Hartley Anderson Limited - Marine Environmental Science and Consultancy Article 12 Risk Assessment Dublin Port Maintenance Dredging 2022-2029 ...
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Hartley Anderson Limited
Marine Environmental Science and Consultancy
Article 12 Risk Assessment
Dublin Port Maintenance Dredging 2022-2029
Foreshore Consent Application
Report to
Department of Housing, Local Government
and Heritage
January 2022
Hartley Anderson Limited
Article 12 Risk Assessment January 2022
Page 1
TABLE OF CONTENTS
SECTION 1 - INTRODUCTION .................................................................................. 2
1.1 Background ................................................................................................... 2
1.2 Relevant consultation responses .................................................................. 2
1.3 Legislative context......................................................................................... 4
SECTION 2 - DESCRIPTION OF PROPOSED WORKS ........................................... 5
2.1 Site location................................................................................................... 5
2.2 Previous maintenance dredging campaigns ................................................. 5
2.3 Proposed dredging campaign 2022-2029 ..................................................... 7
2.4 Spoil disposal site ......................................................................................... 8
SECTION 3 - BASELINE ENVIRONMENT ................................................................ 9
3.1 Ambient noise levels ..................................................................................... 9
3.2 Relevant Annex IV species ........................................................................... 9
SECTION 4 - RISK ASSESSMENT ......................................................................... 15
4.1 Potential impacts associated with dredging programme ............................. 15
4.2 Mitigation measures .................................................................................... 18
4.3 Conclusion .................................................................................................. 18
BIBLIOGRAPHY ...................................................................................................... 19
Hartley Anderson Limited
Article 12 Risk Assessment January 2022
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SECTION 1 - INTRODUCTION
1.1 Background
Arup with Hartley Anderson Limited have been commissioned by the Department of Housing,
Local Government and Heritage (DHLGH) to conduct an Article 121 Risk Assessment of an
application by Dublin Port Company (DPC) for a Foreshore Licence for their proposed
maintenance dredging programme for 2022-2029 and associated dumping at sea of the
dredged material. DPC need to carry out regular maintenance dredging of the navigation
channel, basins and berthing pockets in order to maintain their advertised charted depths and
hence provide safe navigation for vessels to and from the Port. It is proposed to dispose of
the dredged sediments at the existing licensed offshore disposal site located at the entrance
to Dublin Bay to the west of the Burford Bank.
DPC applied to the Environmental Protection Agency (EPA) for a dumping at sea permit on
25th February 20212 for loading and dumping at sea activities associated with the maintenance
dredging programme. The application is currently under assessment by the EPA in
accordance with the requirements of the Dumping at Sea Act 1996 as amended.
A Marine Mammal Risk Assessment prepared by IWDG (Irish Whale and Dolphin Group)
Consulting was submitted as part of the application by DPC for a Foreshore Licence.
1.2 Relevant consultation responses
The licence application was open for public consultation between 21st July 2021 to 20th August
2021. Responses relevant to this Article 12 Risk Assessment are provided in Table 1.1.
Table 1.1: Relevant responses from prescribed bodies to the consultation
Statutory Body Applicant’s Response
NPWS of the Department of Housing Local DPC undertook to implement, in full, all
Government and Heritage mitigation measures set out in the Natura
Impact Statement (NIS) which supported the
Nature Conservation Foreshore Application. DPC confirmed its
The observations and recommendations of the acceptance of the recommended condition by
NPWS were as follows: NPW.
A ‘Screening for Appropriate Assessment &
Natura Impact Statement’ has been submitted in
support of the present application. In this
document the potential effects of the proposed
dredging works in Dublin Port and disposal of the
dredged material on the Burford Bank at the
mouth of Dublin Bay on nearby Natura 2000
sites is considered. Of the 19 Natura sites within
the vicinity of the proposed works, only four were
identified on which the likelihood of significant
effects could not be excluded.
1 Article 12 of the Habitats Directive addresses the protection of species listed in Annex IV(a). The
article applies throughout the natural range of the species within the EU and aims to address their direct
threats, rather than those of their habitats.
2 https://epawebapp.epa.ie/terminalfour/DaS/DaS-view.jsp?regno=S0004-03
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Article 12 Risk Assessment January 2022
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Statutory Body Applicant’s Response
In the case of the Lambay Island Special Area of
Conservation (SAC) the possibility of underwater
noise and disturbance effects on two of the
Qualifying Interests (QIs) for this site could not
be excluded, namely grey seal and harbour seal.
Similarly, the possibility of underwater noise and
disturbance effects on one of the QIs for the
Rockabill to Dalkey Island SAC, namely harbour
porpoise, could not be excluded. In the case of
two of the Special Protection Areas (SPAs)
designated for the protection of birds in Dublin
Bay, namely the South Dublin Bay and River
Tolka Estuary SPA and the North Bull Island
SPA, it is also considered that the possibility of
significant water quality and habitat deterioration
effects on wetland habitat, which is a resource
for wintering or breeding Special Conservation
Interest (SCI) bird species, could not be
excluded.
In Section 5.3 of the Natura Impact Statement
(NIS) measures were set out to minimise any
noise or disturbance effects on marine
mammals, or deterioration of water quality within
the South Dublin Bay and River Tolka Estuary
SPA and North Bull Island SPA by suspended
sediment plumes, arising during the proposed
dredging works.
The NIS concluded that if these mitigation
measures are applied in the course of the
proposed maintenance dredging works, “there
will be no adverse effects upon the integrity of
any European sites and no scientific doubt
remains as to the absence of such effects.” The
NPWS accepted this conclusion of the NIS.
In the light of the above the NPWS
recommended that any Foreshore Licence
issued in response to the present application
shall be subject to the following condition:
That all the measures set out in Section 5.3 of
the NIS supporting the present application to
minimise disturbance to marine mammals, which
are QIs for the Lambay Island SAC and the
Rockabill to Dalkey Island SAC, and to prevent
any deterioration of water quality affecting
wetland habitats in the South Dublin Bay and
River Tolka Estuary SPA and North Bull Island
SPA during the proposed dredging works shall
be implemented in full.
Reason: To preserve the integrity of European
sites protected under the Habitats Directive
(92/43/EEC) and the Birds Directive
(2009/147/EC).”
Hartley Anderson Limited
Article 12 Risk Assessment January 2022
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1.3 Legislative context
The Foreshore Act 1933 (as amended), requires that a lease or licence must be obtained from
the Minister for Housing, Local Government and Heritage for the carrying out of works or
placing structures or material on, or for the occupation of or removal of material from, State-
owned foreshore.
The 1992 EU Habitats Directive (Council Directive 92/43/EC) and Birds Directive
(2009/147/EC) are transposed into Irish law by Part XAB of the Planning and Development
Act 2000 (as amended) and the European Communities (Birds and Natural Habitats)
Regulations 2011 (as amended).
In addition to the requirement to consider potential effects of a plan or project on European
Sites under Article 6(3) of the Habitats Directive, the Directive requires consideration of the
potential effects on species listed under Annex IV of the Directive (termed Annex IV species).
Under Article 12, Annex IV species are afforded strict protection throughout their range, both
inside and outside of designated protected areas. All cetaceans are included in Annex IV of
the Directive.
Hartley Anderson Limited
Article 12 Risk Assessment January 2022
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SECTION 2 - DESCRIPTION OF PROPOSED WORKS
2.1 Site location
The Foreshore boundary of the proposed works is indicated on Figure 2.1, and includes the
proposed areas to be dredged, referred to as the loading areas (492.5 ha), and the offshore
disposal site (212.5 ha, total area – 705 ha). It is proposed that material will be dredged from
the Inner Liffey Channel (Dublin Harbour) and Dublin Bay, along the navigation channel as far
east as the 10m Chart Datum (CD) depth contour, during the 2022 to 2029 maintenance
dredging campaigns.
2.2 Previous maintenance dredging campaigns
The quantities of material removed during the last four maintenance dredging campaigns
(2016 – 2020) are presented in Table 2.1 and Table 2.2. Previous to these maintenance
dredging campaigns, dredging was undertaken in 2012.
The 2016-2018 maintenance dredging campaigns were undertaken in accordance with the
conditions as set out in Foreshore Licence AKC/2016/00262, granted by the Department of
Environment, Communications and Local Government, and Dumping at Sea Permit S0004-
01 granted by the Environmental Protection Agency (EPA).
Table 2.1: Quantity of material dredged from Dublin Port - maintenance dredging
campaigns 2016 to 2018
Dredged quantity
Location
(tonnes, wet weight}
Dumping at Sea Permit
Description 2016 2017 2018
S0004-01 Reference
B008 Alexandra Basin East 16,037 24,000 0
B009 Oil Berths 16,784 28,000 427.5
B010 Ferry Port 31,498 50,000 4,616
B011 River, uncontaminated 367,031 128,000 153,336
B012 South Quays 36,016 51,000 3,496
B013 Sludge Jetty 64,166 30,500 7,494
B016 Bar West 116,551 0 9,188.5
B017 Bar East 101,710 0 0
Total Quantity 749,793 311,500 178,558
(Tonnes, wet weight)
The 2020 maintenance dredging campaign (Table 2.2) was undertaken in accordance with
the conditions as set out in Foreshore Licence FS/2020/03173 granted by the Department of
Environment, Communications and Local Government and Dumping at Sea Permit S0004-02
granted by the Environmental Protection Agency (EPA).
Table 2.2: Quantity of material dredged from Dublin Port - maintenance dredging
campaign 2020
Location Dredged Quantity 2020
(tonnes, wet weight)
Inner Liffey Channel (Dublin Harbour) 92,260
Dublin Bay 399,354
Total Quantity (tonnes, wet weight) 491,554
Hartley Anderson Limited
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Figure 2.1: Foreshore boundary of area (red line) to be dredged and dumpsiteHartley Anderson Limited
Article 12 Risk Assessment January 2022
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The total quantity of material dredged over the 8-year period (2013 – 2020) was 1,731,405
tonnes. The average annual quantity of material dredged was circa 216,000 tonnes per year.
The following relationship was agreed with the EPA for the Alexandra Basin Redevelopment
(ABR) Project to convert between weight (wet tonnes) and volume (cubic metres):
Weight (wet tonnes) = 1.65 x Volume (cubic metres)
Using the above relationship, the average annual volume of material dredged was circa
131,000m3 per annum. However, the volume of maintenance dredging required does vary
significantly from year to year. For example, in 2017, the volume of material dredged from the
inner Liffey channel (Dublin Harbour) was 189,000m3 which accumulated over a one-year
period. In 2020, the volume of material dredged from Dublin Bay was 242,000m3 which
accumulated over a one-year period.
2.3 Proposed dredging campaign 2022-2029
2.3.1 Loading operation
The following volumes and quantities are proposed for the eight-year maintenance dredging
programme based on the knowledge gained from previous maintenance dredging campaigns.
It is proposed that the following annual quantities of material will be dredged from the Inner
Liffey channel and Dublin Bay during the maintenance dredging programme.
• Inner Liffey channel (Dublin Harbour, area within the Bull Walls): The average rate
of siltation within the inner Liffey channel, based on previous maintenance dredging
campaigns, is circa 120,000m3 per annum. The proposed maximum annual
volume to be dredged is 150,000m3. The material to be dredged is mostly silt.
• Dublin Bay (area of navigation channel outside the Bull Walls): The navigation
channel has been dredged from -7.8m Chart Datum to -10.0m CD under the
Alexandra Basin Redevelopment (ABR) Project. Siltation is likely during storm
activity. The proposed maximum annual volume to be dredged is 150,000m3. The
material to be dredged is mostly fine sand.
The proposed quantities / volumes of dredged material are presented in Table 2.3. The
conversion factor of 1.65 (volume to weight), agreed with the EPA for the Alexandra Basin
Redevelopment (ABR) Project, has been used to convert from wet tonnes to volume in cubic
metres.
Table 2.3: Proposed quantity of material to be dredged from Dublin Port
Location Annual Quantity Total (2022-2029)
Inner Liffey Channel 247,500 (tonnes wet weight) 1,980,000 (tonnes wet weight)
150,000m3 1,200,000m3
Dublin Bay 247,500 (tonnes wet weight) 1,980,000 (tonnes wet weight)
150,000m3 1,200,000m3
Total Quantity 495,000 (tonnes wet weight) 3,960,000 (tonnes wet weight)
300,000 m3 per annum 2,400,000 m3
The proposed total annual quantities are the same as that permitted for the maintenance
dredging campaigns 2020 and 2021 under Foreshore Licence FS/2020/03173 and Dumping
at Sea Permit S0004-02.Hartley Anderson Limited
Article 12 Risk Assessment January 2022
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DPC requests the same condition be applied to the current application limiting total quantity
to be dredged to 495,000 tonnes (wet weight) or 300,000m3 per annum for 8 years.
The loading of dredged material will be restricted to those areas of the navigation channel,
basins and berthing pockets which contain sediments which are suitable for disposal at sea
(Class 1 : uncontaminated, no biological effects likely). Confirmation of the suitability of the
dredged sediments for disposal at sea was made through a programme of sediment chemistry
sampling and analysis and eco-toxicological testing (detailed in the Dredge Volumes and
Sediment Chemistry report which accompanied the application).
2.3.2 Dredging windows
The proposed maintenance dredging will be restricted to the summer period (April –
September). Capital dredging works will be restricted to the winter period (October – March).
This separation provides the clarity required by the EPA to enforce separate permits for
maintenance and capital dredging programmes by DPC. The dredging campaign within each
of these periods is expected to last approximately 4-6 weeks, depending on weather
conditions.
A closed period between 1st April and 14th May will operate for loading areas in the inner Liffey
channel upstream of Berth 49, including the main channel and the channel-side berths, but
not including the basins, to protect migrating Atlantic salmon and River Lamprey.
2.4 Spoil disposal site
It is proposed that dredged sediments will be disposed at the existing licensed offshore
disposal site located at the entrance to Dublin Bay to the west of the Burford Bank (6.75 km
from the lighthouse at the end of the Great South Wall), as shown in Figure 2.1.
The dumpsite covers an area of 2.27km2 and is currently used by Dublin Port to dispose of
dredge spoil from licensed capital and maintenance dredging works. The dumpsite has been
in regular use since 1996, before which another nearby location was used.Hartley Anderson Limited
Article 12 Risk Assessment January 2022
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SECTION 3 - BASELINE ENVIRONMENT
3.1 Ambient noise levels
Ambient, or background noise, is defined as any sound other than the sound being monitored
(primary sound) and, in the marine environment, is a combination of naturally occurring
biological and physical sound sources including sediment transfer, waves and rain and that of
a biological origin including fish, crustaceans and from marine mammals. The impact of noise
from human activity is strongly influenced by background or ambient noise, the impact is less
in a noisy environment compared to a quiet environment and it is the intensity and frequency
of this increased noise compared to the ambient levels at a site, which defines its impact. As
ambient noise levels increase, the ability to detect a biologically important sound decreases.
The point at which a sound is no longer detectable over ambient noise is known as acoustic
masking. The range at which an animal is able to detect these signals reduces with increasing
levels of ambient noise (Richardson et al. 1995). This is important when considering the
impact of sound sources on marine mammals by the proposed works.
Ambient noise levels worldwide have been on the rise in recent decades with developments
in industry and, in particular, in commercial shipping. In the North Pacific, low frequency
background noise has approximately doubled in each of the past four decades (Andrew et al.
2002), resulting in at least a 15 to 20 dB increase in ambient noise. In recent years, interest
has grown in the effects of anthropogenic noise on marine life. Ambient noise in Dublin Bay
has been estimated at around 113 dB by Beck et al. (2013) and by McKeown (2014). This
level is higher than that reported for example from Galway Bay and the Shannon Estuary and
reflects the greater vessel traffic at this site.
3.2 Relevant Annex IV species
3.2.1 Reported observations from previous dredging campaigns
A number of dredging campaigns have been carried out since 2016, which provides site
specific information on the receiving environment and interactions with dredging operations.
Maintenance dredging has occurred between April and September while the ABR capital
dredging programme runs from October to March. As the proposed maintenance dredging
will continue to be carried out between April and September only data and records from this
period and not during the winter period are considered.
O’Dwyer et al. (2016) reported 134 sightings of marine mammals during 42 days from 20 June
to 31 July 2016. There were 56 harbour porpoise sightings (42% of the total) (Figure 3.1) with
grey seal accounting for 57% of sightings.
Keogh et al. (2017) reported a total of total of 187 marine mammal sightings between 14 and
30 September 2017. Grey seal was the most frequently recorded species, accounting for 70%
of the total number of individual marine mammals sighted. Harbour porpoise accounted for
22% (Figure 3.2).
Keogh et al. (2018) reported a total of 111 marine mammal sightings between 9 and 22 April
2018. There were 110 sightings of marine mammals on days where loading and dumping
took place with grey seal the most frequently recorded species, with 65 sightings, accounting
for 58% of the total number of marine mammals sighted. Harbour porpoise were recorded on
35 occasions (32%) (Figure 3.3).Hartley Anderson Limited
Article 12 Risk Assessment January 2022
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Figure 3.1: Sightings of harbour porpoise during the 2016 maintenance dredging
programme
Source: O’Dwyer et al. 2016
Figure 3.2: All marine mammal sightings during the 2017 maintenance dredging
campaign
Source: Keogh et al. 2017Hartley Anderson Limited
Article 12 Risk Assessment January 2022
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Figure 3.3: Marine mammal sightings during the 2018 maintenance dredging
programme
Source: Keogh et al. 2018
3.2.2 Harbour porpoise
Harbour porpoise are the most widespread and abundant cetacean in inshore Irish waters,
with highest abundances in the Irish Sea (Berrow et al. 2010). Harbour porpoise were the
most frequently recorded cetacean species during maintenance dredging operations over the
same April to September period, (O’Dwyer et al. 2016; Keogh et al. 2017, 2018). O’Dwyer et
al. (2016) reported three porpoise sightings within Dublin Harbour although most sightings
were outside along the shipping channel and at the disposal site.
As part of the ABR Project in Dublin Port, static acoustic monitoring (SAM) has been ongoing
at the offshore disposal site and at a control site since 2016 (Russell et al. 2018, 2020). SAM
is particularly effective at logging the presence of harbour porpoise but can detect dolphins
too, although not to species level. The results from SAM show harbour porpoise to be present
on most days (98-100%), with highest detections per day typically recorded at the control site
to the south (SAM 4) (Figure 3.4).
Modelling of 2017-2018 SAM data
Generalized linear mixed-effect models (GLMM) were carried out by Russell et al. (2018) using
tide, time of day and tidal phase as factors to explore the fine scale use of the spoil site by
harbour porpoises. Most detections were recorded at the control site (SAM 4) outside the
spoil ground, but of the three locations monitored at the spoil ground, more detections were
recorded in the middle (SAM 2), with significantly more detections during winter, and during
the hours of darkness. The neap phase had the greatest number of detections in comparisonHartley Anderson Limited
Article 12 Risk Assessment January 2022
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with spring and transitional, as well as during times of high tide. The site north of the spoil
ground (SAM 1) had the second highest number of detections with significant trends similar to
SAM 2; more detections during winter and during the hours of darkness. Additionally, more
detections were recorded during neap and transitional tidal phases and at high tides (Russell
et al. 2018).
In summary, results across all days monitored at each of the sites showed porpoises to be
present on average 97-100% of days monitored. Presence was highest inside the spoil
ground during autumn at SAM 3 and during the winter months at SAM 1 and SAM 2 and during
the hours of darkness (incl. dawn and dusk) and a range of tidal cycles and phases
.
Figure 3.4: PAM and SAM positions within the spoil grounds and Dublin Bay
Source: from Russell et al. 2018
Modelling of 2018-2019 SAM data
In summary, results across all days monitored at each of the sites showed harbour porpoises
to be present on an average 99% of days monitored. The highest presence was detected at
all locations during the winter months, during hours of darkness (including dusk) and across a
range of tidal cycles and phases (Russell et al. 2019).
The number of harbour porpoise detections per day on the spoil ground peaked during
dumping activity suggesting that, in some instances, harbour porpoise were more active in the
spoil ground during dumping and did not appear to perceive the activity as a threat or
disturbance. This may be due to a new feeding opportunity associated with dumping, that
outweighed any potential negative impacts.Hartley Anderson Limited
Article 12 Risk Assessment January 2022
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Figure 3.5: Number of harbour porpoise detections per day recorded across all
locations and during periods of capital dredging
Note: (B1=SAM 1, B2=SAM 2, B3=SAM 3, B4=SAM 4, see Figure 3.4) with the grey
transparency box indicating the dates of the first (22-31 Oct), second (23 Nov- 09
Dec 2017), third (06-17 Jan 2018), fourth (15-23 Feb) and fifth (04-14 Mar) capital
dredging (CD) campaign.
Source: Russell et al. 2018, 2019
3.2.3 Bottlenose dolphin
Bottlenose dolphins are widespread and relatively abundant off the Irish coast with most
sightings along the western seaboard (Berrow et al. 2010). Bottlenose dolphins have been
reported throughout the year, though mainly in the summer and from all along the coast, but
mainly off Howth Head and especially from Dún Laoghaire and south to Wicklow. Most
sightings are of small groups though occasionally large groups of greater than 20 dolphins
occur but usually only for short periods. A small group of 3 individual bottlenose dolphins
frequented Killiney Bay from August 2010 to August 2012.
Bottlenose dolphins off Dublin are part of the highly mobile coastal population which has been
recorded all around the Irish coast and some individuals reported off Scotland (O’Brien et al.
2009). Surprisingly, there was no evidence of movement between the east coast of Ireland
and Wales, which holds a large number of this species. Recent genetic evidence (Mirimin et
al. 2011) suggests the existence of three discrete populations of bottlenose dolphins in Ireland:
the Shannon Estuary, an inshore population and an offshore population that ranges from the
Bay of Biscay and the Azores (Louis et al. 2014). The inshore population is highly mobile and
photo-identification has shown individuals recorded off Co Dublin to be part of this population
(O’Brien et al. 2009). This highly mobile Irish coastal population is thought to number between
200-400 individuals. No dolphins have been observed at or near the dredge or dump site by
marine mammal observers during dredging operations.Hartley Anderson Limited
Article 12 Risk Assessment January 2022
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Dolphins were occasionally detected by SAM especially during summer months. No
detections were logged between October to December 2018, some from December 2018 to
August 2019, mainly at SAM3. These were most likely bottlenose dolphins.
Figure 3.6: Sightings of a) bottlenose dolphin b) minke whale and c) Risso’s dolphin
off Dublin Bay
Source: IWDG
3.2.4 Minke whale
Minke whales are widespread and abundant in inshore Irish waters from May to October
(Berrow et al. 2000). They occur seasonally, especially off north County Dublin from Howth
Head to Lambay Island and on the Kish Bank. They are usually solitary but up to five have
been seen foraging in the same area at any one time. They have not been recorded in, or
adjacent to, the dredging or dump site.
3.2.5 Risso’s dolphin
Risso’s dolphin were regularly recorded to the south of Dublin Bay, in the spring and early
summer for a number of consecutive years from 1999 to 2006 but have not been recorded
regularly since 2013. They were likely part of a wider Irish Sea population whose occurrence
is associated with the presence of squid, which may be an unpredictable food source.
3.2.6 Common dolphin and humpback whale
Common dolphins and humpback whales have also been recorded in the western Irish Sea.
Common dolphins are thought to be more abundant in the summer and autumn and tend to
occur further offshore than bottlenose or Risso’s dolphins. They have been recorded from
Rockabill to Dun Laoghaire. Single humpback whales were recorded in July for two
consecutive years in 2010 and 2011 off north Dublin and are thought to be increasing in
number in Irish coastal waters, suggesting they are likely to be more frequently observed off
Dublin in future yearsHartley Anderson Limited
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SECTION 4 - RISK ASSESSMENT
4.1 Potential impacts associated with dredging programme
Section 5.2 of the applicant’s Marine Mammal Risk Assessment provided a comprehensive
literature review of the impact of dredging on marine mammals which informed the risk
assessment of the the proposed Dublin Port maintenance dredging programme described in
Section 5.3. The following information is taken from these sections.
4.1.1 Underwater noise
Dredging activities
Marine mammals, especially cetaceans, have well developed acoustic capabilities and are
sensitive to sound at much higher frequencies than humans (Richardson et al. 1995). They
are less sensitive to the lower frequencies but there is still great uncertainty over the effects
of sound pressure levels on marine mammals and thus the assessment of its impact. Sources
of noise include that generated by the vessel during dredging and transiting to and from the
dump site, the noise generated by dredging and that generated during dumping.
Received levels of dredging noise by marine mammals can exceed ambient levels to
considerable distances depending on the type of dredger used (Richardson et al. 1995).
Hopper dredges produced broadband sound between 20-1000 Hz and the highest levels
occurred during loading. Evans (2000) suggested dredging activities produce sounds varying
from 172-185 dB re 1 ųPa at 1 metre over the broadband range 45 Hz to 7 kHz but there have
been no studies examining the reaction of odontocetes to this activity. Audiograms for
bottlenose dolphins show peak sensitivity between 50-60 kHz and no sensitivity below 2 kHz
and above around 130 kHz (Richardson et al. 1995). Because of rapid attenuation of low
frequencies in shallow water dredge noise normally is undetectable underwater at ranges
beyond 20-25km (Richardson et al. 1995). The effects of low frequency (4-8 kHz) noise level
and duration in causing threshold shifts in bottlenose dolphins were predicted by Mooney et
al. (2009), who found that if the Sound Exposure Level was kept constant significant shifts
were induced by longer duration exposures but not for shorter exposures.
NPWS (2014) identify increased sound pressure levels above ambient do occur due to
dredging which could be detected up to 10km from shore. These levels are thought to
potentially cause masking or behavioural effects but are not thought to cause injury to a marine
mammal. There is no guidance on the effects of noise generated by dumping of dredge
material on marine mammals.
McKeown (2016) made underwater noise measurements during the 2016 maintenance
dredging campaign. The PSD plots of the dredging operation show some lower frequency
tonal components between 200 Hz and 2 kHz were attributed to the pump. The dredging
operation had a higher frequency signal in comparison to the dumping operation.
Sound levels for the dredging operations at ranges of 213 and 268 m were below the
disturbance threshold for harbour porpoise of 140 dB re 1 μPa SPL (RMS) and 140 dB re
1μPa² s SEL. The sound level of 142.7 dB re 1 μPa SPL (RMS) for the dumping operation at
a range of 90 m were 2.7 dB re 1 μPa SPL (RMS) above the disturbance threshold for harbour
porpoise, suggesting porpoise may reactHartley Anderson Limited
Article 12 Risk Assessment January 2022
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Increased noise is restricted to 30m) and showed some evidence of habituation.
Buckstaff (2004) suggested an exposure level of 110-120 dB from vessel noise solicited no
observable effect on bottlenose dolphins. A similar exposure level solicited minor changes in
orientation behaviour and locomotion changes in minke whales (Palka & Hammond 2001).
Harbour porpoise are frequently observed near vessels but tend to change behaviour and
move away and this avoidance may occur up to 1-1.5km from a ship but is stronger with 400m
(cited by Richardson et al. 1995).
4.1.2 Disturbance
During transit
The presence of a dredger in the area will lead to increased vessel traffic and associated
noise. Large vessels produce low frequency sounds and TSHD are large (e.g. MV Freeway
is 92m in length). However, given the busy nature of Dublin Port and shipping lane and
increased ambient noise already experienced at this site (Beck et al. 2013) the presence of
an additional vessel and its associated noise, is extremely unlikely to be significant. The
increased noise above ambient levels generated by the dump vessel will be of relatively short
duration (maximum of 4-6 weeks per annum).
During dumping
The disposal site has been routinely used for the dumping of dredged material, with
approximately eight million tonnes of material dumped at this site between 1997 and 2012 at
an average rate of around 550,000 m3 per annum. The current licence for capital dredging
(Reference number: SOO24-01) permits a maximum of 8,760,000 tonnes (equivalent to
5,300,000 m3) of dredged material may be loaded and dumped at sea up until and including
March 2021.
Increased noise is restricted toHartley Anderson Limited
Article 12 Risk Assessment January 2022
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4.1.3 Physical disturbance and collision risk
The risk of injury or mortality is considered extremely low as marine mammals are exposed to
considerable vessel traffic on a daily basis and would be aware of their presence. The dredge
vessel is slow moving and not able to turn quickly thus any animals in the area would have
sufficient time to avoid any collisions and thus injury or mortality. The chance of actually
releasing dredged material on top of a marine mammal is extremely unlikely. The duration of
the release of dredged material last around 10-20 minutes and the vessel slows down during
spoil release.
4.1.4 Turbidity
Turbidity levels at the disposal site are monitored during and outside of disposal activities
(CEMP). The data indicates that there is no sustained or widespread impact on turbidity due
to dumping. The short term increase in turbidity caused during the dumping process will have
a local impact of short duration and will have no impact on marine mammals or their preferred
prey.
4.1.5 Indirect impacts on preferred prey
No adverse effects on fish species is expected from dredging and disposal operations. SAM
data from the ABR project (Russell et al. 2019, 2020) has recorded an increase in acoustic
detections of harbour porpoise during disposal operations. Increased click detections are
concurrent with increased foraging clicks suggesting harbour porpoises may be taking
advantage of increased foraging opportunities presented during disposal at Burford Bank.
4.1.6 Cumulative effects
There is considerable dredging planned or already licensed in and around the Dublin Bay
area.
The disposal site is currently licensed and used by Dublin Port to dispose of dredge spoil from
the port area to dispose circa 1.1 million m3 of sediment per annum as part of the ABR Project
under Dumping at Sea Permit S0024-01. This will be completed by March 2021. Capital
dredging will be required for the MP2 project totalling 424,644m3 (700,663 tonnes)3 within the
period 2022 to 2031. Additional capital dredging is expected within Dublin Harbour of circa
750,000m3 (1,237,500 tonnes) within the period 2022 to 2029. There will be no overlap with
the dredge disposal from the ABR project but there will be an overlap with the proposed
maintenance dredging and the further capital dredging outlined above.
Burford Bank has also been previously used by Dun Laoghaire Harbour Commissioners,
Howth Yacht Club and Dublin local authorities for the disposal of sediments.
The site has been in operation since 1996, after the previous disposal site located nearby
closed. The area has been subjected to regular dredge spoil disposal since it opened. Table
6 of the applicant’s MMRA outlines the dredge spoil tonnages disposed at the site since 1996.
Although the volumes are large (from 250,000 to almost 2 million tonnes per year), monitoring
during the ABR Project of similar amounts of dredge disposal have indicated no significant
impacts on marine mammals (Russell et al. 2018, 2019, 2020). This suggests there is capacity
for the disposal site at Burford Bank and Dublin Bay to absorb this dredging and disposal
activity.
3 Note that this has been increased to a proposed figure of 668,317m3.Hartley Anderson Limited
Article 12 Risk Assessment January 2022
Page 18
4.2 Mitigation measures
Guidance to Manage the Risk to Marine Mammals from Man-made Sound Sources in
Irish Waters
The mitigation measures recommended by the NPWS are for the presence of a trained and
experienced Marine Observer (MMO) and the use of “ramp up” procedures for noise and
vibration emitting operations. The proposed mitigation measures (Guidance to Manage the
Risk to Marine Mammals from Man-made Sound Sources in Irish Waters) recommended by
the Department of Arts, Heritage and the Gaeltacht in 2014 are designed to mitigate any
possible effects.
The following mitigation measures are proposed to minimise the potential impacts on marine
mammals and to allow animals move away from the area of dredging operations:
1. A dedicated, qualified and experienced Marine Mammal Observer will conduct a 30
minute watch for marine mammals within 200m prior to start up. If a seal or cetacean
(or otter) is sighted within 200m of the TSHD, start-up must be delayed until the
animal(s) is observed to move outside the mitigation zone or the 30 minutes has
passed without the animal being sighted within the mitigation zone.
2. Dredging activities shall only commence in daylight hours where effective visual
monitoring, as performed and determined by the MMO, has been achieved. Where
effective visual monitoring, as determined by the MMO, is not possible the sound-
producing activities shall be postponed until effective visual monitoring is possible.
3. Once normal dredging operations commence, there is no requirement to halt or
discontinue the activity at night-time, nor if weather or visibility conditions deteriorate
nor if marine mammals occur within a 500m radial distance of the sound source, i.e.,
within the MZ.
4.3 Conclusion
With implementation of the above mitigation measures, it is very unlikely that there will be
negative residual impacts from the proposed dredging works on Annex IV species in the area.
It is also very unlikely that any animals will be injured or killed as a result of the proposed
works.
Ongoing static acoustic monitoring of harbour porpoises will allow detection of effects on the
conservation objectives of the Rockabill to Dalkey Island SAC, although base on past evidence
and this assessment, none are expected.Hartley Anderson Limited
Article 12 Risk Assessment January 2022
Page 19
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