4. MODELLING RESULTS
4.6. Modelling of behavioural effect in marine mammals using
Two criteria have been identified for assessing the behavioural effect in marine mammals in Sections 3.2.1 and 3.2.2, both using the level from a single strike in terms of un-weighted SEL. The two criteria are:
HR3-TR-044 v2 26 / 36
150 dB re 1 µPa2s single strike unweighted SEL for behavioural effect in harbour porpoise and pinnipeds, and
145 dB re 1 µPa2s single strike unweighted SEL for minor behavioural effect in harbour porpoise and pinnipeds.
The results of modelling a 10 m pile being installed with a maximum blow energy of 3000 kJ at Horns Rev 3 using these criteria are summarised in Table 4.6 and presented as contour plots in Figure 4.8 and Figure 4.9.
Table 4.6 Predicted impact ranges for behavioural effect using unweighted SELs for marine mammals Behavioural Effect Harbour Porpoise and
Pinniped
(150 dB re 1 µPa2s)
Harbour Porpoise and Pinniped
(145 dB re 1 µPa2s) North
East
Maximum 21.5 km 28.8 km
Minimum 16.7 km 20.3 km
Mean 19.0 km 24.4 km
South Maximum 18.4 km 24.5 km
Minimum 12.3 km 15.5 km
Mean 15.7 km 20.5 km
Figure 4.8 Contour plot showing the estimated impact ranges for the identified unweighted SEL behavioural effect criteria for marine mammals from installing a 10 m diameter pile using a maximum blow energy of 3000 kJ at the North East modelling loca-tion.
Figure 4.9 Contour plot showing the estimated impact ranges for the identified unweighted SEL behavioural effect criteria for marine mammals from installing a 10 m diameter pile using a maximum blow energy of 3000 kJ at the South modelling location.
HR3-TR-044 v2 27 / 36 4.7. Modelling of behavioural effect using the dBht(Species)
Table 4.7and Table 4.8 present summaries of impact ranges out to which a strong behav-ioural avoidance is expected to occur (90 dBht). The tables show that the largest 90 dBht
impact ranges are expected out to a maximum of 24 km for herring and cod from the North East modelling location, with smaller impact ranges predicted for the other species.
These results are summarised in Table 4.7 and Table 4.8 below, and illustrated as con-tour plots in Figure 4.10 to Figure 4.14. It should be noted that ranges for the sand lance/sandeel are very small and have therefore not be shown as figures. Additionally the modelling was undertaken assuming the maximum blow energy will be used, whereas in practice the piling is unlikely to reach this maximum or only for a short period of time.
Table 4.7 Summary of the mean ranges from the North East location out to 90 dBht where a behavioural reaction could occur in individuals from impact piling of a 10 m diameter pile using a blow energy of 3000 kJ.
North East Range to 90 dBht(Species) (km)
Max Min Mean
Cod 23.7 17.4 20.3
Dab 6.9 6.5 6.8
Herring 24.7 17.7 20.5
Sand Lance 0.5 0.4 0.5
Harbour Porpoise 15.5 13.4 14.5
Harbour Seal 10.6 9.2 10.1
Table 4.8 Summary of the mean ranges from the south location out to 90 dBht where a behavioural reaction could occur in individuals from impact piling of a 10 m diameter pile using a blow energy of 3000 kJ South Range to 90 dBht(Species) (km)
Max Min Mean
Cod 17.6 11.4 14.8
Dab 5.1 4.7 4.9
Herring 18.8 12.2 15.8
Sand Lance 0.4 0.3 0.3
Harbour Porpoise 13.3 10.5 12.1
Harbour Seal 8.8 7.8 8.2
HR3-TR-044 v2 28 / 36 Figure 4.10 Contour plot showing the estimated levels of noise in terms of dBht for cod from installing a 10 m
diameter pile using a maximum blow energy of 3000 kJ at the North East (left) and South (right) modelling location.
Figure 4.11 Contour plot showing the estimated levels of noise in terms of dBht for dab from installing a 10 m diameter pile using a maximum blow energy of 3000 kJ at the North East (left) and South (right) modelling location.
HR3-TR-044 v2 29 / 36 Figure 4.12 Contour plot showing the estimated levels of noise in terms of dBht for herring from installing a 10 m
diameter pile using a maximum blow energy of 3000 kJ at the North East (left) and South (right) modelling location.
Figure 4.13 Contour plot showing the estimated levels of noise in terms of dBht for harbour porpoise from in-stalling a 10 m diameter pile using a maximum blow energy of 3000 kJ at the North East (left) and South (right) modelling location.
HR3-TR-044 v2 30 / 36 Figure 4.14 Contour plot showing the estimated levels of noise in terms of dBht for har-bour seal from installing a 10 m diameter pile using a maximum blow energy of 3000 kJ at the North East (left) and South (right) modelling location.
Harbour porpoise – mother and calf © Caroline Höschle
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5. SUMMARY AND CONCLUSION
Subacoustech Environmental has undertaken a study on behalf of Orbicon A/S to assess the impact of underwater piling in the North Sea in relation to the proposed construction of offshore wind turbine foundations as part of the Horns Rev 3 project.
The level of underwater noise from the installation of 10 m diameter piles with a maximum hammer blow energy of 3000 kJ has been estimated by using a proprietary underwater sound propagation model that enables the behaviour of noise with range from the piling to be estimated for varying tidal conditions, water depths and piling locations based on an existing database of measurements of piling noise.
Estimates of underwater noise in terms of sound exposure level and sound pressure level have been made to indicate the range at which each restriction might occur without miti-gation. The range to which noise levels will propagate underwater in the vicinity of the piling at the Horns Rev 3 site have been calculated based on a variety of criteria.
1. Risk of lethal and physical injury, i.e. trauma to internal organs in excess of hear-ing damage, is calculated at ranges of less than 10 metres and less than 100 me-tres, respectively, for any species.
2. A noise exposure leading to a permanent threshold shift (hearing damage) in pinnipeds over the whole piling period, using the 186 dB SEL re 1 µPa2s (Mpw) criterion could occur where an animal is present between 700 m and 2.1 km from the pile at the start of the piling operation, depending on animal and piling loca-tion. This increases to between 5.3 km and 10.4 km for harbour porpoises, based on a criterion of 180 dB SEL.
3. An instantaneous temporary threshold shift (i.e. a short-term reduction in hearing sensitivity) in pinnipeds could occur at between 1.3 km and 2.0 km from the pile, depending on the piling and animal location, based on the 171 dB SEL criteria noted in Southall et al (2007). For harbour porpoises, the distance is 4.9 km to 6.2 km based on 165 dB SEL as noted in Tougaard (2013).
4. The range where injury could occur for fish is calculated using interim criteria proposed by the FHWG in the USA. Based on the 206 dB dB re 1 µPa SPLpeak criterion, injury to fish could occur at distances up to 250 m. Using the 187 dB re 1 µPa2s SEL criterion, and assuming the fish do not flee, the fish would receive the noise exposure within a distance of 9.5 km to 14.6 km from the piling, de-pending on the piling and the fish location. For small fish, under 2 grams, this range extends to 19.4 km at its maximum.
5. The range at which a behavioural effect could occur has been calculated for ma-rine mammals using the 150 dB re 1 µPa2s SEL noted in Brandt et al (2011). This is calculated to occur 12.3 km to 21.5 km from the piling depending on piling and animal location. A minor behavioural effect could occur at up to 28.8 km from the piling, based on 145 dB re 1 µPa2s SEL from the same document.
6. Behavioural response has also been assessed using the dBht(Species). Using this metric, which is based on the specific hearing capabilities of the species un-der consiun-deration, strong avoidance behaviour (90 dBht) in harbour porpoise is expected to occur out to a maximum range of 15.5 km from the piling. A strong
HR3-TR-044 v2 32 / 36 behavioural avoidance is expected out to a maximum range of 10.6 km for har-bour seal.
7. Considering the behavioural response of fish using the dBht(Species) metric, the greatest response is expected from herring, a fish that is particularly sensitive to sound, with a strong avoidance behaviour expected between 12.2 and 24.7 km from the piling. The maximum equivalent range for cod is 23.7 km. Dab, the most sensitive flatfish, could exhibit a strong aversive reaction out to 6.9 km. The sandeel, using the sand lance as a surrogate species, is modelled to show this reaction at distances less than 500 metres.
These ranges are the greatest expected during piling and are only expected when the piling is undertaken at the maximum blow energy. This is not generally a common occur-rence, with a pile typically being driven at much lower blow energies for the majority of time.
Harbour seal inside the Horns Rev 1 Offshore Wind Farm © Graeme Pegram
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