Gammon – Skanska – MBEC Joint Venture

Contract No: HY/2002/21

Hong Kong Shenzhen Western Corridor

Sedimentation Rate Monitoring Report

(Revision 0)

April 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:

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;

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

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:

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

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	838619.010	819250.001	0.996	0.007	0.004
P2	838601.008	819415.012	1.113	0.008	0.005
P3	838942.002	820630.010	1.642	0.006	0.011
P4	839528.009	820880.008	1.837	0.007	0.005
P5	840301.009	821115.010	1.546	0.006	0.006
P6	838897.008	817937.998	1.219	0.010	0.007
P7	838923.007	817923.005	1.215	0.008	0.005

The monitoring date was on 16^th and 17^th April 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	838619.010	819250.001	0.010
P2	838601.000	819415.000	838601.008	819415.012	0.014
P3	838942.000	820630.000	838942.002	820630.010	0.010
P4	839528.000	820880.000	839528.009	820880.008	0.012
P5	840301.000	821115.000	840301.009	821115.010	0.013
P6	838897.000	817938.000	838897.008	817937.998	0.008
P7	838923.000	817923.000	838923.007	817923.005	0.009

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 complying to the specification.