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Side scan sonar survey of the Murray River from

Wentworth through to Mildura through to Red Cliffs in

support of nomination for listing of paddle steamer

shipwrecks on the NSW State Heritage Register

Towing the side scan sonar, Murray River, Mildura 2011. Photo: Frits Breuseker.

Seasee Pty Ltd

Hydrographic Surveys

ABN: 33 003 663 527

PO Box 386, Penrith, NSW, 2751.

Prepared: 20th December 2011

Author: Frits Breuseker

Email: frits7@bigpond.com

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Introduction This side scan survey was commissioned by the Heritage Branch, Office of

Environment and Heritage (OEH), NSW Department of Premier and Cabinet.

Side scan sonar data was collected over a period of four days along a stretch of

the Murray River from Wentworth through to Red Cliffs. The survey was

undertaken primarily to confirm the reported existence of wrecks in the

Mildura bridge area and to record any unknown wrecks along the sections of

river covered by the survey. The sonar data collected will be analysed post

survey and positions of any suspected targets found noted for further study.

Method Statement The participants in the survey were Sarah Ward (Heritage Branch, OEH) and

Frits Breuseker (Seasee Pty Ltd). The Seasee survey boat used was towed from

Sydney over two days to Mildura and is a 17ft de Havilland centre console

pressed aluminium dinghy powered by a 15hp four stroke outboard. This vessel

was well set up for survey work having a shaded forward console area for the

main side scan sonar and chart plotting laptops as well as a side console for the

sounders, GPS and power supplies for the various instruments. This vessel sits

relatively flat in the water having had the centre console moved forward and

utilising a small and efficient four stroke outboard, having the keel of the boat

horizontal makes it much easier to keep the boat tracking straight at the two or

three knots that is the normal survey speed.

The survey area covered was the Murray River from Wentworth, New South

Wales through to Mildura, Victoria and through to Red Cliffs, Victoria. The days

the survey was conducted were on Tuesday 29th November, Wednesday 30th

November, Thursday 1st December and Friday 2nd December 2011. This period

was chosen, on the advice of NSW Maritime, to avoid the summer holiday season

and ensure that recreational boat traffic – which would interfere with the

survey – was avoided.

The side scan equipment used was a Tritech SeaKing 300Khz running on

Tritech’s proprietary software SeaNet Pro. The SeaNet system recorded all

the side scan sonar data during the survey. Positioning was provided by a Koden

KGP-913 GPS feeding the SeaNet software directly such that the sonar scans

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produced were then geo-referenced. Boat positioning was achieved by using Ozi

Explorer chart plotting software running NSW Maritime Boating Maps and

utilising a separate GPS. Map and sonar data datum used throughout is WGS84.

The long sections of the Murray River covered in Day 1 and Day 2 were scanned

using a single pass of the river with the width of the scanning range of the side

scan set such that the entire width of the river was recorded at the one time.

The sections of the river covered in Day 3 and Day 4 were scanned more

intensely as there were known suspected targets in this area that had

previously been located by local resident Jamie Robinson.

Most of the time the boat was driven by Frits Breuseker who monitored the

position of the boat on the river and monitored the sonar image quality as the

survey progressed. Sarah Ward deployed and handled the sonar fish while

monitoring the river depth on a depth sounder set up for that purpose.

Infrequently the river bottom would become too shallow for the depth the

sonar fish was being towed at and the height of the fish would need to be

raised until the shallow area was passed.

The following sections of the report give a daily account of activity.

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Daily Log

Day 1 - 29th November 2011

Survey area: Murray River from Wentworth Lock 10 to Mildura Lock 11.

This section of the Murray River was surveyed with a single pass of the river.

The survey boat travelled as near as possible down the middle of the river with

the scanner set to a range of 100m port and 100m starboard allowing for a

200m total width coverage. This was sufficient to cover the entire width of the

river along this stretch. In this location the Murray River has a fairly

consistent width and depth. Depth was an average of around 5m with a maximum

of 10m (scalloping) at some bends. Width was an average of some 100m to 140m,

the wider sections often occurring at bends.

Figure 1: Survey area Day 1, Murray River, Wentworth Lock 10 to Mildura Lock 11. Image: Courtesy NSW

Maritime (Boating Map 20).

Day 2 - 30th November 2011

Survey area: Murray River from Mildura Lock 11 to Red Cliffs.

This section of the Murray River was also surveyed with a single pass of the

river and along with Day 1 was the second of the long single pass survey runs.

Again the survey boat travelled down the middle of the river with the scanner

set to cover a width of 200m. Some sections of this part of the river were

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wider than Day 1 however the 200m recording width was still sufficient to cover

the entire width. Again, this part of the river had a fairly consistent width and

depth similar to the section of river covered in Day 1.

Figure 2: Survey area Day 2, Murray River, Mildura Lock 11 to Red Cliffs. Image: Courtesy NSW Maritime

(Boating Map 20).

Day 3 - 1st December 2011

Survey area: Mildura Bridge.

This part of the survey concentrated on the river a few kilometres above and

below the Mildura bridge and was surveyed more intensely than the other

sections. Along this section the GPS marks of a number of suspected targets

had previously been reported by local resident Jamie Robinson in 2010. These

marks were not available however prior to the start of the survey so they were

not plotted on the survey boats chart plotter nor a survey grid set up to cover

this section.

To make do as much as possible at the time, the marks were entered into the

chart plotter on the day and some four passes were made along this section of

river, close in to either shore and two more equidistant from the middle of the

river. A shorter scanner range was used allowing for higher resolution images.

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These marks were scanned from different directions and width ranges so as to

record as much information as possible from these particular marks. The marks

are plotted as waypoints 1 through 6 as shown on the chart (see Figure 3);

waypoint 3 is behind waypoint 4.

Figure 3: Survey area Day 3, Murray River, Mildura Bridge area. Image: Courtesy NSW Maritime (boating

map 20).

Day 4 - 2nd December 2011

Survey area: Mildura Lock 11 weir bypass.

This part of the survey covered the short section of the river behind the

Mildura weir around to the rear of Lock 11. This is the natural path of the river

however passing through Lock 11 bypasses this section of the river. The survey

boat was launched at the Mildura Bridge boat ramp, went through Lock 11 north

bound, surveyed the river between point 884 (see Figure 4) to just behind the

weir itself and returned via Lock 11 south bound.

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Figure 4: Survey area Day 4, Mildura Lock 11 weir bypass. Image: Courtesy NSW Maritime (boating map

20).

Analysis and Observations

Water quality

The river water in the survey was quite muddy. While suspended sediment can

only adversely affect image quality, the reduction was not noticeable nor

adversely affected the image quality, see example side scan sonar image -

Figure 5. No water quality testing was undertaken as this is outside the scope

of works.

Silting

It was noted that sonar images of some suspected targets obtained in 2010 by

local resident Jamie Robinson showed more detail than was apparent during this

survey. The level of silting would vary from time to time due to river flow,

floods and ever changing river topography. A specific site could also be subject

to a localised effect such as a large vessel moving over the site on a regular

basis that it had previously not done so. In this case the silting up is believed to

Lock 11

Mildura Weir

Mildura

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be the result of flooding at the end of 2010, however no sedimentary analysis

has been undertaken as it is outside the scope of works.

Figure 5: Example side scan sonar image taken during this survey near Mildura wharf on Day 3 showing

suspected targets. Image: Seasee Pty Ltd.

Side scan

The side scan used was a Tritech SeaKing 300Khz. Tritech also make a lower

frequency unit 150 KHz and a higher frequency unit 675 KHz. The general rule

of thumb with side scans is that the higher the frequency it operates at the

higher the resolution it is capable of but at the expense of range i.e. they

cannot ‘see’ as far as a lower frequency unit. The 300 KHz scanner used in this

survey was ideal for covering the width of the river in one pass with sufficient

resolution to identify suspected targets. When surveying close in to a specific

suspected target or surveying an area more intensely, it would be advantageous,

from a resolution point of view, to use a 675Khz unit. It is the intention of

Seasee to compliment its 300 KHz scanner with a 675 KHz scanner in the

future and use both in surveys such as this one.

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Grids / survey tracks.

In future, when possible, survey grids will be prepared beforehand as well as

waypoints of interest and plotted on the charts being used during the survey.

Post survey reports would then include a map of the survey grids and the survey

boats path in relation to the survey grid. If engaged to carry out such a survey

again, Seasee Pty Ltd would ensure that survey grids were established prior to

survey commencement.

Conclusions / Recommendations

The object of this assignment was to do a survey of the nominated areas of

sufficient standard to: determine if there are undiscovered historic paddle

steamer wrecks that warrant further investigation; further record some known

targets (reported by Jamie Robinson and investigated by the Heritage Branch in

2010), and; assuming these targets are identified to be the remains of historic

shipwrecks, to determine if the finds are suitable to be nominated for inclusion

in the NSW State Heritage Register.

To this end the survey was successful. A brief analysis of the sonar data by

Seasee Pty Ltd has confirmed that at least 30 suspected targets are evident in

the Murray River between Wentworth and Red Cliffs. Several of these targets

are clustered around the Loch 10 Weir at Wentworth. At this stage it is

unknown if these targets are historic paddle steamer wrecks, historic river

barge wrecks or the remains of crane barges used for the construction of the

loch/weir in the early 1920’s. Several other targets are clustered in the river

adjacent to Mildura. Several of these are the original finds reported by Jamie

Robinson in 2010, and several are new finds. Additionally there is a new find at

Red Cliffs, and a new find in the Loch 11 weir pool at Mildura. All of the other

finds are scattered throughout the length of the survey area.

Regardless of location, all of these targets are evident in the raw survey data

provided to the Heritage Branch, OEH, by Seasee Pty Ltd. It was agreed at the

outset of the survey that the Heritage Branch, OEH would undertake a full

analysis of the data once delivered by Seasee Pty Ltd. The data has now been

delivered.

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As the data is geo-referenced (i.e. has a real world, GPS positions attached to

it), all targets in the survey files contain positional information. This means that

each target has its own GPS position/location. This will make it possible for the

Heritage Branch, OEH to marry up the positions of the targets with historical

accounts of lost/scuttled wrecks in the river, and, if the target is a wreck, it

will ultimately help in confirming the identity of that wreck. It also means that

if the Heritage Branch chooses to conduct diving operations, that the physical

location of each target is known. This will make planning and conducting diving

operations much more efficient and effective.

Given this, it is recommended that a detailed analysis be conducted by

archaeologists at Heritage Branch, OEH to determine the nature, identity and

significance of suspected targets. If these targets are historic shipwrecks,

they may be protected by the shipwreck provisions of the NSW Heritage Act

1977, or – if State significant - warrant nomination for inclusion in the NSW

State Heritage Register. If this is the case then some of these targets may

warrant further investigation and recording. Further recording may include a

depth contour map, hardness map, high resolution scans and as aforementioned

diving on the targets themselves.

A depth map may over time help determine how the bottom contour is changing

and hence the level of cover over a given suspected target. A hardness map

would reveal at least an outline of the target below the bottom confirming the

target existence and dimensions. Scanning a specific target warrants using the

highest frequency scanner available as range would then not be an issue. Diving a

target may positively confirm some attributes that may not be possible to

confirm in other ways. If State significant, it may be appropriate to install a

shipwreck or heritage trail to make the wrecks accessible to the public, as its

their heritage.