, Maritime Archaeology: A Technical Handbook Elsevier Academic Press California

[16]      See Green, 2004:159-162 for details of a close-plot survey of the Dutch shipwreck Amsterdam and which provides, amongst other things a good outline of the timber hull shape.

([17])    Maitland, D., 1981, Setting Sails. A tribute to the Chinese Junks. South China Morning Post. Hong Kong