Gammon – Skanska – MBEC Joint Venture

 

 

 

 

Contract No: HY/2002/21

Hong Kong Shenzhen Western Corridor

 

 

Sedimentation Rate Monitoring Report

(Revision 0)

 

 

 

 

 

March 2007

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CONTENT

 

1                    Introduction

 

2                    Methodology

2.1              Hydrographic Field Survey Method

 

3                    Raw Data and Interpolated Data

3.1             Raw Data

3.2             Survey Point Location

 

4                    Summary and Recommendation

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1        Introduction

 

Gammon – Skanska – MBEC Joint Venture (GSMJV) carried out a mudflat sedimentation rate monitoring near Shenzhen Western Corridor (SWC) and Mai Po, Deep Bay, Hong Kong in accordance with the approved Sedimentation Rate Monitoring Plan submitted under Condition 2.4 of the Environmental Permit (No. EP-162/2003/B).

 

The following task were done:

 

  1. Monitored 7 monitoring stations as specified in PS Appendix M9 at Tsim Bei Tsui, Mai Po mudflat and those between SWC and Tsim Bei Tsui;

 

  1. Confirmed the exact locations of the monitoring stations with the engineer prior to the measurement and assisted the verification of the coordinates on site; and

 

  1. The monitoring work took place as per the requirement as stated in Engineer Instruction No. 72.

 

The major specifications of the survey are as follows:

 

  1. The RTK GPS survey should be calibrated with reference to or directly derived from the control points established by the Lands Department; and

 

  1. The coordinates system should be in HK1980 GRID system and Hong Kong principle datum.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2        Methodology

 

2.1            Hydrographic field survey method

 

The hydrographic field survey was carried out to measure the seabed levels of the Mai Po and Inner Deep Bay inter-tidal mudflat at the specified sampling points. The survey mainly applied on RTK GPS surveying technology. The RTK technology was using real time differential GPS technology to survey 3D coordinates (X, Y, Z) of a survey point. When real time differential signal was not available due to surveying and environmental conditions, static GPS surveying would be carried out with equivalent or better accuracy but of longer operation time.

 

The base station was a survey control point directly derived or established from Lands Department, HKSAR. The control station was established at the helipad of Mai Po area. The rover GPS instrument was used for surveying as standard DGPS operation. If there is any problem in using RTK GPS and using the proposed surveying control point, higher precision but longer surveying time static GPS surveying technology with nearby survey control point would be employed. As static GPS using much more observation to increase the observation result, the precision is higher than RTK GPS surveying but it takes much longer time to finish one point. It was a costly approach in term of time when comparing the RTK GPS. Sometimes, both digital data logging and written records were collected in the field. Both readings were checked twice after surveying to ensure no error was in data booking.

 

The base station was set up with double checking procedure to ensure the coordinates derived or provided by Lands Department was correctly input into the base station. The antenna height of the base station was also double checked for the essential input of the base station. The height of the antenna of the rover was measured and entered into the system with double checking procedure. The rover was used to measure known points such as benchmark of Lands Department to check the accuracy of the whole system during the measurement in surveying days. On top of this procedure, more than one survey record was measured at each required location and the mean of at least three records was taken for the final survey result. The survey was also calibrated in the field at the base station and the nearby predefined checkpoint before and after the survey. This was to eliminate any systematic error during the survey at particular environment and particular date under international surveying methodology.

 

All survey point was approached by using real time GPS measurement to the nearest 5m. If the RTK signal is available, the surveying team will get to the nearest point using stake out procedure. If the RTK signal is not available, the surveying team will approach to the nearest position using non-RTK GPS approach within 30m. Should RTK or non-RTK GPS signal is not available within the specific surveying month, leveling, which has higher accuracy and precision, will be used if nearby known benchmark is available.

 

 

3                   Raw data and interpolated data

 

3.1            Raw data

 

The raw data of the survey result are summarized as follows:

 

Name

Northing (m)

Easting (m)

Elevation (m)

Horizontal Precision (m)

Vertical Precision (m)

P1

838619.008

819250.003

0.994

0.008

0.004

P2

838601.006

819415.009

1.110

0.010

0.006

P3

838941.998

820630.015

1.638

0.006

0.009

P4

839528.009

820880.008

1.832

0.011

0.008

P5

840300.996

821115.002

1.542

0.007

0.006

P6

838896.993

817937.998

1.221

0.012

0.007

P7

838923.009

817923.006

1.213

0.010

0.007

 

The monitoring date was on 19th and 20th March 2007.

 

3.2            Survey point location

 

The survey points were very near to the proposed location using digital map and RTK GPS technology for navigation. The proposed locations were displayed on the map to show the distance and direction from the current location to the proposed locations.

 

Point

Proposed Northing (m)

Proposed Easting (m)

Measured Northing (m)

Measured Easting (m)

Distance between Proposed and Measured Point (m)

P1

838619.000

819250.000

838619.008

819250.003

0.009

P2

838601.000

819415.000

838601.006

819415.009

0.011

P3

838942.000

820630.000

838941.998

820630.015

0.015

P4

839528.000

820880.000

839528.009

820880.008

0.012

P5

840301.000

821115.000

840300.996

821115.002

0.004

P6

838897.000

817938.000

838896.993

817937.998

0.014

P7

838923.000

817923.000

838923.009

817923.006

0.011

 

All the survey points were surveyed within 0.1 meter or less.

 

As the terrain was very uneven within 10 meters from the proposed location and in most cases the terrain was relative flat within 10 meters, it is recommended that the survey location due to the operational difficulties should be within in average 10 meters.

 

 

4                   Summary and recommendation

 

The hydrographic survey carried out by GSMJV was fully compliant to the specification.