Dredging sound measurements

Stephen P. Robinson, NPL

WODA Workshop, Paris, 26th March 2015

Contents

Types of dredger and dredging operation

Sources of underwater sound during dredging

- Noise generation mechanisms

Examples of recent studies

- UK MALSF study

- Dutch MAASVLAKTE 2 (MV2)

- Other studies

Conclusions

Common dredging activities

Dredging excavation

Dredging vessels during transport

Dredged material placement.

Common types of dredger

For the majority of projects, one or more of four basic

types of vessel are used:

Cutter Suction Dredgers (CSD),

Trailing Suction Hopper Dredgers (TSHD),

Grab Dredgers (GD)

Backhoe Dredgers (BHD)

Cutter suction dredger

Trailing Suction Hopper Dredger

Grab Dredger

Backhoe Dredger

Examples of recent studies

UK MALSF study

Dutch MAASVLAKTE 2 (MV2)

Reine, Clarke and Dickerson

Other studies

MALSF project P108 details

Funded by the UK Marine Aggregate Levy Sustainability Fund (MALSF)

• Seven TSHD dredgers measured in

three locations around UK

• variety of operational modes

• Water depths: 27 m to 45 m

• Aggregate types: sand, gravel

• Vessel speeds: ~1.5 kts

Partners:

NPL

Loughborough University,

ISVR (University of Southampton)

Gardline Environmental Ltd

Further Collaborations • dstl

– quality check on measured data

– analysis of LF tonal signals

• TNO (Netherlands)

– collaborated on methodology

Trailing Suction

Hopper Dredger

TSHD Vessels

East region

Sand Falcon Arco Axe

Sand Harrier

City of Chichester

Sand Falcon City of London

City of Westminster

Measurement locations

MALSF MEPF P108

01 November 2010

13

Measured vessels

Simultaneous measurements at several ranges from dredger

Hydrophones deployed from survey vessel and recording buoys

Co-linear arrangement of hydrophone positions

Two hydrophones at each measurement station (different depths)

Measured data used to derive source level using propagation model

Different operational modes measured (eg pump on or off)

Measurement Methodology

MALSF MEPF P108

15

f(Hz)

Tim

e (

min

)

Full dredging at the nearest point: buoy50

0 1 2 3 4

x 104

773

774

775

776

777

778

40

50

60

70

80

90

100

110

120

130

140

Full dredging (Sand Falcon)

Example spectrogram

MALSF MEPF P108

16

f(Hz)

Tim

e (

min

)

Drag head lifted: NPL

0 2 4 6 8 10 12

x 104

796.6

796.8

797

797.2

797.4

797.6

797.8

798

798.2

798.4 40

50

60

70

80

90

100

110

120

130

140

f(Hz)

Tim

e (

min

)

Dgar head lowered: NPL

0 2 4 6 8 10 12

x 104

802.2

802.4

802.6

802.8

803

803.2

803.4

803.6

803.8

804 40

50

60

70

80

90

100

110

120

130

140

Power spectral

density spectrogram

showing difference:

(i) draghead raised

(pumping water only)

(ii) draghead lowered

(on sea-bed pumping

sand and gravel)

Drag head raised and lowered

f (Hz)

Tim

e (

min

)

Pump restarted at buoy50

0 1 2 3 4

x 104

830.2

830.4

830.6

830.8

831

831.2

831.4

831.6

831.8

832 40

50

60

70

80

90

100

110

120

130

140

Power spectral

density spectrogram

showing pump being

restarted

(from measurement

buoy at 50 m)

Drag head raised and lowered

Results for different configurations

Received levels at 100 m range for different configurations

Results for measured dredger noise

MALSF MEPF P108

01 November 2010

20

Sand

Falcon.

Different

aggregate:

251: sand

473: gravel

Source levels for different aggregate

MALSF MEPF P108

01 November 2010

21

Geophone Recording

Results for seabed vibration

MALSF MEPF P108

01 November 2010

22

Sand Harrier

Mean SL with

standard

deviation.

Three passes, 2

hydrophones at

each of three

ranges, data

window 2 secs.

Source level repeatability

September 26, 2013 23

Maasvlakte 2 construction

Measurement campaign 2008*:

September 2008

Underwater ambient sound measurements prior to MV2 construction activities

Fixed location ‘Z’

Measurement campaign 2009**:

25 Sep to 5 Oct 2009

Monitor sound during dredging

activities for MV2 construction

Fixed location moved 2 km east due to fishing activity

Source Level measurements of Trailing Suction Hopper Dredgers

*J. Dreschler et al, Measurements of underwater background noise Maasvlakte 2. TNO-DV 2009 C212, May 2009

** C. A. F. de Jong et al, Underwater noise of Trailing Suction Hopper Dredgers at Maasvlakte 2: Analysis of source levels

and background noise, TNO report, 2010.

A – dredging area

B – transit area

C - Maasvlakte 2

Z – ambient sound measurement

24

Dredgers pass close by autonomous platform

Altered shipping lanes

Measurement platform

dredgers

Dredging

related

fishing

2008 2009

Shipping pattern (AIS)

Measurement platform

25

TSHD ‘source level’ measurements

22 September – 1 October 2009 (noise measurements)

7 different dredgers (trailing suction hopper dredgers)

transiting (31 runs), dredging (23 runs), sand laying (2 runs), rainbowing (10

runs) and pumping ashore (2 runs).

Hopper Volume [m3]

Inst

alle

d p

ow

er [

kW]

September 26, 2013

de Jong et al.

Offshore Dredger Sounds:

October 2009

26

Dredger source levels

7 different trailing suction

hopper dredgers (hopper

volume 300 – 20000 m3)

transiting (31 runs)

dredging (23 runs)

sand laying (2 runs)

rainbowing (10 runs)

pumping ashore (2

runs)

Maximum levels

(envelope)

Mainly cavitation

(propellers & thrusters)

September 26, 2013

de Jong et al.

Offshore Dredger Sounds:

Individual dredgers (sand dredging)

September 26, 2013

de Jong et al.

Offshore Dredger Sounds:

27

Speed 1.1 – 2.5 knots Similar characteristics Broadband noise (mostly propeller cavitation) TSHD size dependent

28

MV2 dredgers in transit

Speed 10 – 16.7 knots

Compared with Overseas

Harriette (10-16 kn) at keel

aspect

M/V OVERSEAS HARRIETTE

Arveson & Vendittis, JASA 107(1), 2000

M/V OVERSEAS HARRIETTE

September 26, 2013

de Jong et al.

Offshore Dredger Sounds:

Other studies Reine, Clarke and Dickerson

Large hydraulic CSD fracturing rock while engaged in the New York

& New Jersey Harbour Deepening Project.

Based on a 15 log (R /1m) scaling, the calculated source levels

reached 175 dB re 1 µPa2m2.

Most sound energy was below 2.5 kHz; sound intensity varied

depending on the amount/hardness of the material to be removed.

Other studies Reine, Clarke and Dickerson

BHD removing the fractured rock created by the CSD

Using a 15 log (R/1m) scaling the most intense bottom grab sound was

estimated by back calculation to be 179.4 dB re 1 µPa2m2

Frequency range 3 Hz – 20 kHz, peak frequency = 315 Hz).

Hydraulic ram sounds were approximately 15 dB lower than the grab

sounds.

Information on sound levels from a number of additional components of

the dredging process as well.

Other studies

Nedwell et al. (2008)

Large BHD measured at Lerwick, Shetland (UK).

Based on a ‘conservative’ 10 log (R/1 m) scaling, the estimated

“affected or equivalent” source level during excavation was 163 dB

re 1 µPa2m2.

Underwater sound measured at frequencies from 20 Hz to

approximately 20 kHz; consistent sound was recorded over the

low frequency range from 20 to 80 Hz; peak spectral levels of

sound occurring between 35 and 45 Hz.

Itap (2007)

Measured sounds from a TSHD performing sand extraction off Sylt,

Germany. Based on a 14 log (R / 1m) scaling, estimated “affected

or equivalent” source level of 184 – 188 dB re 1 µPa2m2

Most energy between 100 and 500Hz

Summary and conclusions

Sources of sound from dredging include machinery noise,

propulsion noise, pumping noise, aggregate noise

Noise radiation depends on operational mode: extraction,

transiting, depositing, rainbowing, pumping ashore

Several studies have reported the typical noise levels,

including several which report source levels

Radiated noise is typical of a cargo vessel at modest speed

Dredger noise seems to be highest during transit at speed

Aggregate type can affect radiated levels in kilohertz range

During aggregate extraction, vessel stay on station for

extended period – unusual for commercial vessel

33