UNDERWATER NOISE FROM PILE DRIVING IN
MORETON BAY, QLD
Christine Erbe, JASCO Applied Sciences, Brisbane Technology Park,
PO Box 4037, Eight Mile Plains, Qld 4113, Australia. Email: Christine.Erbe@jasco.com
This article presents measurements of underwater pile driving noise recorded during the construction of the duplicate
Houghton Highway bridge in western Moreton Bay, Queensland. Moreton Bay is a protected marine park, a World Heritage
Site and a Ramsar Wetland, providing habitat for turtles, dugong, sharks, dolphins and whales, some species of which are
listed as vulnerable to endangered. Pile driving noise was measured for small and large piles at various locations and ranges.
Using an acoustic propagation model, a sound map was computed for Bramble Bay. Sound levels were compared to currently
available information on impact thresholds. Ranges greater than those corresponding to impact thresholds were scanned for
the absence of dolphins before and during pile driving in line with a monitoring and response plan.
INTRODUCTION
In 2008, construction of the duplicate Houghton Highway
Bridge began north of Brisbane in western Moreton Bay,
Queensland, Australia. Moreton Bay is a marine park, listed
as a World Heritage and Ramsar Wetland. Of the marine
animals living in Moreton Bay, the Environment Protection
and Biodiversity Conservation (EPBC) Act 1999 lists the
humpback whale (Megaptera novaeangliae), the green turtle
(Chelonia mydas) and the hawksbill turtle (Eretmochelys
imbricata) as vulnerable, the loggerhead turtle (Caretta
caretta) as endangered, and the grey nurse shark (Carcharias
taurus) as critically endangered. Dugong (Dugong dugon)
are listed as vulnerable and Indo-Pacific humpback dolphins
(Sousa chinensis) as rare under the Nature Conservation Act
1992 of Queensland.
With sound travelling much better under water than
light, marine animals, in particular marine mammals, rely on
acoustics for sensing their environment. Man-made underwater
noise has the potential to mask marine mammal communication
sounds, environmental sounds (e.g. surf) useful for navigation,
predator sounds, prey sounds, and odontocete (toothed whale)
echolocation sounds. Noise can alter animal behaviour, animal
distribution and habitat usage patterns. At very high levels
and under certain circumstances, underwater noise can cause
physiological damage to tissues and organs [1].
Pile driving source levels are among the highest of
construction activities [2]. In soft substrates vibratory pile
drivers are used. They contain a system of counter-rotating
eccentric weights, arranged such that horizontal vibrations
cancel out while vertical vibrations get transmitted into the
pile from above. The sound from vibratory pile driving is
continuous and has lower sound levels compared to impact
pile driving. A diesel impact pile driver drops a weight through
a cylindrical tube onto the pile compressing and heating the
air above the pile to the ignition point of diesel fuel injected
into the cylinder. The detonation drives the weight back up.
Alternatively, the weight can be lifted by means of hydraulics
or steam.
When the hammer strikes the pile, sound is created in air
at the top of the pile. Acoustic energy spreads as a spherical
Acoustics Australia
pressure wave through the air. The impact also gives rise to a
stress wave travelling down the length of the pile. This wave
couples with the surrounding medium (first air, further down
water), radiating acoustic energy into the air and water. The
stress wave in the pile also couples with the substrate below
the water, creating an acoustic wave travelling through the
seafloor. Sound travels as compressional pressure (P) waves
and transversal shear (S) waves through the elastic seafloor.
Sound can travel very fast and with low attenuation through
certain types of seafloor. At some distance away from the pile,
acoustic energy can radiate back into the water column from
the seafloor. The sound from impact pile driving is transient
and discontinuous, called pulsed. Within the water column, the
arrival of acoustic pulses from different media and directions
and with different phases and time delays tends to result in a
complex pattern of higher and lower noise level regions, in
particular close to the source.
The level of noise received in the water column at some
distance from the pile depends on a multitude of factors,
including the size, shape, length and material of the pile, the
size and energy of the hammer, the type of sediment and the
thickness of the sediment, the type and depth of the underlying
bedrock, the water depth, bathymetry, salinity and temperature.
MATERIALS AND METHODS
Two types of hollow steel piles were driven during bridge
construction: 624 temporary piles (75cm outer diameter,
12.7mm wall thickness, 28m length) and 156 permanent piles
(150cm outer diameter, 25mm wall thickness, 30m length).
Underwater noise was recorded from two temporary piles at
Pier 2 (on the Brighton shore; 14.5.2008), one permanent pile
at Pier 2 (26.7.2008), one permanent pile at Pier 26 and four
temporary piles at Pier 29 (19 & 20.3.2009). Temporary and
permanent piles were driven with hydraulic piston hammers
(Figure 1), model BSP-CG180 (12t weight, 180kJ maximum
energy) and model IHC-S280 (14t weight, 280kJ maximum
energy) respectively. Temporary piles were driven to about
23m below the seafloor, permanent piles to 26m.
Vol. 37 December (2009) No. 3 - 87
Sound metrics
Peak sound pressure level [dB re 1μPa]:
SPLPk = 20log10 (max(|p(t)|)
where p(t) is the time series of pressure measured in the
water column.
Peak-to-peak sound pressure level [dB re 1μPa]:
SPLPk-Pk = 20log10 (max(p(t)) - min(p(t)))
Root-mean-square (rms) sound pressure level [dB re 1μPa]:
Figure 1: Photo of a temporary pile being driven at Pier 2.
The existing Houghton Highway bridge can be seen in the
background.
Four different systems were utilized to simultaneously
record underwater sound at four different locations and ranges
from the piles. The first two systems were autonomous and
deployed for 2h at ranges > 200m (Sites 1 & 2). The last two
systems were operated manually from a barge drifting close to
the piles being driven.
• Geospectrum Technology Inc. hydrophone model
M15C (sensitivity -202 dB re 1V/μPa) connected to a
Multi Electronique data logger model AURAL-M2.
Bandwidth 16384 Hz.
• High-Tech Inc. hydrophone model HTI 96 (sensitivity
-164 dB re 1V/μPa) connected to a Multi Electronique
data logger model AURAL-M2. Bandwidth 16384 Hz.
• Reson hydrophone model TC4034 (sensitivity -218 dB
re 1V/μPa) with external amplifier from Reson model
EC6067 connected to a SoundDevices data logger
model SDD 722. Bandwidth 48000 Hz.
• Reson hydrophone model TC4043 (sensitivity -201dB
re 1V/μPa) connected to a SoundDevices data logger
model SDD 722. Bandwidth 48000 Hz.
Frequency responses of the hydrophones and recording
systems are measured in the lab every 2 years. In the field,
before deployment and after recovery, each recording system
was calibrated using a G.R.A.S. pistonphone calibrator model
42AC. The system gain was computed from the recorded
calibration signal and applied to the digital recording data to
yield sound pressure in units of μPa.
Pile driving and recording locations were measured with
a GPS. Distances close to the piles were measured with a
Bushnell laser range finder. Water temperature and conductivity
were measured with a CTD from AquiStar, model CT2X. The
water depth was 1m at Piers 2 & 26 at the time of recording
and 1.5m at Pier 29.
88 - Vol. 37 December (2009) No. 3
where the integral runs over the duration of the pulse,
defined as the time over which 90% of the total energy is
received. On a cumulative energy curve, the start-time of a
pulse is taken at the 5% cumulative energy mark, and the endtime of a pulse is taken at the 95% cumulative energy mark.
Sound exposure level [dB re 1 μPa2·s]:
SEL = 10log10 (∫T p(t)2 dt)
which is proportional to the total energy of a plane wave.
1/3 octave band levels: SPL and SEL can be computed in a
series of adjacent bands, each 1/3 of an octave wide. The following
centre frequencies (fc) were used: 10, 13, 16, 20, 25, 32, 40, 50,
63, 80, 100, 126, 160, 200, 251, 320, 400, 500, 640, 800, 1000,
1280, 1585, 2000, 2560, 3162, 4000, 5120, 6310, 8000, 10000,
12589, 15849, 20000, 31623, 40000 Hz. Bandwidth (∆f) increases
with increasing fc: ∆f = (21/6 - 2-1/6) x fc.
Power spectrum density levels [dB re 1μPa2/Hz] give the
mean squared sound pressure in a series of adjacent bands of a
constant 1 Hz width.
Percentiles: The xth percentile is the level below which the
signal falls x% of the time. The 50th percentile is equal to the
median.
Sound propagation model
Sound propagation was modelled by the Range-dependent
Acoustic Model (RAM) [3]. It is based on the parabolic
equation method, assuming that outgoing energy dominates
over scattered energy and computing the solution for the
outgoing wave equation. As an extension to RAM, shear wave
conversion at the sea floor was approximated by the equivalent
fluid complex density approach [4]. RAM yields transmission
loss data in 2D as a function of range and depth. To achieve a
3D sound level map, RAM was run for a fan of radials from the
source, and a tessellation algorithm utilized to seed new radials
as the distance between radial end points exceeded a preset
resolution parameter.
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Table 1: Sound propagation parameters. Depths are below the
seafloor.
The sound propagation model required the geoacoustic
input parameters listed in Table 1. A seismic reflection survey
and a series of bore hole drillings to 30-35m depth were
done by Mapping and Hydrographic Surveys Pty Ltd and the
Geotechnical Branch of the Dept. of Main Roads, providing
P-wave sound speed profiles. Data for attenuation, density and
shear waves were taken from standard reference works [5].
Shear speed was modeled at 418 m/s, shear attenuation at 0.5
dB/ λ. Data below 40m were extrapolated from tables [5]. The
sound propagation model assumed an absorbing layer at 2000m
depth. The speed of sound in the water column was computed
from our temperature and conductivity measurements [6] and
was about 1530 m/s in this shallow water.
shows three single pulses recorded at Site 2 from a temporary
pile at Pier 29. The interpulse (hammering) interval was 1.8s.
Also shown is the complete (17 min) acoustic trace recorded
from this pile. The pressure amplitude (not calibrated in this
plot) rose by a factor 4 (=12 dB) from the beginning of the
trace to the end, because of increasing pile driving energy and
increasing resistance. We observed the same increase at Pier 2.
Sound levels
Figure 3 shows the received SEL of a temporary pile (driven
at Pier 29) and a permanent pile (from Pier 26) recorded at
various ranges. SEL decreased with range due to propagation
losses. The larger permanent piles had higher received levels
than temporary piles at similar range. Pile driving noise was
very broadband (40 Hz to > 40 kHz) near the source. Absorption
as a function of distance increases with frequency, so that at
long ranges only energy at frequencies < 400 Hz remained.
All levels were computed over two minutes of recording. The
statistical variation of SEL was largest at low frequencies and
long ranges where ambient noise was dominant.
RESULTS
Pressure waveform
Figure 3: Measured SEL (in 1/3 octaves) of a temporary (TP)
and a permanent pile (PP) being driven at Pier 29 and 26
respectively. Three lines are shown for each recording: the 90th,
50th and 25th percentiles from top to bottom.
Figure 2: Pile driving waveforms. Single pulses cannot be
resolved in the 17min recording.
The acoustic pressure time series recorded underwater
exhibited a series of pulses, each pulse corresponding to a
single strike of the pile. The pressure rose sharply and then
in a dampened oscillation reduced to ambient levels. Figure 2
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Table 2 summarizes the acoustic properties of the pile
driving signals that originated at Piers 26 and 29, and that were
measured at different ranges. Peak-peak levels were, of course,
highest, followed by peak levels. Root-mean-square levels
were lower, because they represent an average pressure over
the duration of a pulse. Sound exposure levels were lower still.
Broadband SEL were computed by summing up the previously
plotted 1/3 octave SEL on a linear (not dB) scale. The last
column gives the length of the pulse. This is the duration over
which the pulse energy rose from 5 to 95%. Determining the
duration of a pulse is difficult, in particular if the signal is weak
(at long ranges) and the background noise loud, or if the pulse
is spread out due to dispersion and due to time-lagged arrivals
of energy via different propagation paths.
Vol. 37 December (2009) No. 3 - 89
Table 2: Summary of noise level measurements. Means ±
standard deviations are given. *: The permanent pile value @
14m came from Pier 2.
For the temporary pile, the data summarized were all
taken from the end of the pile driving, yielding the highest
level (worst-case). For the permanent pile, levels at 360m and
1330m range were computed from the end also. At 108m, only
the middle section of pile driving was recorded. No closerange data were obtained at Pier 26; the 14m value listed was
measured at Pier 2 at the beginning of the pile being driven.
Ambient noise
in the water. There also was splashing and flow noise around
the hydrophones, the barge and the piles. The reason why the
25th and 50th percentiles of the noise near the piers increased
above 2kHz, was that the rather insensitive recording system
used here ran into its noise floor, which shows up as an upslope
on 1/3 octave plots (because bands get wider with increasing
frequency, adding increasingly more self-noise).
The systems deployed at Sites 1 and 2 were much more
sensitive. There was a bit of water flow noise in the recordings.
At Site 2, the sound of snapping shrimp was clearly audible in
the data. These animals are common in tropical and subtropical
regions throughout the world’s oceans. The snapping sound
occurs when the animal snaps its claw. Near a colony of shrimp,
the ambient noise sounds like continuous crackling (‘frying’
or ‘wood burning’) with energy between 2 and 24 kHz [7].
Spectra measured here matched published spectra very well
[8,9]. There was quite a bit of sand swishing noise at Site 1
(sand swishing over the base of the instrument as evidenced by
the presence of sand in nuts and bolts upon retrieval). Weather
conditions on March 19 and 20 were cloudy with moderate
wind adding to low-frequency noise. We did not see or hear
any boats in the vicinity at the times of recording.
Sound propagation
Figure 4: 1/3 octave levels of SPLrms of ambient noise, computed
in 1s windows, showing statistics over 15 minutes of recording.
Three lines are given for each site corresponding to the 95th, 50th
and 25th percentiles.
SPLrms of ambient noise was computed in 1s windows and
statistics were calculated for a 15 minute recording at each site.
Percentiles of SPLrms in 1/3 octave bands are shown in Figure
4. Close to the piers, right at the construction site, ambient noise
was highest and most variable. Construction activities generated
noise at low-to-mid frequencies. There were occasional peaks
sounding like metal banging (e.g. banging of piles or dropping
of chains and metal) to the ear. Furthermore, this site was about
10-15m from the existing Houghton Highway bridge which
runs parallel to the duplicate bridge under construction. Cars
driving over the existing bridge generated low-frequency noise
90 - Vol. 37 December (2009) No. 3
Figure 5: Received SPLPk (top) and SEL (bottom) from a
permanent pile at Pier 26 (hollow symbols) and a temporary pile
at Pier 29 (solid symbols). Regression for permanent pile (..),
temporary pile (--). SEL as a function of range are shown for a
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single pulse and a 17-minute pulse train. Current suggestions for
fish and dolphin impact thresholds (solid lines). SEL thresholds
for fish injury and cetacean TTS correspond to single pulses only.
SPLPk and SEL values from Table 2 were plotted in Figure
5. The permanent pile levels at 14m range were measured
at the beginning of driving this pile; 12 dB (the increase
from beginning to end measured at Piers 2 & 29) was added
to estimate the levels at the end of driving this pile. The
permanent pile levels at 108m range were recorded when the
middle section was driven, and therefore enlarged by 6 dB to
estimate the end levels. Regression analysis was performed
using a spreading term proportional to the logarithm of range
(R) and an absorption term proportional to range.
Figure 6: Modelled SEL from a temporary pile being driven at
Pier 29 (white asterisk). Recording sites 1 & 2 marked in white.
Dashed line: bridge under construction. Coordinates refer to
UTM Zone 56.
Results of the 3D sound propagation model RAM are
shown in Figure 6 for a temporary pile at Pier 29. Plotted
are the maximum SEL over all depths. Sound energy got
channelled into the deeper waters of Pine River and Hays Inlet.
Shadowing occurred behind the circular rise near Site 1. At
Site 1, the modelled level was 110 dB; compared to 107 dB
measured. At Site 2, the modelled level was 151 dB compared
to 160 dB measured.
DISCUSSION
Comparison with other pile driving measurements
A number of studies have recorded impact pile driving,
only few data are reported in the peer-reviewed literature.
Comparison is difficult, because important information is often
missing (such as geoacoustics of the location, water depth,
pile and hammer parameters). Having said that, some general
trends can be observed. For example, noise increases with pipe
diameter and blow energy [10].
The temporary pile driven at Pier 29 had an outer diameter
of 75cm. Steel piles of 76cm diameter, diesel-driven, produced
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SPLPk = 208 dB re 1 μPa, SPLrms = 192 dB re 1 μPa and SEL
= 180 dB re 1 μPa2s at 10m range [11]. We measured SPLPk =
207 dB re 1 μPa, SPLrms = 194 dB re 1 μPa and SEL = 183 dB
re 1 μPa2s at 14m range--comparable.
The permanent pile driven at Pier 26 had an outer diameter
of 150cm. A hollow steel pile of 168cm diameter, dieseldriven, was recorded at 4, 10 and 20m range; SPLPk was 219,
210 and 204 dB re 1 μPa respectively; SPLrms was 202, 195
and 189 dB re 1μPa [11]. We estimated a maximum SPLPk of
217 dB re 1 μPa and a maximum SPLrms of 201 dB re 1 μPa at
14m range for the end of the pile driving, which is comparable.
A 160cm-diameter pile, driven with an 80-200kJ hammer and
measured at 750m range, had SEL = 162 dB re 1 μPa2s [10].
Our measurement at 750m was less possibly due to the highloss environment in this shallow part of Moreton Bay.
Bioacoustic impact on marine fauna
There is limited knowledge of the effects of pile driving noise
on marine life. The only damage that has ever been observed in
any marine species as a result of near-by pile driving is lethal
injury in fish [12,13]. The latter study was initially carried out
by this author. The piles around which dead fish were seen were
closed-end piles that were driven into rocky ground; a very
different scenario. Post-mortems revealed haemorrhaging and
burst swim bladders. Unfortunately, neither of these projects
was able to produce any information on the sound metrics and
thresholds responsible for the observed damage. A review of
the available scientific information on bioacoustic impact on
fish [11,14] led to the derivation of interim criteria for injury of
fish exposed to pile driving [15]. For any single strike, a sound
exposure level of SEL > 187 dB re 1μPa2s and a peak sound
pressure levels of SPLPk > 208 dB re 1μPa could cause injury.
No study to-date has shown injury in marine mammals
from pile driving. However, data on temporary hearing loss
(TTS: temporary threshold shift) after exposure to intense
sound, including pulsive sound resembling seismic airguns,
has been measured. After a major review effort, marine
mammal noise exposure criteria were released [16]. Injury was
understood as the onset of PTS (a permanent threshold shift)
and extrapolated from TTS data. For PTS in cetaceans (whales,
dolphins and porpoises) from single or multiple pulses, the
threshold was SPLPk > 230 dB re 1μPa and SEL > 198 dB re
1μPa2s (M-weighted [16]). A TTS in a mid-frequency cetacean
was observed at SPLPk > 224 dB re 1 μPa and SEL > 183 dB re
1μPa2s after exposure to a single pulse [17].
These levels were shown as horizontal straight lines in
Figure 5. Looking at the SPLPk criteria, levels for the temporary
pile were below all thresholds. The permanent pile was above
the fish injury threshold over 40m range, but below the cetacean
thresholds. SEL in Figure 5 were not M-weighted and are
thus higher than if they had been weighted for mid-frequency
cetaceans (M-weighting reduces the energy at frequencies
below a few hundred Hz, where most of the pile driving
energy is distributed.). The comparison with SEL criteria is
thus “conservative”. A single pulse from the temporary pile
was below all thresholds; a single pulse from a permanent
pile exceeded the fish injury threshold for ranges <25m and
the cetacean TTS threshold for ranges <35m. Summing SEL
Vol. 37 December (2009) No. 3 - 91
over an entire pulse train (Figure 2b), yielded cumulative SEL
that were 23 dB higher than single-pulse SEL, surpassing the
cetacean PTS threshold over ranges <60m for the temporary
and <100m for the permanent pile. It is unlikely that an animal
would remain within close range for the duration of driving
an entire pile. If an animal starts moving away after receiving
one pulse, and given that received levels drop quickly with
increasing range, the single pulse curves might be more
applicable than the cumulative SEL integrated over an entire
pulse train. There are no data on cumulative SEL thresholds
for fish injury or cetacean TTS; the thresholds plotted are for
single pulses only. It took less than 20 minutes to drive the
recorded piles. If all went well, a maximum number of two
temporary piles and one permanent pile were driven in one
day, yielding a duty cycle (the ratio of pile driving noise being
‘on’ and ‘off’) of 60 min / 24 h = 0.04. It took a minimum of
24-28h before the next set of temporary piles could be driven,
and at least a week in between permanent piles.
Moreton Bay has two resident dolphin species, both
mid-frequency cetaceans, the bottlenose dolphin (Tursiops
truncatus) and the indo-Pacific humpback dolphin (Sousa
chinensis). Local residents and construction workers have
reported sighting dolphins in the area throughout the year.
However, we did not observe any animals within the vicinity
of the piles during the recording, and a shut-down zone of
200m radius was scanned for cetacean presence as part of a
monitoring and management plan, which J.F. Hull, Albem,
the EPA and the Department of Main Roads had worked out.
Elsewhere, harbor porpoises (Phocoena phocoena) avoided
close ranges and responded to pile driving sound at ranges >
21km [18] from larger piles; however, received levels at these
ranges were not reported.
We did not observe any dead fish close to the pile, nor
did we see fish in abundant numbers here. It is possible that
fish temporarily avoided close ranges to the pile; behavioural
thresholds for fish require more research.
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ACKNOWLEDGEMENTS
The duplicate Houghton Highway bridge was built by J.F.
Hull Holdings Pty. Ltd. and Albem Pty. Ltd. in a joint venture.
Their teams were extremely helpful and supportive. Special
thanks go to Gary Christian of Albem and Clayton Smith of
J.F. Hull. It was a pleasure working with them.
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