5.2.1. Noise Impact during the Construction Phase

During the construction phase, the main source of noise is associated with the vessels that will install the wind turbines and their anchoring systems and lay the cable. The underwater noise emission is proportional to the speed of the vessels, which, due to the nature of the work to be carried out, will generally be low (between 3 and 5 knots).

Other sources of noise identified in this phase are the use of acoustic devices for positioning during cable laying or anchor installation (echo sounders, sonars, acoustic positioning systems), the use of pumping equipment and the pressurized water jetting system (jetting), displacement along the bottom, sliding (dragging), and finally machinery on board for lifting and lowering equipment.

One of the main differences between the projected wind farm (with floating foundations) and most wind farms in the world (which have fixed foundations) is that in this case no pile driving activities are carried out for the execution of foundations. Pile hammering is the main source of underwater noise impact identified by the scientific community in association with offshore wind farms, having been analyzed in a large number of studies that show its impact on certain marine species, particularly cetaceans. Consequently, this important impact does not happen in a project such as Parc Tramuntana, as no impulsive, high-energy noise will be generated during construction.

Thus, the noise that may be generated during the construction phase does not differ much from noise associated with other types of maritime works, associated with low frequencies (e.g., navigation), and is of a temporary nature.

According to the consulted literature, the noise generated by cable-laying ships in shallow waters is of the order of 164–188 dB re 1 μPa, at 1 m from the source, acting at frequencies between 0.7 and 50 kHz: surface ship 180 dB (CEDA, 2011) [18], 164–170 dB (Nexans Skagerrak). In relation to underwater activities, a reference of burial works at 1 m from the source is available, with emissions up to 188.5 dB (at 11 kHz) [19] or 174 dB [20]. It should also be noted that modern newly built vessels reduce acoustic emissions and vibrations from engine operation very significantly.

The effects of the construction phase on this variable are considered significant, although the existing risk of direct effects is limited to the presence of wildlife in the vicinity of the noise source, noting that the negative effects would be temporary and that noise generation would be progressive, with a chasing effect that avoids further damage to the animals. The assessment of this impact in the installation phase is therefore moderate (Table 4):


**Table 4.** Assessment of the impact on submarine noise during the construction phase.

As the main corrective measure, the use of modern workboats with low noise emission certifications (e.g., Silent-E) is proposed [21].

#### 5.2.2. Noise Impact during the Operation Phase

During the operation phase of the wind farm, the main source of underwater noise generation will be the wind turbines themselves, which will produce continuous noise due to the movement of the blades, transmitted mainly through vibrations along the floating platform and the bottom-anchoring chains, and to a much lesser extent directly through the water surface, since the change in medium (air/water) produces a significant attenuation of atmospheric sound.

There will also be transient noise related to the movement of the anchor chains on the bottom due to the movement of the floating turbines.

In addition to the noise from the wind turbines, there will be noise from the vessels responsible for maintenance/repair tasks, similar in nature to that expected during the construction phase. The impact of these vessels will have a limited frequency (20 days/year), similar to those currently caused by marine and fishing traffic.

In order to characterize the impact of underwater noise produced by the turbines, the existing literature on the subject was analyzed, coming from the scarce experiences in other floating offshore wind farms, specifically the studies and measurements of underwater noise in the Hywind Tampen wind farm [22], the first floating technology wind farm installed off the coast of Norway, in the North Sea.

In this wind farm, the noise recorded during operation was characterized as continuous and low frequency (25, 50, and 125 Hz). The results did not exceed in any case an SPL of 160 dB re 1μPa (reference level adopted as a threshold to determine the limit of the cetacean disturbance zone, according to *MAGRAMA* recommendations [17]), and the isophone range of 120 dB re 1 μPa, assimilable to the background noise recorded at the Hywind Tampen wind farm site), occurs, according to the developed acoustic modeling on the basis of measurements, at circa 2 km from the wind turbines, with a maximum noise footprint of approximately 40 km2.

Similar experiences in the environmental monitoring phase of a fixed foundation (jackets) wind farm operating at a depth of 25 m off New York Bay, the Block Island Wind Farm [23], show maximum noise values generated during operation of up to 120 dB re 1 μPa at a distance of 50 m from the turbines, at a site with a background noise of 110 dB re 1 μPa.

These levels are considered an approximation to the underwater acoustic footprint that may be produced by Parc Tramuntana, whose increase in the acoustic scenario around the wind turbines will be cumulative depending on the number of wind turbines and the environmental conditions of the surroundings. It is estimated that this acoustic increase will be attenuated to the background noise levels existing at a distance of approximately 2 km or less (since in the case of Tramuntana the background noise is more intense than that existing in the other reference wind farms analyzed).

The expected RMS levels from this distance (around 120 dB re 1 uPa) are significantly lower than the background noise and the thresholds that would cause annoyance to the most sensitive species identified (dolphins and sea turtles), which are not highly abundant in the wind farm site area.

After this analysis, the effects of the operation phase on this variable are considered significant, of partial extension (affecting the area near the wind farm's footprint), and of medium magnitude due to the acoustic levels generated. The risk of direct effects is limited to the presence of fauna in the vicinity of the noise source, which is irregular and periodically distributed. The assessment of this impact during the operation phase is shown in Table 5:


**Table 5.** Assessment of the impact on submarine noise during the operation phase.

The applicable measures are the monitoring of acoustic levels and the recording of cetacean activity in the area, through visual censuses and the installation of hydrophones, to verify the levels and activity of potentially affected fauna.

#### *5.3. Analysis of the Project's Impact on Electromagnetic Fields (EMF)*

This potential impact is only likely to occur during the operation phase, as it is associated with the transmission of electricity generated by the wind farm through the submarine cables.

The interconnection cables (inter-array) installed in the offshore wind farm and the export cables will operate in alternating current at 66 kV–50 Hz. An analysis of the EMF generated by these cables was carried out using numerical modeling based on the *Biot– Savart* analytical calculation for the different cable segments (both the dynamic inter-array cables, which connect the turbines to each other, and the buried export cables, which connect the wind farm to shore). This model adopted a conservative calculation, considering the most unfavorable possible scenario (cable operation at full load), and without considering the shielding effects due to the cable protection armor.

This simulation of EMF levels (see Figure 6) obtains magnetic field levels (B) for the maximum inter-array cables at the surface of the conductors of 90 μT and, for the evacuation cable, a maximum level of 5 μT on the seabed.

**Figure 6.** EMC modeling for the inter-array (**a**) and export (**b**) cables.

The electric field (E) induced by the 66 kV conductors will be zero on the outside of the cables, since it is blocked by the metallic screen of the cable itself.

The potential effects of EMF on aquatic fauna include the possible disorientation of migratory species that use the terrestrial magnetic field for orientation during navigation, behavioral alteration with attraction or repulsion effects (barrier effect), as well as potential physiological damage at the cellular level.

As a reference, it should be noted that normal values of the earth's geomagnetic field can range from 20 to 75 μT, depending on the geographical location.

In order to assess which of these effects could be relevant to the project, a large amount of literature was consulted to analyze the effects of EMF on different species (Table 6):


**Table 6.** Documented effects of EMF on marine species.

In relation to species sensitive to electric fields, elasmobranchs would be the most potentially affected group, whose ability to detect these fields is very sensitive, detecting levels of less than 0.5 V/m (5 nV/cm).

Among the species considered in the bibliography, the most important because of their potential presence and migratory habits are the loggerhead turtle (*Caretta caretta*), the bottlenose dolphin (*Tursiops truncatus*), devil fish (*Mobula mobular*), and the main protected species of elasmobranchs with a potential presence in the study area due to their conservation status: common thresher (*Alopias vulpinus*), basking shark (*Cetorhinus maximus*), tope shark (*Galeorhinus galeus*), bluntnose sixgill shark (*Hexanchus griseus*), shortfin mako shark (*Isurus oxyrinchus*), smooth-hound (*Mustelus* spp.), blue shark (*Prionace glauca*), and spiny dogfish (*Squalus acanthias*).

The maximum magnetic fields generated by the project are within the range of values detectable by marine fauna.

The field generated by the inter-array cables in the wind farm area (up to 90 μT) will be detectable by potentially present species of interest. Considering that the cables analyzed do not alter the electric field, significant effects on elasmobranchs are dismissed, although their behavior will be analyzed during the operation phase. This effect is localized in the closeness of the cables, as the magnetic field levels attenuate rapidly a few meters away.

The potential effects on fauna are considered locally limited; it should be noted that the cable's footprint in the sea bottom is approximately 10,000 m2, less than 1% of the wind farm's area, and barely perceptible (<5 μT) at short distances (<1 m). Due to the extent of these fields and the magnitude of EMF and derived effects, they are not considered to have a significant barrier effect on migratory species.

In the case of the fields associated with the export cables (<5 μT), these are of limited magnitude, close to the levels of natural electromagnetic disturbances that regularly happen (*Nyqvist* et al., 2020) [36], and are therefore expected to be barely perceptible by potentially affected fauna, as the cable is buried deep enough for the field to attenuate to levels that are practically imperceptible at the seabed surface.

It should be noted that in EMF monitoring surveys of buried electrical interconnections, levels of the order of nT are usually detected. Considering its continuous route to the coast, the species of interest potentially affected would be the loggerhead turtle, in the event of passing through to nest on nearby beaches, and the bottlenose dolphin, due to its local presence. However, due to the magnitude of the impact, as described above, the effect on these species is considered insignificant. These values can also be extrapolated to the subway cable line through the HDD.

On the other hand, it should be noted that it is foreseeable that in the operating phase the EMF generated will be lower than that modeled, considering the maximum regular operating loads contemplated and the additional shielding provided by the cable protection armor; according to the literature consulted, these levels would not be capable of causing physiological damage or significant changes in the behavior of the fauna present in the project area.

Anyway, the increase in EMF during the wind farm's operation phase was considered a significant effect, mainly in the wind farm's footprint area (where the inter-array cables are located). This impact is considered moderate, according to the following attribute classification (Table 7).


**Table 7.** Assessment of the impact of EMF on marine fauna.

Among the main mitigation measures, in addition to the design of the cables to reduce EMF through shielding and burial in the evacuation route, it is proposed to monitor EMF levels in the inter-array cables and in the evacuation route, as well as the monitoring of cetaceans, turtles, pelagic communities (including elasmobranchs), and benthic macrofauna.
