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

2/25

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

Contents

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

3/25

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

1 Introduction to the consultation process

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

4/25

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

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

5/25

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.

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

6/25

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).

Planning of the environmental assessment, provision of information and consultation on the preparation of the plan or programme and environmental report

Environmental impact assessment in the preparation phase of the plan or

programme

Preparation of the environmental report

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

1. Describing the state of the environment

2. Specifying the object of the impact assessment and

alternatives

3. Identifying and analysing impacts and assessing their

significance

4. Presenting information on the impacts and comparing

alternatives

5. Making proposals concerning the plan or programme and its implementation and monitoring

Steps of the drafting

process

Tasks of the environmental

assessment

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

7/25

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.

2 Object of the assessment

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

8/25

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 km2. 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

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

9/25

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.

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

10/25

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

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

11/25

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

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

12/25

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

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

13/25

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.

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

14/25

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)

3 Basic premises and conduct of the impact assessment

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

15/25

• 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.

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

16/25

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.

No offshore wind farms in the exclusive economic zone scenario

VE0, or the zero alternative of the environmental assessment, refers to a situation where no offshore wind farm investments will be made.

VE0

Partial implementation scenario

VE1 describes a situation in which offshore wind power projects are implemented on two out of the four designated sites, or Bothnian Bay North and Bothnian Sea West.

VE1

Maximum impact scenario

VE2 describes a situation in which offshore wind projects go ahead on each designated site.

VE2

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

17/25

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

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

18/25

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.

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

19/25

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

Preliminary studies

and planning

Construction Production and

maintenance Decommissioning

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

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

20/25

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.

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

Preliminary studies

and planning

Construction Production and

maintenance Decommissioning

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

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

21/25

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.

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

22/25

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.

Preliminary

studies and

planning

Construction Production

and

maintenance

Decommission

ing

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

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

23/25

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

and planning

Construction Production and

maintenance

Decommissioning

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.

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

24/25

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

Sweco | Provision of information on the initiation of an SEA process and consultation on the assessment plan

25/25

Together with our clients

and the collective

knowledge of our 22,000

architects, engineers and

other specialists, we co-

create solutions that

address urbanisation,

capture the power of

digitalisation, and make our

societies more sustainable.

Sweco – Transforming

society together

Suur-Ameerika 1 / Tallinn 10122 / 626 2802/ [email protected] / www.kliimaministeerium.ee/

Registrikood 70001231

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]