Vastavalt nimekirjale 30.05.2025 nr 6-3/25/2423-2
Soome meretuulepargialade asukohtade valiku
piiriülene keskkonnamõju strateegiline hindamine
Soome on piiriülese keskkonnamõju hindamise konventsiooni (Espoo konventsiooni)
keskkonnamõju strateegilise hindamise (edaspidi KSH) protokolli alusel Eestit teavitanud Soome
meretuulepargialade võimalike asukohtade valiku protsessist. Kirjale on lisatud Soome saadetud
ingliskeelne ülevaade planeeritava tegevuse KSH protsessist ja vastavatest konsultatsioonidest.
Lähtuvalt Soome määratud vastamistähtajast ootame hiljemalt 27.06.2025 põhjendatud arvamusi
selle kohta, kas Eesti peaks osalema Soome meretuulepargialade võimalike asukohtade valiku
protsessi piiriülese KSH menetluses. Juhul kui peate Eesti osalemist menetluses vajalikuks, on
oodatud ka põhjendatud arvamused selle kohta, milline oluline kahjulik piiriülene keskkonnamõju
võib Eestile kaasneda, et sellega saaks arvestada KSH materjalide koostamisel.
Lugupidamisega
(allkirjastatud digitaalselt)
Antti Tooming
elurikkuse ja keskkonnakaitse asekantsler
Lisa: ingliskeelne ülevaade KSH protsessist ja konsultatsioonidest
Lilli Tamm, 626 9133
[email protected]
Suur-Ameerika 1 / Tallinn 10122 / 626 2802/
[email protected] / www.kliimaministeerium.ee/
Registrikood 70001231
Strategic environmental
assessment of
authorities' plans and
programmes (SEA)
concerning potential
offshore wind farms in
the exclusive economic
zone
Provision of information on the initiation of
an SEA process and consultation on the
assessment plan
Contents
1 Introduction to the consultation process ........................................................................ 3
1.1 Background and purpose of the SEA procedure .............................................. 4
1.2 Course and objectives of the SEA procedure ................................................... 5
2 Object of the assessment .............................................................................................. 7
2.1 Content of the draft Government decision on offshore wind farm sites in
the exclusive economic zone ............................................................................ 7
2.2 Life cycle and general technical implementation methods of an offshore
wind power project .......................................................................................... 10
2.2.1 Project life cycle .............................................................................. 10
2.2.2 Common technical implementation methods.................................. 11
3 Basic premises and conduct of the impact assessment ............................................. 14
3.1 Examined implementation alternatives ........................................................... 15
3.2 Identified impact pathways of offshore wind farms ......................................... 17
3.2.1 Impact mechanisms and impact pathways ..................................... 17
3.2.2 Preliminary studies and planning .................................................... 18
3.2.3 Construction .................................................................................... 19
3.2.4 Production and maintenance .......................................................... 20
3.2.5 Decommissioning ........................................................................... 22
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1 Introduction to the
consultation process
The environmental impacts of certain types of plans and programmes of the
authorities must be assessed pursuant to the Act on the Assessment of the
Effects of Certain Plans and Programmes on the Environment (200/2005, the so-
called SEA Act). This obligation also applies to the Government’s decision on
offshore wind farm sites in the exclusive economic zone, even if it is a decision
rather than a plan in the strict sense.
Before the decision is made, the environmental impacts of the draft decision must
be assessed in an SEA process. The Ministry of Economic Affairs and
Employment, which is preparing the decision, has commissioned an assessment
of the draft decision. The SEA assessment will be conducted in 2025 by Sweco
Finland Oy, whose expert team’s competence covers both offshore wind power
and sustainable use of seas in a broader sense, marine ecology, maritime sectors
and the SEA process. The Ministry of the Environment also has its
representatives in the steering group of the assessment.
Object of the assessment in brief
Pursuant to the Act on Offshore Wind Power in the Exclusive Economic Zone
(937/2024), the Government may make a decision that concerns reserving a site
located in Finland's exclusive economic zone for wind energy generation
(offshore wind farm site in the exclusive economic zone), competitive tendering
regarding the site, and the conditions for using the site. Finland's exclusive
economic zone is an international sea area that Finland can exploit for such
purposes as offshore wind power production. The Government will make its
decision on the Ministry of Economic Affairs and Employment's presentation. The
decision will designate one or more sites in Finland's exclusive economic zone
for offshore wind power production as well as specify the timeline for the
competitive tendering process concerning concessions to use the site(s) in
question. The tendering process will be organised by the Finnish Energy
Authority. The decision may additionally impose conditions on the use of the site.
In the SEA process, the assessment is limited to the offshore wind farm sites in
the exclusive economic zone and the transmission connections to land required
for energy generation set out in the draft decision as well as the geographical
area affected by their impacts. While the potential use of the produced energy on
land and its transmission in the mainland grid are not covered by the actual
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impact assessment, their essential aspects can be described as background for
it.
The Ministry of Economic Affairs and Employment submitted key information on
the draft decision to the party carrying out the SEA assessment on 31 March
2025.
Information provision and consultation as part of the SEA procedure
This assessment process will include two national and international consultation
rounds as provided in the Convention on Environmental Impact Assessment in a
Transboundary Context ('Espoo Convention´). The first phase includes a
consultation on the planning of the environmental assessment and preparation of
the environmental report. In the second phase, which is expected to take place
in autumn 2025, a consultation on the actual environmental report will be
organised.
The documents of the present first consultation round describe the conduct of the
assessment and the main features of the issues to be addressed in it. The
statements received in consultations required under the Act on the Assessment
of the Effects of Certain Plans and Programmes on the Environment will be
archived and published in due course as an appendix to the final environmental
report and in summary form (Appendix 1 to the actual environmental report). The
summary will also comment on changes made on the basis of the statements.
1.1 Background and purpose of the SEA
procedure
The objective of the SEA is to carry out an environmental impact assessment
compliant with the SEA Act to support the Government in making its decision on
the offshore wind farm sites in the exclusive economic zone. This is a strategic
environmental impact assessment of plans and programmes ('SEA assessment')
carried out to support the preparation of the public administration's plans and
programmes.
The assessment includes:
1. Identification and assessment of the likely significant environmental
impacts of offshore wind farm sites in the exclusive economic zone
2. The monitoring plan referred to in section 12 of the SEA Act
3. The environmental report referred to in the SEA Act and Decree
4. National information provision and consultation referred to in the SEA Act
in different phases of the work
5. Processing of the statements and views received during the commenting
round and in other consultations as part of the environmental report.
The SEA assessment will support sustainable implementation of offshore wind
power generation by producing background material for private and public actors
in the sector. The assessment will identify framework conditions relating to the
environment and society within the limits of which offshore wind power projects
can be implemented and which can mitigate their harmful impacts and risks. The
commenting round and consultation will strengthen the social acceptance of
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offshore wind farms in the exclusive economic zone while providing basic
information and starting points for project-specific planning for actors in this
sector. The SEA process will support project actors’ ability to manage their risks
by defining the framework conditions for the activities, which will also increase
the attractiveness of wind farms as investments.
The purpose of the SEA assessment procedure and the resulting report is not to
comment on the approval of offshore wind power projects or on the feasibility of
individual wind turbine projects from a technical, economic or legal perspective.
Its aim is to assess the draft decision itself and to produce information on the
impacts of its implementation on the environment. A well-implemented SEA
assessment can boost the benefits or acceptability of plan implementation or
bring up the best ways of identifying and minimising negative impacts.
While the SEA procedure does not replace the statutory environmental impact
assessment procedure (EIA) and permit processes of an individual power plant
project, actors conducting EIA processes can draw on the documents and
statements of the public SEA procedure to improve the quality and acceptability
of their processes.
1.2 Course and objectives of the SEA
procedure
An SEA is an ex-ante assessment carried out before the framework conditions
for concrete projects have been defined; this is why it involves many
uncertainties. Its essential task is to pinpoint the most significant impacts by
putting them in perspective (and by modelling if necessary), to highlight
differences between implementation alternatives, and to identify ways to mitigate
significant impacts.
At the core of the process is gathering relevant existing data, analysing them from
the perspectives of the frame of reference and different stages of the offshore
wind farm project, and refining the results to serve the public administration,
companies and stakeholders alike. The available data determines how detailed
the results will be. Rather than carrying out field studies or producing significant
new data, the SEA is based on existing data and information gaps.
As provided in the SEA Act, the assessment includes describing the current state
and characteristics of the environment in the area under review and assessing
the impacts of the draft decision on, among other things, biodiversity, biota,
vegetation, water, soil, air and climate factors, population, human health, living
conditions and comfort, landscape, urban structure and built environment,
tangible property, cultural heritage, exploitation of natural resources and the
relationships between these factors.
It additionally examines the draft decision's relationship to other plans and
programmes.
The assessment process is carried out ensuring that it meets the requirements
of the Act and Decree (Government Decree 347/2005) on the Assessment of the
Effects of Certain Plans and Programmes on the Environment and relying on the
Guide on environmental assessment under the SEA Act (Paldanius 2017) as well
as the Guide on ecological surveys and ecological impact assessment (Mäkelä
& Salo 2023). The course of the SEA assessment (see Figure 1) is specified in
regulation and guidelines.
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Steps of the drafting Tasks of the environmental
process assessment
Planning of the environmental 1. Describing the state of the
assessment, provision of information and environment
consultation on the preparation of the plan
or programme and environmental report
2. Specifying the object of the
impact assessment and
alternatives
Environmental impact assessment in the 3. Identifying and analysing
preparation phase of the plan or impacts and assessing their
programme significance
4. Presenting information on the
impacts and comparing
alternatives
5. Making proposals concerning
Preparation of the environmental report the plan or programme and its
implementation and monitoring
Consultation on the draft plan or
programme and environmental report
Consideration of the results of the
environmental assessment and approval
of the plan or programme
Figure 1: Course of the SEA process and the content of the different steps. Adapted from the Guide
on environmental assessment under the SEA Act (Paldanius 2017).
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2 Object of the assessment
2.1 Content of the draft Government
decision on offshore wind farm sites in
the exclusive economic zone
The assessment concerns the draft Government decision on offshore wind farm
sites in the exclusive economic zone, even if it is a decision rather than a plan in
the strict sense. Pursuant to the Act on Offshore Wind Power in the Exclusive
Economic Zone (937/2024), the Government may make a decision that concerns
reserving a site located in Finland's exclusive economic zone for wind energy
generation (offshore wind farm site in the exclusive economic zone), competitive
tendering regarding the site, and the conditions for using the site. Finland's
exclusive economic zone is an international sea area that Finland can exploit for
such purposes as offshore wind power production. The Government will make
its decision on the Ministry of Economic Affairs and Employment's presentation.
The decision will designate one or more sites in Finland's exclusive economic
zone for offshore wind power production as well as specify the timeline for the
competitive tendering process concerning concessions to use the site(s) in
question. The tendering process will be organised by the Finnish Energy
Authority. The decision may additionally impose conditions on the use of the site.
At this stage, the draft decision firstly comprises the four proposed offshore wind
farm sites (see Figure 2), without yet commenting on the number that will actually
be put out to tender or the schedule of the tendering processes. Secondly, the
draft decision sets the following conditions:
• The efficiency of site use is 5MW/km2. This means that the wind power
project may ultimately take up a smaller area than the one tendered for
if this efficiency requirement is met.
• The site may be used to exploit wind energy. This also includes a
concession to use the site for secondary energy production (such as a
hydrogen plant) if the necessary permits are obtained.
• The term of the concession is approx. 30 years.
• If the wind farm to be built on the site is connected to the Finnish main
grid, the maximum capacity that can be connected to the main grid
connection point will be 1.3 gigawatts.
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The Government decision concerns the selection of areas as potential sites for
offshore wind farms. Project development by the wind power company, in which
the environmental impacts of the project will be assessed in much more detail in
the EIA process and the permits required for the construction of the wind farm
will be applied for, will only start once the tendering process for each site has
been completed.
Two of the four sites are located in the Bothnian Sea (West and East) and the
other two in the Bothnian Bay (South and North). The sites Bothnian Bay South
and North and Bothnian Sea East are delimited by the boundary of the Finnish
territorial waters; the site Bothnian Sea West is located close to the boundary
between the exclusive economic zones of Sweden and Finland.
The total surface area of these sites is 921 km 2. The surface areas of the sites
are:
• Bothnian Sea West: 211 km2
• Bothnian Sea East: 202 km2
• Bothnian Bay South: 284 km2
• Bothnian Bay North: 224 km2
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Figure 2: Locations of the sites designated in the draft decision to be assessed.
The responsibility for drafting the decision on offshore wind farm sites rests with
the Ministry of Economic Affairs and Employment, which submitted information
on the draft decision essential in terms of the SEA assessment to the actor
carrying out the assessment on 31 March 2025.
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2.2 Life cycle and general technical
implementation methods of an offshore
wind power project
Offshore wind power refers to wind power production in sea areas; wind power
production in land areas is correspondingly called onshore wind power. The
essential feature of offshore wind power is that the sites on which electricity is
produced are located far away from the majority of land-based end users. This is
particularly true for production sites in the exclusive economic zone far from the
coast.
In the context of the SEA assessment, offshore wind power refers to the complex
consisting of turbine units and the infrastructure they need on the production site
as well as transmission of electricity to the onshore grid. The production site
infrastructure includes internal cables and an offshore substation. Power
transmission to land comprises a connection cable leading from the offshore
substation to an onshore connection point. However, the Government decision
on site selection will not apply to cables, and transmission of electricity to land is
not mandatory.
The SEA assessment is based on the available information and current, widely
used solutions in the sector. The SEA assessment does not cover the
manufacture of offshore wind farm components and the origin of raw materials.
The assessment, comparison and selection of different technical solutions for
offshore wind farms are part of the project-specific planning and environmental
impact assessment (EIA) procedure as well as the project’s permit processes.
2.2.1 Project life cycle
The life cycle of an offshore wind farm project covered by the SEA assessment
consists of four phases (see Figure 3). The emissions and waste generated
during the presented life cycle are covered by this assessment. As a stage, the
SEA itself is not included in the presented life cycle and comes before the
preliminary studies and planning of the project.
The preliminary study and planning phase covers surveys and scientific
studies on the site, planning of the farm and electricity grid, and selection of
technical solutions. This phase includes the EIA and permit procedures.
After the studies and planning and once the EIA and permit procedures have
been completed, an offshore wind farm and its infrastructure can be built.
Construction includes seabed intervention, installations at sea, cable laying, soil
disposal, sea and land transport; and also port operations, including intermediate
storage and pre-assembly. The construction activities will depend on the selected
technology and the number of sites to be built.
Once the construction work has been completed, the production and
maintenance phase of the project will begin. This is the phase with the longest
duration. It includes monitoring, servicing and maintaining the turbines and
submarine cables as well as the transport of crews and spare parts needed for
these activities. This phase also involves possible environmental monitoring
obligations and follow-up studies.
The current service life of an offshore wind turbine is approximately 30 years,
after which it will be decommissioned. The decommissioning phase includes
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transport and demolition work on the farm site and activities associated with them
in ports. This phase also comprises any environmental restoration work, recycling
of materials and waste management. This SEA assessment assumes that the
structures will be dismantled above and below water level at the end of the
project, at least to the depth required for maritime safety. In addition, the phase
includes any post-demolition environmental monitoring studies.
Figure 3: The phases and life cycle of an offshore wind power project from
planning to decommissioning.
2.2.2 Common technical implementation methods
Structure and size of the wind turbine
The technical implementation includes deciding on the size of the wind turbine.
In this context, the size refers to the total height of the turbine unit, including the
tower and the rotor with its blades. In other words, the total height is measured to
the tip of the rotor blade when it is pointing upwards. The axis of the wind turbine
can be either horizontal or vertical; in most cases, the axis is horizontal.
The size of the wind turbine affects its power generation capacity: larger turbines
produce more electricity than smaller ones. Fewer larger turbines are needed to
achieve the same production capacity. The size of the wind turbine also affects
its environmental impacts. For example, as larger wind turbines are higher, the
landscape impact and bird collision risks they create are greater, whereas more
seabed foundations need to be built if a larger number of smaller turbines is
decided on. The size of the wind turbines also affects their proximity to each
other: larger wind turbines require more space around them than smaller ones.
In the implementation alternatives of the EIA programmes for projects planned in
Finland, the power plants vary from 15 MW to 30 MW in capacity, and from 260
to 400 metres in total height. In the plan under review, the maximum and
minimum total output have been defined, rather than the capacity or other
technical characteristics of an individual wind turbine.
Foundations and placement
There are various technical solutions for building wind turbines, and the essential
differences in the case of offshore wind turbines concern the implementation of
their foundations. The selection of foundation technology is influenced by the
characteristics of the production site to be set up, including seabed quality and
water depth. The placement of wind turbine units can be decided taking local
environmental and natural conditions into account. Deciding on their placement
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and foundation type will be part of the mitigation measures associated with
individual wind turbines.
The environmental impact assessment programmes for offshore wind power
projects published in Finland (EIA programmes for offshore wind power projects
in the economic zone) and the Swedish Environmental Protection Agency's
compilation report (Bergström et al. 2021) discuss foundation solutions for
offshore wind turbines. They can be roughly divided into seabed foundations and
floating solutions.
Seabed foundations include piled, gravity-based and tripod foundations, the most
common type of which is the piled foundation. While the different foundation
solutions have their limitations regarding seabed quality and depth, what they all
have in common is that the structures are anchored to the seabed.
Floating foundations, which are mainly anchored to the seabed using cables,
have also been developed for wind turbines. As their name suggests, the power
plants float on the surface of the sea. Power plants with floating foundations can
be placed in deeper water areas that those with foundations on the seabed, and
the depth on the site must be at least 60 metres. However, floating power plants
are a relatively new technological solution, and their feasibility has its own
problems. In the Gulf of Bothnia the ice creates specific difficult conditions, and
in their current development phase, using floating power plants in challenging ice
conditions presents problems.
Electricity transmission solutions and their placement
Offshore wind farms essentially include wind turbines located on the production
site at sea, cables within the production site, offshore substations and possible
transmission cables from the production site to onshore electricity infrastructure.
Each offshore wind farm needs an offshore substation for electricity transmission
purposes. Cables connect each turbine on the production site to the offshore
substation. The substation consists either of a switchgear that assembles cables
of equal voltage from different turbines and feeds the power downstream, or a
transformer substation where transformers are used to convert the generated
electricity into the form in which it can be transmitted to the mainland. The
required voltage depends on the selected cable technology; this determines the
voltage that the transformers will produce and whether the electricity will be
transmitted as DC or AC.
From the substation, the submarine cable transfers electricity along the bottom
to an onshore substation. The transmission cables are laid along a prepared
cable route on the seabed. On soft bottoms, it is also common to immerse the
cables in the bottom sediment, for example by ploughing, and to protect them in
shallower sections of the transmission route using such materials as rocks or
concrete where the cable meets the land (Niras Consulting ltd. 2015). The cable-
laying technique to be used depends on the topography and quality of the bottom.
Each production site needs at least one transmission cable to feed the energy
downstream unless it is, for example, converted into hydrogen on the production
site in the future. If several cables are used for electricity transmission at sea, the
area affected by seabed interventions in connection with cable laying will grow.
When planning cable routes, the bottom quality and water depth as well as the
ecological values and conservation status of the area must be taken into
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consideration. While ecological values can be considered in the alignment of the
route, as a rule it must be as straight as possible. Due to technical challenges
and environmental impacts, the aim is to avoid uneven seabed and the need for
excavation. Other human activities in marine areas, including fishing and
shipping, must also be accounted for in cable placement. Similarly, existing
pipelines and cable routings with their safety distances must be taken into
account. Wrecks to be protected and possible war-time explosives must
additionally be considered in terms of cable routings. Consequently, cable
routings have certain framework conditions that determine the placement of
cables: the production site, electricity recipient, security of supply, other users of
the sea area, social needs and environmental conditions.
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3 Basic premises and conduct
of the impact assessment
This chapter discusses the environmental impacts of offshore wind farms and
their submarine cables as well as their assessment at a general level. In practice,
the impacts of the production site and an individual cable routing depend on their
precise locations and are assessed as part of the EIA and permit procedures.
The impacts of different functions and structures on the environment vary during
the project's life cycle. Construction-phase impacts are different from those
created during the operational or decommissioning stages. Traditionally, the
impact assessment examines the permanence (temporal duration and
reversibility), strength and direction of the changes caused by the activities
(negative/positive) (Mäkelä & Salo 2023). The same breakdown of projects into
different phases and the determination of impact types apply to different projects:
power transmission cables and biogas plants, wind turbines, roads or onshore
power lines alike.
Three alternative scenarios, or theoretical possibilities of implementing the plan,
are specified and used as an assessment tool. As defined in the SEA Act, these
scenarios are called implementation alternatives. One of them is the so-called 0
alternative, meaning that the plan does not go ahead at all. The other two
alternative scenarios are based on the theoretical maximum implementation on
all sites in accordance with the given framework conditions and a possible partial
implementation scenario. The scenarios do not comment on the feasibility,
likelihood or implementation schedule of any of the alternatives.
According to guidelines issued by the Finnish Environment Institute and the
Ministry of the Environment (Mäkelä & Salo 2023), the impacts of anthropogenic
activities on the environment may, for instance, be of the following types:
• negative or positive
• direct or indirect (secondary)
• cumulative
• permanent or temporary
• reversible or irreversible
• impacts manifesting over the short, medium and/or long term
• combined impacts.
When analysing the object of the impact, the sensitivity of the object is significant.
It is determined on the basis of the following factors:
• the object’s ability to withstand negative changes (tolerance)
• the object’s ability to recover from changes (resilience)
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• the object's importance, for example from the socio-economic or
environmental perspective
Assessing the significance of the impact, which consists of the magnitude of the
change and the sensitivity of the object, is also essential when assessing
environmental impacts. In case of the marine environment, for example, certain
species are more sensitive to change than others, the variety of small details or
rare quality of certain habitats may make them more difficult to replace, and the
presence of a certain natural resource may mean that an area is of national
importance for some industry. The completed assessment report also describes
the way in which the significance of an individual impact or object is determined.
This SEA assessment takes into account other plans, including offshore wind
power projects in territorial waters. In offshore wind farm projects, the assessment
of combined impacts also plays an important role due to the large size of the
projects and the high total number of offshore wind power projects planned for
the Gulf of Bothnia.
3.1 Examined implementation alternatives
The SEA assessment examines three implementation alternatives, based on
which the assessment looks at alternative scenarios, seeking to identify
significant impacts of the plan. While different scenarios are called
implementation alternatives in the wording of the Act, at SEA level, the
assessment in practice means analysing scenarios rather than evaluating
feasibility.
By law, one of them is the so-called zero alternative, in which the plan or
programme (in this case the draft decision) will not implemented or introduced at
all. In this assessment, the zero alternative would mean that the sites would not
be put out to tender or investments would not go ahead.
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No offshore wind farms in the exclusive
economic zone scenario
VE0 VE0, or the zero alternative of the
environmental assessment, refers to a
situation where no offshore wind farm
investments will be made.
Partial implementation scenario
VE1 describes a situation in which offshore
VE1 wind power projects are implemented on two
out of the four designated sites, or Bothnian
Bay North and Bothnian Sea West.
Maximum impact scenario
VE2 VE2 describes a situation in which offshore
wind projects go ahead on each designated
site.
Figure 4: SEA assessment scenarios and their three implementation alternatives (VE).
The partial implementation scenario (VE1) includes two of the four sites to be
assessed, or Bothnian Bay North and Bothnian Sea West (see Figure 5). In this
scenario, the sites were selected with the aim of assessing impacts and impact
pathways that are as different as possible. The sites selected for the scenario
differ from each other significantly in two ways: they are geographically far from
each other in the north-south direction, and at different distances from the coast.
Selecting sites that are geographically distant from each other for consideration
highlights differences between the characteristics of the different sea areas. The
sites' different distances from the coast bring up different impacts on the coast.
In addition, a greater distance from the coast requires longer cable runs and
consequently increases the impacts.
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Figure 5: Sites to be assessed in the different scenarios. The partial implementation scenario (VE1)
covers two out of the four sites, or Bothnian Bay North and Bothnian Sea West. The maximum impact
scenario covers all four areas.
3.2 Identified impact pathways of offshore
wind farms
3.2.1 Impact mechanisms and impact pathways
An impact refers to a change in the current state of the environment, which can
be positive or negative. In order for the impact to be assessed, sufficient
information must be obtained about the current state of the environment, the
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source of the impact, the impact mechanism, the object, and sensitivity of the
object.
The SEA procedure is an ex-ante assessment based on existing environmental
data in which the impacts are catalogued and assessed in general terms. The
more detailed impacts of each offshore wind power project will be investigated
later.
The impacts and impact pathways of offshore wind farms vary depending on the
location of the production site and the project's life cycle stage. Among other
things, the location of the production site determines which objects affected by
the impacts there are in the impact area of the wind farm: the ecological values
of the site and its location in relation to these values and other plans will enhance
or mitigate the significance of the impact pathways.
The impact pathways of an offshore wind power project also vary during its life
cycle: in the construction phase the pathways are different from those in the
operational or decommissioning phases (see EIA programmes for offshore wind
power projects in the exclusive economic zone). The intensity of the impacts also
varies during the project life cycle: for example, the noise impacts are greater in
the construction phase but of shorter duration than during the operational phase.
The impacts of each implementation alternative are described in more detail in
the environmental report. The environmental report also deals with mitigating
impacts.
3.2.2 Preliminary studies and planning
The impact pathways of the preliminary study and planning phase in the area
under review arise from surveys and studies carried out on the production site
and along cable routings. Some of them may comprise desktop studies based on
existing data that have already been collected. However, offshore wind power
projects require field studies and sampling on the project site to determine
environmental impacts and to support the wind farm's technical planning.
Field studies mean more marine traffic in the area under review as it is depth
sounded, its environment is surveyed, and the characteristics of the seabed are
examined. Seabed surveys also interfere with the seabed as samples are
collected and drilling required for foundation design takes place. Samples are
additionally collected from the seabed to determine concentrations of harmful
substances in the sediment (incl. heavy metals), making it possible to select
disposal sites for the construction phase based on sediment quality.
The decisions and solutions made in this work phase will indirectly affect all other
life cycle stages.
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Preliminary studies Construction Production and Decommissioning
and planning maintenance
While the impacts of this phase itself are mild, decisions made during it will affect
the environmental impacts of all other life cycle stages.
Key impact pathways identified for the phase:
• Disturbance caused by maritime traffic and surveys
• Organisms move away or suffer from stress.
• Birds, fish, marine mammals, invertebrates in underwater
habitats
• Interference with the seabed when collecting samples and conducting
studies
• Highly localised destruction of benthic fauna and seabed habitat
3.2.3 Construction
Construction period impacts are relatively short-lived but also intensive. Wind
turbine construction and cable laying require significant volumes of marine traffic
and seabed intervention. The construction phase produces the first permanent
environmental changes of the project.
The seabed on the production site is prepared for building the foundations; the
extent of this disturbance depends on the seabed quality and the chosen
foundation technique. To construct the foundations, sediment may be removed
by dredging, in which case the dredged sediment will be transported to disposal
sites identified in the preliminary studies. Cable laying involves immersing the
cable in soft sediments, whereas on hard bottoms separate protection methods
of the cables may be necessary. On hard sediments, blasting may also be
needed when building the foundations, and the same applies to cable laying if
the bottom is uneven.
Depending on the selected solution, foundation construction involves piling,
anchoring and casting as well as transport of foundation elements. Foundations
that require piling or blasting cause short-term loud noise. During and after the
construction of power plant foundations, noise and movement caused by
construction and marine traffic will create disturbance. Increased marine traffic
during the construction phase combined with localised temporary loss of benthos
at the foundations may expose the offshore wind farm site to the spread of
invasive species; no research evidence is available on this issue, however.
(Bergström et al. 2021)
The construction-phase environmental impacts consequently stem from physical
interventions in the seabed and disturbance caused by other construction work.
Seabed intervention also causes the sediment to mix with the water column,
which may result in the dissolution of contaminants in the sediment into the water
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and the release of nutrients into the water column for a short time. Benthic
habitats at the foundations are destroyed. In terms of soil disposal and cable
laying, impacts on the seabed in the construction phase are temporary.
The greatest sources of impact during the construction phase consequently are
the construction of foundations and cable-laying, in connection of which the
seabed is disturbed.
Preliminary studies Construction Production and Decommissioning
and planning maintenance
The impacts of this phase are powerful but short lived.
Key impact pathways identified for the phase:
• Disturbance caused by marine traffic, construction of wind turbines and
cable laying:
• Organisms move away or suffer from stress.
• Birds, bats, fish, marine mammals, invertebrates in
underwater habitats
• Hearing damage caused by construction noise
• Birds, fish, marine mammals
• Potential spread of alien species
• Seabed interventions during construction of foundations and cable laying
• Localised destruction of benthic habitat
• Mixing of sediment nutrients with the water column
• Deterioration of water quality
• Dissolution of sediment contaminants in the water column
• Deterioration of water quality, accumulation of harmful
substances in biota
3.2.4 Production and maintenance
Compared to the construction phase, the impacts during the production and
maintenance phase are spread over a longer period but their intensity is lower.
The noise impact is an example of the difference in the duration and intensity of
the impacts between the construction phase and the production phase: blasting
noise during the construction phase is short and intensive, while the vibrations
and humming of an operating wind turbine are less severe but long-term. As part
of production and maintenance, power plants are serviced. In case of faults, it
may also be necessary to repair power plants and cables, in which case spare
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parts are transported to the site requiring maintenance. In the event of a cable
failure, the cable must be lifted from the seabed and repaired on a surface vessel.
Marine traffic and repairs cause disturbance to the fauna in the area, and bottom
sediment interventions may be necessary in connection with repairs, causing
temporary disturbance to the benthic habitats and mixing sediment with the water
column.
In the production phase, wind turbines generate constant noise, especially below
the water level. Noise affects different organisms differently. In fish, for example,
the impact depends on the species: some species are driven away by the wind
turbine's noise and vibration, while others are attracted to the foundations of
offshore wind farms in open water areas. It should be noted that waves also
cause continuous natural underwater noise.
While there is no marine traffic on the offshore wind power production site under
normal conditions, in an emergency ships may navigate between wind turbines.
Offshore wind farms prevent trawling on the production site and also bottom
trawling along cable routes. In practice, the production site provides an area for
fish and benthic animals where they are protected from trawling. As bottom
trawling is discontinued, this may reduce the mixing of sediment with the water
column on the production site.
Hard underwater structures of wind turbines and protective structures for cables
may also create new habitats for species of hard bottoms; this is called the
artificial reef effect (Bergström et al. 2021 & Vehanen et al. 2010). The strength
of the reef effect is influenced by such factors as the diversity and scale of the
structures (Vehanen et al. 2010).
Wind turbine structures also affect currents and sea state, which in turn may have
an impact on biota. Currents have a direct impact on microalgae, which in turn
affect other organisms both directly and indirectly as part of the food web.
While there is no noise from operational cables, a magnetic field is created
around them which may affect magnetosensitive fish species, including migrating
eels and benthos close to the cable. Studies show that eel migrations are not
prevented but may be slowed down (Niras Consulting ltd 2015). Any sediment
covering the cables weakens the magnetic field and its extent in the water
column. While the service life of the cable is around 40 years, the risk of
disruptions and repairs increases after approx. 10 years of use. In other words,
seabed interventions after the construction phase are a special case (Niras
Consulting ltd 2015). The impact of the installation depends on the habitats and
organisms of the installation site and seabed characteristics.
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Preliminary Construction Production Decommission
studies and and ing
planning maintenance
While the impacts of this phase are long-lasting, they are weaker than in the
construction phase.
Key impact pathways identified for the phase:
• Operation and maintenance of wind turbines:
• Wind turbine flicker and noise
• Disturb birds, bats and fish; the impact is species specific
• Bird collisions with blades
• New hard bottom habitat
• Disturbance caused by maintenance
• Organisms move away or suffer from stress
• Intensity and objects depend on the measure
• Electromagnetic field created by cables
• Slowing down of fish migrations
• Magnetosensitive benthic animals are driven away or decline
• Impacts of power plant structures on other anthropogenic activities
• Prevention of fishing
• Protection zone for fish
• Barrier to navigation
• Reduction of noise from shipping
• Interference caused by wind turbine structures hampers radar use
3.2.5 Decommissioning
When the power plant ceases to operate, its structures will be demolished,
making it possible to take the production site into other uses and giving ecological
values a possibility to recover. At minimum, the wind turbine structures above sea
level are dismantled, and underwater structures are removed sufficiently to make
the area available for navigation. Concrete obligations to dismantle offshore wind
turbines in Finland's exclusive economic zone have as yet not been laid down in
legislation, and no case-law on this matter exists in Finland.
Decommissioning causes disturbance to biota through dismantling operations
and increased marine traffic. Depending on the scale of the demolition measures,
for example if the wind turbine foundations are removed, the activities result in
interference with the seabed comparable to the construction phase. At this stage,
dredging and soil disposal are unlikely to be necessary.
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The dismantling of the foundations may have greater impacts on the environment
than leaving them at the bottom, as long as it is ensured that no harmful
substances dissolve in water from the foundation structures.
In addition to demolition, this life cycle stage also includes any restoration
measures aimed at promoting the recovery of ecological values in the impact
area of the wind park, as well as monitoring of the state of the environment.
Preliminary studies Construction Production and Decommissioning
and planning maintenance
The impacts of this phase are similar to the construction phase but weaker.
Key impact pathways identified for the phase:
• If structures are removed completely
• The hard bottom habitat created during the operational stage around
the foundations and protective structures of cables will be destroyed
and species will be lost.
• The noise from demolition work causes disturbance to biota,
especially underwater.
• When a cable is removed, sediment is mixed in the water column;
nutrients and contaminants in the sediment are dissolved in water.
• The environment recovers close to its original state
• If the structures are removed to a depth that enables navigation
• Disturbance caused by demolition work drives away animals,
especially birds and fish.
• The hard bottom habitat created around the foundations and
protection structures for cables is preserved.
• The environment does not recover to its original state.
• Bottom trawling will not be possible on the production site.
• After demolition, the disturbance caused by noise and flicker by the wind
turbines and the bird collision risk are eliminated.
• Electromagnetic fields generated by cables disappear.
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References
Bergström, L., Öhman, M., Berkström, C., Isæus, M., Kautsky, L., Koehler, B.,
Nyström Sandman, A., Ohlsson, H., Ottvall, R.,Schack, H. & Wahlberg, M. 2021
– Effekter av havsbaserad vindkraft på marint liv, En syntesrapport om
kunskapsläget 2021. Naturvårdsverket rapport 7049
Act on the Assessment of the Effects of Certain Plans and Programmes on the
Environment (200/2005, SEA Act)
Mäkelä, K. & Salo, P. 2023. Luontoselvitykset ja luontovaikutusten arviointi, Opas
tekijälle, tilaajalle ja viranomaiselle (Ecological Surveys and Ecological Impact
Assessment. A Guide for Surveyors, Customers and Authorities). Finnish
Environment Institute reports 43/2023.
Niras Consulting ltd. 2015. Subsea cable interactions with the marine
environment, Expert review and recommendations report. Renewables Grid
Initiative.
Paldanius, J. 2017. Guide on environmental assessment under the SEA Act
Environmental administration guidelines 2/2017.
EIA programmes for offshore wind energy projects in the exclusive economic
zone: Navakka, Wellamo, Vågskär, Bothnia
Government Decree on the Assessment of the Effects of Certain Plans and
Programmes on the Environment (347/2005, in Finnish)
Vehanen, T., Hario, M., Kunnasranta, M. & Auvinen H. Merituulivoiman
vaikutukset rannikon kaloihin, lintuihin ja nisäkkäisiin – Kirjallisuuskatsaus. 2010.
Finnish Game and Fisheries Institute reports 17/2010
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