Appendix G: Underwater Acoustics

Transcription

1 Appendix G: Underwater Acoustics

2 Appendix G.1: Underwater Noise Modelling

3 Submitted to: Jonathan Ashburner Affric Limited Lochview Office Loch Duntelchaig Farr Inverness IV2 6AW Submitted by: Sam East Subacoustech Environmental Ltd Chase Mill Winchester Road Bishop s Waltham Hampshire SO32 1AH Tel: +44 (0) Tel: +44 (0) jonathan.ashburner@affriclimited.co.uk Website: sam.east@subacoustech.com Website: Underwater noise propagation modelling at Port of Cromarty Firth, Invergordon, Scotland Sam East 2 nd May 2018 Subacoustech Environmental Report No. P226R0103 Document No. Date Written Approved Distribution P226R /04/2018 S East T Mason Jon Ashburner (Affric) P223R /04/2018 S East T Mason Jon Ashburner (Affric) P223R /05/2018 S East T Mason Jon Ashburner (Affric) This report is a controlled document. The report documentation page lists the version number, record of changes, referencing information, abstract and other documentation details. [Title]

4 List of contents List of contents Introduction Survey area Impact Piling Assessment overview Measurement of underwater noise Units of measurement Quantities of measurement Modelling methodology Detailed modelling inputs Assessment criteria Modelling results Impact piling - 2 m cylindrical pile Impact piling sheet piles Summary and conclusions References Report documentation page Subacoustech Environmental Ltd. I [Status]

5 1 Introduction Subacoustech Environmental have been instructed by Affric Limited to undertake acoustic propagation modelling for impact piling of cylindrical and sheet piles in relation to the proposed Phase 4 Development at the Port of Cromarty Firth. Port of Cromarty Firth is located at Invergordon, Scotland and serves the offshore energy sector as well as being the busiest cruise port in Scotland. The Port Authority has proposed to extend the existing berths to provide capacity for supporting the offshore wind sector, accommodating the largest cruise ships, and preparing the port for future offshore decommissioning opportunities. The Cromarty Firth is populated by a range of marine mammal species including Bottlenose Dolphins, Harbour Porpoise, Grey Seals and Harbour Seals. Larger marine mammals may be also found in the Moray Firth. Migratory fish, particularly salmon and sea trout are also present, particularly during the migration season. The purpose of the modelling is to estimate the received sound pressure levels in the region from proposed piling works, with particular concern for the impacts from noise on marine mammals and fish. This report has been prepared by Subacoustech Environmental Ltd for Affric Ltd and presents the results and findings of the modelling assessment. 1.1 Survey area Figure 1-1 details the area of the terminal site on the north shore of Cromarty Firth, Invergordon, Scotland. The area of operational activity for the works is relatively small and a single representative modelling location has been selected (approximate coordinates: N, W). This is approximately the centre of the red circle in the figure below. Figure 1-1 Image showing the location of the Port of Cromarty Firth and entrance to the Moray Firth (Image 2018 DigitalGlobe, GetMapping plc, Data SIO, NOAA, U.S. Navy, GEBCO. Map Data 2018 Google) Subacoustech Environmental Ltd. 1

6 1.2 Impact Piling The proposed works involve the installation of cylindrical and sheet piles. Whilst the piles may be set using vibro piling, it is anticipated that a significant amount of impact piling will be required to drive them to depth. Noise levels from impact piling are primarily dependent on the hammer energy used to drive the pile and the length of pile in contact with the water (usually the water depth). Frequency characteristics of the sounds emitted exhibit some variation according to pile dimensions. Impact piling of cylindrical piles of up to 2m has been modelled using source level data obtained from measurement studies of similar sized piles. Impact piling of sheet piles has been modelled based on impact piling of 0.6 m monopiles. This approach has been used by Subacoustech on other projects and has shown good agreement with measurement data from impact piling of sheet piles. 1.3 Assessment overview This report presents a detailed assessment of the potential underwater noise from impact piling at the Port of Cromarty Firth and covers the following: Review of background information on the units for measuring and assessing underwater noise; Discussion of the approach, input parameters, criteria and assumptions for the noise modelling undertaken; Presentation of detailed subsea noise modelling using unweighted metrics and interpretation of the results using suitable noise metrics and criteria; and Summary and conclusions. Subacoustech Environmental Ltd. 2

7 2 Measurement of underwater noise Sound travels much faster in water (approximately 1,500 ms -1 ) than in air (340 ms -1 ). Since water is a relatively incompressible, dense medium, the pressures associated with underwater sound tend to be much higher than in air. As an example, background levels of sea noise of approximately 130 db re 1 µpa for UK coastal waters are not uncommon (Nedwell et al, 2003 and 2007). 2.1 Units of measurement Sound measurements underwater are usually expressed using the decibel (db) scale, which is a logarithmic measure of sound. A logarithmic scale is used because rather than equal increments of sound having an equal increase in effect, typically a constant ratio is required for this to be the case. That is, each doubling of sound level will cause a roughly equal increase in loudness. Any quantity expressed in this scale is termed a level. If the unit is sound pressure, expressed on the db scale, it will be termed a Sound Pressure Level. The fundamental definition of the db scale is given by: Level = 10 log 10 ( Q Q ref ) where Q is the quantity being expressed on the scale, and Q ref is the reference quantity. The db scale represents a ratio, for instance, 6 db really means twice as much as (such as a doubling of peak or RMS pressure, exposure etc). It is, therefore, used with a reference unit, which expresses the base from which the ratio is expressed. The reference quantity is conventionally smaller than the smallest value to be expressed on the scale, so that any level quoted is positive. For instance, a reference quantity of 20 µpa is used for sound in air, since this is the threshold of human hearing. A refinement is that the scale, when used with sound pressure, is applied to the pressure squared rather than the pressure. If this were not the case, when the acoustic power level of a source rose by 10 db the Sound Pressure Level would rise by 20 db. So that variations in the units agree, the sound pressure must be specified in units of root mean square (RMS) pressure squared. This is equivalent to expressing the sound as: Sound Pressure Level = 20 log 10 ( P RMS P ref ) For underwater sound, typically a unit of one micropascal (µpa) is used as the reference unit; a Pascal is equal to the pressure exerted by one Newton over one square metre; one micropascal equals one millionth of this. 2.2 Quantities of measurement Sound may be expressed in many ways depending upon the type of noise, and the parameters of the noise that allow it to be evaluated in terms of a biological effect. These are described in more detail below Sound pressure level (SPL) The Sound Pressure Level is normally used to characterise noise and vibration of a continuous nature such as drilling, boring, continuous wave sonar, or background sea and river noise levels. To calculate the SPL, the variation in sound pressure is measured over a specific time period to determine the Root Mean Square (RMS) level of the time varying sound. The SPL can therefore be considered a measure of the average unweighted level of sound over the measurement period. Subacoustech Environmental Ltd. 3

8 Where an SPL is used to characterise transient pressure waves such as that from seismic airguns, underwater blasting or impact piling, it is critical that the period over which the RMS level is calculated is quoted. For instance, in the case of pile strike lasting, say, a tenth of a second, the mean taken over a tenth of a second will be ten times higher than the mean taken over one second. Often, transient sounds such as these are quantified using peak SPLs Peak sound pressure level (SPL peak) Peak SPLs are often used to characterise sound transients from impulsive sources, such as percussive impact piling and seismic airgun sources. A peak SPL is calculated using the maximum variation of the pressure from positive to zero within the wave. This represents the maximum change in positive pressure (differential pressure from positive to zero) as the transient pressure wave propagates. A further variation of this is the peak-to-peak SPL where the maximum variation of the pressure from positive to negative within the wave is considered. Where the wave is symmetrically distributed in positive and negative pressure, the peak-to-peak level will be twice the peak level, or 6 db higher Sound exposure level (SEL) When assessing the noise from transient sources such as blast waves, impact piling or seismic airgun noise, the issue of the period of the pressure wave is often addressed by measuring the total acoustic energy (energy flux density) of the wave. This form of analysis was used by Bebb and Wright (1953, 1954a, 1954b and 1955), and later by Rawlins (1987) to explain the apparent discrepancies in the biological effect of short and long-range blast waves on human divers. More recently, this form of analysis has been used to develop criteria for assessing the injury range from fish for various noise sources (Popper et al, 2014). The Sound Exposure Level (SEL) sums the acoustic energy over a measurement period, and effectively takes account of both the SPL of the sound source and the duration the sound is present in the acoustic environment. Sound Exposure (SE) is defined by the equation: SE = p 2 (t)dt 0 T where p is the acoustic pressure in Pascals, T is the duration of the sound in seconds, and t is the time in seconds. The Sound Exposure is a measure of the acoustic energy and, therefore, has units of Pascal squared seconds (Pa 2 s). To express the Sound Exposure on a logarithmic scale by means of a db, it is compared with a reference acoustic energy level (P 2 ref) and a reference time (T ref ). The SEL is then defined by: SEL = 10 log 10 ( T p2 (t)dt 0 P 2 ) reft ref By selecting a common reference pressure P ref of 1 µpa for assessments of underwater noise, the SEL and SPL can be compared using the expression: SEL = SPL + 10 log 10 T Where the SPL is a measure of the average level of the broadband noise, and the SEL sums the cumulative broadband noise energy. This means that, for continuous sounds of less than one second, the SEL will be lower than the SPL. For periods greater than one second the SEL will be numerically greater than the SPL (i.e. for a sound of ten seconds duration, the SEL will be 10 db higher than the SPL, for a sound of 100 seconds duration the SEL will be 20 db higher than the SPL, and so on). Subacoustech Environmental Ltd. 4

9 Weighted metrics for marine mammals have been proposed by the National Marine Fisheries Service (NMFS) (2016), these assign a frequency response to groups of marine mammals and are discussed in detail in the following section. Subacoustech Environmental Ltd. 5

10 3 Modelling methodology Whilst a range of different noise generating activities may be undertaken in the course of the project, impact piling is expected to generate the highest levels of underwater noise and is likely to have an effect over the largest area of water. Two scenarios have been selected for detailed underwater noise modelling. 3.1 Detailed modelling inputs To estimate the likely noise levels from impact piling operations, modelling has been carried out using an approach that is widely used and accepted by the acoustics community, in combination with publicly available environmental data and information provided by Affric Ltd. The approach is described in more detail below. Modelling of underwater noise is complex and can be approached in several different ways. Subacoustech have chosen to use a numerical approach that is based on two different solvers: A parabolic equation (PE) method for lower frequencies (12.5 Hz to 250 Hz); and A ray tracing method for higher frequencies (250 Hz to 100 khz). The PE method is widely used within the underwater acoustics community but has computational limitations at high frequencies. Ray tracing is more computationally efficient at higher frequencies but is not suited to low frequencies (Etter, 1991). This study utilises the dbsea implementation of these numerical solutions. These solvers account for a wide array of input parameters, including bathymetry, sediment data, sound speed and source frequency content to ensure as detailed results as possible. These input parameters are described in the following sections Bathymetry The bathymetry data used in the modelling was supplied by Find Mapping Ltd; this data has a resolution of 1 arc second (a grid of squares measuring approximately 30 m by 60 m). A high tide of 4.3 m (Mean High Water Springs, MHWS) has been used throughout the modelling as this represents a conservative case with regards to noise propagation. The estuarine nature of the area along with depths maintained for the port, gives rise to a highly variable bathymetry throughout the area with a deep channel along the centre of the firth with a variable coastline. Figure 3-1 shows the bathymetry used in the modelling and the location of the works. Due to limitations of underwater bathymetric surveys, the precise coastline and features in very shallow waters inaccessible to survey vessels are not well represented. This does not have a significant effect on modelling results except for short transects as the sound propagates in the direction of the coast. Subacoustech Environmental Ltd. 6

11 Figure 3-1 Bathymetry in the Cromarty Firth indicating the location and extent of the modelling Sound speed profile Given the shallow water and tidal nature of the Cromarty Firth, it has been assumed that the water column is mixed and that a constant sound speed with depth is a reasonable assumption. The speed of sound in the water has been calculated as 1491 m/s for all depths using temperature and salinity data from Marine Scotland (Bresnan et al. 2016) and the underwater sound speed equation from Mackenzie (1981) Seabed properties The seabed properties used for modelling were assumed to be predominantly a mixture of sand and mud. Geo-acoustic properties for the seabed were based on available data from Jensen et al. (2011) and are provided in Table 3-1. Seabed type Compressive sound speed in substrate (ms -1 ) Density profile in substrate (kg/m 3 ) Attenuation profile in substrate (db/wavelength) Sand/mud Table 3-1 Seabed geo-acoustic properties used for modelling Impact piling source levels The proposed impact piling operations at Port of Cromarty Firth is based on installation of 2 m diameter cylindrical piles, and sheet piles. The maximum blow energy of 500 kj has been assumed for cylindrical piles and for sheet piles this is 120 kj. The source levels used for the modelling of these two hammer energies is based on Subacoustech s extensive database of impact piling noise, with the predicted source level calculated from the blow energy and water depth of a piling location. These have been shown to be the primary factors determining the subsea noise levels produced. As the model assumes that the noise source acts as a single point, the water depth at the noise source (accounting for tide) has been used to adjust the source level to allow for the length of the pile in contact with the water. The unweighted SPLpeak source levels estimated for piling at Port of Cromarty Firth are: db re 1 µpa SPLpeak (Cylindrical piles kj hammer energy) db re 1 µpa SPLpeak (Sheet piles kj hammer energy) Subacoustech Environmental Ltd. 7

12 k 1.2k 1.6k 2k 2.5k 3.2k 4k 5k 6.3k 8k 10k 12.5k 16k 20k 25k 32k 40k 50k 64k 80k 100k Band Level (db re 1 µpa) Underwater noise propagation modelling at Port of Cromarty Firth, Invergordon, Scotland These source levels equate to single strike SEL source levels of db re 1 µpa 2 s for a 500 kj hammer and db re 1 µpa 2 s for a 120 kj hammer. The SPLpeak third octave levels used for modelling are illustrated in Figure 3-2. This shows that the sound may be characterised as broadband with the maximum energy at frequencies between 150 Hz and 1 khz Tubular Piling db re 1 µpa²s Sheet Piling db re 1 µpa²s Third Octave Band Frequencies (Hz) Figure 3-2 Source third octave band levels to be used to model impact piling (SPL peak) It is possible (dependant on the piling hammer employed) that the energy and strike rate of the piling hammer will slowly increase (ramp-up) over time, however due to the limited information available, this modelling has assumed the same blow energy and strike rate (1 strike per second) over the entire duration of 1 hour. If a ramp-up or soft start were introduced it would likely act as a mitigating factor to the overall noise levels. Subacoustech Environmental Ltd. 8

13 3.2 Assessment criteria Background Over the past 20 years it has become increasingly evident that noise from human activities in and around underwater environments can have an impact on the marine species in the area. The extent to which intense underwater sound might cause an adverse environmental impact in a species is dependent upon the incident sound level, sound frequency, duration of exposure, and/or repetition rate of the sound wave (see for example Hastings and Popper, 2005). As a result, scientific interest in the hearing abilities of aquatic animal species has increased. These studies are primarily based on evidence from high level sources of underwater noise such as blasting or impact piling, as these sources are likely to have the greatest environmental impact and therefore the clearest observable effects. The impacts of underwater sound can be broadly summarised into three categories: Physical traumatic injury and fatality; Auditory injury (either permanent or temporary); and Disturbance. The following sections discussed the agreed upon criteria for assessing these impacts in key marine species. The metrics and criteria that have been used in this study to assess environmental effect come from the latest NOAA report concerning underwater noise and its effects on marine mammals (NMFS, 2016) and Popper et al (2014) for the impacts of noise on species of fish Marine mammals Since it was published, Southall et al (2007) has been the source of the most widely used criteria to assess the effects of noise on marine mammals. NMFS (2016) was co-authored by many of the same academics from the Southall et al (2007) paper, and effectively updates it. In the updated guidelines, the frequency weightings have changed along with the criteria. As a result, the criteria have generally become more strict and potential impact ranges may increase substantially in some cases. The NMFS (2016) guidance groups marine mammals into functional hearing groups and applies filters to the unweighted noise to approximate the hearing response of the receptor. The hearing groups given in the NMFS (2016) are summarised in Table 3-2. The auditory weighting functions for each hearing group are provided in Figure 3-3. Hearing group Example species Generalised hearing range Low Frequency (LF) Cetaceans Baleen Whales 7 Hz to 35 khz Mid Frequency (MF) Cetaceans High Frequency (HF) Cetaceans Phocid Pinnipeds (PW) (underwater) Dolphins, Toothed Whales, Beaked Whales, Bottlenose Whales (including Bottlenose Dolphin) True Porpoises (including Harbour Porpoise) True Seals (including Harbour Seal) 150 Hz to 160 khz 275 Hz to 160 khz 50 Hz to 86 khz Table 3-2 Marine mammal hearing groups (from NMFS, 2016) Subacoustech Environmental Ltd. 9

14 Weighting Function (db) Underwater noise propagation modelling at Port of Cromarty Firth, Invergordon, Scotland Frequency (Hz) LF Cetaceans MF Cetaceans HF Cetaceans Phocid Pinnipeds Figure 3-3 Auditory weighting functions for low frequency (LF) cetaceans, mid frequency (MF) cetaceans, high frequency (HF) cetaceans and phocid pinnipeds (PW) (underwater) (from NMFS, 2016) Based on the species of marine mammal located near the ferry terminal works only the first four weighting groups (LF Cetacean, MF Cetacean, HF Cetacean, and Phocid Pinnipeds) have been considered in this study. Further discussion of the species weightings applied for this study are given in section NMFS (2016) presents unweighted peak criteria (SPLpeak) and cumulative, weighted sound exposure criteria (SELcum) for both permanent threshold shift (PTS) where unrecoverable hearing damage may occur and temporary threshold shift (TTS) where a temporary reduction in hearing sensitivity may occur in individual receptors. Table 3-3 summarises the NMFS (2016) criteria for onset of risk of PTS and TTS for each of the key marine mammal hearing groups for impulsive noise. In the assessment of cumulative SEL values, a fleeing animal model has been used assuming that the receptor flees the source of the noise at a constant speed of 1.5 m/s (precautionary for most species), for the duration of the piling entire duration. Cumulative SEL is then calculated based on Lepper et al. (2012). Impulsive noise TTS criteria PTS criteria SEL Functional cum SPL peak SEL cum (weighted) (unweighted) (weighted) Group db re 1 µpa 2 s db re 1 µpa db re 1 µpa 2 s SPL peak (unweighted) db re 1 µpa 2 s LF Cetaceans MF Cetaceans HF Cetaceans PW Pinnipeds Table 3-3 Assessment criteria for marine mammals from NMFS (2016) for impulsive noise (blasting and impact piling) Subacoustech Environmental Ltd. 10

15 3.2.3 Fish The effects of noise on fish have been assessed using criteria from Popper et al. (2014), which gives specific thresholds for mortality and potential mortal injury, recoverable injury and TTS, masking and behaviour from various stimuli, including impact piling. Species of fish are grouped by whether or not they have a swim bladder and whether the swim bladder is involved in its hearing. The criteria for impulsive noise are given in unweighted SPLpeak and SELcum values and are summarised in Table 3-4. Impact Piling Mortality & potential Impairment Type of animal mortal injury Recoverable injury TTS Fish: no swim bladder > 219 db SELcum > 216 db SELcum > 213 db SPLpeak > 213 db SPLpeak >> 186 db SELcum Fish: swim bladder not 210 db SELcum 203 db SELcum involved in hearing > 207 db SPLpeak > 207 db SPLpeak > 186 db SELcum Fish: swim bladder 207 db SELcum 203 db SELcum involved in hearing > 207 db SPLpeak > 207 db SPLpeak 186 db SELcum Table 3-4 Assessment criteria for species of fish from Popper et al. (2014) for impact piling noise Masking and behavioural effects have only an indicative assessment approach which is reproduced in Table 3-5. This summarises the effect of the noise as having either a high, moderate or low effect on an individual in either the near-field (tens of metres), intermediate-field (hundreds of metres), or far-field (thousands of metres). Impact Piling Type of animal Fish: no swim bladder Fish: swim bladder not involved in hearing Fish: swim bladder involved in hearing Masking (N) Moderate (I) Low (F) Low (N) Moderate (I) Low (F) Low (N) High (I) High (F) Moderate Behaviour (N) High (I) Moderate (F) Low (N) High (I) Moderate (F) Low (N) High (I) High (F) Moderate Table 3-5 Summary of the qualitative effects on fish from impact piling noise from Popper et al. (2014) (N=Near-field, I=Intermediate-field, F=Far-field) Subacoustech Environmental Ltd. 11

16 3.2.4 Weighted source levels To undertake the modelling for the NMFS (2016) criteria with regards to the weighted criteria, the source levels were first adjusted using the auditory weighting functions shown in Figure 3-3. This alters the source level for each functional group as shown in Figure 3-4 and Figure 3-5, for the 500 kj hammer energy. All weighted source levels are presented in Table 3-6. Noise from impact piling is predominantly low frequency in nature and reduces at frequencies above 1 khz. The source levels given in Figure 3-4 and Figure 3-5 show that the weighting makes only a modest difference to source levels for LF cetaceans when frequency weightings are applied compared to significant reduction seen with MF and HF cetaceans. Figure 3-4 Unweighted and NMFS (2016) weighted SEL source level third octave values for LF and MF cetaceans (Piling 500 kj) Figure 3-5 Unweighted and NMFS (2016) weighted SEL source level third octave values for HF cetaceans and phocid pinnipeds (Piling 500 kj) Impact piling source level (500 kj) (single pulse SEL) Impact piling source level (120 kj) (single pulse SEL) Unweighted db re 1 µpa 2 s db re 1 µpa 2 s LF Cetaceans db re 1 µpa 2 s db re 1 µpa 2 s MF Cetaceans db re 1 µpa 2 s db re 1 µpa 2 s HF Cetaceans db re 1 µpa 2 s db re 1 µpa 2 s Phocid Pinnipeds db re 1 µpa 2 s db re 1 µpa 2 s Table 3-6 Unweighted and NMFS (2016) weighted single strike SEL source levels. Subacoustech Environmental Ltd. 12

17 4 Modelling results 4.1 Impact piling - 2 m cylindrical pile Unweighted SPL peak The SPLpeak noise level from impact piling for a 2 m diameter cylindrical pile using a blow energy of 500 kj is presented in Figure 4-1 for the maximum noise level in the water column. These results have been analysed for their potential impact on marine mammals and fish using the criteria detailed in section 3.2 in Table 4-1 and Table 4-2. Figure 4-1 Impact piling 2 m cylindrical pile (500 kj blow energy), unweighted SPL peak Threshold Criteria SPL peak Impact piling (500 kj) (unweighted) SPL peak Maximum range LF Cetaceans TTS 213 db re 1 µpa < 10 m MF Cetaceans TTS 224 db re 1 µpa - HF Cetaceans TTS 196 db re 1 µpa 55 m PW Pinnipeds TTS 212 db re 1 µpa < 10 m LF Cetaceans PTS 219 db re 1 µpa - MF Cetaceans PTS 230 db re 1 µpa - HF Cetaceans PTS 202 db re 1 µpa 18 m PW Pinnipeds PTS 218 db re 1 µpa - - the threshold is greater than the source level and so will not be exceeded at any range. Table 4-1 Maximum ranges to NMFS (2016) SPL peak injury criteria for marine mammals from impact piling noise (500 kj) based on the maximum level in the water column. Subacoustech Environmental Ltd. 13

18 Threshold Criteria SPL peak (unweighted) Impact piling (500 kj) SPL peak Maximum range Fish (no swim bladder) injury 213 db re 1 µpa < 10 m Fish (with swim bladder) injury 207 db re 1 µpa < 10 m Table 4-2 Maximum ranges to Popper et al. (2014) SPL peak injury criteria for species of fish from impact piling noise based on the maximum level in the water column Cumulative SEL (SEL cum) The noise from impact piling is a multiple pulse source with receptor species exposed to multiple noise events over a time period, and as such cumulative SEL values have been calculated assuming piling lasting 1 hour. Figure 4-2 shows the predicted unweighted SEL for a single strike used to inform the cumulative SEL calculations (application of weighting and fleeing animal). Table 4-3 presents the resulting impact ranges for marine mammal groupings. Calculations for marine mammals assume a receptor fleeing in the direction of the transect at a precautionary speed of 1.5 m/s. Figure 4-2 Impact piling, 2 m cylindrical pile (500 kj), single strike SEL Subacoustech Environmental Ltd. 14

19 Range (m) Underwater noise propagation modelling at Port of Cromarty Firth, Invergordon, Scotland Threshold Criteria SEL cum (weighted) Impact piling (500 kj) SEL cum (1 hour) Maximum range Bearing of Maximum range (degrees) Area of Exceedance (km 2 ) LF Cetaceans TTS 168 db re 1 µpa 2 s 7.0 km MF Cetaceans TTS 170 db re 1 µpa 2 s < 10 m < 0.01 HF Cetaceans TTS 140 db re 1 µpa 2 s 2.7 km PW Pinnipeds TTS 170 db re 1 µpa 2 s 690 m LF Cetaceans PTS 183 db re 1 µpa 2 s 690 m MF Cetaceans PTS 185 db re 1 µpa 2 s < 10 m < 0.01 HF Cetaceans PTS 155 db re 1 µpa 2 s 690 m PW Pinnipeds PTS 185 db re 1 µpa 2 s 90 m 066 < 0.01 Table 4-3 Maximum ranges to NMFS (2016) weighted SEL cum injury criteria for marine mammals from impact piling noise for a 500 kj blow energy assuming a fleeing animal and 1 hour of piling based on the maximum level in the water column Given the narrow shape of the Cromarty Firth, the maximum range only applies to a small number of transects. Figure 4-3 and Figure 4-4 show the PTS and TTS impact ranges for LF and HF cetaceans alongside the overall transect length PTS - Area: 0.12 km² TTS - Area: 7.34 km² Transect length Bearing Figure 4-3 NMFS (2016) LF cetacean PTS and TTS impact ranges for each transect and overall transect length, impact piling, 2 m cylindrical pile (500 kj), fleeing animal (1.5 m/s) Subacoustech Environmental Ltd. 15

20 Range (m) Underwater noise propagation modelling at Port of Cromarty Firth, Invergordon, Scotland PTS - Area: 0.12 km² TTS - Area: 2.76 km² Transect length Figure 4-4 NMFS (2016) HF cetacean PTS and TTS impact ranges for each transect and overall transect length, impact piling, 2 m cylindrical (500 kj), fleeing animal (1.5 m/s) No data exists on the behavioural response of fish to pile driving in the field (Popper et al. (2014)) and as such a precautionary approach of basing cumulative SEL calculations for fish on a stationary animal (i.e. one that does not flee from the noise source) and assume a continuous exposure of 1 hour (3600 pile strikes), the results of which are presented in Table 4-4. This is a conservative approach and if a fleeing animal were assumed, impact ranges would be reduced. Threshold Bearing Criteria SEL cum (unweighted) Impact piling (500 kj) SEL cum (1 hour) Maximum range Fish (no swim bladder) mortality and potential mortal injury 219 db re 1 µpa 2 s < 10 m Fish (no swim bladder) recoverable injury 216 db re 1 µpa 2 s 10 m Fish (with swim bladder not involved in hearing) 210 db re 1 µpa 2 s 30 m mortality and potential mortal injury Fish (with swim bladder involved in hearing) 207 db re 1 µpa 2 s 50 m mortality and potential mortal injury Fish (with swim bladder) recoverable injury 203 db re 1 µpa 2 s 100 m Table 4-4 Maximum ranges to Popper et al. (2014) unweighted SEL cum injury criteria for species of fish from impact piling noise for 2 m cylindrical pile (500 kj) assuming a stationary animal and 1 hour of piling based on the maximum level in the water column TTS criteria for fish is conservatively assessed against a semi-qualitative threshold of 186 db re. 1 µpa 2 s. The value of 186 db re. 1µPa was specifically for fish with a swim bladder involved in hearing (previously termed hearing specialist). For impact piling of a 2 m cylindrical pile with a 500 kj hammer energy, 186 db re. 1 µpa 2 s would occur at a maximum range of 1400 m. For species with a swim Subacoustech Environmental Ltd. 16

21 bladder not involved in hearing, such as Atlantic salmon and sea trout, the actual range at which a fish may incur a TTS injury will be considerably less than 1400 m. 4.2 Impact piling sheet piles Unweighted SPL peak The SPLpeak noise level from impact piling for a sheet piles using a blow energy of 120 kj is presented in Figure 4-5 for the maximum level in the water column. These results have been analysed for their potential impact on marine mammals and fish using the criteria detailed in section 3.2 in Table 4-1 and Table 4-6. Figure 4-5 Impact piling, sheet pile (120 kj blow energy), unweighted SPL peak Threshold Criteria SPL peak Impact piling (120 kj) (unweighted) SPL peak Maximum range LF Cetaceans TTS 213 db re 1 µpa - MF Cetaceans TTS 224 db re 1 µpa - HF Cetaceans TTS 196 db re 1 µpa < 10 m PW Pinnipeds TTS 212 db re 1 µpa - LF Cetaceans PTS 219 db re 1 µpa - MF Cetaceans PTS 230 db re 1 µpa - HF Cetaceans PTS 202 db re 1 µpa < 10 m PW Pinnipeds PTS 218 db re 1 µpa - - the threshold is greater than the source level and so will not be exceeded at any range. Table 4-5 Maximum ranges to NMFS (2016) SPL peak injury criteria for marine mammals from impact piling of sheet piles (120 kj) based on the maximum level in the water column. Threshold Criteria SPL peak (unweighted) Impact piling (120 kj) SPL peak Maximum range Fish (no swim bladder) injury 213 db re 1 µpa - Fish (with swim bladder) injury 207 db re 1 µpa < 10 m - the threshold is greater than the source level and so will not be exceeded at any range. Table 4-6 Maximum ranges to Popper et al. (2014) SPL peak injury criteria for species of fish from impact piling noise (120 kj) based on the maximum level in the water column Subacoustech Environmental Ltd. 17

22 4.2.2 Cumulative SEL (SEL cum) Figure 4-6 shows the predicted unweighted SEL for a single strike used to inform the cumulative SEL calculations for impact piling of sheet piles (120 kj). Table 4-7 presents the resulting impact ranges for marine mammals. Calculations for marine mammals assume a receptor fleeing in the direction of the transect at a precautionary speed of 1.5 m/s. Threshold Criteria SEL cum (weighted) Figure 4-6 Impact piling, sheet pile (120 kj), single strike SEL Impact piling (120 kj) SEL cum (1 hour) Maximum range Bearing of Maximum range (degrees) Area of Exceedance (km 2 ) LF Cetaceans TTS 168 db re 1 µpa 2 s 960 m MF Cetaceans TTS 170 db re 1 µpa 2 s < 10 m < 0.01 HF Cetaceans TTS 140 db re 1 µpa 2 s 690 m PW Pinnipeds TTS 170 db re 1 µpa 2 s 280 m 066 < 0.01 LF Cetaceans PTS 183 db re 1 µpa 2 s 20 m 066 < 0.01 MF Cetaceans PTS 185 db re 1 µpa 2 s < 10 m < 0.01 HF Cetaceans PTS 155 db re 1 µpa 2 s 280 m 066 < 0.01 PW Pinnipeds PTS 185 db re 1 µpa 2 s < 10 m < 0.01 Table 4-7 Maximum ranges to NMFS (2016) weighted SEL cum injury criteria for marine mammals from impact piling noise for sheet piling (120 kj blow energy) assuming a fleeing animal and 1 hour of piling based on the maximum level in the water column Given that the maximum range only applies to a small number of transects, Figure 4-7 and Figure 4-8 show the PTS and TTS impact ranges for LF and HF cetaceans alongside the overall transect length for impact piling of sheet piles. Subacoustech Environmental Ltd. 18

23 Range (m) Range (m) Underwater noise propagation modelling at Port of Cromarty Firth, Invergordon, Scotland Bearing PTS - Area: 0 km² TTS - Area: 0.7 km² Transect length Figure 4-7 NMFS (2016) LF cetacean PTS and TTS impact ranges for each transect and overall transect length, impact piling of sheet piles (120 kj), fleeing animal (1.5 m/s) Bearing PTS - Area: 0 km² TTS - Area: 0.41 km² Transect length Figure 4-8 NMFS (2016) HF cetacean PTS and TTS impact ranges for each transect and overall transect length, impact piling of sheet piles (120 kj), fleeing animal (1.5 m/s) Subacoustech Environmental Ltd. 19

24 No data exists on the behavioural response of fish to pile driving in the field (Popper et al. (2014)) and as with cylindrical piles, a precautionary approach of basing cumulative SEL calculations for fish on a stationary animal. This also assumes a continuous exposure of 1 hour (3600 pile strikes), the results of which are presented in Table 4-8. This is a conservative approach and if a fleeing animal were assumed, impact ranges would be reduced. Threshold Fish (no swim bladder) mortality and potential mortal injury Fish (no swim bladder) recoverable injury Fish (with swim bladder not involved in hearing) mortality and potential mortal injury Fish (with swim bladder involved in hearing) mortality and potential mortal injury Fish (with swim bladder) recoverable injury - the threshold will not be exceeded at any range. Criteria SEL cum (unweighted) Impact piling (120 kj) SEL cum (1 hour) Maximum range 219 db re 1 µpa 2 s db re 1 µpa 2 s < 10 m 210 db re 1 µpa 2 s < 10 m 207 db re 1 µpa 2 s < 10 m 203 db re 1 µpa 2 s 13 m Table 4-8 Maximum ranges to Popper et al. (2014) unweighted SEL cum injury criteria for species of fish from impact piling noise for sheet piling (120 kj) assuming a stationary animal and 1 hour of piling based on the maximum level in the water column TTS criteria for fish is assessed against a semi-qualitative threshold of less than 186 db re. 1µPa 2 s based on fish with swim bladder involved in hearing. For impact piling of sheet piles with a 120 kj hammer energy, 186 db re. 1 µpa 2 s would occur at a maximum range of 270 m. For species with a swim bladder not involved in hearing, such as Atlantic salmon and sea trout, the actual range at which a fish may incur a TTS injury will be considerably than 270 m. Subacoustech Environmental Ltd. 20

25 5 Summary and conclusions Subacoustech Environmental has undertaken a study of noise propagation from impact piling at Port of Cromarty Firth, Invergordon, Scotland for Affric Limited. The level of underwater noise from impact piling of 2 m cylindrical piles and sheet piles has been estimated using a parabolic equation (PE) method for lower frequencies and a ray tracing solution at higher frequencies. The modelling considers a wide variety of input parameters including source noise levels, frequency content, duty cycle, seabed properties and sound speed. The complex bathymetry in the area is accounted for by using the highest resolution data publicly available. Input parameters for water depth and animal swim speeds were chosen that would provide a conservative estimate of noise propagation and impact ranges. Modelling results have been assessed in terms of the criteria provided by NMFS (2016) for SPLpeak and SELcum for marine mammals and Popper et al. (2014) for SPLpeak and SELcum for fish. In the case of the NMFS (2016) criteria, the 1/3 octave band spectrum of the source level has been weighted according the LF, MF, HF and PW frequency weightings stipulated in the guidelines. Results indicate that noise from both impact piling and sheet piling are likely to affect much of Cromarty Firth and extend into the Moray Firth (albeit at a much reduced level). For installation of cylindrical piles, assuming a hammer energy of 500 kj, maximum impact ranges have been calculated as follows: Low frequency cetaceans (e.g. baleen whales): PTS could occur up to 690 m and TTS could occur up to 7,000 m from the piling. Mid frequency cetaceans (e.g. common dolphin): both PTS and TTS are unlikely to occur except in very close proximity (<10 m) to the piling. High frequency cetaceans (e.g. harbour porpoise): PTS could occur up to 690 m and TTS could occur up to 2,750 m from the piling. Pinnipeds (e.g. harbour seal): PTS could occur up to 90 m and TTS could occur up to 690 m from the piling in water. Fish: Non-recoverable injury could occur at distances up to 50 m. Fish TTS: Using the semi-qualitative criteria, TTS impacts could be expected to a maximum range of 1,400 m for the most sensitive species and significantly below this for less sensitive species. For the installation of sheet piles, assuming a hammer energy of 120 kj the maximum impact ranges are estimated to be: Low frequency cetaceans (e.g. baleen whales): PTS could occur up to 20 m and TTS could occur up to 690 m from the piling. Mid frequency cetaceans (e.g. common dolphin): Both PTS and TTS are unlikely to occur except in very close proximity (<10 m) to the piling. High frequency cetaceans (e.g. harbour porpoise): PTS could occur up to 280 m and TTS could occur up to 690 m from the piling. Pinnipeds (e.g. harbour seal): PTS would only occur in very close proximity to the piling (<10 m) and TTS could occur up to 280 m from the piling in water. Fish: Non-recoverable injury could occur at distances up to 13 m. Subacoustech Environmental Ltd. 21

26 Fish TTS: Using the semi-qualitative criteria, TTS impacts could be expected up to a maximum range of 270 m for the most sensitive species and significantly below this for less sensitive species. Results for both types of pile are based on a fleeing animal model for marine mammals (1.5 m/s) and a stationary animal model for fish. It is acknowledged that bathymetry data is based on sampling at specific intervals and then interpolated. In certain circumstances this results in discrepancies in the data, especially around complex coastal areas such as Cromarty Firth. Certain features which are smaller than the resolution of the data (such as harbour walls) may be missing and not accounted for in the results. Results have been presented based on all 180 transects obtained from the best available bathymetry data but no attempt has been made to adjust the data. Care should be taken when drawing conclusions and it may be appropriate to disregard certain transects completely. In this project, a number of transects along bearings between 000 to 084, in the direction of the existing port are likely to fall into this category. Subacoustech Environmental Ltd. 22

27 References 1. Arons A B (1954). Underwater explosion shock wave parameters at large distances from the charge. J. Acoust. Soc. Am. 26, 343, Barrett R W (1996). Guidelines for the sage use of explosives underwater. MTD Publication 96/101, Marine Technology Directorate, 1996, ISBN Bebb A H, Wright H C (1953). Injury to animals from underwater explosions. Medical Research Council, Royal Navy Physiological Report 53/732, Underwater Blast Report 31, January Bebb A H, Wright H C (1954a). Lethal conditions from underwater explosion blast. RNP Report 51/654 RNPL 3/51, National archives reference ADM 298/109, March Bebb A H, Wright H C (1954b). Protection from underwater explosion blast. III. Animal experiments and physical measurements. RNP Report 57/792, RNPL 2/54, March Bebb A H, Wright H C (1955). Underwater explosion blast data from the Royal Navy Physiological Labs 1950/55. Medical Research Council, April Etter P C (1991). Underwater acoustic modelling: Principles, techniques and applications. Elsevier Science Publishers Ltd, Essex. ISBN Hansom J D (2007). Loch Maddy Sound of Harris Coastline. Coastal Geomorphology of Great Britain. accessed on 3rd January Hastings M C and Popper A N (2005). Effects of sound on fish. Report to the California Department of Transport, under Contract No. 43A , January Jensen F B, Kuperman W A, Porter M B, Schmidt H (2011). Computational Ocean Acoustics. Modern Acoustics and Signal Processing. Springer-Verlag, NY. ISBN: Lawrence B. (2016) Underwater noise measurements rock breaking at Acheron Head. Measurements.pdf accessed on 24th November Lepper, P.A. et al., Assessment of cumulative sound exposure levels for marine piling events. IN: Popper, A.N and Hopkins, A. (eds). The Effects of Noise on Aquatic Life: Advances in Experimental Medicine and Biology, 730 (VII), Mackenzie K V (1981). Nine-term equation for the sound speed in the oceans. J. Acoust. Soc. Am 70(3), pp National Marine Fisheries Service (NMFS) (2016). Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing: Underwater Acoustic Thresholds for Onset of Permanent and Temporary Threshold Shifts. U.S. Dept. of Commer., NOAA. NOAA Technical Memorandum NMFS-OPR Nedwell J R, Thandavamoorthy T S (1989). Risso s dolphin (Grampus griseus) hearing thresholds in Kaneohe Bay, Hawaii. In Kastelein R A et al (eds.) Sensory Systems of Aquatic Mammals, 49-53, De Spil Publ. Woerden, Netherlands. 16. Nedwell J R, Langworthy J, Howell D (2003). Assessment of sub-sea acoustic noise and vibration from offshore wind turbines and its impact on marine wildlife initial measurements of underwater noise during construction of offshore wind farms, and comparison with background noise. Subacoustech Report ref: 544R0423, published by COWRIE, May Subacoustech Environmental Ltd. 23

28 17. Nedwell J R, Parvin S J, Edwards B, Workman R, Brooker A G, Kynoch J E (2007). Measurement and interpretation of underwater noise during construction and operation of offshore windfarms in UK waters. Subacoustech Report Ref: 544R0738 to COWRIE. ISBN: Popper A N, Hawkins A D, Fay R R, Mann D A, Bartol S, Carlson T J, Coombs S, Ellison W T, Gentry R L, Halvorson M B, Løkkeborg S, Rogers P H, Southall B L, Zeddies D G, Tavolga W N (2014). Sound Exposure Guidelines for Fishes and Sea Turtles. Springer Briefs in Oceanography, DOI / Rawlins J S P (1987). Problems in predicting safe ranges from underwater explosions. Journal of Naval Science, Volume 14, No. 4 pp Southall B L, Bowles A E, Ellison W T, Finneran J J, Gentry R L, Green Jr. C R, Kastak D, Ketten D R, Miller J H, Nachtigall P E, Richardson W J, Thomas J A, Tyack P L (2007). Marine Mammal Noise Exposure Criteria: Initial Scientific Recommendations. Aquatic Mammals, 33 (4), pp Subacoustech Environmental Ltd. 24

29 Report documentation page This is a controlled document. Additional copies should be obtained through the Subacoustech Environmental librarian. If copied locally, each document must be marked Uncontrolled copy. Amendment shall be by whole document replacement. Proposals for change to this document should be forwarded to Subacoustech Environmental. Document No. Draft Date Details of change P226R /04/2018 Initial writing and internal review P226R /04/2018 Issue to client for review and comment P226R /04/2018 Updated with client comment. P226R /05/2018 Further update with client comment Originator s current report number P226R0103 Originator s name and location R Barham; Subacoustech Environmental Ltd. Contract number and period covered P226; March 2018 April 2018 Sponsor s name and location Fiona Henderson; Affric Limited Report classification and caveats in use [Status] Date written April 2018 Pagination Cover + i + 25 References 20 Report title Underwater noise propagation modelling at Port of Cromarty Firth, Invergordon, Scotland Translation/Conference details (if translation, give foreign title/if part of a conference, give conference particulars) Title classification Unclassified Author(s) Sam East Descriptors/keywords Abstract Abstract classification Unclassified; Unlimited distribution Subacoustech Environmental Ltd. 25