appendix 11.2 full mai conducted in 2008 · appendix 11.2.docx page 1 1 marine archaeology...

Appendix 11.2

Full MAI conducted in 2008

Highways Department Agreement No. CE 43/2010 (HY) Central Kowloon Route - Design and Construction

APPENDIX 11.2.DOCX Page 1

1 Marine Archaeology Investigation conducted in 2008

1.1 Geophysical Survey Results

1.1.1 Geological Background of the Area

The survey area is dominated by superficial deposits that are from the Holocene and Quaternary period. The sediments are undivided and mainly dark grey marine mud, called the Hang Hau Formation. From an archaeological perspective, the Hang Hau Formation has high archaeological potential. The formation consists of relatively homogenous very soft, greenish grey silty clay and has a high moisture content. Therefore, the Hang Hau Formation sediments potentially provide an excellent substrate for the preservation of archaeological material. Additionally, the soft nature of the sediments would make it possible for archaeological material to be buried within the formation, where it would have greater protection than if it were exposed on the seabed. Across the study area the formation is between 2 and 8 m thick which is sufficient to bury archaeological features.

The survey area is surrounded by reclaimed land to the NE and NW, while to the south is Kowloon Bay. Special geological feature or structure is not noted in the survey area.

1.2 Reduction of Observations and Interpretation

1.2.1 Sounding Data

For sounding readings, the influence of wave action was corrected in real time by the TSS320 motion compensator. The smoothed sounding data was then reduced to levels below Principal Datum (PD) using the measured tide levels.

1.2.2 Side Scan Sonar Data

Processing and interpretation of side scan sonar data was carried out using the C-View interpretation software. All features were individually marked or grouped into regions using on- screen digitising. All offsets and laybacks were applied to the C-View system. The subsequently generated interpretation files were then imported to the Auto CAD environment on a line by line basis where the interpretation was reconciled and a detailed check was performed.

The interpretation of the side scan sonar records in this area identified the following features on the seabed:

• Seafloor with shallow trenches and scars

• Small area with occasional scars at the survey margin to the south

• Two sonar contacts



1.2.3 Seismic Data

Seismic data showed that the survey area was covered by marine deposits in variable depths.

However, the area was heavily masked as expected which blocked the interpretation work for

sub bottom geology.

Masking is probably caused by the presence of organic materials on the seabed (e.g. discharge

from the water outfall) and the gas bubbles so generated absorb the seismic energy, thereby

preventing reflections from deeper horizons:

Figure 1 Example of Seismic Data

Masking shielded the

penetrating of seismic signals Marine deposits

10ms

20ms

30ms

Seabed

Seabed

Marine deposits

10ms

20ms

30ms

Masking shielded the

penetrating of seismic signals



1.2.4 Magnetic Data

The earth’s magnetic field is locally distorted by:

• Changes in the magnetic susceptibility of sediments and the solid geology

• Magnetic anomalies caused by made-made ferrous metal objects

In this case, the residual anomalies were interpreted as ferrous metal objects on or beneath the seabed.

Magnetic data are plotted in the form of profiles. These are inspected by an experienced geophysicist for anomalies likely to have been caused by the pipelines and other ferrous objects. Following is an example from this survey.



Figure 2 Example of Magnetic Data

Alignment of the existing pipeline has been successfully detected by the magnetometer.

1.2.5 Presentation

The results have been presented in Annex A to Annex F.

1.2.6 Sounding Plan

The most obvious features on the sounding plan are the two depressions, 3-4m deep, located close to the barges. The depressions are believed related with the operation of barges nearby. Apart from these two items, seabed is relatively featureless.

The seabed varies between –1m PD and –8m PD within the survey area.

1.3 Sea bed Features

1.3.1 Characteristics of Sea Bed Features

As shown on the drawing, shallow trenches undulating on the seabed is common in the survey area. Anchor scars are observed on soft seabed sediments when barges and other commercial boats anchor. Examples of side scan images are shown below for reference.



Figure 3 Example of Side Scan Sonar data showing anchor scars and shallow trenches

Figure 4 Side Scan Sonar data showing Sonar Contacts 1 and 2

Anchor scar

Shallow

trenches

Anchor scars

Shallow

trenches



Two sonar contacts were detected with details listed below:

Table 1 Sonar Contacts Identified

Contact

number

Latitude

Longitude

Easting

Northing

Dimensions (m) Description

SC001 22° 19.253' N

114° 11.638' E

838282.5E

820038.2N

0.4x0.4x0.2 Unidentified Object

SC002 22° 19.248' N

114° 11.632' E

838272.1E

820029.2N


1.3.2 Detection of Pipeline and Other Unidentified Ferrous

Objects

The existing gas pipeline extending from the seawall in NW was mapped by the magnetometer along with several unknown anomalies within the area, caused by ferrous metal objects either on or below the seabed. Details are listed below and shown in Annex G.

Table 2 Existing Gas Pipeline

Contact number Latitude

Longitude

Easting

Northing

Dimensions Description

MC001 22° 19.158' N

114° 11.621' E

838251.9E

819864.3N

355nT Gas Pipeline

MC002 22° 19.205' N

114° 11.673' E

838341.6E

819949.6N

729nT Unknown

MC003 22° 19.167' N

114° 11.614' E

838240.0E

819880.2N

398nT Gas Pipeline

MC004 22° 19.216' N

114° 11.670' E

838336.7E

819970.7N

448nT Unknown

MC005 22° 19.223' N

114° 11.678' E

838350.5E

819984.0N

525nT Unknown

MC006 22° 19.233' N

114° 11.675' E

838344.6E

820002.4N

709nT Unknown

MC007 22° 19.171' N

114° 11.603' E

838222.6E

819887.1N

398nT Gas Pipeline

SC001 –

Unidentified

Object

SC002 –

Unidentified

Object



Contact number Latitude

Longitude

Easting

Northing

Dimensions Description

MC008 22° 19.181' N

114° 11.597' E

838211.0E

819906.5N

808nT Gas Pipeline

MC009 22° 19.186' N

114° 11.587' E

838194.0E

819915.4N

1030nT Gas Pipeline

MC010 22° 19.196' N

114° 11.579' E

838180.0E

819933.0N

629nT Gas Pipeline

MC011 22° 19.201' N

114° 11.570' E

838164.7E

819942.9N

599nT Gas Pipeline

MC012 22° 19.211' N

114° 11.563' E

838152.8E

819961.5N

1612nT Gas Pipeline

MC013 22° 19.218' N

114° 11.553' E

838136.4E

819973.6N

569nT Gas Pipeline

MC014 22° 19.224' N

114° 11.545' E

838121.8E

819984.6N

241nT Gas Pipeline

MC015 22° 19.234' N

114° 11.538' E

838110.0E

820003.6N

1097nT Gas Pipeline

MC016 22° 19.225' N

114° 11.618' E

838248.0E

819986.4N

79nT Unknown

MC017 22° 19.253' N

114° 11.637' E

838280.4E

820038.4N

68nT Unknown

1.3.3 Contoured Isopachs of Traceable Marine Deposits

Since seismic data was adversely affected by masking, only those above the masking zone were traceable and presented in Annex F. The drawing shows that the survey area is covered with marine deposits comprising soft mud.

1.3.4 Summary of Geophysical Survey Results

The side scan sonar survey data indicated the presence of two sonar contacts. These both lie outside the footprint of the tunnel but within the area that will be dredged. The magnetic survey identified a total of 17 magnetic contacts. 11 of these are directly connected the submarine gas pipeline and the additional 6 remain unidentified. Of these one lies directly within the tunnel footprint and the other 5 within the area that will be dredged. One is directly associated with sonar contact 1. It is possible that these unidentified ferrous objects on or below the seabed could be artefacts such as cannon or other cultural resources. In total, there were 8 contacts requiring further investigation as shown in the following table.

Table 3 Remaining Contacts Requiring Further Investigation

Contact

number

Latitude

Longitude

Easting

Northing


SC001 22° 19.253' N

114° 11.638' E

838282.5E

820038.2N


SC002 22° 19.248' N

114° 11.632' E

838272.1E

820029.2N


MC002 22° 19.205' N

114° 11.673' E

838341.6E

819949.6N

729nT Unknown



Contact

number

Latitude

Longitude

Easting

Northing


MC004 22° 19.216' N

114° 11.670' E

838336.7E

819970.7N

448nT Unknown

MC005 22° 19.223' N

114° 11.678' E

838350.5E

819984.0N

525nT Unknown

MC006 22° 19.233' N

114° 11.675' E

838344.6E

820002.4N

709nT Unknown

MC016 22° 19.225' N

114° 11.618' E

838248.0E

819986.4N

79nT Unknown

MC017 22° 19.253' N

114° 11.637' E

838280.4E

820038.4N

68nT Unknown

Annex G presents the location of the magnetic and sonar contacts within the study area and

alignment corridor. The seismic reflection data showed that there is 2-10m of Marine Deposit

across the study area, which is sufficient to protect and bury archaeological resources.

1.3.5 Visual Diver Survey

The aim of the diver inspection was to locate all of the 8 targets and establish their archaeological potential.

The diving team successfully located every target. They were all identified as being of modern origin. They included some scrap metal objects, construction waste and tyres. There was clear evidence for seabed disturbance from anchored ships. On the shore very close to the study area is an aggregate sorting plant, which can be seen clearly in Figure 6. The barges, which regularly use this location, disturb the seabed with their anchors.



Figure 6 Remaining Dive Boat within Study Area showing Aggregate Plant and Barges

It was also significant that in some sections the seabed looked as it had been recently dredged as there was no debris at all which is uncommon in Hong Kong.

Figure 7 to Figure 14 are photographs from the diver survey. It was not possible to obtain clear photographs of all of the contacts due to the very poor water quality at this location.

Highways Department

APPENDIX 11.2.DOCX

Figure 7 Modern Debris Found at Location of SC001

Figure 8 Modern Debris Found at Location of SC002

Agreement No. CE 43/2010 (HY) Central Kowloon Route

Modern Debris Found at Location of SC001

Modern Debris Found at Location of SC002

Agreement No. CE 43/2010 (HY) Central Kowloon Route - Design and Construction

Page 10

Highways Department

APPENDIX 11.2.DOCX

Figure 9 Modern Debris Found at Location of MC002

Figure 10 Modern Debris Found at Location

Agreement No. CE 43/2010 (HY) Central Kowloon Route

Modern Debris Found at Location of MC002

Modern Debris Found at Location of MC004

Agreement No. CE 43/2010 (HY) Central Kowloon Route - Design and Construction

Page 11



1.4 Identification of Potential Impacts

As there is no underwater cultural resource within the study area there will be no negative impact from the construction works.

1.5 Recommendation of Mitigation Measures and EM&A Requirements

There is no archaeological resource on the seabed within the study area and therefore no mitigation is required.

1.6 Conclusion

Each phase of the MAI was completed successfully. The Marine Archaeological

Investigation covered 100% of the study area. There was no object on the seabed that

indicated submerged archaeological remains. It is therefore concluded that there is no

archaeological resource on the seabed within the study area.

Annex A

Echo Sounding Track Plot

tyhkt187

tyhkt187

ROUTE

Annex B

Seismic and Side Scan Sonar Track Plot

tyhkt187

tyhkt187

ROUTE

Annex C

Magnetic Survey Track Plot

tyhkt187

tyhkt187

tyhkt187

ROUTE

Annex D

Contoured Sounding Plan

tyhkt187

tyhkt187

ROUTE

Annex E

Sea Bed Features

tyhkt187

tyhkt187

ROUTE

Annex F

Contoured Isopachs of Traceable Marine Deposits

tyhkt187

tyhkt187

ROUTE

Annex G

Locations of Sonar Contact and Magnetic Anomalies in Relation to the Proposed Tunnel Location

aac1.public

Rectangle

aac1.public

Rectangle

Appendix 11.2G

aac1.public

Text Box

Appendix 11.2G

appendix 11.2 full mai conducted in 2008 · appendix 11.2.docx page 1 1 marine archaeology...

Documents