multibeam survey in southern taranaki bight...6 multibeam survey in southern taranaki bight 1 survey...

Multibeam Survey in Southern Taranaki Bight

Prepared for Trans-Tasman Resources Ltd.

April 2013

© All rights reserved. This publication may not be reproduced or copied in any form without the permission of the copyright owner(s). Such permission is only to be given in accordance with the terms of the client’s contract with NIWA. This copyright extends to all forms of copying and any storage of material in any kind of information retrieval system.

Whilst NIWA has used all reasonable endeavours to ensure that the information contained in this document is accurate, NIWA does not give any express or implied warranty as to the completeness of the information contained herein, or that it will be suitable for any purpose(s) other than those specifically contemplated during the Project or agreed by NIWA and the Client.

Authors/Contributors: Arne Pallentin Peter Gerring Susanne Woelz Mark Fenwick

For any information regarding this report please contact: Arne Pallentin Ocean GIS Analyst Ocean Sediments +64-4-386 0603 [email protected] National Institute of Water & Atmospheric Research Ltd 301 Evans Bay Parade, Greta Point Wellington 6021 Private Bag 14901, Kilbirnie Wellington 6241 New Zealand Phone +64-4-386 0300 Fax +64-4-386 0574

NIWA Client Report No: WLG2013-8 Report date: April 2013 NIWA Project: TTR11301/MULTIBEAM


Contents

Executive summary .............................................................................................................. 5

1 Survey Plan.................................................................................................................. 6

1.1 Objectives ............................................................................................................ 6

1.2 Survey Schedule .................................................................................................. 7

1.3 Survey Narrative .................................................................................................. 7

2 Equipment ................................................................................................................... 8

2.1 Navigation ............................................................................................................ 8

2.2 Applanix POS/MV ................................................................................................ 8

2.3 Kongsberg EM3002 ............................................................................................. 8

3 Survey Data ................................................................................................................. 9

3.1 Multibeam Data .................................................................................................... 9

4 Survey Blocks ........................................................................................................... 12

4.1 Outfall pipeline extension ................................................................................... 12

4.2 Instrument mooring site ...................................................................................... 13

4.3 FPSO vessel mooring site .................................................................................. 14

4.4 Tailing dump site ................................................................................................ 15

4.5 Dianne Lip & Christina Lip .................................................................................. 16

5 Acknowledgements ................................................................................................... 17

Appendix A Calibration ........................................................................................... 18

Appendix B Data package ...................................................................................... 19

Figures Figure 1-1: Overview of the survey area. 6

Figure 2-1: Plot of the SVP profiles collected. 9

Figure 3-1: Example for data with interpolation. 11

Figure 4-1: Map showing the bathymetry along the planned route of the extension of the Wanganui outfall pipeline. 12

Figure 4-2: Map showing the bathymetry of the instrument mooring site. 13

Figure 4-3: Map showing the bathymetry at the planned FPSO mooring site. 14

Figure 4-4: Map showing the bathymetry at the planned tailing dump site. 15

Figure 4-5: Map showing the bathymetry at the Dianne & Christina lips and surroundings. 16


Reviewed by Approved for release by

John Mitchell Neville Ching Ocean Geology Group

5 Multibeam Survey in Southern Taranaki Bight

Executive summary Trans-Tasman Resources Ltd. (TTR) contracted NIWA to provide services related to environmental studies in Southern Taranaki Bight. In work schedule W, Variation 2, dated 24/10/2012 TTR asked NIWA to conduct a multibeam bathymetry survey covering:

� the potential extension route for the Wanganui outfall pipeline,

� oceanographic instrument mooring,

� FPSO vessel mooring,

� tailing dump site

� and the Dianne and Christina Lip mining areas. These two areas were subsequently extended into one continuous area on request of TTR.

The unstable, windy conditions experienced in late 2012, La Niña year, resulted in delays in the survey work, and as a result it took until March 2013 to finalise the field work, originally scheduled for completion in November 2012. Additionally the expected 80h of survey time were increased to 138.5h, a result of the increased survey area and the less favourable sea conditions which forced a reduction in survey speed.

The depth range and seafloor morphology of the areas varies widely. The shallowest measured depth was just under 10m water depth at the end of the Wanganui outfall pipeline, the deepest in the planned FPSO mooring site area with just under 80m water depth. The most unusual morphological feature is a field of what appears to be rocky outcrops, rising 1-5m above the seafloor, in the Southwest corner of the instrument mooring site area. While the tailings dump site and mining areas are dominated by the large, northwest – southeast trending sediment bodies of the Rolling Ground, the deeper FPSO mooring site is largely flat and slowly dipping to the southwest. The outfall pipeline corridor is in generally flat, dipping away from the coastline, but also shows small c 50cm high patchy rises and an erosional channel at its outward end. More details are visible and these are described in the Survey Blocks section.


1 Survey Plan

1.1 Objectives The areas to be surveyed were prioritised by TTR as follows:

1. Outfall pipeline extension

2. Instrument mooring site

3. FPSO vessel mooring site

4. Tailing dump site

5. Dianne Lip

6. Christina Lip

The two lip areas were subsequently joined into one area as requested by TTR. The survey order was partially reversed for the instrument & vessel mooring sites and the tailing dump site (in parts) due to operational requirements, but were surveyed within days of each other. These changes were made to minimise transit times to and from the survey area.

Figure 1-1: Overview of the survey area. Red outlines indicated planned survey blocks.

Multibeam Survey in Southern Taranaki Bight 7

1.2 Survey Schedule Voyage Number: TTR-multibeam

Voyage Name: Southern Taranaki Bight multibeam

Project Number: TTR11301/multibeam

Start: 24th October 2012

End: 24th March 2013

Survey Hours: 138.5h

Weather Downtime: 2 days

Area: Southern Taranaki Bight

Vessel: RV Ikatere

Survey Personnel: (4) Arne Pallentin (Survey Leader)

Peter Gerring (Co Survey Leader)

Susanne Woelz

Mark Fenwick

1.3 Survey Narrative 29/09/2012 0600 – 2100 Work on pipeline corridor, transiting to and from Mana

marina, completed work on the pipeline corridor and started work on the instrument mooring site.

20/11/2012 0300 – 1845 Transit from Mana to survey site, working on FSPO mooring (finished) & dump site, boat stays in Wanganui

21/11/2012 0630 – 1915 Work on tailings dump site, boat stays in Wanganui

22/11/2012 0620 – 2130 Work on instrument mooring site (finished), transit back to Mana due to changing weather and forecast.

15/12/2012 1600 – 1930 Transit to Wanganui.

16/12/2012 0620 – 1900 Work at tailing dump site, boat stays in Wanganui.

17/12/2012 0630 – 1330 Work at tailing dump site (finished) & mining area, stopped survey work at 1330 due to sea state, boat stays in Wanganui.

18 & 19/12/2012 Weather downtime.

20/12/2012 0620 – 1845 Work at mining area, boat stays in Wanganui.

21/12/2012 0630 – 1500 Work at mining area, stopped work at 1330 due to sea state, boat stays in Wanganui.


22/12/2012 0700 – 2100 Work at mining area, boat stays in Wanganui.

23/12/2012 0800 – 1130 Transit to Mana Marina due to weather conditions & forecast. Christmas break.

08/02/2013 0300 – 2200 Work on mining area, transiting to and from Mana marina.

23/03/2013 1500 – 2030 Transit to Wanganui from Wellington.

24/03/2013 0600 – 1730 Work at mining area, finished survey.

25/03/2013 0700 – 1200 Transit to Wellington.

2 Equipment

2.1 Navigation The primary positioning system used was the position derived from the Port side Applanix POS/MV GPS Antenna, differentially corrected by the Fugro SeaStar XP Wide Area Differential GPS (WADGPS) service.

The differential corrections consist of pseudo-range corrections generated by the Fugro SeaStar XP WADGPS system. These corrections were uplinked through a Fugro monitoring station and received on board the vessel via the Pacific Ocean Region (POR) satellite.

2.2 Applanix POS/MV Heave and attitude were provided by an Applanix POS/MV 320 motion sensor on Ikatere. The POS/MV generates attitude data in three axes. Measurements of roll, pitch, and heading are accurate to 0.02º or better (manufacturer’s specifications) regardless of the vessel’s latitude. Heave measurements supplied by POS/MV maintain an accuracy of 5% of the measured vertical displacement or ±5cm (whichever is the larger) for movements that have a period up to 20 seconds (manufacturer’s specifications).

2.3 Kongsberg EM3002 The Kongsberg EM3002 multibeam echo sounder (MBES), centred on 300 kHz, was used throughout the survey. The multibeam was operated to obtain the maximum swath width with a maximum beam angle of 65°/65°. MBES data was collected using the Kongsberg Seafloor Information System (SIS) software.

The EM3002 multibeam worked well in the water depths experienced during the survey. Swath widths were narrow due to the shallow water depths but well within the expected ranges for these conditions. Line spacing throughout the survey was approximately 3x water depth.

Most errors are predictable and easily corrected for with the exception of sound speed. The predictable errors are normally accounted for by a patch test of the system prior to the start of surveying. Ikatere was fitted with the EM3002 in September 2012 in preparation for this survey, and a patch test completed in October 2012 in Wellington Harbour (Appendix A).

The unmeasured change in sound speed through the water column is unpredictable and can potentially result in significant depth and positioning errors. This error source is mitigated


through continually monitoring the bathymetry data for evidence of sound speed artefacts during sounding operations. The surface sound speed is continuously measured and used to calculate departure angles at the transducer and is also used as a real-time indicator of sound speed changes throughout the water column.

SVP profiles were planned to be collected before the start of survey work each day and whenever a change in velocity was observed. The nature of the water masses in the survey area were such that repeat SVPs were required every 6-8 hours of survey time, most likely related to changes in water temperature during the day and changes in tidal flow. SVP profiles were required to adjust for velocity errors caused by these changes. Despite this there is still some evidence of velocity error in the outer sectors of the data especially over areas of very flat seabed.

Figure 2-1: Plot of the SVP profiles collected. Note the variability of the profiles.

3 Survey Data

3.1 Multibeam Data The Kongsberg EM3002 multibeam echo sounder and SIS software were used for data acquisition. SIS was used to display the previous sounding coverage as well as the current sounding coverage and was used to provide planning and navigation for the data acquisition personnel and the boat driver. Raw data files were then imported into CARIS HIPS for processing and cleaning.

To ensure the intended survey area was completed in the available time, overlap between lines was kept to a minimum and vessel speed as close to 8 knots as possible. As a result the vessel’s acoustic noise was greater and the outer beams noisier which had an impact on the visual appearance of the bathymetry coverage and minor loss of accuracy of the depth data in the outer beams. This loss of accuracy is in the order of centimetres, with the TPU


elevation accuracies dropping from millimetres at the centre of swath to centimetres at the outer beams, while staying well within IHO order 2 accuracies.

All data collected by this survey were backed up at the end of each survey day and then transferred to NIWA Greta Point on the survey team’s return.

Survey datum for the bathymetry data is Mean Sea Level (MSL).

3.1.1 On-board Processing The raw Kongsberg EM3002 data were imported into CARIS HIPS V7.1 software for initial processing to ensure that the acquired data was of the required quality.

Field-sheets were created for each area/site. These were later used for final processing and for data export.

3.1.2 On-shore Processing

Multibeam For the final processing on-shore tide data from the NIWA tide model (below) was applied to the CARIS HIPS data. Navigation and Attitude data was examined on a line by line basis, before merging and computing Total Propagated Errors (TPE) for the data. These statistics are used for the computation of Combined Uncertainty Bathymetry Estimate (CUBE) surfaces.

The bathymetry data were examined and cleaned in CARIS HIPS, initially using the swath editor on a line by line basis, followed by gridding the data using the CUBE surfacing tool and final cleaning completed using the CARIS subset editor. This workflow allows the cleaning of data in comparison with adjacent lines, resulting in a more efficient and rigorous process. The final digital terrain models were gridded at 2.5m cell size with the exception of the outfall pipeline route which was gridded at 1m cell size. This higher resolution was possible due to the shallower water depth in this survey block. A 5x5 nearest neighbour interpolation was then run to fill in any insignificant holes in the resulting DTM (Figure 3-1: Example for data with interpolation.). The resulting surfaces were exported as ESRI ASCII grid files for use in standard GIS applications. Additionally geo-referenced TIFF images of colour coded bathymetry were exported to be used in common GIS packages and for the generation of the maps included in this report. Colour ranges were set to ‘by area’ allowing finer details do be observed, and ‘by region’ using a 10m to 80m depth scale for colouring. This allows for the direct visual comparison between all data sets.

These data have been processed following recognised hydrographic methodology to enable the provision of this report.


Figure 3-1: Example for data with interpolation. Left side: without interpolation, right side: with 5x5 nearest neighbour interpolation (empty cells only).

Tide Data Tide data was extracted from the NIWA tide model for multiple positions, one adjacent to each survey site, with extracted data stretching over the specific times of survey. The data was formatted to the CARIS *.tid data format necessary for input to CARIS HIPS. All raw tide data files are included in the data pack (Data package). Times are in UTC and the tide value with reference to Mean Sea Level (MSL). See below an example header with a few lines. The tide value is given in millimetres.

NIWA Tide Model Forecast for 174.160 deg E -40.030 deg N Time is GMT Height Datum is: MSL 18-Nov-2012 24:00:00 670 19-Nov-2012 00:05:00 707 19-Nov-2012 00:10:00 743 19-Nov-2012 00:15:00 778 19-Nov-2012 00:20:00 811 …


4 Survey Blocks

4.1 Outfall pipeline extension

Figure 4-1: Map showing the bathymetry along the planned route of the extension of the Wanganui outfall pipeline.

A two line wide corridor was swath mapped along the planned route of the extension of the outfall pipeline. The corridor starts in the northeast with the end of the existing pipeline clearly visible in the multibeam data. The seafloor gently dips towards the southwest. About 4/5ths along the extend of the mapped corridor the seafloor is markedly more variable with patchy highs and channel beds. In the last 5th of the corridor an area of sediment waves is visible.


4.2 Instrument mooring site

Figure 4-2: Map showing the bathymetry of the instrument mooring site.

The bathymetry at the instrument mooring site is marked in the southwest by an area of what appears to be rocky outcrops, 1-5m above the surrounding seafloor. A shoal in the central part of the area interrupts the otherwise gentle dip to the southwest. During the survey of this area and transits past the area on the way to other survey blocks it was noted that there is a significant number of recreational fishermen targeting this area.


4.3 FPSO vessel mooring site

Figure 4-3: Map showing the bathymetry at the planned FPSO mooring site.

The FPSO mooring site lies to the south of the shoals of the ‘Rolling Ground’. These are just visible on the seafloor at the north to northwest edge of the area. Otherwise the seafloor here is gently dipping to the southwest.


4.4 Tailing dump site

Figure 4-4: Map showing the bathymetry at the planned tailing dump site.

The tailing dump site lies within the field of large, northwest – southeast stretching sediment bodies that form the shoals of the “Rolling Grounds”. The largest, and shoalest, of these is visible in the northeastern side of the area, followed to the southwest by consecutively deeper lying ridges.


4.5 Dianne Lip & Christina Lip

Figure 4-5: Map showing the bathymetry at the Dianne & Christina lips and surroundings.

The extended Christina & Dianne lips lie to the west of the “Rolling Ground”. The east of the area is marked by a large, northwest – southeast trending sediment body. From here the seafloor in general dips to the southwest, with numerous elongate sediment ridges on top of this more general slope. In water depths greater than 40m these sediment bodies are no longer observed. In the southern part of the area, just deeper than the 40m line, a field of small, very elongate sediment ripples is visible.


5 Acknowledgements All aspects of the survey were successful thanks to the hard work of all involved.

The survey could not have been successfully completed without the professional efforts of all involved. We would like to acknowledge the efforts of the boat masters and crew of Ikatere and NIWA Vessels Company. The boat crew of Ikatere were, as always, helpful and professional and all work was carried out efficiently. Boat masters and crew included Andrew James, Chris Jonson, Mike Carson, John Headfield, Chris Healy and Matthew McGlone. Tide data processing was provided by Nigel Goodhue. The small but dedicated survey party also performed up to high expectations as attested to by the quality of the data obtained. John Mitchell & Neville Ching provided editorial comments and advice during the writing of this report.


Appendix A Calibration A calibration check for mounting angle off-sets on the EM3002 multibeam echosounder was performed in Wellington Harbour prior to departure to the survey area for the start of the survey. For calibration checks NIWA utilises the well-surveyed area around the wreck of the South Sea.

Calibration checks were made using the SIS SeaCal software. A set of survey lines are run, input into SeaCal and the resulting calculation provides all off-set values in one computation run. The results file is included on the DVD (directory ‘calibration’, file seacal_20120927_15953.res).

The off-sets calculated were then added to the base settings in the installation settings of the SIS software. The added off-sets were: roll = -0.137°, pitch = 1.213°, heading = -0.451°.

During the survey the system operator is constantly monitoring the collected data. No artefacts typically seen as a result of off-sets errors were observed in the field data.


Appendix B Data package All processed data as well as the electronic versions of this report (in PDF format) are available on the accompanying DVD.

Tide data Tide data is included in the ‘tide’ directory on the DVD as ascii files.

Processed data All processed data is included as ESRI ASCII grid file and GeoTIFF files on the DVD. These are:

FPSO_Mooring_250cm_bathymetry.asc (ESRI ASCII grid)

FPSO_Mooring_250cm_bathymetry.tif (colour coded TIFF with local stretch range)

FPSO_Mooring_250cm_bathymetry_10_2_80.tif (colour coded TIFF with stretch from 10m to

80m (min/max))

Instrument_Mooring_250cm_bathymetry.asc

Instrument_Mooring_250cm_bathymetry.tif

Instrument_Mooring_250cm_bathymetry_10_2_80.tif

Mining_Site_250cm_bathymetry.asc

Mining_Site_250cm_bathymetry.tif

Mining_Site_250cm_bathymetry_10_2_80.tif

Outfall_Pipeline_Extension_1m_bathymetry.asc

Outfall_Pipeline_Extension_1m_bathymetry.tif

Outfall_Pipeline_Extension_1m_bathymetry_10_2_80.tif

Tailings_Dump_Site_250cm_bathymetry.asc

Tailings_Dump_Site_250cm_bathymetry.tif

Tailings_Dump_Site_250cm_bathymetry_10_2_80.tif

Report The PDF version of this report in included on the DVD under the ‘report;’ directory.

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