C140.10 Report Spatial management...Dutch

Transcription

Spatial management, ecological
impacts and monitoring in relation
to offshore wind energy development
on the Dutch Continental Shelf
We@Sea research area 2
J. Asjes (Imares)
Spatial management, ecological
impacts and monitoring in
relation to offshore wind energy
development on the Dutch
Continental Shelf
A review of the results of We@Sea Research Line
2: Spatial Planning and Environmental Aspects
Authors: J. Asjes1, R. Hille Ris Lambers1, T. Reijs2, J.T. van
der Wal1, S. van Heteren3, K. Wijnberg4, B. Perez Lapeña4,
4
4
1
5
Report number C140/10
IMARES Wageningen UR
(IMARES - Institute for Marine Resources & Ecosystem Studies)
Client:
We@Sea
P/a. ECN
Postbus 1
1755 ZG PETTEN
Publicatiedatum:
31 March 2010
1 IMARES. P.O. Box 68, 1970 AB IJmuiden, the Netherlands.
2 TNO
3 Deltares/TNO
4 UT
5 Seamarco
6 ECN
7 TNO
IMARES is:
•
an independent, objective and authoritative institute that provides knowledge necessary for
an integrated sustainable protection, exploitation and spatial use of the sea and coastal
zones;
•
an institute that provides knowledge necessary for an integrated sustainable protection,
exploitation and spatial use of the sea and coastal zones;
•
a key, proactive player in national and international marine networks (including ICES and
EFARO).
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A_4_3_2-V11.2
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Contents
Contents................................................................................................................... 3
1. Introduction .......................................................................................................... 5
1.1. The Wind Energy at Sea Program (We@Sea) .................................................. 5
1.2. Research Line 2: Spatial Planning and Environmental Aspects ........................... 6
1.3. Developments since the start of We@Sea ...................................................... 6
1.3.1. Existing Wind Farms and new plans ................................................... 6
1.3.2. Spatial Management at the Dutch Continental Shelf ............................. 9
1.3.3. The monitoring and evaluation program “Offshore Wind Farm
Egmond aan Zee” (NSW-MEP) ............................................... 10
1.4. The International Setting ........................................................................... 11
1.5. Consequences for Research Line 2 .............................................................. 12
1.6. Structure of the report .............................................................................. 12
2. Objectives of Research Line 2................................................................................. 13
3. Overall achievements and results ........................................................................... 15
3.1. Site-atlas and cumulative impacts ............................................................... 15
3.1.1. Introduction ................................................................................. 15
3.1.2. We@Sea Site Atlas ....................................................................... 15
3.1.3. Analysis of seabed and soil quality required for wind farms ................. 17
3.1.4. Integration application cumulative effects; CUMULEO 1.0 ................... 20
3.1.5. Analysis techniques for georeferenced monitoring data....................... 21
3.2. Morphological and Ecological Impacts .......................................................... 22
3.2.1. Morphological impacts ................................................................... 22
3.2.2. Impacts on marine mammals ......................................................... 24
3.2.3. Impacts on grey seals ................................................................... 25
3.2.4. Hearing sensitivity of Harbor Seals .................................................. 29
3.2.5. Results of NSW-MEP research related to marine mammals .................. 34
3.2.6. Impacts on birds .......................................................................... 35
3.2.7. Impacts on fish and benthos .......................................................... 40
3.2.8 Impact on benthic systems (fish and benthos) ................................... 40
3.2.9. Results of NSW-MEP research related to benthos and fish ................... 48
Impacts on benthos ............................................................................... 48
3.3. New Monitoring Techniques (WP4) .............................................................. 49
3.3.1. Introduction ................................................................................. 49
3.3.2. WT-Bird for monitoring of bird collisions ........................................... 49
3.3.3. Bird Radar ................................................................................... 52
3.3.4. A ship-based hydrophone system for detection and classification of
cetacean echolocation signals ................................................ 53
3.4 Figures .................................................................................................. 54
3.4.1. DIDSON ...................................................................................... 57
4. Gaps and missing knowledge ................................................................................. 60
4.1 Short summary of We@Sea research findings. ............................................... 60
4.2 Gaps and suggestions for further research .................................................... 61
4.2.1. Data 61
4.3 Cumulative and Interaction effects ............................................................... 62
4.3.1. An integrated approach to planning ............................................... 62
5.
conclusions .................................................................................................... 63
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6
Quality Assurance ........................................................................................... 64
References .............................................................................................................. 65
Appendix 1 Summaries of all research projects within Research line 2.............................. 67
2004-003 Site atlas cumulative effects ............................................................... 68
2005-004 Integration application cumulative effects; Cumuleo 1.0 development ...... 70
2005-005 Analysis of seabed and soil quality required for wind farms ..................... 72
Long-term stability .......................................................................................... 72
2005-012 We@Sea Site - Atlas ......................................................................... 76
2006-006: GIS-technology and the analysis and forecasting of change in the
marine environment ........................................................................................ 79
2004-001 Mussel 'map of opportunities' at the Nordsea ........................................ 81
2004-007: The influences of wind farms on benthos and fish ................................. 83
2004-012 PhD@Sea: Morphology ...................................................................... 86
2005-006: The effect of wind farms on the settling of gray seals at the North
Sea (Halichoeros grypus .................................................................................. 88
2006-005: Underwater hearing sensitivity of harbour seals for tonal signals and
noise bands(Phoca vitulina) .............................................................................. 90
2007-003: Seabirds on wind ............................................................................. 93
2004-006: A ship based hydrophone system for detection and classification
of cetacean echolocation signals........................................................................ 97
2004-007: The influences of wind farms on benthos and fish ............................... 100
2005-022: Low cost en sea-clutter resistant radar for monitoring birds ................. 102
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1. Introduction
This report summarizes results of research within the topic ‘Spatial Planning and Environmental Aspects’
(Research Line 2) of the Wind Energy at Sea (We@Sea) program, and general developments related to
spatial management and environmental issues concerning wind energy on the Dutch Continental Shelf
(DCS), as well as the role of (the results of) We@Sea research and We@Sea partners. In addition, it
highlights gaps and missing knowledge and presents recommendations for future research.
1.1. The Wind Energy at Sea Program (We@Sea)
2004 marked the start of We@Sea, a research program with the aim to develop, integrate and
disseminate knowledge in order to facilitate the advance of 6000 MW of wind energy within the Dutch
part of the North Sea (see text box). The We@Sea consortium consisted of more than 30 organizations
directly or indirectly involved in the development of wind energy on the North Sea and was partly
subsidized by the Dutch government within the framework of BSIK8.
Central Objective We@Sea Program:
The central objective of the knowledge program is to develop a structural basis for longterm business development in the Netherlands, for the purpose of preparing, designing,
constructing, operating, maintaining and, in due course, dismantling offshore wind power
plants.
The We@Sea consortium consists of offshore wind farm developers, the offshore technology sector, the
energy sector, the wind energy technology sector, investors, energy consultants, logistics organizations,
environmental NGO’s and research organizations, including two universities. All organizations were
directly or indirectly involved in technological and environmental issues as well as research related to the
development of offshore wind energy.
8 http://www.senternovem.nl/bsik/index.asp
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1.2. Research Line 2: Spatial Planning and Environmental Aspects
We@Sea research was organized along 7 lines. This report focuses on the results of Research Line 2
(RL2): ‘Spatial Planning and Environmental Aspects’ whose objective was ‘to survey spatial planning and
environmental requirements to provide potential investors with reliable and relevant information on local
conditions in orderto enable them to start with their site selection and development.’ For more
information on the work packages and their objectives: see chapter 2.
1.3. Developments since the start of We@Sea
Since the start of the We@Sea project in 2004 the development of offshore wind energy in the North Sea
and on the Dutch Continental Shelf (DCS) accelerated intensively. Outside the scope of the We@Sea
program, a considerable amount of knowledge was developed. We summarize some of these
developments below.
1.3.1. Existing Wind Farms and new plans
In 2004 concrete plans for two offshore wind farms existed; the Offshore Windpark Egmond aan Zee
(OWEZ9) and the Princess Amalia Wind Farm (Q710). Currently, both these wind farms are operational
(figure 2). In 2005 the Dutch government freed the market for the development of offshore wind energy
within the DCS. AS a result, 10 project developers initiated the development of a total of 20 wind farms
within the Dutch part of the North Sea (figure 1). (A map of the locations for wind farms for which a
(draft) permit is issued by the Dutch government at the moment is presented in figure 2.) For each of
these initiatives an Environmental Impact Assessment (EIA) as well as an Appropriate Assessment within
the framework of the Habitats Directive was carried out. These assessments were all carried out based
on existing and best available information as well as expert judgments. Both the EIA’s and the
Appropriate Assessments considerably enhanced and integrated existing knowledge with respect to
environmental and ecological impacts of Offshore Wind Energy at Sea.
9 www.noordzeewind.nl
10 www.prinsesamaliawindpark.eu
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Figure 1. Overview of all initiatives (in yellow) for offshore wind farms on the Dutch Continental Shelf.
Source: http://www.noordzeeloket.nl/activiteiten/windenergie/algemeen/
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Figure 2. Overview of licensed (green areas) locations for offshore wind farms and existing wind farms
(bleu areas) at the Dutch Continental Shelf. Source:
http://www.noordzeeloket.nl/activiteiten/windenergie/algemeen/ .
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1.3.2. Spatial Management at the Dutch Continental Shelf
In 2009 The Dutch government issued a new spatial management plan for the DCS within the framework
of the National Water Plan (NWP11) which takes into account the recent developments with respect to
wind energy development and Marine Protected Areas. With respect to wind energy and other uses at
sea the NWP states:
‘Within international frameworks, the Cabinet is giving priority to the following activities that are of
national importance for the Netherlands:
•
Sand extraction and replenishment: sufficient space for protecting the coast, counteracting flood
risk and for fill sand on land;
•
Sustainable (wind) energy: space for 6,000 Megawatt of wind energy on the North Sea
in 2020 (at least 1,000 km2 , creating conditions for further (international) growth
after 2020;
•
Oil and gas field development: extracting as much natural gas and oil from the Dutch fields in
the North Sea as possible;
•
Sea shipping: building a system of traffic separation schemes, clearways and anchoring areas
allowing safe and prompt handling of shipping;
•
Defence areas at sea.’
These objectives have considerable consequences for spatial management of the DCS. In order to
facilitate the development of wind energy at sea four areas were designated (figure 3):
1. ‘Borssele’
2. ‘IJmuiden’
3. The area off the Holland coast between Hoek van Holland and Texel
4. North of the Wadden Islands
The latter two areas are still under discussion at the moment and should be regarded as ‘search areas’.
Draft Policy Document on the North Sea (2008):
As part of the policy aimed at sustainable, clean and economical energy generation, the number of wind
turbines at sea will be drastically expanded. The Cabinet program ‘Clean and Efficient’ targets a
sustainable energy generation of 20% by 2020, with the target increasing to 40% by 2050. In addition, a
target figure of an installed power capacity of 6,000 MW of wind energy in the North Sea in 2020 has been
formulated. The Cabinet wants the installed capacity to be as cost-effective as possible before 2020 and
seeks to lay the foundations for further (international) growth after 2020. Achieving this objective is of
national importance.
11http://www.rijksoverheid.nl/documenten-en-publicaties/publicaties-pb51/nationaal-waterplan-2009-2015engels.html
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Figure 3. Future spatial management of the Dutch Continental Shelf. Yellow areas indicate areas
designated for wind energy. Dashed yellow areas indicate search areas for wind energy. Source:
http://www.noordzeeloket.nl/noordzeebeleidNWP/nationaal_waterplan/nwp/ .
For the development of offshore wind energy after 2020 the Dutch government aims for areas much
further from the coast (yellow arrows, figure 3). Many partners within the We@Sea consortium also
contributed significantly to this policy process.
1.3.3. The monitoring and evaluation program “Offshore Wind Farm Egmond aan Zee” (NSW-MEP)
During the construction and exploitation of the “Offshore Wind farm Egmond aan Zee” (OWEZ) a large
scale monitoring and evaluation program was initiated to evaluate both the technical characteristics as
well as the environmental impacts of the wind farm. This monitoring program focuses on the following
topics pertaining to environmental impacts of the wind farm:
•
Impacts on marine mammals, both seals and porpoises;
•
Impact on birds, both seabirds and migrating birds;
•
Impacts on fish and fish behavior;
•
Impacts on benthos;
•
Impacts with respect to underwater noise.
The program was commissioned by NUON and Shell. The ecological research is carried out by IMARES,
Bureau Waardenburg and Royal NIOZ. All these organizations were also members of the We@Sea
consortium. Several research projects carried out within We@Sea research line 2 were combined with,
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and /or supplemental to research carried out within the framework of NSW-MEP. Although the program
runs until 2012, some of the NSW-MEP studies have been completed, and are available at
http://www.noordzeewind.nl/ .
1.4. The International Setting
In Denmark, United Kingdom and Germany offshore wind farms have been, or are currently being
developed together with targeted research programs (figure 4). Many of the results of these studies have
been reported in the international literature and are available on the web. In this report we mainly focus
on the Dutch situation, but touching upon these studies where available and relevant.We refer to the
individual We@Sea research reports for details on the international context of the results.
Figure 4. Overview of Wind Energy targets and initiatives in the North Sea. Source: ?
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1.5. Consequences for Research Line 2
The development of offshore wind energy within the North Sea has accelerated, especially within the
past 5 years. As a result, our knowledge of, and questions on, spatial and environmental aspects of
offshore wind energy development has changed. Keeping this in mind, we have nevertheless summarized
–all- results of the We@Sea RL2 program within this final report in order to be as complete as possible.
Within the next two to three decades the planned development of many new wind farms within the DCS
and the greater North Sea necessitates the addressing of gaps in our knowledge with respect to
environmental issues and spatial management. One obvious example being the cumulative impacts of
multiple wind farms. We are convinced that the results of this program can contribute to filling in these
gaps.
1.6. Structure of the report
In chapter 2 research performed under Research Line 2 is evaluated against the original objectives of
RL2. Chapter 3 summarizes and highlights the main results of all research projects within RL2. Where
appropriate, results of the NSW-MEP program and other assessments have also been integrated within
this chapter. Finally, Chapter 4 touches upon the gaps in knowledge related to spatial and environmental
aspects of wind energy at sea. Annex 1 contains all executive summaries of the We@Sea RL2 research
reports.
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2. Objectives of Research Line 2
Research within research line 2 was originally structured along 5 work packages (WP):
1. Decision support system for site selection, including site atlas;
2. Safety control
3. Environmental improvement;
4. Challenges for Nature;
5. Communications strategy for public awareness.
The objective of WP 1 was the development of a decision support system balancing the design and
profitability of offshore wind farms with environmental risks and opportunities. Research related to this
work package was conducted especially during the early phase of the We@Sea program. These included
studies on the design of a decision support tool to assess cumulative impacts of offshore wind farms, as
well as studies on the definition and technical specifications of a GIS system for site selection, i.e. the
Site Atlas. Furthermore GIS techniques to study environmental impacts of offshore wind farms were
developed. Finally, seabed data were gathered and analyzed to facilitate site selection for offshore wind
farms in relation to seabed characteristics,
WP 2 dealt with safety aspects related to offshore wind energy development. The objective was to assess
the risks of accidents, safety aspects for personnel and environmental risks. One study was carried out,
but it was decided that it was more appropriate to report back on this within Research Line 5,
Installation, Operation and Maintenance (reference).
The objective of WP3 was to study the environmental burden along the entire lifespan of a wind farm:
i.e. related to the production of turbines, the construction of offshore wind farms, their operation and
maintenance, and their future decommissioning. No research was performed on this topic.
The objective of WP4 ‘Challenges for Nature’, was to study the ecological impacts of offshore wind farms
on the North Sea marine ecosystem was the Besides studies directly focusing on the effects on seals,
birds, fish and benthos, new monitoring techniques were also developed. Most of these projects were
combined with or were supplemental to NSW-MEP research. In addition, under this workpackage, the
morphological impacts of offshore wind farms were addressed
The last work package of RL2 focused on the communication of results of RL2 research to relevant
stakeholders and the organization of meetings with these stakeholders. While no targeted research
project was performed within the framework of this WP, several workshops, meetings and conferences
related to the environmental aspects of offshore wind farms have taken place in the past five years.
Many of these were organized or attended by We@Sea. From the start of the We@Sea program a RL2
theme group was formed to discuss and evaluate research proposals and results within the framework of
RL2. This group consisted of We@Sea partners particularly interested in the RL2 research.
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Research within research line 2 was originally structured along 5 work packages (WP):
6. Decision support system for site selection, including site atlas;
7. Safety control
8. Environmental improvement;
9. Challenges for Nature;
10. Communications strategy for public awareness.
The objective of WP 1 was the development of a decision support system balancing the design and
profitability of offshore wind farms with environmental risks and opportunities. Research related to this
work package was conducted especially during the early phase of the We@Sea program. These included
studies on the design of a decision support tool to assess cumulative impacts of offshore wind farms, as
well as studies on the definition and technical specifications of a GIS system for site selection, i.e. the
Site Atlas. Furthermore GIS techniques to study environmental impacts of offshore wind farms were
developed. Finally, seabed data were gathered and analyzed to facilitate site selection for offshore wind
farms in relation to seabed characteristics,
WP 2 dealt with safety aspects related to offshore wind energy development. The objective was to assess
the risks of accidents, safety aspects for personnel and environmental risks. One study was carried out,
but it was decided that it was more appropriate to report back on this within Research Line 5,
Installation, Operation and Maintenance (reference).
The objective of WP3 was to study the environmental burden along the entire lifespan of a wind farm:
i.e. related to the production of turbines, the construction of offshore wind farms, their operation and
maintenance, and their future decommissioning. No research was performed on this topic.
The objective of WP4 ‘Challenges for Nature’, was to study the ecological impacts of offshore wind farms
on the North Sea marine ecosystem was the Besides studies directly focusing on the effects on seals,
birds, fish and benthos, new monitoring techniques were also developed. Most of these projects were
combined with or were supplemental to NSW-MEP research. In addition, under this workpackage, the
morphological impacts of offshore wind farms were addressed
The last work package of RL2 focused on the communication of results of RL2 research to relevant
stakeholders and the organization of meetings with these stakeholders. While no targeted research
project was performed within the framework of this WP, several workshops, meetings and conferences
related to the environmental aspects of offshore wind farms have taken place in the past five years.
Many of these were organized or attended by We@Sea. From the start of the We@Sea program a RL2
theme group was formed to discuss and evaluate research proposals and results within the framework of
RL2. This group consisted of We@Sea partners particularly interested in the RL2 research.
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3. Overall achievements and results
In this chapter we summarize the main results of studies performed within the framework of Research
Line 2 of We@Sea.
3.1. Site-atlas and cumulative impacts
3.1.1. Introduction
The research presented in this section mainly relates to Work Package 1 of RL2. We carried out research
for the development of a site atlas to facilitate decision making in relation to offshore wind farm
planning(Reijs et al 200.), Furthermore, we developed a prototype of a tool for the analyses of
cumulative impacts of multiple wind farms in the North Sea (van Dokkum et al 2005; van der Wal et al
2007). Finally techniques for analysis of the impact of offshore wind farms, taking into account the
spatio-temporal variation in the datasets were developed. (Perez-Lapena en Wijnberg, 2010). The results
of these studies are summarized in the next three sections.
3.1.2. We@Sea Site Atlas
Central theme of the We@Sea Site-Atlas project was the allocation of all relevant information required
for the construction and operation of offshore wind turbines in a safe and economically sound manner
with minimal environmental impact. This theme was subdivided into three subprojects. First, specific
demands by different parties for the Site-Atlas were assessed (subproject 1). Second, an inventory of
already existing available knowledge was supplemented by additional relevant information. Third, layout
and presentation issues in the development of a structured Site-Atlas framework base were addressed.
The demand side assessment allocated key areas where specific knowledge was required, as well as
parties that indicated a need for such dedicated inputs. An example of potential We@Sea databases is
provided below:
Examples
•
•
•
•
of potential We@Sea databases
Biology: plankton, benthos, birds, fish, sea mammals, etc.
Physical parameters: seabed (soil composition, sand dunes, et cetera), wind, wave patterns
Economic parameters: wind turbine/farm yield, O&M costs, grid connection, wind farm
design options (wind turbine make & type, configuration et cetera).
Site specific issues: optional North Sea use applications, Marine Protected Areas etc.
Phases
Offshore wind power development parties include offshore wind technology and transport logistics
suppliers, project developers, utilities, investors, and insurance companies. In addition research
organizations, government bodies, environmental and other action groups, energy consultants, and O&M
service providers.
The assessment method involved conducting a number of interviews and workshops with parties as
indicated above, where a difference was made between three distinct offshore wind farm project phases:
•
•
•
Planning;
Construction;
Operation.
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The overview of main findings was subdivided into nine main categories:
1.General (policy issues, management control and protection);
2.Soil and water;
3.Nature and environment (ecological processes, species, habitats, eco-labeling);
4.Human activities (fishery, recreation, transport, energy and mineral resources, military defense,
aviation, business);
5.Coastal protection;
6.Energy yield (offshore wind turbine technology development, costs and benefits of wind power
generation);
7.Perceptions, involvement, natural history and landscape added value aspects;
8.Design.
The above questions themselves have been put forward to various organizations each with their own
specific perceptions and viewpoints. These parties include the commercial business sector, the public
sector, and other organizations with a key focus on social issues including (perceptions on) wind power
acceptance.
Comprehensive
As part of the overall assessment, an inventory of available in-house knowledge was conducted within
Dutch and foreign We@Sea-partners. This resulted in a data overview and dataset composition ranked
by subject.
From the assessment it became clear that there is already a comprehensive amount of information on
offshore wind power available. However, a sizable proportion includes geographical maps, which often
lack essential background information. In such situations it remains unclear which specific datasets have
been visualized on these maps. This makes conducting an independent data analysis almost impossible.
One specific field for which data is still largely lacking is for so-called cumulative effects.
Linking datasets
The next step involved linking dedicated demand and supply datasets in order to determine their internal
match, and further to pinpoint potential information provision gaps. The Site-Atlas concept aimed at
making all these data available in a systematic and easily accessible manner. For this project three
alternative Site-Atlas options were explored:
•
A website linking to organizations in possession of a relevant database and additional (scientific)
literature reference sources;
•
We@Sea conducts an intermediate role by providing datasets and models to its partners;
•
GIS functionality linked to datasets and models:
•
Displaying data with the aid of dedicated maps;
•
Information search function for specific areas;
•
Online models partly based upon GIS data.
Discussions with We@Sea partners and other parties clearly indicated a preference for a website with
links to organizations. A variant worth considering is offering organizations the possibility of ‘filling’ the
We@Sea website with their own data. One essential precondition for this scenario is that all datasets
meet stringent standards in terms of accuracy and reliability as formulated by We@Sea’s program
bureau. As offshore wind power development takes place in a still young but highly dynamic (market)
environment, an additional key demand is that the database is kept up to date, which requires a
continuous effort.
Though it is not part of We@Sea’s remit to search for data, the program bureau does have a primary
task in developing a system incorporating suitable methodologies to effectively direct and control specific
research projects. This in-house capability is particularly important with regard to policy procedures for
offshore wind farms, one of the main bottlenecks hampering overall progress. In this case and for other
relevant (related) issues the program bureau can indicate what specific knowledge gaps exist and require
sustained research effort.
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Specific phases
Information required depends on specific offshore wind farm development phases like site assessment,
installation, operation, and demolishing/recycling. It has also become clear that the application of a
We@Sea Site-Atlas needs to be strongly linked with offshore wind farm monitoring programs currently
conducted at the Dutch section of the North Sea and elsewhere.
3.1.3. Analysis of seabed and soil quality required for wind farms
Spatial planning, specifically location selection by means of decision-support systems requires reliable
and relevant data. Environmental data on the composition of seabed sediment, the composition and
structure of subsurface layers, seabed morphology, and hydro- and morphodynamics play an important
role in determining the primary suitability of a location for wind-farm development,. A large-scale
overview of physical seabed parameters, linked to design aspects of individual turbine-support structures
and entire offshore wind farms, allows the identification of areas of different suitability before detailed
site surveys are carried out. For the Netherlands offshore territory between the latitudes of Texel and
Hoek van Holland, This project provides an overview of seabed characteristics relevant for determining
first-order suitability to wind-farm development.
Physical seabed-sediment characteristics, such as grain size, mud content, and degree of cohesion are
important parameters in seabed behavior during and after wind-farm construction. Seabed sediment
plays a role in erodibility of the seabed (scouring) and in the formation of suspended-sediment plumes.
The most suitable parameter characterizing the grain size of seabed sediments in the (sandy) research
area is the median grain size of the sand fraction (63-2000 µm), which shows an overall fining from
south to north. The northward-fining pattern is overprinted along the coast, where fines are captured by
river-mouth sediment sinks, and exposed where the receding shoreface exposes tidal and shoreface
deposits. It is also interrupted off Texel, where gravel is exposed on the seabed, washed out of till
deposited during an Ice Age.
A second seabed-sediment parameter is percentage mud content. In the research area, this is generally
lower than 2. Near the coast, higher values occur, particularly near the entrance to Rotterdam Harbor.
Cohesive sediment lies at or close to the surface only in the dredge spoils of Rotterdam Harbor, and
where peat or early Holocene clay are cut by shipping lanes or by the receding shoreface, close to shore.
The structure and composition of the subsurface is an important factor governing the stability and cost of
turbine foundations. Knowledge of the subsurface is also necessary for calculating opportunity costs
when valuable resources are (temporarily) no longer exploitable or when archeological treasures are
disturbed. Fine-grained deposits, locally more than 10 m thick, are sensitive to compaction and affect the
behavior and yield of wind turbines. Locations characterized by thick clayey units in the subsurface are
potential exclusion areas. The presence of exploitable quantities of sand for concrete and mortar in a
particular area can play a role in determining if wind-farm development makes economic sense
A fully functioning layer model for the upper 50 m of the seabed subsurface is not yet available. The
description of the structure and composition of the subsurface is therefore frequently based on far-fromperfect digital grids of the extent and thickness of individual layers. Information on the geotechnical
parameters of these layers is scarce. By grouping geotechnical data on a Formations and Member scale,
useful constraints on the range of various parameters for each unit can be defined on the range of
various parameters for each unit.
Water depth is directly linked to turbine height and thus to construction cost. Morphology (i.e. difference
between crests and troughs of bedforms) is a measure of potential dynamics as a result of migrating
bedforms. Water depths in the NCP range from 0 to more than 50 meters. In the relatively shallow part
of the NCP between the latitudes of Texel and Hoek van Holland, the water depth increases gradually
from the coast toward the border with the U.K. shelf. This gradual increase is overprinted by large-scale
elongate ridges several kilometers in width, up to 100 km in length and 10-20 m in height. These tidal
ridges are most commonly found far offshore, where they have a north-south orientation. However, they
also occupy shallower areas closer to the coast, where they are connected to the shoreface at an oblique
angle. The research area is also characterized by sand waves: smaller-scale bedforms that have
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wavelengths of several hundreds of meters en heights up to 10 m. In general, sand-wave height
decreases from the southwest to the northeast.
Morpho- and hydrodynamics are important in scouring and in the long-term stability of wind turbines.
Areas with rapidly migrating large-amplitude bedforms, particularly sand waves, are characterized by a
large variability in water depth through time. Migration rates are highest near the coast and decrease
both in an offshore direction and toward the southwest. They range from almost 20 m/y in the extreme
northeast of the research area to less than 1 m/y in the southwest. Given a life span of 30 years, wind
turbines in the northeast will be affected by several passing sand waves, whereas turbines in the
southwest will probably experience less variability in water depth, even though sand waves are higher in
this area.
Determining the relative importance of the various physical parameters governing the suitability of the
seabed for the development of wind farms is difficult. There are no set rules to define and compare
economic and environmental costs. Nevertheless, a first-order suitability assessment can be made by
implementing a penalty-point system. For each location on the NCP, penalty points are assigned when
unfavorable sediments are present in the shallow subsurface. For the Brown Bank Member and the
Naaldwijk Formation, variable layer thickness is available as a grid, and translated into six classes of
penalty points. Moderate-to-high gravel percentages of the seabed sediment generate penalty points as
gravel habitats are rare, and because gravel is a valuable resource. An increasing number of penalty
points with increasing mud percentage reflects the fact that construction activities (particularly cable
trenching) disturb large volumes of seabed sediment. For bathymetry, deeper water is less favorable
than shallower water. Finally, high-amplitude sand waves give more penalty points than low-amplitude
sand waves.
The aim of this translation exercise is a semi-quantitative classification of the research area into
consistently defined suitability areas. The resulting applied geological map (Figure 1) is a useful element
in decision-support systems. This first-order suitability grid for the NCP was made using readily available
grids for various seabed and subsurface parameters affecting the economic and environmental cost of
wind-farm development.
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Figure 1. First-order suitability of the NCP for wind-farm development
This approach has several drawbacks. First, -not all underlying grids are up-to-date. Second, -several
grids do not cover all of the research area. Third, -many other thickness grids are absent altogether.
Finally, the presence or absence of units used in the construction of the suitability grid does not reflect
their maximum extent, but rather their presence at the top of the Pleistocene and Holocene sequences.
Despite these drawbacks, the first-order grid is a suitable means in assessing the potential economic and
environmental cost of wind-farm development. It enables the definition of exclusion zones, is a source of
information in environmental-impact studies, and provides a developer with a semi-quantitative decisionmaking tool when comparing the suitability of two or more competing areas.
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3.1.4. Integration application cumulative effects; CUMULEO 1.0
There is growing demand for improved understanding of the cumulative environmental effects linked to
multiple North Sea offshore wind farms. Knowledge on how to effectively quantify such cumulative
offshore effects is currently insufficient: For instance, a conceptual understanding with regard to effects
summation is almost totally lacking. This shortcoming is reinforced by lack of basic information on
specific 'nature values'. Simultaneously these combined data are essential background data for allocating
eventual cumulative effects on the distribution and ecology of certain species.
The main objective was to develop rules for the calculation of cumulative effects linked to multiple
offshore wind farms located in a confined area. These have been developed for a variety of themes
including landscape & perception, and nature & environment (birds, sea mammals, fish, and sea fauna).
This project further marks a first dedicated effort to develop a conceptual knowledge base for describing
cumulative effects linked to multiple offshore wind farms spaced relatively close to each other. These
interaction effects have been studied for various 'subject groups' including birds, underwater sound and
benthos as well as landscaping/perceptions in relation to operational and new planned offshore wind
farms.
Dedicated support tool
This study describes main results of a development track aimed at designing a dedicated support tool for
describing offshore windfarm-related cumulative effects. The tool is named CUMULEO 1.0, and the
acronym stands for 'CUMULative Effects of Offshore wind farms'. The calculation rules are based upon
the current state-of-the-art with regard to available knowledge, but can be refined and updated with the
latest knowledge In the future. However, the project excludes cumulative effects linked to offshore wind
farms in a combination with other North Sea user functions.
New Dutch legislation regarding application rules for the 'Wet beheer
rijkswaterstaatwerken (WBR)12' came into effect December 31, 2004. Perhaps most importantly, the
legislation clears the way for constructing new offshore wind farms in the Dutch Exclusive Economic Zone
(EEZ), and supports the government objective to build a cumulative 6,000 MW offshore wind capacity by
2020. In response to the new legislation a total of 78 developer consortia submitted 'starting documents'
subdivided over 48 different sites, each known as a 'unique location'. Interestingly the cumulative
installed capacity of these 48 locations adds up to 21,000 MW, a factor 3.5 higher than the initial 6,000
MW offshore wind objective.
The Dutch government further decided to delegate selection of offshore locations to market parties,
instead of choosing for a steering role that involves determining preference locations. This offshore wind
power positioning has fuelled demand for a dedicated support tool,such as CUMULEO. Cumulative effects
have to be viewed in relation to the currently already intensive use of the Dutch EEZ for a range of
different activities including shipping, commercial fishery and mining. Furthermore, it is vital to pay
sufficient attention to key natural values and other relevant issues requiring protection at national as well
as European (EU) legislative levels. As part of Environmental Impact Analysis (in Dutch MER) rulings for
new planned offshore wind farms, developers are obliged to provide comprehensive background
information to the responsible authorities. That package includes sufficient clarification on cumulative
effects linked to already operational and/or other planned wind farm projects, as well as additional
ongoing and/or planned North Sea user applications.
GIS technology basis
CUMULEO is based upon Geographic Information System (GIS) technology essential considering the
three-dimensional nature of disturbances to natural and environmental features. CUMULEO v1.0 as a
12 http://rijkswaterstaat.nl/wegen/wetten_en_regelgeving/wet_beheer_rijkswaterstaatwerken/
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main function comprises a sequence of working steps, which can all be performed with the aid of GISbased maps developed as part of the We@Sea Site atlas project.
The calculation rules have been applied initially as part of a fictitious scenario, analyzing the cumulative
effects of 10 'small' offshore wind farms of 100 MW each (all 28 x 3.6 MW). These fictitious ten wind
farm sites are all located off the North Sea coast off the province of Zuid Holland.
Furthermore, per theme we developed a calculation rule based on several predefined assumptions. Next
step was analyzing this theme scenario with as its basis the outcomes of a cumulative effects search.
This was followed by determining an eventual need for further optimizing, with a main focus at either
calculation rules and/or basic background information. That in turn can provide the basis for future
We@Sea projects. The calculation rules have finally been tested at planned Dutch North Sea wind farms
OWEZ and Princess Amalia.
3.1.5. Analysis techniques for georeferenced monitoring data
Evaluating and monitoring the impact of human activities on the marine environment is a requirement
for sustainable marine development. A major issue within the We@Sea project is how to study the
impact of offshore wind farms on marine fauna while the background signal (i.e. the undisturbed
situation) is poorly understood. Distribution patterns of marine fauna have high spatial and temporal
heterogeneity and are therefore difficult to characterize with few dedicated surveys in the impacted
area.. Moreover, the understanding of the resulting pattern at this local scale will be influenced by the
patterns at larger scales and by dynamic factors (ecological, physical, human activities) occurring at the
location and time of the surveys. Assessing whether changes in the composition of marine fauna from
the pre-construction to the post-construction situation are indeed evidence of impact is a challenging
task.
In this research we support ecological experts in the We@Sea project by performing a transparent
analysis of multiple spatio-temporal data sets that contain (direct or indirect) information on the impact
of offshore wind farms on marine fauna.
The objectives of this study therefore are:
1.
To develop a method to identify whether the number of a given species observed after the
construction of an offshore wind farm is evidence of change due to the wind farm presence.
2.
To test the method with data collected for assessing the impact of offshore wind farms on
seabirds
Fig. 2.
In this study we have developed a method, based on geostatistical simulation to assess whether
observations of spatio-temporally varying abundance of marine fauna (count data) in the wind farm area
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and its surroundings are evidence of impact of the wind farm on marine fauna. The data set should
consist of data collected both before and after the construction of the offshore wind farm. The method
can accommodate (a) expert knowledge on site-specific and species-specific information regarding
species behavior in relation to biological and physical factors as well as human activities, and (b)
statistical properties of the collected data over various temporal and spatial scales, including effects of
varying surveying layout.
To demonstrate the applicability of the method in real impact assessment studies the method has been
applied to the case of the Egmond offshore wind farm and its impact on guillemots (Uria aalge). Results
showed that the number of guillemots observed during the post-construction period in the impact and
control areas did not provide evidence for either positive or negative impact of the wind farm on this
seabird species. This conclusion holds for the current level of understanding of how guillemots respond to
various dynamic physical conditions as well as the lack of coinciding monitoring data of the physical
conditions at the day of survey. If we wish to assess impact of wind farms on seabirds, monitoring of
known explanatory physical conditions at both the local and the larger scales is needed.
Our findings illustrate once more that impact assessments on marine fauna, and seabirds in particular,
are inherently surrounded by uncertainties due to the complexity of the problem at hand combined with
the inability to collect sufficient amounts of accurate data for the assessments. With the developed
method we expect that these uncertainties can be handled more explicitly in the decision making process
on offshore wind farm development. The method can be extended (and currently is) to acquire insight in
the probability of reaching a wrong conclusion about impact of offshore wind farms on marine fauna, in
which the case that impacts remain undetected is of particular interest. This extension involves
examination of the effects of i) survey effort and design, ii) spatial distribution of environmental factors,
and iii) spatial autocorrelation in species abundance on the ability to detect an impact when it is indeed
present. Results of analysis for different combinations of these factors will provide information for the
design of optimal monitoring strategies balancing costs and effectiveness in detecting harmful impacts
that are potentially present. This is to be done such that further developments can continue, but that
notions about acceptable risks of specific ecological impacts for reaching targets of renewable energy are
quantified and honored.
Results of this study have been presented on international scientific conferences (NEED REFERENCES)
and have been (and will be) submitted to international peer reviewed scientific journals.
3.2. Morphological and Ecological Impacts
3.2.1. Morphological impacts
Introduction
This project carried out within WP4 of RL2 as part of a PhD project studied the morphological impacts of
offshore wind farms, and developed a system to predict the large-scale effects of human activities, e.g.
wind farms, on the North Sea seabed on a long timescale.
Natural and Human Induced Seabed Evolution
The North Sea is a highly dynamic area, where a tidal current flows over a sandy seabed. It is an
intensively used area where various human activities take place. The seabed is rich in oil and gas and
many oil and gas platforms connected to the shore with pipelines, mostly buried below the seabed.
Telephone and data cables are placed up and in the seabedrunning from one country to another. In
addition the North Sea is a biologically rich area, and is intensively fished.. The sand of the seabed is
mined and used for large infrastructural projects. As important harbors face the North Sea, intensive
shipping takes place and there are many shipping lanes, which require dredging. In addition, large areas
are reserved for offshore wind farms and other functions such asmilitary terrains. The seabed of the
North Sea is not flat, but is shaped in several wavy patterns, ranging from small ripples to large sand
banks. Sand banks have a wave length between 1 and 10 km and can have a height of several tens of
meters. Somewhat smaller features are sand waves. Their length varies between 100 and 800 m and
they can be up to 10 m high from trough to crest. As the North Sea is a very dynamic area, both in
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natural and a morphological sense, and as many human activities take place here, it is important to
know what the large-scale effects of human activities on the seabed will be.
W e developed a system for predicting the large-scale effects of human activities on the North Sea
seabed on a long timescale (van der Veen, 2008). This system implemented idealized morphodynamic
models in a GIS (Geographical Information System) also containing data on the North Sea environment.
We predicted the occurrence of sand banks and sand waves in the North Sea and compared these results
with observations of these large-scale bed forms. The results show that we are able to correctly predict
the occurrence of sand banks and sand waves in large parts of the North Sea, The models predicting the
morphological effects of human activities cannot be validated yet. However, as they are based on the
same principles as the models used to predict the occurrence of sand banks and sand waves, of which
the results are compared with observations of large-scale bed forms in the North Sea.
We assume that the models predicting the effects of human activities do not show any morphological
evolution, if the model that predicts the occurrence of sand banks does not predict the occurrence of
sand banks at this particular location. This because, the underlying mechanisms of the models on human
activities are based on the same 2DH flow conditions that are necessary for sand bank development. We
connected idealized morphodynamic models to the GIS to create a tool that used to predict the effects of
human activities on the North Sea seabed. The models use site-specific input to give predictions for an
arbitrary location in the North Sea.
The first application of this system is large-scale sand extraction. Due to large construction project, such
as the enlargement of the Rotterdam harbor, the demand for sand is rising and more offshore resources
will be used to fulfill the need. This means that more large-scale sand pits will be created in the North
Sea. The North Sea is a shallow shelf sea where the tide flows over a sandy bed. Therefore, the presence
of sand pits can influence the morphological behavior of this seabed.
The second application is offshore wind farms. We investigated the influence of offshore wind farms on
the large-scale morphodynamics of the seabed. The need for sustainable energy is increasing, wind
energy is one of the forms of renewable energy that can be harvested efficiently. We developed a
morphodynamic model to investigate the effect of offshore wind farms on the seabed. By implementing
the model in the GIS environment, the model allowed us to calculate the effects of a wind farm using
site-specific and farm design input parameters. In figure .. the morphological effects of a wind farm in
the Humber estuary and the Q7 wind farm close to the Dutch coast after 100 years are shown. We
observed that the effects of the Q7 wind farm (located off the coast of Ijmuiden) are much smaller than
the effects of the Humber wind farm. Predicted morphological changes after 100 years at the Q7 wind
farm ranged from maximum 10 cm erosion to maximum 20 cm sedimentation. Predicted changes at the
Humber site were 4 times larger.
Figure 3 Seabed change in meter due to the Humber wind farm (left) and the Q7 wind farm (right) after
100 years. The values above the plot denote the lowest point of the seabed (min) and the highest bed
elevation (max) in meter.
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By implementing idealized morphodynamic models in a GIS environment we were able to predict the
occurrence of large-scale bed forms on the North Sea seabed. Also, by implementing models predicting
the effects of human activities in the GIS system, we were able to give an indication of the large-scale
morphological effects of these human activities in the North Sea, thereby providing a rapid assessment
tool to predict the morphological effects of human activities on the seabed.
3.2.2. Impacts on marine mammals
Introduction
There are three potential impacts of offshore wind farms (OWF’s) on marine mammals in the North Sea:
•
The direct impact of underwater noise produced during pile hammering: The intense
underwater noise produced during pile hammering can lead to death, hearing loss, or hearing
damage in marine mammals. Marine mammals, especially dolphins and porpoises, are highly
dependant on their hearing capability (sonar) in finding their food, for orientation and
communication;
•
The loss of major feeding or nursery habitats: If an OWF (or a cluster of OWF’s), becomes
unattractive for marine mammals (for example because of the underwater noise produced during
operation or because of its presence) and the OWF is situated in an important feeding or nursery
habitat, this might lead to the loss of these habitats and consequently may have an impact on
the population;
•
Influence on migration routes due to disturbing influences of underwater noise during
construction and operation of OWF’s: Several species of marine mammals are dependant of
daily migration routes between for example the coast, e.g. seals resting on sand banks, and
offshore feeding habitats. A single OWF or a cluster of OWF’s might lead to a barrier in these
migration routes if they exhibit disturbing effects.
On the other hand it is possible that OWF’s may develop into an attractive feeding or resting habitat for
marine mammals if they lead to an increase in prey species. It is possible that fish abundance within the
wind farms could increase due to either the introduction of new habitats due to the presence of turbines,
as well as the absence of fisheries in the wind farm area.
On the Dutch Continental Shelf, three species of marine mammals are most abundant: the harbor
porpoise, Phocoena phocoena, the harbor or common seal, Phoca vitulina, and the grey seal,
Halichoerus grypus. Other species also occasionally occur, such asthe bottlenose dolphin, Tursiops
truncates, the white-beaked dolphin, Lagenorhynchus acutorostrata, the white sided dolphin,
Lagenorhynchus acutus and the Minke Whale, Balaenoptera acutorostrata.
Knowledge on these species is relatively low, but we assume that they are rare in comparison to seals or
porpoises. Seals are monitored at their ‘haul-out’ sites in coastal areas by airplane, i.e. Wadden Sea and
Delta areas, but information on their (feeding) migration routes in the North Sea, let alone information
on important habitats in the North Sea, is still very scarce. This information is very important in order to
assess the impacts of (clusters of) OWF’s on habitats or migration routes. Monitoring of porpoises and
dolphins is executed during bimonthly surveys by airplane, which is mainly focused on birds. With
respect to marine mammals, these aerial surveys can say something about presence and absence of
species. However the method used in this monitoring program is not sufficient for a quantitative
assessment of the distribution and the population of porpoises and dolphins. Monitoring of porpoises and
dolphins is also performed during ship-based surveys. However these are not carried out on a regular
basis and do not cover the entire DCS or North Sea. Only in the SCANS project, a coordinated North Sea
wide monitoring of cetaceans was carried out in 1994 and 11 years later in 2005 (figure ..). The
information of SCANS led to the first relatively reliable estimate of the harbor porpoise population in the
North Sea, and insight in changes in the distribution of this species in the North Sea.
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Figure 4 Two figures, left 1994 and right 2005, showing major shift in the distribution of harbor porpoise
in the North Sea, Source: SCANS II: http://biology.st-andrews.ac.uk/scans2/inner-furtherInfo.html
Research related to the impact of offshore wind farms on marine mammals in the Netherlands has
focused on three topics:
•
Studies on the presence/absence of harbor porpoises in an offshore wind farm in relation to the
surrounding reference areas and the baseline situation, i.e. the period before construction of the
wind farm (NSW-MEP) in comparison to the impact situation, i.e. during operation of the wind
farm;
•
Studies on the migration routes, distribution and habitat preferences of seals, both common and
grey seals, on the Dutch continental shelf (NSW-MEP and We@Sea);
•
Studies on the hearing sensitivity of seals and porpoises (NSW-MEP and We@Sea).
•
A study on the impact of pile-hammering by carrying out ship-based surveys during the pilehammering period and analyzing stranded porpoises along the Dutch coast (NSW-MEP).
Furthermore studies have been and are carried out on the production of under water sound during the
construction and the operation phase of OWF’s (NSW-MEP). These data can be indirectly used to assess
the impact of under water noise on marine mammal species.
3.2.3. Impacts on grey seals
In order to assess possible effects of wind farming on the marine environment, basic data are essential.
Both general and local knowledge should be made available to estimate effects on a local scale, and give
insights into possible interactions between local phenomenon and this relatively new activity (so-called
interaction effects).
In the case of marine mammals in the Netherlands, studies have been conducted in relation to harbor
seals and harbor porpoise within the framework of the NSW-MEP program (Brasseur et al in press,
Scheidat et al in press). For grey seals in Dutch waters, identifying a cause and effect relationship
between the wind farm (construction and operation) and the well-being of the seals was not possible due
to insufficient information available for this species.
Therefore a study was started within the framework of We@Sea to focus on grey seals. The study was
set up to gain an understanding of the possible effects of large-scale development of wind farms at sea
on grey seals (Halichoerus grypus) in Dutch waters. However, in lack of references on the grey seals in
Dutch waters, the prerequisite of this study was to gather basic data on the species. The study included
3 parts: 1. population development, 2. diet and 3. habitat use. This study permits for a (preliminary)
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assessment of the effects of the construction and operation of the wind farms Princess Amalia and the
Offshore Wind farm Egmond aan Zee (OWEZ).
Grey seal numbers have grown impressively in Dutch Wadden Sea in the past 30 years; from an
occasional individual to a maximum count of over 2000 animals during the moult, when most animals are
observed (fig ,,; reference). In addition, growing numbers of grey seals are observed in the Dutch Delta
area, sometimes exceeding the number of harbor seals (Strucker et al., 2007.). Presumably, most
animals originated from the British coasts, where the largest grey seal population in the world resides.
2500
Number of seals
2000
1500
Moult
Other
Pup
1000
02-Mar-04
06-Jun-01
10-Sep-98
15-Dec-95
20-Mar-93
24-Jun-90
28-Sep-87
01-Jan-85
0
27-Nov-06
500
Figure 5 Exponential growth of grey seals in the Dutch Wadden Sea during the moult (March/April 18.74%), the pupping period (December – February -19.76%) and during the remaining time ‘other’ 14.65%.
Other strongholds of grey seals on the continent are found in Germany, but numbers remain below
several hundred. This heightens the responsibility to protect them in the framework of the Habitat
Directive. Yearly monitoring of the population development will show when the population stabilizes both
in size as well as in the use of the haul outs. The data on the relative importance of the different haul
outs plays an important role in assessing the distribution when at sea.
We conducted dietary studies to define what the animals eat in the Dutch waters. These might give
insight into possible changes in diet if animals are attracted to wind farms. In this part of the study we
showed that grey seals along the Dutch coast primarily feed on a variety of demersal fish species, mainly
sole in spring and flounder in autumn. This is comparable to the diet of grey seals from the east coast of
the UK, though more sandeel is eaten there. On average, prey is seldom larger than 20cm and only
slightly larger compared to the harbor seals’ diet.
As scat analysis (like all methods for dietary research of cryptic animals) creates a bias, additional
information was collected for fatty acid analysis. However, the results of this analysis are not yet
satisfactory. In the near future, we expect to use this method in parallel to scat analysis to more fully
understand the dietary preference of the species.
Finally, from our spatial distribution studies we conclude that the Dutch North Sea zone plays an
important role for grey seals, both in terms of migration and foraging (figure ..). Although most seals
spend the majority of their time close to their central place (haul-outs), our model (REFERENCES)
predicts that areas further offshore such as the Frisian front and the Dogger Bank provide suitable
foraging areas. McConnell et al (1999) found that grey seals from UK populations travel to and feed on
the Dogger Bank. Large distance migrations along the continental coasts and to the UK are observed.
This suggests that the Dutch population is indeed open. Consequently, increase in human activity along
these migration routes has the potential to disturb the seals. In our small sample size, a relatively large
number of seals are found to make these journeys suggesting that it is common practice for these seals
to travel such long distances. In terms of preference to particular areas, our model indicates that the
grey seals prefer sandy areas and shallow waters. This lends support to previous studies in which similar
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results were found (e.g. Aarts et al 2008, and in the case of harbor seals, Brasseur et al 2009). These
findings allow the prediction of spatial distribution, even in areas with little telemetry data.
The use of the offshore area seems crucial to understand the possible influence of wind farming. This in
turn requires an understanding of the ‘normal’ behavior of the seals, i.e. habitat use, and the ability to
accurately track individuals in their 3-dimensional environment. Additionally, it is necessary to
understand if and how this ‘normal’ behavior changes in the presence of a wind farm or multiple wind
farms. We have some understanding of grey seals in Dutch waters, i.e. numbers, haul out patterns, and
phenology (as recently reviewed in Brasseur et al., 2008). However our knowledge on the seals’
distribution at sea is still lacking. Moreover this study shows that this can be somewhat hampered by the
large individual variation of the animals. In this study we have gone through large efforts to gather more
detailed information on the seals’ habitat use (preference) and on which factors influence their
distribution (both natural and human). Habitat maps such as figure… can be used in discussions
on spatial management with respect to choices on further development of offshore wind farms.
We did not succeed in calculating the effect of pile driving activity at the wind farm, as the number of
seals tagged at that moment were too low. In addition, many seals were too far from the area to
perceive any activity. As a first guess based on circumstantial evidence; the seals seem to move towards
the wind farm area more after the pile driving stopped. This is shown by the tracks of the seals that were
tagged during the pile driving activity.
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Figure 6 Modeled seal preference using the preferences for the various environmental characteristics
described in the report, but after removal of the effect of distance to the haulout site. This map provides
a rough indication of where seals would be if they would not be constrained to return to their haulout.
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3.2.4. Hearing sensitivity of Harbor Seals
In order to improve the assessment of the audibility ranges of underwater sound related to offshore wind
farms, the hearing thresholds of 2 harbor seals were tested for both tonal signals and noise bands.
Methods study 1
The underwater hearing sensitivities of two one-year-old female harbor seals were quantified in a pool
built for acoustic research, using a behavioral psychoacoustic technique. The animals were trained to
respond when they detected an acoustic signal and not to respond when they did not (go/no-go
response). Pure tones (0.125-0.25 kHz) and narrowband FM (tonal) signals (center frequencies 0.5-100
kHz) of 900 ms duration were tested. Thresholds at each frequency were measured using the up-down
staircase method and defined as the stimulus level resulting in a 50% detection rate.
Figure 7 Harbor seal at the listening station waiting for a sound signal.
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Figure 8 Trained response of the harbor seal after it detected a sound signal (swim away from listening
station)
Results study 1
The audiograms of the two seals did not differ statistically: both plots showed the typical mammalian Ushape, but with a wide and flat bottom (figure ..). Maximum sensitivity (54 dB re 1 µPa, rms) occurred at
1 kHz. The frequency range of best hearing (within 10 dB of maximum sensitivity) was from 0.5 to 40
kHz (6 ⅓ octaves). Higher hearing thresholds (indicating poorer sensitivity) were observed below 1 kHz
and above 40 kHz. Thresholds below 4 kHz were lower than those previously described for harbor seals,
which demonstrates the importance of using quiet facilities, built specifically for acoustic research, for
hearing studies in marine mammals.
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Figure 9 The average underwater hearing threshold (in dB re 1µPa, rms) of the two study animals in the
present study, shown as a line, and the underwater hearing thresholds found for harbor seals in previous
studies [Møhl, 1968 a (± 500 ms ■); Terhune, 1988 (500 ms □); Turnbull and Terhune, 1993 (repeated
signals, 50 ms, 10/s ○); Kastak and Schusterman, 1998 (500 ms ▲); Southall et al., 2005 (500 ms ●)].
The numbers between brackets indicate the signal durations used in the studies.
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Importance for development of wind energy at sea
The results suggest that under unmasked conditions many anthropogenic noise sources and sounds from
conspecifics are audible to harbor seals at greater ranges than formerly believed. This means that both
the sounds produced during the construction of wind parks (pile driving) and during the operational
phase, are audible over wider ranges than formerly believed. However, audibility does not relate 1-to-1
to “effect on behavior”. To determine the effect on behavior “dose-response” studies with harbor seals
are needed like those conducted for ACME sounds and tones (Kastelein et al., 2006 a, b), but then for
specific wind farm related sounds.
The study is published in the Journal of the Acoustical Society of America (Kastelein et al., 2009a).
Methods study 2
Fourteen narrowband noise signals (1/3-octave bands but with some energy in adjacent bands), at 1/3octave center frequencies of 0.2-80 kHz, and of 900 ms duration, were tested. Thresholds at each
frequency were measured using the up-down staircase method and defined as the stimulus level
resulting in a 50% detection rate.
Results study 2
Between 0.5 and 40 kHz the thresholds corresponded to a 1/3-octave band noise level of ~60 dB re 1
µPa (S.D. ± 3.0 dB) (figure ..). At lower frequencies the thresholds increased to 66 dB re 1 µPa and at
80 kHz the thresholds rose to 114 dB re 1 µPa. The 1/3-octave noise band thresholds of the two seals
did not differ from each other, or from the narrowband frequency modulated tone thresholds at the same
frequencies obtained a few months before for the same animals.
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Figure 10 The mean underwater hearing threshold (dB re 1µPa, rms) of the two study animals in the
present study for 1/3-octave noise bands (▲), and the mean underwater hearing thresholds for tonal
signals (□) of the same animals, with the same equipment, in the same environment four months earlier
(Kastelein et al., 2009).
Importance for development of wind energy at sea
These hearing threshold values of this study can be used to calculate detection ranges of underwater
calls and anthropogenic noises by harbor seals. Most windpark related sounds are not tonal, but noise
bands. The study shows that harbor seal hearing is equally sensitive to noise bands as to tonal signals.
Published knowledge on various harbor seal hearing parameters is mostly based on tonal signals, and
may thus be used by acousticians to calculated audibility ranges of anthropogenic sounds, including
windpark related sounds.
The study is published in the Journal of the Acoustical Society of America (Kastelein et al., 2009b).
Role of results in international context
Both studies have been published in a high ranking journal specialized in acoustic studies. Because the
harbor seal occurs in all coastal areas of the temperate waters of the Northern Hemisphere, the interest
in these studies is high. The studies are not only useful for calculating the detection ranges of sounds
produced during all phases of offshore wind parks, but also for calculating detection ranges of all
anthropogenic underwater sounds. One study has already been referred to in a recent overview of
OSPAR about the effects of anthropogenic sound and marine fauna (OSPAR Commission, 2009).
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Suggestions for further hearing and behavioral response research related to offshore wind farms and
anthropogenic underwater sound in general
(Note: Similar behavioral studies have been conducted by SEAMARCO during the last 3 years for specific
naval related sounds (for the Ministry of Defence); these studies are at the moment (March 2010) in the
analysis phase and will be published in scientific journals later this year).
Harbor seals
1.
Underwater hearing sensitivity of harbor seals in noise (critical ratios).
2.
Directionality of hearing in harbor seals (directivity index).
3.
Temporary hearing Threshold Shift (TTS) in harbor seals.
4.
Equal-loudness contours in harbor seals.
5.
Startle response sound levels for harbor seals to windpark related sounds.
6.
Avoidance sound levels for harbor seals to windpark related sounds
Harbor porpoises
1.
Temporary hearing Threshold Shift (TTS) in harbor porpoises.
2.
Equal-loudness contours in harbor porpoises.
3.
Startle response sound levels for harbor porpoises to windpark related sounds.
4.
Avoidance sound levels for harbor porpoises to windpark related sounds
Marine fish
1.
Effect of certain specific anthropogenic sounds on marine fish.
3.2.5. Results of NSW-MEP research related to marine mammals
Impact of pile hammering during construction of the OWEZ wind farm
During the construction phase of the OWEZ wind farm studies were performed to analyze the possible
impact of pile hammering on porpoises (Leopold & Camphuysen, 2008). Ship-based surveys and
analyses of stranded animals were carried out. During construction no porpoises were detected in the
area. This was probably caused by a combination of factors, i.e. densities of porpoises are generally low
in the period during which pile hammering occurred, the presence of all ships present in the area might
have scared off the animals, pingers and a ‘ramp-up’ procedure during pile hammering were also used to
ward off the animal. Analyses of stranded data did not show increased strandings of porpoises in the
vicinity and down-stream of the construction site. Pathological observations on stranded specimens, in
order to study possible damage to the inner ear, could not be performed. It was concluded that timing
and high before-pile driving noise levels made it very unlikely that porpoises got in harm’s way during
construction of OWEZ.
Impact of the Offshore Wind Farm Egmond aan Zee (OWEZ) on harbour porpoise
The presence/absence of Harbour Porpoises within and in the vicinity of the Offshore Wind Farm Egmond
aan Zee (OWEZ) was studied using acoustic porpoise detectors called T-PODs (Brasseur et al 2004,
Scheidat et al in press). Observations were carried out before construction of OWEZ (T0), within the wind
farm (T1) and in a so-called reference area. The impact of the wind farm was investigated by using a
basic
Before-After-Control-Impact (BACI) design. The results showed that porpoise click activity increased in
the impact area (wind farm) in comparison to the reference area (north and south of the wind farm). The
cause for this could not be determined, but may be linked to an increase in food availability, i.e.
increased numbers of fish, due to the so-called reef effect of wind farms and turbines and/or the absence
of fisheries within the wind farm. These results deviate from studies that were carried out at Danish wind
farms that showed a negative impact at the Nysted farm and no impact at Horns Rev (Tougaard et al
2006 a & b). This highlights that results from one wind farm cannot be directly translated to other farms.
34 of 110
Habitat preferences of harbor seals in the Dutch coastal area: analysis and estimate of effects
of offshore wind farms
The distribution and migration routes of harbor seals on the Dutch part of the North Sea were studied by
means of telemetry techniques (Brasseur et al in press). Data were analyzed in order to determine the
distribution, habitat preferences and impact of existing wind farms. Results showed that harbor seals in
the DCS have a preference for areas relatively close to the haul out, relatively shallow areas and areas
with sediments with low mud content. Furthermore indications were found that seals tend to avoid
shipping activity and that tagged seals avoided the area of the wind farms during the construction phase
when pile hammering occurred up to at least 40 km away. After operation the seals were found closer to
the wind park then during construction.
3.2.6. Impacts on birds
Introduction
With respect to birds there are several potential impacts of OWF’s that are relevant. All bird species can
experience a direct impact of wind farms due to collisions with wind turbines. Seabirds can be disturbed
by the presence of the wind farms or activities associated with the (construction of) wind farms which
can lead to loss of feeding or resting habitats. Wind farms can also act as barriers within important
migrations routes of seabirds, i.e. between their breeding sites and feeding areas. Also other migrating
birds along the Dutch coast or birds migrating between the Netherlands and the UK can experience these
effects. The severity of all these potential impacts will be enhanced if more wind farms are developed in
the North Sea (cumulative impacts) and several national and international plans for wind farms are
developed in such a way that clusters of OWF’s may become barriers in migration routes.
Within We@Sea one major study was executed in which the impact of offshore wind farms were studied.
The results of this study are summarized below.
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Objectives
This research serves four objectives:
1. To generate a map of the North Sea indicating in which areas wind farms would have an adverse
effect on seabirds.
2. To find explanatory variables for the bird distribution in the biologically rich Frisian Front area.
3. To determine the gradient in bird fluxes in a transect perpendicular to the Dutch coast.
4. To develop innovative instruments for scientific research.
Results
Bird sensitivity map
Bird distribution data have been gathered and brought together in one database from various sources:
Rijkswaterstaat, NIOZ, IMARES and Bureau Waardenburg. An algorithm for bird sensitivity to wind farms
depending on species characteristics was applied based on Garthe & Hüppop (2004) yielding an index
number for bird risks; the wind farm sensitivity index (WSI). The overall risk map was constructed from
the combined species distribution maps and species risk indices.
WSI Max over all seasons
Max WSI all Seasons
WSI Avg over all seasons
AVG WSI all Seasons
20 % lowest values
20 % lowest values
20 % low values
20 % low values
20 % values less concern
20 % values less concern
20 % values concern
20 % values concern
20 % values major concern
20 % values major concern
Figure 1. Year-round maps of seasonal maximum (left) and average WSI values across the Dutch
Continental Shelf, combining aerial and ship-based data (ducks excluded). The data are plotted in five,
20 percentile, classes. Areas of concern and of major concern are plotted in orange and red, respectively,
while areas of less concern (the lower, 0-60 percentiles) are plotted in various shades of green.
36 of 110
Explanation of bird distribution in Frisian Front
The Frisian Front attracts many seabirds (Dewicke et al 2002; Leopold 1991). It hosts a number of
typical North Sea bird species such as Northern Fulmar (Fulmarus glacialis), Northern Gannet (Morus
bassanus), Lesser Black-backed Gull (Larus fuscus) and Common Guillemot (Uria aalge). For the latter
two species, the area is of particular importance during the reproductive period. Lesser Black-backed
Gulls fly back and forth from their breeding colonies on the Wadden Sea islands to their foraging areas at
and around the Frisian Front (Ens et al 2009). Male Common Guillemots escort their still flightless chicks
from the British breeding colonies to the Frisian Front and undergo a complete feather moult during this
period (Camphuysen 2002).
The Frisian Front is rich in both demersal and pelagic fish. Whereas Common Guillemots are able to
reach this fish at any depth at any time (potential diving depths exceed Frisian Front bottom depths, cf
Hedd et al 2009), most fish swim too deep to be preyed upon by surface feeders, such as Lesser Blackbacked Gulls. This is unless factors come in to play that bring these fishes to the surface. Under natural
circumstances, pelagic fish can be driven to the surface by hunting predators, such as cetaceans (e.g.
Harbour Porpoise Phocoena phocoena), birds (e.g. Common Guillemot) or predatory fish (e.g. Mackerel
Scomber scombrus). In an attempt to escape, schools of small pelagic fish may migrate to the surface,
where they can be preyed upon by surface feeders. These ‘feeding frenzies’, which are attended by
several predatory species, are called ‘multi-species feeding associations’ (MSFA). Alternatively, otherwise
unattainable fish become available through anthropogenic fishing, whereby discards are thrown
overboard. These two mechanisms are not mutually exclusive and birds may use them opportunistically.
We surveyed birds and sampled fish in the upper water column in the Frisian Front area. The
interrelationship between fish, birds and environmental parameters yields knowledge on the distribution
of birds at sea, which is important for spatial planning of wind turbines.
Both fish sampling and echosounder scans revealed low densities of small pelagic fish near the water
surface during daytime (figure 1). Daytime biomass of fish species known as prey for Common
Guillemots (Sprat Sprattus sprattus, ScadTrachurus trachurus, Herring Clupea harengusi, Whiting
Merlangius merlangus and Mackerel Scomber scombrus) did not correlate with observed Common
Guillemot densities and guillemots were not seen foraging during the day. However, several Common
Guillemots were observed to start diving at sunset. A nocturnal fish sampling revealed a much higher fish
biomass (especially Herring and Sprat) in the upper water layers after sunset. A peak in diving activity
during crepuscular periods (the twilight zone) has been reported for Common Guillemots (Nevins et al
2004; Hedd et al 2009). Suspending foraging to crepuscular periods when prey migrates upwards may
energetically be favourable, as diving depth can be minimized (which may especially demanding for
chicks) and hunting success may be higher (Helfman 1993).
Although MSFAs have been observed at the Frisian Front in the past, none were observed during our
2009 survey. This can probably be explained by the absence of large fish schools and the low numbers of
potential MSFA drivers. The only potential MSFA driver present in good numbers – Common Guillemots –
were not foraging during daytime and therefore did not produce MSFAs diurnally. Hence, MSFAs could
not supply Lesser Black-backed Gulls with diurnal foraging opportunities. Lesser Black-backed Gulls
where mainly seen following the observation ship or – if within sight – following fishing vessels. This,
combined with the virtual lack of natural foraging behaviour indicate that at least during daytime, Lesser
Black-backed Gulls rely on fishing vessels discards rather than MSFAs. Man thus plays an important role
in making unavailable fish available to gulls.
37 of 110
Figure 2.
Figure 2. Left: Typical echogram from the upwards beaming towed body with mounted 200 kHz
splitbeam transducer. The red marks are probably fish(schools). In the first meter from the surface, the
echogram shows a lot of noise, caused by reflections from the rough sea. Right: Acoustic distribution
(NASC) of all fish species by 1 meter depth layers.
Figure 3. Results from the ship-based bird survey in the Frisian Front area during 2-6 August. Left panel:
density of Common Guillemots and fish tracks. Right panel: Lesser Black-backed Gulls and their
associations with floating matter. Many gulls associated with the ship during the fish sampling (compare
with fish track locations in left panel).
38 of 110
Gradient in bird fluxes
It has been hypothesized that there is a gradient in bird fluxes going towards the coast. However,
research so far has not provided proof for this. Currently employed bird radar stations are located
relatively close to shore, providing only half the picture. In this project a bird radar station has been
located at an offshore site. By comparing bird fluxes measured at different distances from shore, the
hypothesized gradient in bird movements can be quantified and tested. Project results are, however, not
yet available.
Innovative instruments
In order to collect data on the fish distribution in the upper layer of the water column, we developed
three innovative instruments. First, we built an acoustic sensor for the upper water layer. Normally,
these sensors face downwards and are towed behind the ship. The newly developed acoustic sensor
faced upward, scanning the water column from the towing depth (approximately 7m) up to the water
surface. In order to avoid disturbance of fish by the ship, towing the sonar in the wake of the ship should
be avoided. Therefore, the sonar was dragged at an angle with the ships’ bearing, which was achieved by
shaping it like a wing, making it ‘fly like a kite in the water’. Second, we developed a new fishing net that
enabled us to fish the top three meters of water with a reasonably large net opening. Third, we adapted
a special net for plankton surveys with a fixed net opening to operate in North Sea waters. Like the
acoustic sonar, these nets had to be towed at an angle with the ships’ bearing, which was achieved by
shearing boars (paravanes).
Figure 4. From left to right: acoustic underwater kite, surface trawl net and floating plankton net.
Implications for the development of wind energy at sea
This project has generated a map of the North Sea that shows the areas where wind turbine parks can
be planned best to have the least impact on birds. It will show what gradient in bird fluxes is present off
the Dutch coast and it has given us a deeper understanding of explanatory variables for the distribution
of birds at sea. Last but not least it has given us a set of innovative instruments to better survey the
marine environment.
39 of 110
3.2.7. Impacts on fish and benthos
Introduction
The potential impacts of offshore wind farms on the fish community and the benthos community can be
as follows:
•
Pile hammering associated with the construction of the foundation for offshore wind turbines
may result in damage to fish and fish larvae or changes in fish behavior due to the high levels of
underwater noise associated with this;
•
Underwater noise produced during the operational phase of offshore wind farms may change fish
behavior;
•
The presence of offshore wind farms may cause changes in seabed characteristics which can
influence the distribution of benthic species and demersal fish species;
•
Absence of fisheries within the offshore wind farm, because fishing is not allowed, may change
the characteristics of both the fish and the benthos community because detrimental impacts
from fisheries will be absent;
•
The presence of the offshore wind farm and the wind turbines may lead to the introduction of a
new habitat for fish and benthos.
Within We@Sea one research project has been carried out which focused on the impact of offshore wind
farms on the benthic community, both fish and benthos. This research is described below.
3.2.8 Impact on benthic systems (fish and benthos)
In this study we examined the potential of wind farms in the North Sea for the conservation of both
commercial, and non-commercial demersal fish species, the benthic fauna on which they feed, and the
response of fishers to the closure of fishing areas as a result of the recent implementation of wind farms
near IJmuiden. Within this study we addressed:
1.
2.
3.
4.
5.
A description of the prevalence of fish and benthos
The relationships between benthos and fish
The effects of protected areas for benthos and fish
Suitability maps for wind farms, based on fish and benthos mortality
The change in fishing intensity as a result of the development of wind farms.
Through 1) maps of the distribution of fish and benthos from survey data, 2) & 3) modeling the food web
relationships between benthos and demersal fish, and their relationships with the area covered by wind
farms, 4) mapping the (potential) mortality of trawling on fish and benthos and 5) mapping the change
in distribution of fishing effort based on VMS data, we address the placement of wind farms and their
potential effects on fish, benthos and fishers. This report will also serve as a basis for future peer –
reviewed publications in scientific literature, and as a basis for future work.
Most important results:
1. The distribution maps of the boxcore fauna and the dredge fauna show that the fauna density is
particularly high in the coastal zone and at the Frisian Front. The Doggerbank only shows a high density
for the boxcore fauna. For biodiversity the Frisian Front and the Oystergrounds have the highest figures.
See Figures 1 and 2
40 of 110
BOXCORE
Total Fauna Density
55°30'0"N
55°0'0"N
54°30'0"N
54°0'0"N
53°30'0"N
N/m2
15 - 125
126 - 500
501 - 2,000
53°0'0"N
2,001 - 8,000
8,001 - 33,877
20 - 517
517 - 769
769 - 897
897 - 1,149
1,149 - 1,646
1,646 - 2,626
2,626 - 4,561
52°30'0"N
52°0'0"N
4,561 - 8,379
8,379 - 15,911
15,911 - 30,773
51°30'0"N
3°0'0"E
4°0'0"E
5°0'0"E
6°0'0"E
7°0'0"E
Fig. 1. The density of the macrobenthos of the DCS based on the boxcore data. The three grey spots
indicate the wind farm and two reference areas. With kriging the density of the non-sampled areas is
interpolated on the basis of the sampled stations (grey open circles).
41 of 110
DREDGE
Total Fauna Density
55°30'0"N
55°0'0"N
54°30'0"N
54°0'0"N
53°30'0"N
N/m2
53°0'0"N
1-3
4 - 12
13 - 50
51 - 200
52°30'0"N
201 - 879
1-8
8 - 11
11 - 13
52°0'0"N
13 - 16
16 - 23
23 - 41
41 - 80
51°30'0"N
80 - 172
172 - 385
3°0'0"E
4°0'0"E
5°0'0"E
6°0'0"E
7°0'0"E
Fig. 2.
Fig. 2. The density of the large macro-infauna and the epifauna of the DCS based on the Triple-D dredge
data. With kriging the density of the non-sampled areas is interpolated on the basis of the sampled
stations (grey open circles). For the white areas data were not available and could not be interpolated
42 of 110
2. Based on maps of potential benthos mortality to trawling, wind farms (provided no fishing is allowed)
will have a maximum positive effect in the coastal zone above the Frisian Wadden Islands, the northern
part of the Broad Fourteen, and the southern part of the Doggerbank, as beamtrawling has the largest
impact on the bottom fauna in these areas. See Figure 3.
DREDGE
Mortality
55°30'0"N
55°0'0"N
54°30'0"N
54°0'0"N
53°30'0"N
53°0'0"N
52°30'0"N
52°0'0"N
% (Density)
5 - 10
51°30'0"N
10 - 15
>15
3°0'0"E
4°0'0"E
5°0'0"E
6°0'0"E
7°0'0"E
Fig. 3. The mortality (percentage that will die) of the non-mobile macrobenthos species after the passage
of a beamtrawl over the area. The density data are based on the Triple-D dredge surveys, and the
mortality data are taken from or are interpolated from Bergman & van Santbrink (2000). For ease of
interpretation the mortality data are split up into 3 groups. Areas with a macrobenthos mortality lower
10% are striped green, those with a mortality between 10 and 15% are striped yellow, while areas with
a mortality higher than 15% are striped red.
43 of 110
3. For fish: Although results are inconclusive, given the concentration of many of the discard vulnerable
classes near shore, it would seem that, for some considerations can be made based on species with a
largely asymmetrically, and or distinctly distributed sensitivities to mortality. For instance a consideration
may be made to prevent discards (both of small commercial and non-commercial nature), while
preserving commercial fish landings. This could be done by placing wind farms nearshore in areas where
biomass of discard vulnerable size classes is high. This is especially the case for commercial species
plaice, dab, and for many of the non-commercially fished species. Alternatively, policy may be prioritized
towards preserving larger individuals, in which case the opposite strategy holds true. (see figure 4, for
Dab (Limanda Limanda, illustrating smaller size classes, vulnerable to discarding closer to shore, while
larger size classes further away from shore)
Given the concentration of many of the discard vulnerable classes near shore, and the increasing costs of
building wind farms further off shore, it would seem that, for demersal fish near shore wind farms, within
or near the 12 mile zone are to be recommended, although, as mentioned above, a study optimizing the
placement of wind farms given the costs and expected conservation effects would be of utmost use.
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Fig. 4) Distribution of vulnerable Limanda limanda (dab), in autumn (left) and spring (right), for small
(upper) and large (lower) fish.
45 of 110
4. Model results suggest that increasing the area of wind farms can lead to different effects. For single
wind farms, the reduction in trawling mortality can result in shifts in benthic composition within the wind
farm. On a scale where these effects translate to the growth and population dynamics (i.e. for a large
area covered in wind farms) these shifts in benthic composition may translate to both increases and
decreases in fish and benthic composition, depending on current mortality levels.
See Figure 5.
Figure 5a: Schematic representation of the system which we model. The two benthos populations H
(hard bodied) and S (soft bodied) each consist of a juvenile (J) and an adult (A) stage. Fish (F) and
resources (R) are considered unstructured. Arrows indicate biomass flows, either through maturation
(blue) or feeding (black).
Figure 5b: Qualitative transitions in long term densities (equilibrium) of benthos and fish in large and
small MPAs as a function of trawling mortality. Notation as In figure 5a.
46 of 110
5. In a literature review (Coolen, 2008) it was studied if the closure of wind farms for fishing activities
had a positive effect on (local) benthic species and fish species on a population level. The closure of
fisheries in a wind farm area will most likely have a positive effect on the local benthic fauna for wind
farms of any size. For migratory benthic organisms, a wind farm must have a minimum size of 2,500
km2. For limited migratory fish the wind farm should have a minimum size of 10,000 km2 for it to have
a positive effect on population level. This is not feasible within the current plans for wind farms totaling
an area of 1,000 km2.
6. From our maps with the distribution of fishing effort, It is clear that as of yet, no outspoken effect of
closure of the wind farm areas can be seen in terms of fishing effort. Dramatic changes in fishing effort
reflect decreases in fleet capacity concurrently occurring within the same timeframe. changes in fishing
effort seem to be, as for now, more the result of socio-economic considerations with regard to fleet
capacity, than any perceived change in catch, positive or negative, around wind farms. It remains to be
seen how fishing effort will redistribute in the years to come as a consequence of the development of
benthos and fish within the existing wind farms, and with the possible building of more wind farms in the
North Sea.
See Figure 6, as an example for shifts in beam trawling placement as a function of the building of wind
farms.
Figure 6 Fishing effort(hrs), before, after and normalized difference for the Dutch beam trawl fleet before
(2004/2005) and after ( 2007/2008) the building of wind farms Q7 and MEPOWEZ (denoted in green
outline) Brown lines denote the 12 Nautical mile boundary, and the boundaries of the Dutch Exclusive
Economic Zone (EEZ)
Implication of the results for wind energy at sea:
In making a decision about the best place for building a wind farm at the NCP the most recent data for
bottom fauna are now available (e.g. to avoid areas with high biodiversity and fauna abundance) and
areas where the exclusion of beam trawling will have the largest effect are known (immediate positive
effect of wind farms on the bottom fauna large).
There is now a conceptual model available for studying interactions between fish and benthos in relation
to extremes in wind farm coverage, although further extension and study of this model would lead to
more precise predictions on the exact nature of wind farm cumulative effects.
Another important conclusion deriving from this study is that conflicting recommendations can be made
based on whether to conserve which species or species group, or depending on optimality considerations
for fishing effort. Considering the different recommendations derived from the study of benthic mortality
rates (i.e. red areas in figure 3), or derived from fish distributions (Areas near to the coast), decisions on
47 of 110
placements of wind farms will then depend on a prioritization of which species and/or stage to conserve.
Recently developed programs for optimal spatial conservation design such as MARXAN (Ball and
Possingham 2000, Possingham et al 2000) or MARZONE (Watts et al 2009) do allow for the optimization
of many considerations, both biological and economic, and would be the best way forward to balance
considerations based on benthos, fish, fishers, and wind farms.
3.2.9. Results of NSW-MEP research related to benthos and fish
Impacts on benthos
No major differences in the benthic community were found a few months after completion of the OWEZ
wind farm (Daan et al 2009). In addition, when compared to the surrounding areas, no difference in
bivalve recruitment was found (Bergman et al. 2009) A very well developed and diverse hard substrate
community with a clear zonation according to depth, and dominated by the common mussel, Mytilus
edulis was found on the wind turbines (Bouma & Lenkeek 2009)
Impacts on fish
Before, and 1 year after construction of the wind farm the composition and abundance of pelagic and
the demersal fish communities was sampled within the wind farm as well as in reference areas. Both fish
communities showed large interannual variability and no clear impact of the wind farm on the fish
community was been observed (Ybema et al, 2009; Hille Ris Lambers & Ter Hofstede, 2009). Sampling
of both demersal and pelagic fish will be repeated in 2011.
48 of 110
3.3. New Monitoring Techniques (WP4)
3.3.1. Introduction
We@Sea recognized that the increasing demand for ecological research around Offshore Wind Farms also
necessitated the development and application of new and/or improved monitoring techniques. Without
these techniques, several current and future research topics related to offshore wind farm development
would be hard or impossible to address. The We@Sea research in which promising new monitoring
techniques were developed or applied is described below.
First, the development of WT-Bird: a system to monitor bird collisions in wind farms. Monitoring bird
collisions under offshore conditions is impossible without the use of these kind of systems. In contrast to
the situation on land, it is virtually impossible to count bird casualties due to collisions with wind turbines
by means of observes. Furthermore, though feasible, monitoring bird collisions with traditional observer
methods is very time consuming and therefore very expensive. Moerover, these observations cannot be
performed at night. The WT-Bird system described below, is a possible solution to these problems.
Second, the ROBIN-Lite system, a radar system developed to detect bird movements in and around
offshore wind farms is described. There are only a few radar systems available worldwide to study bird
movements and ROBIN-Lite is one of these systems and a promising one.
The third monitoring technique that has been developed deals with the underwater detection of porpoises
by means of acoustic techniques. Porpoises and dolphin are very rare and difficult to monitor in the North
Sea, mainly due to their behavior and the presence of very turbid waters. Therefore traditional observed
techniques to monitor the species, either by plane or by ship, are very time-consuming and therefore
very expensive. In addition, cetacean species are highly protected in the North Sea and receive a lot of
attention related to the impact of offshore wind farms. A technique to monitor porpoises and dolphins by
means of an array of hydrophones was developed. These can be easily mounted on a ship and makes it
possible to detect cetaceans under water and determine their positions.
Finally a new sonar technique: the DIDSON was applied in the Offshore Wind farm Egmond aan Zee
(OWEZ). DIDSON makes it possible toobserve fish and fish behavior in turbid waters.The applicability
and testing of this technique as well as the results of the observations are summarized below.
3.3.2. WT-Bird for monitoring of bird collisions
We aimed to make the bird collision monitoring system WT-Bird, which has only been tested at a single
onshore wind turbine, available for offshore application. This would make it possible to count and register
actual bird collisions with wind turbines offshore at a larger scale and over a long period of time, and
would greatly improve the validation of collision risk models.
The WT-Bird system uses acceleration sensors inside the blades to detect audible vibrations from a bird
collision. These sensors are connected to a measurement system in the rotor that processes the impact
signal in real-time to detect impacts among other noises from the turbine and other external sources, cf.
Figure 1.
49 of 110
Figure 1: Simplified scheme of rotor blade with a single acceleration sensor that picks up vibrations from
several sources.
When a collision is detected a trigger is released. This trigger event starts a number of predefined
actions. First the recorded vibration monitoring data around the trigger event is stored and an e-mail
alert message is sent to the operator. Second, selected video recordings, of at least 30 seconds before to
30 seconds after the collision event, are stored. These video recordings are performed by cameras are
mounted outside the tower. A computer inside the tower permanently acquires and stores the video
images in a temporary buffer. Figure 2 shows the video equipment mounted outside of the Nordex
N80/2.5MW turbine in the ECN Wind turbine Test park Wieringermeer (EWTW).
Figure 2: Outdoor equipment of the WT-Bird prototype on the tower of a Nordex N80 turbine at EWTW
(left: video camera, right: infrared lights and precipitation sensor)
ECN and E-Connection Project initially planned for a series of tests to be conducted in a coastal wind
farm located on the Oosterschelde Storm Flood Barrier, in order to test and calibrate the monitoring
system in offshore-like conditions. However these tests could not start, because of warranty discussions
with the wind turbine manufacturer.
Within the term of We@Sea, no suitable alternative locations to perform the tests were found. Recently,
however NoordzeeWind, Vestas and ECN have started to investigate the possibilities for retrofit
installation of WT-Bird on one or more turbines in the OWEZ wind farm.
Meanwhile ECN has continued monitoring with the current prototype on a Nordex N80/2.5MW turbine at
the ECN Wind Turbine test site Wieringermeer, which has provided valuable operational experience on
the systems reliability and maintenance, as well as with data analysis of collisions and other events.
50 of 110
Because of rapid product developments several novel camera types were available showing considerable
improvement of the image quality at night. This improved image quality, however, is still not sufficient to
recognize birds in full darkness.
In general the system has shown to be reliable with only little maintenance effort. In the monitoring
period one bird collision, as well as a number of other events has been recorded. Figure 1 shows a series
of video images of a detected bird collision. The bird, which enters the camera field of view in the upper
left corner, hits a blade that is moving downwards. After the collision the bird falls to the ground in an
almost straight line. Figure 2 shows a video registration from a series when ice plates slide from the
blades and break into smaller parts. The blue arrows indicate the locations of the ice sheets. The video
images and the sound fragments from several events of falling ice clearly differ from those of a bird
collision, so an operator should be able to distinguish between these different events.
Figure 3: Bird collision on 2008-04-25, composite picture from video images
51 of 110
Figure 4: Triggered video registration of ice falling off from a blade on 2007-03-19.
3.3.3. Bird Radar
In order to prevent bird strikes, radar has been used by the military for decades to monitor bird
movements. And although these radars have been proven to be effective in tracking thousands of
birds simultaneously, widespread use of bird radars has been hindered by the prohibitive costs and
specialized character of these military radars. However, recent developments have led to the
construction of radar systems based upon common and affordable maritime radars. With the
development of these low cost systems, bird radar has become within the reach of a much larger
community including stakeholders within areas of civil aviation, impact and risk assessment and
bird migration research.
Within these application areas, the rapid growth of large scale offshore wind farms has created an
emerging interest in the deployment of bird radar for risk and impact assessments within or near
these farms. However, deploying these systems in an offshore environment create many
challenges including the need for unmanned operation, remote control, transfer of large amounts
of data and wave generated noise that affects radar detection of birds in adverse weather
conditions.
As partner in the WE@SEA program, TNO aims at contributing to this emerging field by the
development of a low-cost bird radar system. This system, ROBIN Lite, combines many years of
experience in developing and deploying radar for bird strike prevention with modern and
affordable radar systems. The current system consists of horizontal S-band maritime radar that is
capable of tracking birds up to many kilometers. Connected to this horizontal system is a
proprietary TNO design of a pan-tilt radar system providing height and wing beat frequency
information of tracked birds. This combination of horizontal and pan-tilt radars creates a system
that is capable of tracking birds in three dimensions with a solid basis towards species-recognition.
The main aim of the WE@SEA bird radar research is to develop a sea-clutter resistant system
52 of 110
suitable for offshore deployment. Sea clutter is the noise generated in the radar signal due to radar
reflections of sea waves. This noise severely hampers the detection of birds in an offshore
environment. To address this challenge an advanced filtering approach, named DEKODO, has
been employed to suppress sea clutter and improve detection capabilities. This filter, originally
developed to detect small surface vehicles at high sea states, is capable of detecting and
predicating wave fronts and can use this information to improve signal to noise ratios. Data for
testing this filter has been collected at two sites, one at the Pier of Scheveningen and one at the
Oosterschelde. Using this data it has been demonstrated that suppression of sea clutter is
successful, however the severe performance requirements of the filter has become a serious threat
for real-time deployment. After extensive testing and performance improvements alternative for
DEKODO has been studied. One promising solution, still subject of current research, combines
both wave front tracking and advanced classification algorithms to distinguish bird tracks from
wave front tracks. Using previous recorded data is has been shown that wave front tracking is
possible without performance degradation.
Offshore deployment of bird radar requires high levels of automation, remote control and data
transfer capabilities. During extensive testing at both a wind farm in Dresden and a site at a
military airport in Woensdrecht the ROBIN Lite did perform well. It supports continuous
unmanned operation, supports long distance mass data transfer using WiFi, ADSL and SATCOM
links and allows a high level of remote control. Remote includes the ability to start and stop the
4 / 23
system from a remote location, configure the system and provide full database access. One aspect
still under development is the ability to restart the radar themselves, which under normal
circumstances requires an operator to manually operate a switch on the radar systems.
Given the broad and international market interest in the Robin Lite system, TNO has decided to
spin-off the further development and marketing in a recent startup called Robin Radar Systems.
3.3.4. A ship-based hydrophone system for detection and classification of cetacean echolocation signals
The main aim within this project was to develop an improved, system for underwater detection of
porpoises and dolphins supporting visual observation surveys as an alternative to existing techniques,
such as towed-hydrophone arrays. This new system benefits from the lower noise condition underneath
the ship’s bow compared to the noise induced wake of the propeller zone, in which the traditional
systems are towed. Cetacean echolocation signals are received through a ship-based forward-facing
semi-circular 12-channel hydrophone array and was developed for permanent underwater use on the
bow of FRV “Tridens” or other relevant ships (Figure 1).
The dome shell and mechanical construction of the housing (1000 (l) x 800 (w) x400 (h) mm) were
designed to withstand slamming forces developed on the bow of FRV “Tridens” at a sailing speed of 17
knots according to the classification of the American Bureau of Shipping High speed naval craft 2003.
The analogue hydrophone signals are simultaneously digitized at 16 bit resolution on two data acquisition
cards and sampled with 500 kHz rate to support the maximum frequency range of harbour porpoise
echolocation signals.
A study was done on the effects of slamming forces on the sensor dome installed underneath the bow of
FRV “Tridens” and with these results the dome shell was designed and critical aspects of the design
negotiated (finite elements calculation) (Figure 2).
A software framework was developed to distinguish echo-location signals of cetaceans, to identify
cetacean species and to plot the acoustic encounters as an overlay on an oceanographic GIS map
together with the ship’s course (Figure 3). The software supports detection of dolphin vocalizations in a
range of 2 to 150 kHz and also a number of operational functions such as replay and simulation modes.
53 of 110
The equipment was tested at sea on the former pilot boat “Kluut” (Figure 4), while artificial echo-location
signals were projected at known distances from another vessel “Blue Marlin”. The tests, showed that the
system functions in principle, but that detection algorithms were not sensitive enough. A thorough
refinement of the software modules for click and burst detection increased the system’s sensitivity.
Although this system is a prototype version the results are promising and offer great opportunities for
high speed sailing and operations on smaller vessels, which enables surveys through hazardous coastal
zones, like wind farms, while new software functions, like mapping and sorting of detections are standard
and will reduce post analysis time. This new approach has great potential, does not require deck
handling/time and is a serious candidate to replace the current towed techniques.
3.4 Figures
Figure 1 Sensor position marked in red underneath the bow approximately 4 m below the waterline of
FRV ”Tridens”.
54 of 110
Figure 2 Result of finite elements calculation showing some deformation due to slamming pressure of 0.2
MPa (in mm).
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Figure 3 Example of the click monitor window of the detection software (top). The channel with the
highest click intensity is separately highlighted and a directional arrow is pointed so as to match the
listening direction of its hydrophone relative to the vessel. The bottom picture shows the GIS map
window with the overlay of sailed track and encountered click detections
Figure 4 Detail the preparations of the field test with a provisional construction of the sensor dome against
the bow of MV “Kluut”.
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3.4.1. DIDSON
The objective of this study was to develop a methodology for monitoring of fish behavior in the direct
surroundings of artificial reef elements such as wind turbines, ship wrecks, pipelines and offshore
platforms which are known to attract fish. For this purpose a dual high frequency sonar (DIDSON) was
used (Figure ..). More specifically, we assessed the effect on the outcome of the large scale acoustic
surveys which studied the effect of wind farms on pelagic fish within the framework of NSW-MEP,.
These surveys were executed in 2003 and 2007 and are to be executed again in 2011. The reason to
collect observations directly near the monopiles was that fish densities at close distance to the turbine
might be very different than farther away due to the so-called “reef effect” This might lead to bias
when comparing the baseline hydro acoustic observations with observations in the wind farms.
Figure
Figure 5. Deployment device to operate the Didson at the transects from an inflatable boat. The device is
put on the boat’s inflatable board making a stable platform for a pole with the DIDSON sonar (arrow)
attached to it. The small picture pillow shows a screen shot from the DIDSON, Above the scour bed
(stones) numerous fish are visible with to the right the monopile.
The qualitative results from this study clearly show that fish concentrations around the monopiles are
much higher in the first 15 – 20 meters. Overall fish density was on average a factor 37 higher above the
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scour bed around the monopiles than in the open water habitats in between monopiles. Length of the
observed fish mainly ranged from 10 - 40 cm. Figure .. shows that the density of fish around the
monopile recorded with the DIDSON is relatively high. Fish concentrations farther away than 20 m from
the monopiles are more similar to the concentrations of fish found in the 2003 survey when the wind
farm had not yet been built.
4
3
Didson Monopile,
june 2009
2
1
0
4
3
Didson Transition,
june 2009
2
Frequency of occurrence
1
0
4
3
Didson Open Water,
june 2009
2
1
0
80
60
Acoustic Survey, NSW (T0)
april 2003
40
20
0
120
100
80
60
40
20
0
Acoustic Survey, Coast (T0)
april 2003
0
1
10
100
1000
10000
100000
1000000
Abundance class (kg/km2)
Figure 6 Frequency histogram of the estimated density of horse mackerel from the 15 Didson
observations in three different habitats (‘scour bed directly around the monopile’, ‘transition’ habitat
directly outside the scour bed and ‘open water’ in the wind farm) and compared to the acoustic samples
in the baseline 2003 hydro acoustic survey within the wind farm planning area, ‘NSW’, and the reference
area, ‘coast’).
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The significance of the results for the development of wind power at sea
The results from this study offer insight in the way impact studies for wind farms at sea should be set up.
We show what the possible bias in a large scale hydro acoustic survey would be for different levels of
density around the monopiles. Densities higher than 100 times the density in open water leads to an
underestimation of 8% (Figure 3..). The factor 37 found from the Didson data of the OWEZ wind farm
would lead to an underestimation of 3% in hydroacoustic surveys. We do not yet know the species
composition around the monopiles and how this changes during the season. For this, hydro acoustic
surveys and Didson observations should be carried out in complement focusing on different temporal and
spatial scales ranging from meters to kilometers, and from tidal, daily to seasonal.
Apart from the findings above which address the objective of the study, the study confirms the
expectation that monopiles function as artificial reefs for some fish species. This knowledge can be used
by the managers of marine areas marked out for the building of wind farms. The area may thus have
some potential of refuge for some commercial fish species or have some value as nature reserve due to
the introduction of new habitats.
Potential bias in overall fish density estimates based on open
water surveys in the windpark
1.200
1.001
1.000
0.992
Bias factor
1.000
0.921
Monopile avoidance
Monopile indifference
Monopile attraction
0.800
0.535
0.600
0.400
0.200
0.103
0.000
0
1
10
100
1000
10000
Fish density directly around monopile relative to open water
Figure 7 Potential bias in fish abundance estimates (based on hydro acoustic surveys) when small scale
(<20m) attraction or avoidance to the monopiles in the wind farm OWEZ is not taken into account.
Our findings have a general value. It is likely that monopiles in other wind farms, on sandy bottoms,
have a similar effect on the fish behaviour and small scale distribution as found in our study. This effect
may be different for wind farms built in rocky areas, as in rocky areas monopiles as a habitat for fish are
more similar to the surrounding natural rocky structures. In contrast, monopiles in the sandy areas in
this study are markedly new habitats, attracting different species.
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4. Gaps and missing knowledge
4.1 Short summary of We@Sea research findings.
The We@Sea program has contributed important information concerning impacts of offshore wind farms
on the marine environment, in addition to contributing to the development of promising new monitoring
techniques for fish, birds, and cetaceans. These techniques have their application both within as well as
outside of wind farm related monitoring.
In the past five years Dutch research programs outside the framework of We@Sea have also enhanced
knowledge related to environmental impacts of offshore wind farms. The NSW-MEP program (see chapter
3) studied the impacts of the OWEZ wind farm on benthos, fish, birds and marine mammals and will be
finished in 2011 (Lindeboom, 2010 in prep.). Finally, within the framework of the Birds and Habitat
directives several Environmental Impact Assessments and ‘Appropriate Assessments’ for all new
initiatives for developing offshore wind farms on the Dutch Continental Shelf (DCS) were finalized in the
past few years. These studies were based on available data and knowledge, and highlighted that further
research is needed on impacts of underwater noise (especially related to pile hammering) on fish larvae
and breeding colonies. (referenties).
In other countries surrounding the North Sea the impacts of offshore wind farms on the ecosystem has
been researched and published. The most extensive environmental monitoring programs have been
carried out in Denmark, (referentie). In other countries surrounding the North Sea most studies are still
ongoing and as such not yet published.
With the push for more sustainable energy, wind farms are increasingly being planned and built in the
North Sea. The results from the We@Sea program, as well as from national and international monitoring
and evaluation programs on environmental impacts of wind farms should serve to inform and influence
the planning and design of new wind farms on as well as influence the design and scope of
Environmental Impact Assessments (EIA’s) and Appropriate Assessments (AA’s) for these wind farms.
Within the We@Sea program, the following progress has been made:
•
Maps for wind farm suitability based on various criteria have been made: based on seabed and
subsurface parameters (Section 3.1.3), morphodynamic models of seabed evolution (Section
3.2.1), bird distribution data and the Wind farm sensitivity index (Section 3.2.3), and fishing and
its impacts on fish and benthos (Section 3.2.5). These maps are meant to inform debate on the
pros and cons of wind farm placement.
•
We@Sea research filled in some of the gaps in knowledge on grey seal population development,
diet and habitat use, as well as the hearing sensitivity of harbor seals (Section 3.2.2), enabling
more informed environmental impact studies. In addition, guidelines for collecting and archiving
environmental data have been developed within the Site-Atlas Project. (Section 3.1.1)
•
New monitoring techniques were developed; the bird collision monitoring system WT-Bird
(Section 3.3.2), The ROBIN-Lite bird radar (Section 3.3.3), and a ship borne cetacean
monitoring system (Section 3.3.4). In addition, statistical techniques for the analysis of highly
spatial and temporally variable data (as is often the case for marine fauna) were developed.
These all contributed to an improved base for the future monitoring of wind farm impacts.
•
A promising new high frequency sonar device, the DIDSON, was tested successfully for suitability
for assessing fish distribution and the factors determining this within wind farms (Section 3.3.5).
•
Both a GIS-based tool for assessing cumulative effects within the marine environment,
CUMULEO (Section 3.1.4) as well a conceptual model for the cumulated effects of wind farms on
benthos and fish (Section 3.2.5) were developed, facilitating scenario evaluation for the impacts
of multiple wind farms on the environment.
We point to these sections and the individual reports for specific recommendations arising from this
research.
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4.2 Gaps and suggestions for further research
The contributions of We@Sea outlined within each individual section have been highlighted above. We
stop here to take a helicopter view; synthesizing We@Sea research and highlight the importance of 1)
data collection archiving and updating, 2) Cumulative and Interaction effects with (multiple) wind farms,
3) marine spatial planning and the importance of an integrated vision on placement of marine wind
farms.
4.2.1.
Data
Assessing the environmental impacts of a wind farm under high information uncertainty has been a
recurring theme within We@Sea and allied research. For birds (Section 3.2.3), current bird radar is
located far too close to shore to provide a complete picture on hypothesized gradients in bird fluxes, in
addition while Multi Feeding Associations of birds have been observed in the past, they were not
observed during the 2009 survey period, thus not giving a complete picture on the trophic
interrelationships between different species, and how these are affected by wind farms.
For grey seals, the study of impacts of the wind farm was hindered by lack of fundamental knowledge on
grey seal behavioural ecology. While the We@Sea research filled in some of the gaps (Section 3.2.2),
there is still insufficient information on the seals’ distribution at sea and the large individual variation
within the population poses a challenge to the characterization of this in the future.
Within the allied project MEP-NSW the distribution of pelagic fish has been found so variable on a year to
year basis that a characterization as to the effects of wind farms within statistical bounds is difficult (See
also section 3.2.5). Though the redistribution of pelagic fish has been found within the wind farm with
the aid of promising new high frequency sonar device (DIDSON: Section 3.3.5) it is still at this stage not
possible to determine what exact effect the wind farm has on the behavior of fish. It is intuitive that
marine mammals might avoid the wind farm during pile driving, and harbor seal audiograms funded
partly by We@Sea (Section 3.2.2 ) have found that many anthropogenic noise sources and sounds from
conspecifics are audible to harbor seals at greater ranges than formerly believed. This means that both
the sounds produced during the construction of wind parks (pile driving) and during the operational
phase, are audible over wider ranges than formerly believed. However, the studies of avoidance during
pile hammering were challenged by a low number of tagged harbor seals, making only educated guesses
possible. The question as to how harbor seals, let alone other marine mammals, respond to underwater
noises such as pile-driving, remains.
We@Sea research has, among others, highlighted the lack of basic knowledge for bird feeding
distributions, grey seal reproduction dynamics and feeding, and the uncertainty in our knowledge of the
ecology of the sea. To a certain extent, this uncertainty may be attributed to the lack central data
warehouse, where all relevant data pertinent to environmental characteristics can be found. The creation
of such a site atlas (Section 3.1.1) has highlighted the importance for such a central point for data
collection, as well as the challenges faced in the creation and continuation of such a site. Unfortunately,
the creation of such a site was challenged by legal and practical issues among partners, as have many
similar initiatives in the past. A practical and legally feasible framework for data sharing and warehousing
involving multiple parties remains a challenge.
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4.3 Cumulative and Interaction effects
Several of the We@Sea research projects have produced maps for decision support for optimal wind farm
placement for minimal environmental impact (Sections 3.1.3, 3.2.1, 3.2.3, and 3.2.5). These maps are
focused on specific, single organisms or pressures (i.e. birds, marine mammals, benthos, fish, or
fishing). This raises the issue as to how wind farm placement impacts on the interactions between these
different actors. It may well be that shifts in abundance and behavior impact indirectly, compound across
different trophic levels and lead to quite possibly non-intuitive results. For instance, our results from
benthos-fish interactions (Section 3.2.5), suggest that a shift in fishing mortality due to wind farm
placement may either increase or decrease benthic biomass, depending on size of the wind farm and the
initial mortality before wind farm placement. Finding the nature of such interaction effects induced by
wind farm placement, is not a trivial task. One study, on Multi-Species Feeding Associations (Section
3.2.3) has touched upon the challenges in studying interactions between different species, let alone the
implications of the shift in interactions between species. First, finding the right trade-off between
statistical resolution and survey costs for studying –one- species is already a bit of an issue, however the
implications of studying the interactions between two species, let alone a whole food web may require
more survey resolution as a whole than when studying the species separately. This requires enlightened
survey design, where intelligent choices on survey resolution can be made through support by
predictions given through modeling, and the further development of statistical techniques for the analysis
of highly spatial and temporally variable data, such as already pioneered in Section 3.1.5.
While individual wind farms may have non-measurable impacts on the environment, the cumulative
effects of several individual wind farms require consideration of the effects of each wind farm in
conjunction with all other wind farms and manmade activities in the sea. How do the cumulative
redistributions of mortality, species distributions and species interactions scale with area and distribution
of wind farms? This is a key question raised by results of research of We@Sea and others. The creation
of CUMULEO 1.1 (Section 3.1.4) has gone partway towards resolving this issue, yet it must be stressed
that cumulative effects methodologies are still developing, and are limited by the lack of data and
knowledge on the nature and magnitude of cumulation with wind farm area and placement.
4.3.1.
An integrated approach to planning
We@Sea, as well as many other monitoring programs have focused on the effects of wind farm(s) on
specific, individual environmental factors (for instance on sediment, birds, marine mammals, fish,
benthos), and in some cases on the interaction between two of these factors (benthos-fish, Section
3.2.5; fish-birds & fish-fishers Section 3.2.3). In many cases this research has led to the production of
maps of optimal placement of wind farms based on these criteria. However the recommendations arising
from these maps are sometimes conflicting or exclusive; for instance recommendations for wind farm
placement arising from seabed and subsurface parameters, point to wind farm placement near certain
coastal areas (figure X, Section 3.1.3), whereas maps created using the bird wind farm sensitivity index
(figure X, Section 3.2.3) point to these same coastal areas as areas of major concern for wind farm
placement. Perhaps one way forward,the usage and development of techniques for both weighing and
trading-off the different environmental impacts as well as the socio-economic constraints involved in
wind farm placement. In addition, the role of wind farms and wind farm placement must also be
considered within the context of the many other conflicting usages of the sea. Quantitative models and
methods for prioritization of environmental and economic interests, such as, for instance MARXAN (Ball
and Possingham 2000, Possingham et al 2000) or MARZONE (Watts et al 2009) are widely used tools for
marine spatial planning which could accommodate at least a partial weighing of these interests. In
addition broad stakeholder participation in the process of planning and evaluation of the use of sea is to
be recommended as a means of fostering broad societal support for the outcome of such a hypothetical
exercise.
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5.
conclusions
Research line 2 of We@Sea generated many new scientific results with respect to the environmental
aspects related to offshore wind farms during the past 5 years. Furthermore new monitoring techniques
have been developed of which some are now being used in studies around offshore wind farms. Other
techniques showed promising results but need further development. Finally new methodologies were
developed that can aid in integrated assessment of the development of multiple wind farms on the North
Sea and in determining cumulative impacts. Most of these methodologies are promising but also need
further development in order to be applicable in future planning issues around offshore wind farms on
the North Sea.
Despite these extensive research programs a lot of research questions still remain. Furthermore it is
expected that in the period 2011-2013 three new offshore wind farms will be build on the DCS and that
from 2014-2020 around 5000 MW of offshore wind energy will be installed on the DCS. Anticipating this,
the Dutch government has started the development of an integral ecological research program, which is
expected to start in 2010 and last for 5 to 10 years (Boon et al, 2010 in prep.) The (intermediate) results
of this research program will be used in future environmental legislation and future spatial planning
related to offshore wind farms on the DCS. However, it is possible that the plans for development of
offshore wind farms run far ahead of the knowledge necessary to estimate the impacts on the
environment of these wind farms.
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6
Quality Assurance
IMARES utilises an ISO 9001:2008 certified quality management system (certificate number: 578462009-AQ-NLD-RvA). This certificate is valid until 15 December 2012. The organisation has been certified
since 27 February 2001. The certification was issued by DNV Certification B.V. Furthermore, the chemical
laboratory of the Environmental Division has NEN-AND-ISO/IEC 17025:2005 accreditation for test
laboratories with number L097. This accreditation is valid until 27 March 2013 and was first issued on 27
March 1997. Accreditation was granted by the Council for Accreditation.
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References
Kastelein, R. A., van der Heul, S., Verboom, W. C, Triesscheijn, R.J.V., and Vaughan- Jennings, N.
(2006a). “The influence of underwater data transmission sounds on the displacement of captive harbour
seals (Phoca vitulina),” Marine Environmental Research 61, 19-39.
Kastelein, R.A., van der Heul, S. Terhune, J. M., Verboom W.C. and Triesscheijn, R.J.V. (2006b).
“Deterring effects of 8-45 kHz tone pulses on harbor seals (Phoca vitulina) in a large pool,” Marine
Environmental Research 62, 356-373.
Kastelein, R. A., Wensveen, P. J., Hoek, L., Verboom, W. C., and Terhune J. M. (2009a). “Underwater
detection of tonal signals between 0.125 and 100 kHz by harbor seals (Phoca vitulina)”, J. Acoust. Soc.
Am. 125, 1222-1229.
Kastelein, R. A., Wensveen, P., Hoek, L., Terhune, J. M. (2009b). “Underwater hearing sensitivity of
harbor seals (Phoca vitulina) for narrow noise bands between 0.2 and 80 kHz”, J. Acoust. Soc. Am. 126,
476-483.
OSPAR Commission (2009) Overview of the Impacts of Anthropogenic Underwater Sound in the marine
Environment. Bio Diversity Series, pp 133.
Camphuysen CJ 2002. Post-fledging dispersal of Common Guillemots Uria aalge guarding chicks in the
North Sea: The effect of predator presence and prey availability at sea. Ardea 90(1): 103-119
Dewicke A, Rottiers V, Mees J & Magda V 2002. Evidence for an enriched hyperbenthic fauna in the
Frisian front (North Sea). Journal of Sea Research 47: 121-139
Garthe S & O Hüppop 2004. Scaling possible adverse effects of marine wind farms on seabirds:
developing and applying a vulnerability index. Journal of Applied Ecology 41: 724-734
Ens BJ, Bairlein F, Camphuysen CJ, de Boer P, Exo, K-M, Gallego N, Klaassen, RHG, Oosterbeek K &
Shamoun-Baranes J 2009. Onderzoek aan meeuwen met satellietzenders. Limosa 82:33-42
Hedd A, Regular PM, Montevecchi WA, Buren AD, Burke CM & Fifield DA 2009. Going deep: common
murres dive into frigid water for aggregated, persistent and slow-moving capelin. Marine Biology
156:741–751
Helfman GS 1993. Fish behaviour by day, night and twilight. In: Pitcher TJ (ed). Behaviour of teleost
fishes, pp. 479–512. Fish and Fisheries Series 7, Chapman and Hall, London
Leopold MF (1991) Toppredatoren op het Friese Front: zeevogels en zeezoogdieren. In: de Gee A, Baars
MA & van der Veer HW (eds). De Ecologie van het Friese Front. NIOZ Rapport 1991-2: 79-89, NIOZ
Texel
Nevins HM, Harvey JT & Adams J (2004) Diving behavior and aerobic dive limit of the Common Murre
(Uria aalge). Chapter 3 in: Nevins HM (2004) Diet, demography, and diving behaviour of the Common
Murre (Uria aalge) in central California. MSc thesis, San Francisco State University
Hyder, 1999
Hyder. Consulting guidelines for the assessment of indirect and cumulative impacts as well as impact
interactions. Brussels: EC DGX1 Environment, Nuclear Safety and Civil Protection; 1999.
Canter and Kamath, 1995 L.W. Canter and J. Kamath, Questionnaire checklist for cumulative impacts,
Environ Impact Assess Rev 15 (1995), pp. 311–339
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Justification
Rapport C140/10
Project Number:
430.2501.301
The scientific quality of this report has been peer reviewed by the a colleague scientist and the head of
the department of IMARES.
Approved:
Dr. ir. R. Hille Ris lamberts
Researcher
Signature:
Date:
Approved:
2010
Dr. ir. T.P. Bult
Head of Fisheries Department
Signature:
B.a.:
Date:
2010
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Appendix 1 Summaries of all research projects within Research line 2
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2004-003 Site atlas cumulative effects
Placing a large number of offshore wind turbines at the North Sea as envisaged by the Dutch
government for the period until 2020 puts increasing demand at available sea space. It can be expected
that this development will cause a number of challenges and especially competition with existing user
functions within the available North Sea space. These key user functions as a consequence will be limited
in their demand for space, and include interlinked effects. This report describes the definition phase of an
application project closely linked to a We@Sea “Site atlas” research sister project. The main aim of this
application is enabling a balanced judgement between different aspects linked to and associated with
developing offshore wind farms. The focus thereby is at cumulative effects such future offshore wind
farms may impose at nature, marine environment and (marine) safety.
A definition of “Cumulative effects” as mentioned in this study mainly refers to what interaction(s) may
take place when two or more offshore wind farms are distanced relatively close to each other. However,
cumulative effects can also occur already within a single offshore wind farm. Here, wind turbines directly
facing the dominant wind direction capture for instance a larger quantity wind energy compared to
equivalents positioned in their wake. There is also a clear trend for new planned & built offshore wind
farms to grow in average size (MW base). Some of these new projects cover an area similar or even
larger compared to several smaller wind farms built in the past.
Interaction
Assume that as part of an experiment individual turbines are systematically added to the existing stock.
It then seems logical to assume that total wind farm effect (i.e. in terms of energy yield or space
utilisation) each time linearly increases with the effect of a single unit added. In a situation when this is
no anymore valid and the effect either increases faster, or alternatively is reduced less than expected,
the interaction that occurs can be described as a “Cumulative effect.”
Cumulative effects can be relatively easy determined for a single offshore wind turbine, or a wind farm of
limited size. An appropriate common instrument is in such cases a so-called Environmental Impact
Assessment (EIA; in Dutch MER). However, cumulative effects linked to a large number of wind farms
being built are at the moment rather difficult to predict.
A positive decision favouring the construction of a new offshore wind farm at a planned location does
depend on several main considerations. One essential precondition is that the specific location has not
been claimed for one or multiple alternative and often-competing user functions. Three main decision
criteria include:
1. Cost and benefits. An offshore wind farm has to earn revenues to the owner/operator,
otherwise it will simple not be built;
2. Environmental and safety aspects (i.e. EIA). The offshore wind farm should not cause
unacceptable environmental damage and other harmful effects, and/or unacceptable risk of
damage and injuries;
3. Social cost-benefit analysis, whereby envisaged benefits should at least match added costs.
As a trend these social wind project aspects gain in importance as part of the overall decisionmaking process.
Cumulative aspects do play a key role in all three main “Go – No go” project criteria. In many
circumstances whereby a linear link between number of turbines and associated effects is expected,
‘effect summation’ is applied as method. In a number of cases interactions play a key role and can either
amplifying, mitigating, or threshold effects be determined.
Main themes
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With regard to cumulative effects, as part of the study effort a number of main themes have been
identified as important. These include birdlife, shipping safety, energy yield, below water surface noise
emission, landscape/ perceptions and above water noise. A commission responsible for the Dutch MER
explicitly names cumulative effects on birdlife and shipping safety as important. For wind farm
owners/operators by contrast energy yield is a factor of crucial importance.
The researchers found that current calculation rules applied in MER studies are unsuited to deal with
these cumulative effects. At the same time including cumulative effects is regarded important for both
individual MER procedures as well as strategic future use of Dutch territorial waters (NCP). It is therefore
crucial to create improved understanding of these cumulative effects and start developing state-of-theart calculation rules and adapted methodologies. Simultaneously, time pressure is high due too the fact
that during 2005 – 2007 a substantial number of offshore wind farm MER studies will be conducted plus
project concessions issued.
Finally, this ‘definition study’ contains an inventory of potential cumulative effects described per specific
theme, with a focus at state-of-the-art and the nature of dedicated know-how gaps. The inventory
specifically shows that developing better-adapted calculation rules and methodologies will not be easy.
That in turn is largely due to the fact that required fundamental (background) knowledge at the moment
is either scarce or insufficiently available. Considering the tight timeframe it is therefore recommended to
already commence developing temporary rulings on cumulative effects based upon state-of-the-art
know-how. It is further recommended to join-in with existing research and simultaneously start
preparations for well-defined future studies, both aimed at finding appropriate solutions for current
know-how gaps. Such a determined dedicated approach has the potential to result within a two-year
period into a set of optimised calculation rules/methodologies and/or an optimised data set for carrying
out these calculations.
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2005-004 Integration application cumulative effects; Cumuleo 1.0 development
The CUMULEO development effort further builds on main findings of the We@Sea 'Site atlas cumulative
effects' definition study (report 2004-003).
There is growing demand for improved understanding of cumulative effects linked to the planned building
of multiple North Sea offshore wind farms. At the moment there is insufficient relevant know-how
available on how to deal effectively with the issue of quantifying such cumulative offshore wind farm
effects. Conceptual know-how is for instance almost totally lacking with regard to effects summation.
This shortcoming is reinforced by the fact that basic information on specific 'nature values' almost lacks
completely too. Simultaneously these combined data are essential background data for being able to
allocate eventual cumulative effects like those on the distribution and ecology of certain species.
The main project objective was to develop calculation rules focused at determining cumulative effects
linked to multiple offshore wind farms, all located in a confined area. These calculation rules have been
developed for a variety of themes including landscape & perception, and nature and environment (birds,
sea mammals, fish, and sea fauna).
This project further marks a first dedicated effort to develop a conceptual know-how base necessary for
describing cumulative effects linked to several offshore wind farms spaced relatively close to each other.
These interaction effects have been studied for various 'subject groups' including birds, under water
sound, benthos and landscaping/perceptions in relation to operational and new planned offshore wind
farms.
Dedicated support tool
This report describes main results of a development track aimed at designing a dedicated support tool for
describing offshore wind farms related cumulative effects. The tool is named CUMELEO 1.0, and the
acronym stands for 'CUMULative Effects of Offshore wind farms'. The calculation rules themselves are
based upon the current state-of-the-art with regard to available know-how base. In future when relevant
new know-how becomes available, these calculation rules can be refined. However, the project excludes
cumulative effects linked to offshore wind farms in a combination with other North Sea user functions.
New Dutch legislation regarding application rules for the 'Wet beheer
rijkswaterstaatwerken (Wbr)' came into effect at December 31, 2004. Perhaps most important, the
legislation clears the way for constructing new offshore wind farms in the Dutch Exclusive Economic Zone
(EEZ). It is also in support of the government objective to build a cumulative 6,000 MW offshore wind
capacity by 2020. In response to the new legislation a total of 78 keen developer consortia submitted
'starting documents' subdivided over 48 different sites, each known as a 'unique location'. Interestingly
the cumulative installed capacity of these 48 locations adds up to 21,000 MW, a factor 3.5 higher than
the initial 6,000 MW offshore wind objective.
The Dutch government further decided to delegate selection of offshore locations to market parties,
instead of choosing for a steering role that involves determining preference locations. This offshore wind
power positioning has fuelled demand for a dedicated support tool like CUMULEO. Cumulative effects
have to be viewed in relation to the currently already intensive use of the Dutch EEZ for a range of
different activities including shipping, commercial fishery and mining. Furthermore, it is vital to pay
sufficient attention to key nature values and other relevant issues all requiring protection at national as
well as European (EU) legislative levels. As part of Environmental Impact Analysis (in Dutch MER) rulings
for new planned offshore wind farms, developers are obliged to provide comprehensive background
information to the responsible authorities. That package includes sufficient clarification on cumulative
effects linked to already operational and/or other planned wind farm projects, as well as additional
ongoing and/or planned North Sea user applications.
GIS technology basis
With regard to main functionally aspects CUMULEO is based upon Geographic Information System (GIS)
technology, which is essential considering the three-dimensional disturbances to nature and specific
values that need protection. CUMULEO v1.0 as a main function comprises a sequence of working steps,
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which can all be performed with the aid of GIS-based maps earlier developed as part of the We@Sea Site
atlas project.
The calculation rules have been applied first as part of a fictive scenario, which analyses cumulative
effects on ten 'small' offshore wind farms of 100 MW each (all 28 x 3.6 MW). These fictive ten wind farm
sites are all located off the Zuid Holland province Noth Sea coast.
Furthermore, per theme a calculation rule has been developed on the basis of several predefined
assumptions. Next step was analyzing this theme scenario with as its basis the outcomes of a cumulative
effects search. This was followed by determining an eventual need for further optimizing, and with a
main focus at either calculation rules and/or basic background information. That in turn can provide the
basis for future We@Sea projects.
The calculation rules have finally been tested at planned Dutch North Sea wind farms OWEZ (former
NSW) and Princess Amalia (former Q7-WP).
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2005-005 Analysis of seabed and soil quality required for wind farms
Spatial offshore wind farm location selection and planning requires reliable and relevant data that can be
obtained with the aid of decision-supportsystems.
Compiling an overview of necessary main parameters was therefore considered desirable within the
framework of the We@Sea researchprogramme, for which purpose a research area West of the Dutch
coastline had been allocated.
The central research question formulated was finding answers to the influence of abiotic seabed
characteristics linked to the windfarm construction phase and exploitation costs during operation.
In biology, abiotic components are defined as non-living chemical and physical factors in the
environment.
Figure 1. Research area West of the Dutch coastline.
Long-term stability
A second interlinked main question is on long-term wind turbine stability and efficiency. Various physical
parameters provide essential process know-how and system knowledge, which in turn can be translated
into applicationmodels. Two key envisaged benefits linked to this approach are avoiding unnecessary
field research at unsuitable locations, and substantial investment costs saving during a wind farm
preparation phase.
When determining the suitability or non-suitability of a specific location for offshore wind-farm
development, obtaining environmental data on the composition of seabed sediment layers is essential.
Additional data on the composition and structure of subsurface layers, seabed morphology, andhydroand morphological dynamic variables are required too. Furthermore, a comprehensive overview of
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physical seabed main parameters linked to specific design aspects of individual turbine-support
structures and complete offshore wind farms, allows sea area identification with a well-defined
suitability ranking order. This preparation process has to be completed first before engaging into detailed
site surveys.
Sediment grain size
Physical seabed-sediment characteristics are important parameters in seabed behavior during and after
wind-farm construction. Seabed sediment composition plays a role in the degree of seabed erosion
(scouring) and in the formation of suspended-sediment plumes. The most suitable parameter for
characterizing seabed sediment grain size in a (sandy) research area is by taking the median of a sand
fraction (63 - 2000µm). This typically shows finer grain sediments measured along a South - North
geographical line. However, the northward direction finer grain sediment pattern is overridden along the
coastline, where finer sediment particles are relatively abundant. The global pattern is further interrupted
when moving offshore from Texel, a Dutch North Sea island, where a seabed gravel layer lies fully
exposed.
A second relevant seabed-sediment parameter is mud content. In the research area, this share is
generally less than 2%. Near the coastline, higher values do occur, particularly near the Rotterdam
harbour entrance.
Both structure and composition of the seabed subsurface are important parameters governing the
stability and cost of turbine foundations.
Value lost
Detailed seabed subsurface knowledge is also essential when analyzing the value lost to society in case
valuable resources have become temporarily or no longer exploitable. The same situation may apply
when archaeological treasures are being disturbed.
Locally, fine-grain sediment deposit thickness generally measures over 10 metres. Such locations are
potential offshore wind farm exclusion areas.
A fully functioning layered model for the upper 50 metres of the seabed subsurface is not yet available.
Any description of subsurface structure and composition must therefore necessarily be based upon
imperfect grids for establishing both extent and thickness of individual seabed soil layers.
Information on main geotechnical parameters of these layers is scarce, but
can be applied to constrain their ranges.
Morphology, like for instance the difference between migrating seabed crests
and troughs, is a potential seabed dynamics phenomenon. Between the Texel and Hoek van Holland
geographical latitudes water depth increases gradually from 0m at the coastline to about 35 metres at
the territorial boundary with the UK continental shelf. However, large-scale tidal ridges measuring up to
10 - 20m in height interrupt this gradual water depth increase pattern.
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Sand waves
The research area is also characterized by sand waves - smaller-scale seabed formations with heights
measuring between 1 - 10m. In general, sand waves height decreases in Southwest to North Eastern
direction. Sand-wave migration rates are highest near the coast, and range from almost 20metres per
year to the extreme Northeast of the research area to less than 1m annually in the South Western part.
A rule of thumb is that water depth is linked directly to wind turbine foundation height measured from
seabed to the sea surface and thus represents a measure of cumulative installation cost.
Simultaneously, there are no set rules to define and compare seabed-related economics and
environmental costs. A first order area suitability assessment for future wind farms can be conducted by
implementing a penalty-points system, which has resulted into a first usable geological grid design. Such
a geological grid can be regarded a building block within decision-support systems. In this specific
exercise it shows that the most suitable areas for Dutch offshore wind-farm development are situated off
the Zuid-Holland province coastline.
Useful instrument
Finally, a penalty-points approach also has several imperfections and application drawbacks. Not all
underlying grids appear to be up-to date.
Several of these grids for instance offer no full area coverage, and many thickness values linked to
specific grids are also missing. In addition, the availability of units applied during a suitability grid design
does not reflect their maximum extent but instead show a presence at the top of the Pleistocene and
Holocene sequences. Despite these drawbacks, the first order grid design serves as a useful instrument
for assessing potential economic and environmental costs linked to offshore wind farm development.
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Table 1: Stratigraphic units present in the subsurface of the North Sea Basin. Table 1: Stratigraphic units
present in the subsurface of the North Sea Basin.
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2005-012 We@Sea Site - Atlas
Organisation TNO division Construction and Spatial Development
TNO project number 016.54109
Report name We@Sea site-Atlas
Research Area RL-2
Report numbers WE@SEA 2005-012
TNO-rapport 2007-D-R0073/A
ISBN-number 978-90-5986-232-6
Authors Th.A.M. Reijs
G.M. Bouma
J.T. van der Wal
V.G. Blankendaal
Date January 30, 2007
We@Sea Site-Atlas
The Site-Atlas project has been conducted as part of the We@Sea research programme and fits under
research line 2 named ‘Spatial planning and environmental aspects.’ Central theme of the We@Sea SiteAtlas project was allocating all relevant information required for the construction and operation of
offshore wind turbines in a safe and economically sound manner and with minimised environmental
impact.
For the assessment this central theme has been subdivided into three main research items or
subprojects. At first specific demands for the Site-Atlas by different parties involved have been assessed
(subproject 1). The second subproject involved an inventory of already existing available know-how
supplemented by additional relevant information sources. A third and final subproject focused at layout
and presentation issues, and encompassed the development of a structured Site-Atlas framework base.
The demand side assessment allocated key areas where specific know-how is required, as well as these
parties that indicated a need for such dedicated inputs. An example of potential We@Sea databases is
provided below:
Examples of potential We@Sea databases
• Biology: plankton, benthos, birds, fish, sea mammals, et cetera
• Physical parameters: seabed (soil composition, sand dunes, et cetera), wind, wave patterns
• Economic parameters: wind turbine/farm yield, O&M costs, grid connection, wind farm design options
(wind turbine make & type, configuration et cetera).
• Site specific issues: optional North Sea use applications, Marine Protected Areas et cetera
Some of the offshore wind power development parties include offshore wind technology and transport
logistics suppliers, project developers, utilities, investors, and insurance companies. In addition research
organisations, government bodies, environmental and other action groups, energy consultants, and O&M
service providers.
Phases
The assessment method itself involved conducting a number of interviews and workshops with parties as
indicated above, whereby a difference was made between three distinct offshore wind farm project
phases:
- Planning;
- Construction;
- Operation.
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The overview of main findings was subdivided into nine main question categories:
1. General (policy issues, management control and protection);
2. Soil and water;
3. Nature and environment (ecological processes, species, habitats, eco-labelling);
4. Human activities (fishery, recreation, transport, energy and mineral resources, military defence,
aviation, business);
5. Coastal protection;
6. Energy yield (offshore wind turbine technology development, costs and benefits of wind power
generation);
7. Perceptions, involvement, natural history and landscape added value aspects;
8. Design.
The above questions themselves have been put forward from various organisations each with their own
specific perceptions and viewpoints. These parties include the commercial business sector, the public
sector, and other organisations with a key focus on social issues including (perceptions on) wind power
acceptance.
Comprehensive
As part of the overall assessment an inventory check of already available in-house know-how base with
Dutch and foreign We@Sea-partners was conducted. That in turn resulted into a data overview and a
datasets composition ranked on subject.
From the assessment it became clear that there is already a comprehensive amount of information on
offshore wind power available. However, a sizable proportion includes geographical maps but these often
lack essential background information. In such situations it remains unclear which specific datasets have
been linked to information made visible on these maps. Conducting an independent data analysis
becomes then almost impossible.
One specific field where data are still largely lacking are so-called cumulative effects, and a better
understanding requires in-depth investments.
Linking datasets
The next step involved linking dedicated demand and supply datasets in order to determine their internal
match, and further to pinpoint potential information provision gaps.
The Site-Atlas concept idea aimed at making all these data available in a systematic and easily accessible
manner. The design of such a Site-Atlas is not limited to one concept only. For this project four potential
alternative options have been explored:
•A website with specific links to organisations in possession of a relevant
database and additional (scientific) literature reference sources;
•We@Sea conducts an intermediate role by providing datasets and models to its partners;
•GIS functionality linked to datasets and models:
-Displaying data with the aid of dedicated maps;
-Information search function for specific areas;
•Online models partly based upon GIS data.
Discussions with We@Sea partners and other parties involved clearly indicated a main preference for the
first option (website with links to organisations). A variant worth considering is to offer organisations in
possession of a relevant database the possibility of ‘filling’ the We@Sea website with their own data that
they are willing to make available. However, one essential precondition is that in the latter scenario all
datasets made available do meet stringent standards in terms of accuracy and reliability as formulated
by We@Sea’s programme bureau. An additional key demand is to keep the database up to date, which
requires a continuous effort. That in turn is due to the fact that offshore wind power development takes
place in a still young but highly dynamic (market) environment.
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It is in principle not part of We@Sea’s main task package to conduct data inventory search projects. On
the other hand the programme bureau does have a primary task in developing a system incorporating a
suitable methodology that enables We@Sea to effectively direct and control specific research projects.
This in-house capability is particularly important with regard to policy procedures for offshore wind
farms, today one of the main bottlenecks hampering overall progress. In the latter case and for other
relevant (related) issues the programme bureau can indicate what specific know-how gaps do exist and
require a sustained research effort.
Specific phases
Information required finally depends on specific offshore wind farm development phases like site
assessment, installation, operation, and demolishing/recycling. It has also become clear that the
application of a We@Sea Site-Atlas needs to be strongly linked with offshore wind farm monitoring
programmes that are conducted currently at the Dutch section of the North Sea and elsewhere.
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2006-006: GIS-technology and the analysis and forecasting of change in the marine
environment
Analysing and forecasting of change in the marine environment; a method for identifying
impact of large-scale offshore wind farms on marine fauna
The North Sea provides a range of services to a variety of commercial sectors. These include fishery,
shipping and port development, tourism, oil & gas extraction, while offshore wind power development is
an activity of more recent date. Next to these economical services, the North Sea also provides home to
diverse fauna.
Marine environment monitoring and studying the environmental impact of multifunctional North Sea
space usage are in that respect considered of key importance. As such this offshore wind power related
research project fits into a wider context with clear and comprehensive sustainable development
objectives laid down for the vast and intensely used area.
Marine ecosystem & offshore wind farms
With respect to offshore wind farms, attempts are being made within the We@Sea project context, as
well as through additional research efforts to assess their overall impact on the marine environment.
More specifically, attention is focused at monitoring direct and/or indirect impacting effects that offshore
wind farms might impose upon organisms and habitats being part of the North Sea marine ecosystem.
However, assessing such impact based on monitoring data is far from simple. One of the reasons is that
the marine environment itself represents a complex system, with many different types of organisms and
phenomena interacting in an inter-related and often unpredictable manner.
For instance, a decrease in numbers of a given seabird species after wind farm completion can be viewed
as an indicator of a negative post-construction impact effect. But a question to be raised here is whether
this decrease in seabird numbers can be attributed solely to the new wind farm. Or are other likely
contributing causes to blame, such as sea temperature front location and/or natural variability unrelated
to such a specific project? Understanding spatio-temporal behaviour of specific species and their
interrelation with other marine phenomena is therefore an essential prerequisite for assessing whether or
not there has in fact been any measurable impact.
An earlier literature review clearly indicated that when conducting impact assessment studies involving
seabirds, the method should include external factors other than the presence of an offshore wind farm.
These factors may be physically understood relationships (e.i. temperature fronts attract seabirds
because of good feeding conditions), statistically described and/or observed long-term trends within
large-scale seabird distribution patterns. All these factors may generate variability in species patterns
that need to be accounted for when assessing possible post-construction situation deviations in and
around a specific offshore wind farm. Therefore, in order to assess post-construction wind farm effects on
seabirds in a scientifically sound manner, information on species
“history”, and actual dynamic factors affecting the numbers of seabirds counted during surveys should be
included.
Research challenges
Insight in marine fauna spatio-temporal behaviour is often hampered by high variability occurring over
different scales, a phenomenon that turns data collection and a proper understanding of accumulated
findings into a complex task. Analysing seabird distribution inside a given area for instance shows spatial
variation that may be related to patterns in external factors (such as water turbidity), plus annual
variations among others due to population dynamics. In addition seasonal, monthly, weekly, or daily
variations may occur, related for instance to potential spatio-temporal variations in food resources and
daily rhythms. Therefore, changes in a marine fauna situation can be related to wind farm presence but
may also be caused by ecological, physical and other factors including human activities like commercial
fishery.
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Besides above-mentioned conceptual issues, wind farm impact studies represent considerable challenges
related to data collection limitations. Marine data collected for impact studies for instance tend to be
scarce and patchy distributed in both space and time and are affected by detection errors (due to for
instance varying visibility conditions, or seabirds may be diving to catch prey). The fact that data
characteristics tend to violate statistical assumptions required for their analysis is another main issue.
Furthermore, data values can become blurred by other factors occurring at a different scale.
As a consequence, marine ecologists face a real challenge on how to proceed with these impact
assessment studies. The latter require an analysis procedure capable of accommodating species
behaviour in both space and time. The research projects main aim is to develop such a procedure. This
procedure should also be capable of accommodating site- and species specific knowledge in a flexible
manner such that it can handle increasing insight over time. In a practical sense, the framework should
enable ecologists to assess whether accumulated observations on given species numbers provide
sufficient evidence of possible changes resulting from (a) wind farm presence.
Results
As part of this research project an analysis method based on geo-statistical simulation has been
developed. The method assesses whether observations of spatio-temporal variation in marine fauna
abundance (count data) within the wind farm area and its surroundings, both pre- and post construction, offer indeed evidence of impact.
The method comprises two main aspects:
1. Explicitly account for time-varying spatial structure in species abundance over various scales
2. Account for the effect of differences in pre- and post-construction survey effort and design.
In order to demonstrate the method’s applicability in a real impact assessment environment, it is
currently being applied at the OWEZ (former Egmond aan Zee) offshore wind farm site. The goal is to
identify whether, based on pre- and post-wind farm construction monitoring of guillemot abundance,
changes occurred in the number of guillemots in the wind farm area that are unlikely explained by known
patterns of variability. See also:
http://www.seaonscreen.org/vleet/index‐eng.php?use_template=ecomare.html
&item=sea&pageid=guillemot.htm
No evidence
Based on the analysis carried out to date (September 2009) it is expected that the monitoring results will
not provide sufficient evidence of measureable impact caused by the Egmond wind farm. This conclusion
is valid for current levels of understanding on how guillemots respond to various dynamic physical
conditions. Finally for assessing the impact of wind farms on seabirds, monitoring known explanatory
physical conditions at both localised and larger scales is required.
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2004-001 Mussel 'map of opportunities' at the Nordsea
The Dutch 6,000 MW offshore wind power objective for 2020 puts a considerable claim to the use of
available North Sea space. However, it also offers unique opportunities for alternative user functions
including mussel cultivation. At the moment this activity takes typically takes place in sheltered shallow
water coastal areas worldwide.
This report discusses the current status in the world regarding commercial offshore mussel cultivation in
deep-water open sea. Secondly, with as its functional bases ‘natural’ mussel growth locations, an
indicative map marking those Dutch North Sea areas potentially suitable for mussel cultivation and/or
mussel seed collection has been drawn up. Conducting mussel cultivation activities in deeper water and
at open sea as a novel marine development and economic activity is still at an infant stage. Furthermore,
a clear majority of all available information on the subject originates from universities and research
institutes, and typically not from commercial parties. And while it is indeed true that several companies
did commence already with commercial mussel cultivation at open sea, no examples have been found of
projects operational for several years undisturbed.
Innovation leap forward
Developing open sea mussel cultivation necessitates a leap forward in terms of innovation, including the
development of a different expertise field compared to what is available today in the Netherlands. In
other words, the nature of demanding North Sea offshore conditions requires the development of a
dedicated integrated cultivation technology (support) package adapted to these specific circumstances.
In addition, potential future successes linked to open sea mussel cultivation will be to a large extent
location bound. Furthermore, a variety of factors pledge for gradual step-by-step mussel cultivation
nursery development including extensive pilot testing at location. Some potential uncertainties include
for instance actual seed production, storm damage risks, and sufficient materials durability. In addition
risks of yield losses due too premature mussel separation from their growth cultivation ropes and/or
losses caused by predation. Besides technological obstacles that need overcoming, it is equally important
to consider alternative ways to prevent potential conflicts breaking out between different North Sea user
application groups like shipping, sand extraction, and fishing.
The bulk of research project conclusions do seem in support of open sea mussel cultivation as a
technically feasible venture, but simultaneously the economic feasibility remains at the moment largely
unclear. The latter uncertainty is especially linked to the fact that new and innovative technologies are
required and these for the greatest part still need developing. For the specific Dutch situation a pilot
project spread over different locations and conducted during a 3 – 4 year period, can substantially
improve understanding on the overall economics linked of open sea mussel cultivation. Equally important
is to draw sufficient attention to appropriate legislation that is controllable and workable at the same
time.
Only after completing a systematic and above all realistically designed pilot phase it will be possible to
properly judge on overall feasibility and the potential of commercial North Sea based mussel cultivation.
Mussel opportunity map
Based upon results found during mussel growth field measurements at floating buoys, a mussel
cultivation opportunity map indicates potentially suitable locations for mussel cultivations and/or mussel
seed production. A first indicative result drawn from studying mussel growth at buoys clearly shows that
the phenomenon occurs within the entire North Sea area. However, the same buoy field measurements
performed at different North Sea geographical areas show that some do better than others in terms of
total mussel numbers counted. In addition, substantial differences were found between individual North
Sea buoys with regard to mussel weight increase, whereby meat percentage is a common measure for
mussel quality. And despite the fact that mussel quality varies during the seasons, and measurements
were not taken within the same season(s), the actual mussel meat percentage as such offers a
reasonable quality indicator. It will finally be essential to conduct a series of specific measurements in
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order to determine overall suitability of given specific locations for mussel cultivation and/or mussel seed
production. If proven viable and successful open sea mussel cultures can potentially contribute towards a
measured offshore wind power energy generation cost reduction.
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2004-007: The influences of wind farms on benthos and fish
An exploration of suitability for wind farm placement in the Dutch North Sea with particular
reference to benthos and demersal fish
Many offshore wind farms are currently being planned in the Dutch section of the North Sea, and often
these areas are closely spaced to commercial fishery sites. That in turn may have serious nature
conservation related implications on organisms habituating these areas, but may also impact the fishery
industry (“spill-over” effect). Whether or not these area closures will be effective depends both on
species interaction within wind farms, and dedicated location specific conditions. This research project
applies existing data from routine surveys aimed at examining the distribution of demersal fish and
benthos. Benthos is a variety of organisms that live near, on, or into the seabed, known as benthic zone.
They live in or near marine sedimentary environments, from tidal pools along the foreshore, out to the
continental shelf, and then down to the abyssal depths. In addition, the project analyses their potential
sensitivity to mortality and thus potential response to wind farm placement, for which specific
recommendations are given. Furthermore, a derived model analyzes the effects of area closure on
interactions and population dynamics for both fish and benthos. It finally studies the shift in fishing effort
by Dutch trawlers as a result of the recent construction of two wind farms near Egmond aan Zee (OWEZ
and Princes Amalia).
Undisturbed benthos
A desk study conducted by the North Sea Foundation examines and evaluates a wide variety of variables
and potential effects linked to offshore wind farm construction and operation. One of the main topics
studied was whether closure to fishing activities will have a positive effect on (local) benthic species and
fish species on a population level scale. A 2008 review revealed for instance that no evidence in support
of any positive effect resulting from small closed areas on fish species population levels was found.
Furthermore benthos within European offshore wind farm boundaries was generally found to remain
undisturbed by wind turbines. Only for sessile benthic species a positive effect is expected.
In addition natural variations in benthic fauna was found to be of such a large extent that differences
between wind farms and reference areas are regarded as non-significant. Another finding was that
epifauna on the monopiles and supporting rocky substrate around the structures did not differ
significantly from reference areas with a similar soil surface. At two Swedish wind farms, mussels
occurring on the piles were also located at the surrounding sandy sea bottom. And within a Danish wind
farm organisms that normally live on rocks, were again found on mussel stacks that had dropped from
the monopile foundations onto the sandy sea bottom.
Large differences were detected during research on fish presence in and around wind farms, set against
undisturbed reference areas. However, natural variation in fish populations was also found to be high,
while detected differences were within natural variation of these areas and therefore non-significant.
During calm weather, divers observed several fish species around monopiles of spinning wind turbines.
During such low-wind conditions the installations produce relatively little noise. However, while turbines
noise can potentially disturb fish, current knowledge on these effects is insufficient for informed decision
making on (preferred) wind farm locations.
Wind farm size
A potential effect linked to existing operational wind farms is the spreading of organisms from piles and
rocks to the sandy sea bottom where they disrupt the existing ecosystem.
Closure of wind farm areas for fishery activities will most likely show a positive effect on local benthic
fauna and this observation is valid for wind farms of any size. For migratory benthic organisms, a wind
farm must have a minimum 2,500km2 size. And in order to have a positive impact on population level
for limited migratory fish a wind farm requires a minimum 10,000km2 size.
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However, both above sizes do not fit within current Dutch government plans for building wind farms
totaling an area of “only” 1,000 km2.
Within the above context it should also be noticed that the bulk of evidence on (potential) effects
resulting from offshore wind farm placement has been derived from either only a single or few projects.
And as such conclusions from this literature review do not necessarily apply for the scaling up to multiple
wind farms occupying large areas of North Sea space.
Marine Protected Areas (MPA ’s) are valuable tools for conserving nation's natural and cultural marine
resources as part of an ecosystem approach to management. As part of this research three aspects
connected to MPA closure for fisheries, benthos, fish and fishers have to be taking into account and were
all examined. One assumption is that closure of a marine area will have a positive effect on communities
at a scale larger than the protected area itself. These envisaged effects might either occur directly
through organism mortalities reduction within a protected area, or indirectly caused by changes in
resource availability due to shifts in species composition and abundance.
Composition and disturbances
Recent studies examine effects of benthic community composition and productivity disturbances by
linking them indeed to marked shifts within these areas. Translating such shifts in community
composition to resource availability for benthic fish thereby remains open as a new research topic. That
in turn makes an effects extrapolation linked to area closure on fish difficult.
A main conclusion derived from this research is that when fish are treated as a dynamic population, as
would be the case in a large MPA, all elements of a food web can coexist at low mortality. And only in
sufficiently large MPA ‘s fish is dynamically coupled to benthos in such a manner that the system can
facilitate coexistence through preferential feeding on prey species most resistant to trawling mortality. In
small MPA ‘s by contrast, where fish move in and out of the area constantly, such facilitated coexistence
is not possible. In that latter case, (preferred) soft benthic species will go extinct at low trawling
intensity, a situation where predation is the dominant source of mortality. At high trawling intensity by
contrast, predation mortality is relatively minor and the hard species goes extinct.
The suitability of protected areas for fish and benthos recovery is dependent on location, size, positioning
relative to other protected areas, and species-specific considerations. Results further differ depending on
life history (fecundity, offspring) and habitat specific (spawning, nursery, or migration
areas) factors. For highly mobile and/or migratory species, protected area effects are less obvious
compared to those for benthic macro-fauna, whose lifecycle is more likely to take place entirely within a
protected area.
Bottom trawling
North Sea fauna for several decades has already been influenced heavily by bottom trawling most
probably causing severe alterations in composition, density and biomass quantily. Literature suggests
that the entire Dutch Continental Shelf (DCS) surface area during 1994 alone was trawled 1.36 times.
For this and other reasons it is virtually impossible to construct precise maps of the past North Sea
bottom fauna situation due too largely lacking and therefore incomplete hard data. Available maps
therefore with certainty do not provide a real picture of the original undisturbed (non-fished) North Sea
fauna.
But even though current North Sea maps provide a far from conclusive picture some remarks can be
made regarding species with a largely asymmetrically, and/or distinctly distributed sensitivity to
mortality. One potential consideration is to prevent discards while preserving commercial fish landings.
This might be achieved by building wind farms at near shore locations, areas where biomass consisting of
discard vulnerable size classes is high. That in turn is especially true for commercial fished species plaice,
dab, and many non-commercially fished species. Alternatively, government policy may instead be
prioritized towards preserving larger individuals, in which case an opposite strategy holds true.
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Many discard vulnerable classes are concentrated near shore. Combined with increasing costs associated
with building wind farms further away from shore, locating wind farms near shore (≤12-mile zone) is
recommended for demersal fish benefit. Further research aimed at optimizing wind farms based upon
both costs considerations and expected conservation effects will in the latter respect be of utmost value.
Fishery effects
Wind farm area closure will also affect commercial fishery. And as fishery activities may redistribute as a
result of area closure, fishing pressure can either increase or decrease within these areas. The following
changes in fishing effort can potentially be envisaged:
1. Redistribution of fishing effort to shipping activity;
2. Possible redistribution of fishing activity around the borders of a wind farm, due too fishers
response to a “spill-over effect.”
Examining wind farm closure effects on redistribution fishing effort during the period 2004/2005
compared with years 2007/2008, made clear that no explicit effects have become apparent. In terms of
a perceived “spillover effect”, beam trawlers do show increased fishing effort in between the two
operational Dutch wind farms. However, this area also coincides with a common shipping route for
IJmuiden-based beam trawlers heading to northern fishing regions. Increased fishery activities may
therefore reflect an early start of beam trawling on their way north, reinforced by a concentration effort
caused by a restriction in shipping routes.
Real long-term changes in fishing behavior as a result of area closure are at the moment far from clear.
This despite a given fact that current changes in
fishing effort seem especially the result of socio-economic considerations with regard to fleet capacity.
Far less likely is any perceived change in fish catch around wind farms, positive or negative. It therefore
remains to be seen whether and to what extend commercial fishing effort will redistribute in the years to
come. This also needs to be weighed against benthos and fish development within existing wind farm
boundaries and new additional North Sea projects at various planning stages.
Taking into account different options derived from studying benthic mortality rates and/or near shore fish
distribution, future wind farms will require prioritization between benthos, fish, fishers, and a
requirement for more wind power.
Finally conflicting recommendations can be made based upon different main objectives. One potential
focus is conserving certain species or a species group, while an alternative focus might be to create
optimised conditions for commercial fishing activities. Applying currently developed optimization software
can potentially prove of great benefit by prioritizing these potentially conflicting interests.
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2004-012 PhD@Sea: Morphology
Natural and Human Induced Seabed Evolution; the occurrence of large-scale bed patterns and
the effects of human activities on the North Sea seabed.
Organisation Twente
PhD thesis report
University, The Netherlands
Natural and Human Induced Seabed Evolution; the occurrence of largescale bed patterns and the effects of human activities on the North Sea
seabed.
Research Area
Report numbers
RL-2
WE@SEA 2004-012
ISBN 978-90-365-2613-5
Funding
EU-project HUMOR (EVK3-CT 2000-000037)
PhD@Sea, which is funded under the Dutch Government BSIK
programme and supported by the WE@SEA consortium.
Author
Henriët van der Veen
Date
21 February 2008
The North Sea is a highly dynamic water mass, where tidal currents flow over a sandy seabed. This
intensively used sea space is characterised by a wide range of different human activities that are being
conducted simultaneously. The North Sea seabed is rich in natural resources like oil and gas, which has
resulted into the construction of multiple oil and gas platforms to extract these valuable natural
resources. The platform structures themselves are connected to transport and processing facilities
onshore via pipelines typically buried into the seabed. In addition telephone and data cables are located
either above or into the seabed interlinking countries one to another.
Economic importance
Since the North Sea is a biologically rich area, fishing activities always formed an important economic
activity. Some sections in addition still contain unwelcome but substantial numbers of sea mines
originating from World War I as well as WW II. Other areas in turn are in use for accommodating largescale infrastructural projects. And as many important European harbours are located along North Sea
shores intensive shipping movements is one of the logical consequences. That in turn necessitates that
many shipping lanes need to be dredged on a regular basis in order to safeguard vessel passage. In
addition, large sea areas have been reserved for building offshore wind farms and/or serve other specific
functions like air force practice.
With regard to seabed topology the North Sea is neither flat nor smooth, but instead shaped in patterns,
ranging from small ripples to large sand banks. Sand banks feature wavelengths between 1 and 10 km
and can extend to a height of several tens of meters.
Somewhat smaller in size are so-called sand waves. Their length varies between 100 to 800 metres, and
they typically measure up to 10 m high from trough to crest.
The North Sea is a very dynamic sea area, both in natural and morphological sense. Due to a delicate
combination with many human activities taking place simultaneously, it is essential to determine the
nature as well as (interacting) implications linked to large-scale morphological effects of these human
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activities. One distinct human activity that quickly gains in overall importance is the planned construction
of multiple North Sea offshore wind farms over the next decades.
As part of this thesis research a system capable to predict such large-scale effects on the North Sea
seabed interlinked to various human activities put upon a long timescale has been developed. This was
achieved by implementing idealized morpho-dynamic models in a GIS (Geographical Information
System) that also contains specific data on the North Sea environment.
Correct prediction
During this research project the occurrence of sand banks and sand waves in the North Sea was
predicted and these were later compared with observations indicating the occurrence of such large-scale
seabed features. The results above all show that for large sections of the North Sea it is indeed possible
to correctly predict the occurrence of sand barks and sand waves at specific locations.
The new models that predict morphological effects linked to human activities cannot be validated yet.
However, these models are based upon the same principles as models used to predict the occurrence of
sand banks and sand waves. The latter are validated against North Sea observations of these large-scale
seabed sand deposit settings, this may give trust in the models that are applied to predict morphological
effects of human activities.
It is assumed that models predicting human activity linked effects do not show any morphological seabed
evolution, when the model that predicts sand bank effects does not predict sand bank occurrence. In
other words, the model that predicts the occurrence of sand banks does not indicate the occurrence of
sand banks at that particular location. This is due to the fact that underlying principles or mechanisms of
the models predicting effects of human activities are based by on the same 2DH flow conditions that are
necessary for sand bank development.
By connecting idealized morpho-dynamic models to a GIS it is possible to create a tool well suited for
predicting human activity linked effects to North Sea seabed conditions. The models apply site-specific
inputs to provide predictions for an arbitrary location in the North Sea.
Offshore wind farms
A first main application of the new system is large-scale sand extraction. Due to major construction
projects like the planned Rotterdam harbour enlargement, demand for sand is rising steeply. Offshore
resources will increasingly be required to fulfil these needs for large sand quantities, implying for
instance that multiple large-scale sand pits need to be created in the North Sea space. And as the North
Sea is a ‘shallow shelf sea’ where the tide flows over a sandy bed, the presence of sand pits can
influence seabed behaviour.
Future offshore wind farms are a second main future application for the new system. As part of the
research project influences of offshore wind farms on large-scale seabed morpho-dynamics effects were
studied. With reason, as the need for renewable energy is rising and wind power is one of the main
power sources that can be harvested effectively. The research project resulted into the development of a
morpho-dynamic model that enables studying the effects of offshore wind farms on the seabed.
Implementing this model in a dedicated GIS environment, offers the possibility to calculate seabedinduced effects induced by a wind farm while applying site-specific and farm design input parameters.
Finally, implementing idealized morpho-dynamic models in a GIS environment enables the prediction of
the occurrence of large-scale North Sea seabed sand deposits. This is achieved by implementing specific
models predicting effects of human activities within a GIS system. That in turn makes it feasible to
provide an indication of large-scale morphological effects resulting from these North Sea human
activities. The end result is a rapid assessment tool for predicting human activity inked morphological
effects at the seabed.
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2005-006: The effect of wind farms on the settling of gray seals at the North Sea (Halichoeros
grypus
Grey seals (Halichoerus grypus) in the Dutch North Sea: population ecology and effects of
wind farms
There is growing but circumstantial evidence that anthropogenic actions such as offshore wind farms
might influence life and wellbeing of marine mammals. Construction and operational activities, including
traffic movements in relation to installation upkeep, augment human influence already dominantly
present in a heavily exploited Southern section of the North Sea.
The main focus of this research effort is to gain understanding of possible effects large-scale offshore
wind farm development in Dutch territorial waters might inflict upon grey seals (Halichoerus grypus).
Defining effects of human activities such as the construction of offshore wind farms requires either a
measured change or just its absence in seal population. Effects may either occur in numbers,
distribution, diet, or dedicated habitat. In the specific case of grey seals residing in Dutch waters,
identifying a cause and effect relationship between a wind farm (construction and operation) and seals
wellbeing was not an easy to accomplish task. In fact progress was hampered by the fact that insufficient
information has in the past been collected on this relatively new species. In lack of such detailed
references on grey seals in Dutch waters, a prerequisite of this new study was to include basic data on
the species. A summary of data on population development, diet and specific habitat issues is presented
has been the main focus of this research.
Impressive past growth
Population studies show that grey seal numbers did experience impressive growth during the past three
decades. Within this period the numbers increased from occasional individuals to a maximum 2000
mammal count during the moult season, a period when the animals can most frequently be seen.
Growing grey seal numbers have also been observed in the Dutch Delta, sometimes even exceeding the
number of harbour seals. Presumably, the majority of these animals originated from the British island
coasts where the worlds largest grey seals population resides.
Other grey seal strongholds on European continental coasts are found in Germany, but their number
count remains below a couple of hundreds. It is thereby clear that the Netherlands accommodates the
largest number of this seal species. That given fact reinforces a responsibility to protect these creatures
within the Habitat Directive framework. Annual population development monitoring will show when they
as a group stabilise both in size as well in the use of haul-outs.
Based on scat analysis results, grey seals all along the Dutch coast mainly feed on a variety of benthic
prey species. Most common is that they eat sole during spring and flounder in the autumn. This feed
pattern is comparable to the diet of grey seals residing along the UK east coast, even though in these
areas a larger quantity of sand eel is eaten. And on average prey length seldom exceeds 20cm, which is
only slightly larger compared to harbour seals primary diet.
Dietary research
Because a scat analysis – like all methods applied for cryptic animals dietary research – does create a
bias, additional information was collected for fatty acid analysis. However, results of the latter analysis
are not yet satisfactory. In the near future researchers therefore expect to use this method in parallel to
scat analysis in order to gain better understanding on dietary preferences of these seal species.
One of the main conclusions with regard to spatial distribution of individual seals is that the Dutch North
Sea zone is an important area for grey seals in terms of migration and foraging. And although a majority
seals spend most of their time near their central location (haul-outs), a model applied predicts that areas
further offshore such as the Frisian front and the Dogger Bank provide suitable foraging areas too. Past
research indicates that grey seals originating from UK populations travel to and feed at the Dogger Bank.
Large distance migrations along continental coasts and to the UK have been observed as well. This in
turn suggests that the Dutch grey seals population is indeed “open”. Consequently, an increase in human
activity along these migration routes holds the risk that seal populations might become disturbed. In this
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small sample size a relatively large number of seals is found to make journeys as described above. And
that suggests a rather common practice for the grey seals to travel such long distances. In terms of
preference to particular areas, the same model applied indicates that grey seals prefer sandy areas and
shallow waters. These findings are in support of previous research where similar results were found for
grey as well as harbour seals. Equally important, it allows prediction of spatial distribution, even in areas
with little available telemetry data.
“Normal” seal behaviour
Understanding the possible influence(s) of wind farms is crucial in an overall offshore area utilisation
context. That in turn requires thorough understanding of “normal” seal behaviour, i.e. habitat use and a
capability to accurately track individual mammals in their 3-dimensional environment. Furthermore, it is
essential to understand if and in what manner these “normal” behaviour patterns change due to wind
farm presence. This research team already has gained some understanding of the grey seals
phenomenon in Dutch waters, i.e. numbers, haul-out patterns, and phenology. The latter branch of
biology studies cyclical biological events, such as flowering, breeding, and migration, in relation to
climatic conditions. Phenological records of the dates on which seasonal phenomena occur provide
important information on how climate change affects ecosystems over time.
The available know-how base regarding seals distribution at sea is much more limited. This research
further shows that attempts to acquire fresh knowledge can somewhat be hampered by large individual
variations between these mammals. But despite this given complication substantial efforts have been
taken to obtain more detailed information on seal habitat use (preferences) and on factors that influence
their distribution, both natural and human interference based.
Finally, when attempts were made to calculate effects of wind farm pile driving upon seals, the effort was
hampered by at that moment were relatively low seal numbers. Furthermore, many seals were at a far
away distance from the wind farm construction area and to big in order to suffer any effect of these piledriving activities. And though circumstantial, seals seem to move towards he wind farm construction area
once pile driving have ceased, a phenomenon observed by seal tracks tagged during the actual activity.
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2006-005: Underwater hearing sensitivity of harbour seals for tonal signals and noise
bands(Phoca vitulina)
Harbour seals (Phoca vitulina) show the most extensive geographic distribution of any seal species. They
inhabit the eastern Baltic Sea as well as both eastern and western Atlantic Ocean (300 to 800 north) and
Pacific Ocean (280 to 620 north) coastal areas. This specific species leads an amphibious life, resting on
land, while migration, foraging and courtship activities occur underwater. During the breeding season,
male harbour seals produce underwater vocalizations described as growls and short broadband-pulsed
calls.
Importance of sound
In order to determine the importance of sound to harbour seals during various activities, information is
required on their underwater hearing sensitivity. Harbour seals main activity examples include
communication, reproduction, predator avoidance, navigation, and disturbance potential by
anthropogenic noise. This underwater hearing sensitivity has been scientifically analysed and tested for
pure tones as well as frequency-swept tones. However, in each of in total seven previous reports that
were analysed, in fact only the sensitivity of a single harbour seal at part of the frequency hearing range
was studied. Moreover, in each of these past research projects different equipment, methodologies, and
signal parameters have been applied, with the animals involved being of various ages, and all were
males. In addition, some of the hearing thresholds may have been influenced (masked) by research
pool-related background noise.
And as harbour seals are found in coastal waters, these are typically places with busy human activities.
For assessing potential disturbances by anthropomorphic noise sources, it is essential to obtain robust
underwater hearing threshold curves for this pinniped species. For meeting that objective a quiet testing
environment and a representative number of animals are both necessary preconditions. To meet these
specific requirements, a pool and filtration system with special acoustic features designed for hearing
studies was built at a quiet location in the Netherlands. And especially for this hearing trial, two healthy
one-year-old female harbour seals were also obtained. Final aim was to determine underwater hearing
thresholds for both seals over their entire hearing range, by applying a psychoacoustic behavioural
technique.
Acoustic signal response
The animals were trained to respond when detecting an acoustic signal and not to respond when they did
not (go/no-go response). The test range included pure tones (0.125 - 0.25 kHz) and narrow-band FM
(tonal) signals (centre frequencies 0.5 - 100 kHz) with 900ms duration. In addition, an up-down
staircase method was applied for quantifying detection thresholds at each frequency range. The resulting
underwater audiograms (50% detection thresholds) of the two seals did not differ in statistical terms:
both plots showed a typical mammalian U-shape, but with a wide flat bottom. Maximum sensitivity (54
dB) occurred at 1 kHz, while the best hearing range – defined as 10 dB from the maximum sensitivity varied from 0.5 to 40 kHz (6⅓ octaves). Higher hearing thresholds - indicating reduced sensitivity - were
observed below 1 kHz and above 40 kHz. Thresholds below 4 kHz proved lower than those previously
described for harbour seals. This in turn demonstrates the importance of applying quiet facilities built
specifically for meeting these acoustic research marine mammal hearing studies demands.
The biggest hearing research challenge is maintaining a low background noise level, and great care was
therefore given to this issue during the trials. The single main factor influencing a specific ‘LF’ part of the
background noise spectrum within a pool is wind. This caused airborne noise during wind speed increase
plus increased soil vibrations. During the four-month research period wind speeds were relatively low
compared to previous years, which meant that background noise levels in the pool remained very low
and even partly below sea state 0.
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Absolute audiograms
It is important to know whether the audiograms obtained during the research project were in fact
“absolute audiograms”, or signals impacted by pool-related background noise.
0.125 - 0.5 kHz range signals were therefore only tried under wind force conditions below 2 Beaufort,
because false alarms did occur at higher wind speeds. The latter is probably caused by the fact that both
animals reacted to background noise elements resembling test signals. Still, the false alarm rate was
generally highest for lower frequencies (< 1 kHz in this research). A majority of transient background
noise signals prone to trigger false responses originate from this part of the spectrum range. As both
seals were tested within the same sessions, any differences between thresholds obtained must have
been due to differences in hearing sensitivity and/or individual differences in response criteria,
motivational state, or behaviour. But equipment specification variations and settings, methodologies,
personnel or background noise could not be held responsible for any of these threshold differences.
Furthermore, in a majority of previous studies focused at pinniped hearing, except two experiments,
pure tones were used as stimuli. Only the hearing of a Pacific walrus (Odobenus rosmarus divergens) and
two Steller sea lions (Eumetopias jubatus) have in the past been tested with narrow-band FM tonal
signals.
With humans FM signals tend to cause a slightly higher arousal effect compared to pure tones and
therefore slightly lower hearing thresholds, more specifically < 5 dB depending on centre and modulation
frequency. However, the use of FM signals instead of pure tones probably had little effect on the
thresholds found in this research, an assumption based upon a hearing test with 250 Hz signals on a
Pacific walrus. In that latter trial case no threshold difference was found between narrow-band FM signals
like those applied in the present research – with frequency modulation being only 1% of centre
frequency - and pure tone signals.
Signal duration
Hearing thresholds depend on signal duration, whereas integration time is also frequency-dependent and
decreasing with frequencies going up. However, the 900 ms signal duration used during the research was
probably
longer than the harbour seal’s hearing system integration time.
Above 4 kHz, thresholds found in previous hearing studies and those found in the present research
proved similar. However, below 4 kHz present thresholds found were up to 20 dB lower than those
values obtained in previous studies. These differences themselves may have been caused by a variety of
reasons. One option is that low frequency signals were masked by background noise in the previous
studies.
Another potential reason is that animals in those cases may have suffered “TTS” due to high background
noise levels caused by pumps before the hearing tests were conducted.
Third, signal duration in a majority of the previous studies was shorter compared to the current project
duration, and that in turn can possibly cause a hearing threshold increase. The latter factor is not
attributable to integration time. It is on the contrary most likely due to the fact that it proves difficult for
these animals to distinguish between transient signals as part of background noise and test signals.
Finally there may have been individual, gender, health condition, or age-related differences in hearing
sensitivity between these animals undergoing such tests.
Ecological significance
Key research project finding is that harbour seal hearing is more sensitive below 4 kHz than found in
previous studies. Harbour seal’s hearing frequency range in fact shows overlap with the loudest and most
common anthropogenic noise sources. Anthropogenic noise effects on marine mammals are highly
variable in both nature and magnitude, and harbour seals show avoidance behaviour to certain sounds in
specific contexts. Anthropogenic noise might also reduce the time harbour seals stay for foraging
purpose in particular areas, thus potentially harming their physiological condition and potential
reproductive success. In addition to harbour seal hearing sensitivity, the avoidance rate and disturbance
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zones around sound sources both depend on several other factors. Examples include general background
noise level, water depth, ocean floor sediment properties and spectrum, source level and anthropogenic
noise duration.
In general, based on current findings, many anthropogenic noise sources are audible at greater ranges
than formerly believed possible.
Finally based on the small minimum audible angles for low frequencies, researchers concluded earlier
that harbour seals are low frequency hearing specialists. This research shows that harbour seals possess
can in fact hear very well at wide frequency range, and that they are capable to hear lower frequencies
better in quiet conditions than previously expected
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2007-003: Seabirds on wind
Birds at Sea; studies into the possible impacts of wind farms on seabirds
This research project addresses four different main objectives:
1. Generate a map of the North Sea indicating at which areas wind farms would have an adverse
effect on seabirds;
2. Find explanatory variables for bird distribution in the biologically rich Frisian Front area;
3. Determine the bird fluxes gradient in a transect perpendicular to the Dutch coast;
4. Develop innovative instruments for dedicated scientific research.
Bird distribution in Frisian Front
The Frisian Front attracts many seabirds and hosts a number of typical North Sea bird species. These
include for instance the Northern Fulmar (Fulmarus glacialis), Northern Gannet (Morus bassanus), Lesser
Black-backed Gull (Larus fuscus) and Common Guillemot (Uria aalge). For the latter two species, this sea
area is of particular importance during the reproductive period. Lesser Black-backed Gulls fly back and
forth from their breeding colonies at the Waddenzee islands to their foraging areas in and around the
Frisian Front. Male Common Guillemots escort their still flightless chicks from the British breeding
colonies to the Frisian Front and undergo a complete feather moult during this period.
The Frisian Front is also rich in both demersal and pelagic fish. Common Guillemots are capable to reach
this fish at any depth and any time (potential diving depths exceed Frisian Front actual water depths.
Most fish by contrast swim too deep for risking falling prey to surface feeders, such as Lesser Blackbacked Gulls. This observation is valid unless factors come into play bringing these fishes to the sea
surface.
Upper water column
In this research project surveyed birds and sampled fish in the upper water column as part of the Frisian
Front area were extensively studied. The interrelationship between fish, birds and environmental
parameters yields fresh insight into the distribution of seabirds, which in turn is an important input for
offshore wind turbine spatial planning.
Under natural circumstances, pelagic fish can be driven to the sea surface by hunting predators, such as
cetaceans (e.g. Harbour Porpoise Phocoena phocoena), birds (e.g. Common Guillemot) or predatory fish
(e.g. Mackerel Scomber scombrus). In an attempt to escape this danger, schools of small pelagic fish
may try migrating to the surface, where they face the risk of becoming prey to surface feeders. These
‘feeding frenzies’, which are attended by several predatory species, are called ‘multi-species feeding
associations’ (MSFA). Alternatively, otherwise unattainable fish become available through anthropogenic
fishing, whereby discards are thrown overboard. These two mechanisms are considered not mutually
exclusive and birds may use them opportunistically.
Low densities
In this research project surveyed birds and sampled fish in the upper water column of the Frisian Front
area were extensively studied. The interrelationship between
fish, birds and environmental parameters yields fresh insights onto the distribution of seabirds, which in
turn provides important information for facilitating offshore wind turbine spatial planning.
Both fish sampling and ‘echo-sounder’ scans revealed low densities of small pelagic fish near the water
surface during daytime (Figure 1). Daytime fish species biomass, a well-known prey for Common
Guillemots (Sprat Sprattus sprattus, ScadTrachurus trachurus, Herring Clupea harengusi, Whiting
Merlangius merlangus and Mackerel Scomber scombrus) did not correlate with observed Common
Guillemot densities. Especially noticable, these guillemots could not be seen foraging during daytime.
However, several Common Guillemots were observed to start diving at sunset. A nocturnal fish sampling
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revealed a much higher fish biomass concentration (especially Herring and Sprat) in the upper water
layers after sunset. A peak in diving activity has been reported for Common Guillemots during
crepuscular periods (the twilight zone). Suspending foraging to crepuscular periods when prey migrates
upwards may be favourable energetically, as diving depth under these circumstances can be minimized.
The latter activity can be especially demanding for chicks, while hunting success is potentially higher.
Hypothesis
A hypothesis was that the Frisian Front is rich in fish, which are hunted at by subsurface predators
making the fish available to gulls in MSFAs. Although MSFAs have been observed at the Frisian Front in
the past, none were observed during a 2009 project survey. This can probably be explained by the
absence of large fish schools and the low potential MSFA driver numbers. The only potential MSFA driver
present in good numbers – Common Guillemots – were not foraging during daytime and therefore did
not produce MSFAs diurnally. Hence, MSFAs could not supply Lesser Black-backed Gulls with diurnal
foraging opportunities. Lesser Black-backed Gulls where mainly observed when following the observation
vessel or – if within sight – following fishing vessels. This, combined with the virtual lack of natural
foraging behaviour indicate that at least during daytime, Lesser Black-backed Gulls rely on fishing
vessels discards rather than MSFAs. Man thus plays an important role in making otherwise unavailable
fish available to gulls.
Figure 1 Left: Typical echogram from the upwards-beaming towed body with a mounted 200 kHz splitbeam transducer. The red marks are probably fish (schools). In the first meter water down from the
surface, the echogram shows a lot of noise, caused by reflections from the rough sea conditions. Right:
Acoustic distribution (NASC) of all fish species subdivided by 1-metre depth layers.
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Figure 2 Results from the vessel-based bird survey in the Frisian Front area during August 2-6. Left
panel: density of Common Guillemots and fish tracks. Right panel: Lesser Black-backed Gulls and their
associations with floating matter. Many gulls associated with the vessel during the fish sampling.
Compare this with fish track locations in left panel.
A second hypothesis is on a gradient in bird fluxes when approaching towards the coast. Currently bird
radar stations are typically located relatively close to shore, providing only part of the required input
data. In the context of this project a bird radar station has been located at an offshore site. By
comparing bird fluxes measured at different distances from shore, the hypothesized gradient in bird
movements can be quantified and tested. However, at this stage project results are not yet available
which implies a lacking proof in either supporting or rejecting this latter hypothesis.
Innovative instruments
In order to collect relevant data on fish distribution in the water column upper layer, the research team
developed three innovative instruments. At first an acoustic sensor for the upper water layer was built.
Normally these sensors face downwards and are towed behind a vessel. The newly developed acoustic
sensor by contrast faces upward, scanning the water column from towing depth (approximately 7m) up
to the water surface. In order to avoid fish being disturbed by vessel-induced movements, towing the
sonar in the vessel wake should be avoided. Therefore, the sonar device was dragged at an angle with
the vessel’ bearing. This was achieved by giving the device a distinct wing shape that made it ‘fly like a
kite in the water’. Secondly, a new fishing net with a reasonably large net opening was developed,
enabling researchers to fish the upper three metres of the water column. Thirdly, a specially adapted net
featuring a fixed net opening was developed for conducting plankton surveys in North Sea waters. Like
the acoustic sonar, these nets had to be towed at an angle with the vessels’ bearing, which was
structurally achieved by employing shearing boars (paravanes).
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Figure 3 From left to right: acoustic underwater kite, surface trawl net and floating plankton net.
Bird sensitivity map
Bird distribution data were finally accumulated and put into a single database originating from three
different sources: Rijkswaterstaat, NIOZ, IMARES and Bureau Waardenburg. Furthermore, a specific
algorithm for determining bird sensitivity to wind farms depending on species characteristics was applied
to this database. The Bird sensitivity map as a main project result serves as an overall risk map and was
constructed based upon combined species distribution maps and species risk indices. It above all offers
an advanced capability to pinpoint these specific areas where offshore wind farms can be planned best
with the least impact upon seabirds. The map does also show what gradient in bird fluxes is present off
the Dutch coast, and it provides also improved understanding of explanatory variables linked to the
distribution of birds at sea. Last but not least it has provided the participating research institutes with a
set of innovative instruments offering superior capabilities for surveying the marine environment.
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2004-006: A ship based hydrophone system for detection and classification of cetacean
echolocation signals
The Cetaceans are one of the most distinctive and highly specialized orders of mammals. They include
the largest animal that has ever lived, the blue whale; the highly intelligent and communicative dolphins;
the tusked narwhals and blind river dolphins and singing humpback whales - nearly eighty living species
in all.
Source: www.ucmp.berkeley.edu/mammal/cetacea/cetacean.html
Cetacean vocalisations
Toothed whales produce two types of vocalisations:
•Social calls i.e. “whistles”; with this sound they communicate with others, like wolves each dolphin call
is unique per specimen, which leaves opportunities to estimate numbers;
•Echolocation; Like bats these calls are used to navigate and prey targeting. This specific type of sound
can be described as an impulsive type of waveform, a so-called click, with a number of amplitude
changes decaying in time.
The first type of sound signatures occur mostly in the lower frequency band < 20 kHz, while echolocation
signals can range up to 150 kHz.
Echolocation has been demonstrated in several cetacean species.
Toothed whales produce forward-projected bursts of impulsive type of sound of high intensity and
frequency. Each pulse is brief and has been found to range from 50 - 200 s in duration. In most cases
intervals between pulses enable to receive an echo from specific targets before a new pulse is emitted.
Acoustic properties of these sonar signals vary per species, with the centre frequency as their most
distinctive parameter. The habitat of species can partly be recognised in the frequency where the energy
peaks.
Of all cetaceans species harbour porpoise are the hardest animals to spot visually as only the upper part
of their body appears above water surface during breathings. Sighting of these animals further depends
on weather conditions. This visual capability in fact rapidly declines between 1 to 2 Beaufort and is
probably limited to maximum wind force 3 Beaufort conditions.
And as cetacean produce vocalisations with unique acoustic properties and patterns, acoustics are a
logical choice in extending the observation programmes and make full benefit of ship and survey time.
Sound signatures
Dutch observation programmes focus mainly on harbour porpoise abundance in the Dutch economic zone
of the North Sea. However, because acoustic properties of cetacean vocalisations are unique for each
species the technical approach of a detection system requires flexible techniques to filter these individual
sound signatures from their background noise. Next step is to identify species from these parameters, of
which the properties are known from literature.
At present acoustic sensor array’s, so-called towed hydrophone array’s, connected to computercontrolled filter/capture techniques are employed as an aid to visual observations.
However, there are a number of technical disadvantages linked to these technologies applied today:
•A submerged acoustic hydrophone array towed behind a vessel as an observation instrument turns
insensitive in frontal sailing direction. This ‘forward view’ is common practice for ‘normal’ visual
observations;
•Hydrophone elements typically consist of cylindrical shaped piezo elements with their highest sensitivity
in a direction perpendicular to the element axis, which is equivalent to sailing direction. And in case
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spherical hydrophones are applied the actual numbers are too low to ensure an accurate bearing
calculation and/or a sufficient left - right ambiguity;
•An array is towed in the cavitation-prone vessel wake zone. This zone typically contains similar
impulsive propeller noise masking the low frequency part of a received signal bandwidth, and/or may
introduce false click detections that can potentially jeopardize cetacean click detection;
•Traditional detection system processing applies electronic circuits to detect cetacean signals, whereas to
reduce data a high frequency spectrum is enveloped into a lower frequency band.
Hydrophone array
These above identified imperfections led to an idea to position a hydrophone channel array underneath
the frontal hull bow section. Such an array spans a 180-degree horizontal forward-facing arc with narrow
horizontal directionality - little angular overlap between adjacent hydrophones - and wide vertical
directionality. A second feature of this novel cetaceans detection approach is that the system is located in
the most-quiet vessel section with minimised impact of the propulsion system and/or other dominant
sound emitting sources. With other maritime detection techniques, like for fish this front position
advantage was already recognised as being superior during the early days of fishery technology
development. At present both sonar and echo Souder transducers applied in modern trawlers are all
positioned at the hull front side.
When for instance 12 hydrophone channels are applied each channel would cover a 15-degree angle
(1800 in total). The third part of the research effort was to design a permanent all-weather proof
system, thereby eliminating a need to mount and remove the sensor dome anew for each next survey.
The sensors further need to be resistant against the impact of slamming forces during vessel operation,
but without loosing acoustic transparency and by maintaining a suitable degree of sensitivity. The most
logical target vessel to apply this new technology at was a research vessel FRV “Tridens”, which is
frequently used for visual observations. This vessel as an added advantage offers the required elevation
from where cetaceans can be spotted over a wide distance. Another advantage is that this technology
can be applied during other surveys all year round.
Sailing speed
Sensor design and commissioning involved a study by Delft (NL) based manufacturer Lightweight
Structures on the feasibility of the project’s ambition. This design specification package involves
operating a permanently mounted sensor dome underneath the bow part of the “Tridens” that is capable
to withstand a maximum 17 knots sailing speed. A sensor dome containing all measuring equipment is
positioned approximately 4 - 5 metres below water surface.
Based upon this perspective and specification particulars of the ”Tridens” actual slamming forces were
calculated and applied for sensor dome design, materials selection and production methodology
development.
As part of the research project an advanced 12-channel cetacean detector has now been developed,
which for permanent marine submerged application is fitted at the bow of the FRV “Tridens”. Cetacean
echolocation signals are received through a ship-based forward-facing semi-circular 12-channel
hydrophone array. Both housing dome shell and mechanical construction (1000 (l) x 800 (w) x400 (h)
mm) were designed to withstand slamming forces at the vessel bow during a 17-knot sailing speed.
These marine specifications are in accordance with American Bureau of Shipping 2003 classification
standards for high-speed naval craft.
Analogue signals are simultaneously digitised at 16-bit resolution on two data acquisition cards, and
sampled with a 500 kHz rate in order to support the maximum frequency range of harbour porpoise
echolocation signals.
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Distinguishing echolocation signals
The powerful software framework developed simultaneously is capable of distinguishing between
echolocation signals by cetaceans, identify cetacean species, and plot acoustic encounters as overlay on
oceanographic GIS maps together with the ship’s course. The software supports detection of dolphin
vocalisations within a range of 2 - 150 kHz, added by a number of operational functions such as replay
and simulation modes. Equipment trial tests have been performed offshore on board a former pilot vessel
named “Kluut”, while artificial echolocation signals were projected at pre-determined distances from a
second vessel, the “Blue Marlin”. The tests proved that system functions principally operated according
to expectation, but the trials also revealed that detection algorithms were not sensitive enough.
Following the trials both software click and burst detection modules have been thoroughly revised.
And although still a prototype version stage and requiring further optimising effort both regarding
hardware and software systems, overall results are promising. That in turn offers great opportunities for
high-speed sailing and operations performed with smaller vessels, and enables surveys through
hazardous coastal zones characterised by large man made structures like wind farms. The new software
development approach as a key advantage reduces post analysis time as main functions like mapping
and sorting of detections are standard features integrated within the software architecture. Finally it has
become clear already that this new approach offers great otential turning it into a serious candidate for
replacing current methods and techniques.
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2004-007: The influences of wind farms on benthos and fish
Natural and Human Induced Seabed Evolution; the occurrence of large-scale bed patterns and
the effects of human activities on the North Sea seabed.
Organisation
Twente University, The Netherlands
PhD thesis report
Natural and Human Induced Seabed Evolution; the occurrence of large-scale
bed patterns and the effects of human activities on the North Sea seabed.
Research Area
Report numbers
RL-2
WE@SEA 2004-012
ISBN 978-90-365-2613-5
Funding
EU-project HUMOR (EVK3-CT 2000-000037)
PhD@Sea, which is funded under the Dutch Government BSIK programme and
supported by the WE@SEA consortium.
Author
Henriët van der Veen
Date
21 February 2008
The North Sea is a highly dynamic water mass, where tidal currents flow over a sandy seabed. This
intensively used sea space is characterised by a wide range of different human activities that are being
conducted simultaneously. The North Sea seabed is rich in natural resources like oil and gas, which has
resulted into the construction of multiple oil and gas platforms to extract these valuable natural
resources. The platform structures themselves are connected to transport and processing facilities
onshore via pipelines typically buried into the seabed. In addition telephone and data cables are located
either above or into the seabed interlinking countries one to another.
Economic importance
Since the North Sea is a biologically rich area, fishing activities always formed an important economic
activity. Some sections in addition still contain unwelcome but substantial numbers of sea mines
originating from World War I as well as WW II. Other areas in turn are in use for accommodating largescale infrastructural projects. And as many important European harbours are located along North Sea
shores intensive shipping movements is one of the logical consequences. That in turn necessitates that
many shipping lanes need to be dredged on a regular basis in order to safeguard vessel passage. In
addition, large sea areas have been reserved for building offshore wind farms and/or serve other specific
functions like air force practice.
With regard to seabed topology the North Sea is neither flat nor smooth, but instead shaped in patterns,
ranging from small ripples to large sand banks. Sand banks feature wavelengths between 1 and 10 km
and can extend to a height of several tens of meters.
Somewhat smaller in size are so-called sand waves. Their length varies between 100 to 800 metres, and
they typically measure up to 10 m high from trough to crest.
The North Sea is a very dynamic sea area, both in natural and morphological sense. Due to a delicate
combination with many human activities taking place simultaneously, it is essential to determine the
nature as well as (interacting) implications linked to large-scale morphological effects of these human
activities. One distinct human activity that quickly gains in overall importance is the planned construction
of multiple North Sea offshore wind farms over the next decades.
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As part of this thesis research a system capable to predict such large-scale effects on the North Sea
seabed interlinked to various human activities put upon a long timescale has been developed. This was
achieved by implementing idealized morpho-dynamic models in a GIS (Geographical Information
System) that also contains specific data on the North Sea environment.
Correct prediction
During this research project the occurrence of sand banks and sand waves in the North Sea was
predicted and these were later compared with observations indicating the occurrence of such large-scale
seabed features. The results above all show that for large sections of the North Sea it is indeed possible
to correctly predict the occurrence of sand barks and sand waves at specific locations.
The new models that predict morphological effects linked to human activities cannot be validated yet.
However, these models are based upon the same principles as models used to predict the occurrence of
sand banks and sand waves. The latter are validated against North Sea observations of these large-scale
seabed sand deposit settings, this may give trust in the models that are applied to predict morphological
effects of human activities.
It is assumed that models predicting human activity linked effects do not show any morphological seabed
evolution, when the model that predicts sand bank effects does not predict sand bank occurrence. In
other words, the model that predicts the occurrence of sand banks does not indicate the occurrence of
sand banks at that particular location. This is due to the fact that underlying principles or mechanisms of
the models predicting effects of human activities are based by on the same 2DH flow conditions that are
necessary for sand bank development.
By connecting idealized morpho-dynamic models to a GIS it is possible to create a tool well suited for
predicting human activity linked effects to North Sea seabed conditions. The models apply site-specific
inputs to provide predictions for an arbitrary location in the North Sea.
Offshore wind farms
A first main application of the new system is large-scale sand extraction. Due to major construction
projects like the planned Rotterdam harbour enlargement, demand for sand is rising steeply. Offshore
resources will increasingly be required to fulfil these needs for large sand quantities, implying for
instance that multiple large-scale sand pits need to be created in the North Sea space. And as the North
Sea is a ‘shallow shelf sea’ where the tide flows over a sandy bed, the presence of sand pits can
influence seabed behaviour.
Future offshore wind farms are a second main future application for the new system. As part of the
research project influences of offshore wind farms on large-scale seabed morpho-dynamics effects were
studied. With reason, as the need for renewable energy is rising and wind power is one of the main
power sources that can be harvested effectively. The research project resulted into the development of a
morpho-dynamic model that enables studying the effects of offshore wind farms on the seabed.
Implementing this model in a dedicated GIS environment, offers the possibility to calculate seabedinduced effects induced by a wind farm while applying site-specific and farm design input parameters.
Finally, implementing idealized morpho-dynamic models in a GIS environment enables the prediction of
the occurrence of large-scale North Sea seabed sand deposits. This is achieved by implementing specific
models predicting effects of human activities within a GIS system. That in turn makes it feasible to
provide an indication of large-scale morphological effects resulting from these North Sea human
activities. The end result is a rapid assessment tool for predicting human activity inked morphological
effects at the seabed.
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2005-022: Low cost en sea-clutter resistant radar for monitoring birds
Organisation
Report name
TNO division Defense, Security and Safety
Final report WE@SEA project ROBIN Lite bird radar development aimed at
maritime bird migration monitoring
Report numbers
WE@SEA 2005-022 + 2006-013
TNO 015.35126 + 032.11223
Author
Addy Borst, M.Sc.
Date
May 15, 2008
Introduction
At the end of 2007 offshore wind farms with a total capacity of about 1,100 MW were operational in
Europe, while new projects are being added regularly in a number of countries. The EU’s objective is to
have 40,000 MW offshore wind power operational by 2020 in European waters.
Environmental Impact Assessment (EIA) forms an integral part of each offshore wind farm planning
stage, and these studies include bird migration monitoring. Until today there were no effective radarbased monitoring systems available with a key operational focus at tracking bird movements. As part of
the WE@SEA research program TNO division Defense, Security and Safety engaged into developing a
dedicated bird tracking radar system under the product trade name ROBIN Lite. One of the main project
and product development objectives was that ROBIN Lite enables the continuous and systematic
registration of bird migration in a predefined area around offshore wind farms. A second main project
objective is that the radar system can be remote controlled, operate independent from unmanned
offshore wind farms, and that the bird-migration data can be transmitted onshore.
Despite the fact that the Robin Lite system development, testing and optimizing process has not been
completed yet, substantial commercial interest is expressed already from Dutch as well as foreign
parties.
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The project execution process itself also faced a number of setbacks, for instance with regard to signal
interference issues. That necessitated intermediate system redesign, which in turn required additional
funding exceeding the initial budget and also caused considerable project progress delay.
Due to the importance attached by TNO towards accomplishing a fully operational and tested ROBIN Lite
system, a decision was made to fund this crucial last project stage towards commercialisation from
internal TNO resources.
ROBIN Lite bird radar development objectives
During the next decennia a large number of offshore wind farms are planned in the North Sea. It is also
envisaged that offshore wind farms will in future provide a significant share of total electricity demand in
the Netherlands. However, environmental effects and potential constraints are without exception closely
linked to planned as well as operational (offshore) wind farms.
Project developers are obliged to conduct an EIA, aimed at quantifying any positive and negative
environmental effects linked to the building and operation of offshore wind farms. Such an EIA in
addition has to contain specific project measures aimed at alleviating and/or significantly reducing these
negative wind farm effects.
An important part of an EIA is dedicated towards the potential impact of offshore wind farms to fish,
birds, sea mammals and other water born organisms. With regard to local effects on birds like accidental
collisions,
habitat loss, and/or wind farms posing a barrier to migration routes and general freedom of movement
all need to be quantified. Until today quantifying all these effects has proven very hard to accomplish.
This is true for bird monitoring in general but especially tracking offshore bird migration offshore is highly
complex and a very time consuming process. It is in fact a combination of the logistical efforts required
(i.e. transportation and local stay) and specific challenges linked to observing bird movements during
night hours above the water surface.
Radar for bird observation
Radar has always been regarded one of the potentially most important available tools for bird
observation and especially bird flight movements in a marine environment during the dark. Radar
observation as a key advantage is fully independent of visual conditions (i.e. darkness, foggy weather).
It is in addition possible to register and electronically store all bird movements at random and scattered
in a wide area, and low as well as high altitudes. Finally with the aid of high-level automation tools key
variables including flight directions, flight speeds, and bird flock densities can be quantified.
Bird radar systems require sufficient range to cover a given wind farm object and a wide area stretching
several kilometres around it in order to adequately track and analyse bird migration behaviour. Today’s
bird radar systems are all based upon maritime ‘shipping-type’ radars. Under ideal circumstances these
systems are indeed capable to detect small objects including birds above land at a range spanning
several kilometres. However, above a water surface the detection range is often much more limited due
too wave reflection effects. Under regular sea state (= wave height) conditions, and in a combination
with wave reflection and multi-path effects (= sea clutter), the actual radar detection range is seldom
more then 1 kilometre. But in practice this range is often restricted to less than 500 metres. As sufficient
area around an offshore wind farm is required to enable adequate bird migration pattern studies, the
latter range is considered rather limited.
Low-cost bird radar
TNO has the internal capabilities and other necessary means to develop a relatively low-cost bird radar
system, which does meet the above indicated range and detection sensitivity requirements. In addition
this radar system, thanks to advanced built-in automation capabilities, requires substantially less manhours for data processing compared to compatible radar systems. These combined product features
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qualifies TNO’s bird radar system as an ideal tool for continuous bird migration monitoring in the vicinity
of offshore wind farms.
The system itself is in essence a combination of maritime radar technology applied in the shipping
industry and an FMCW-type radar TNO already applies in other applications. The latter is fitted already
with a commercially available DEKODO sea-clutter filter and ROBIN bird detection algorithms. Besides
sea-clutter filtering, additional filters for handling wind turbine rotor
reflection issues have been incorporated. Rotor reflection as a phenomenon is highly predictable and the
required filtering method as a challenge is therefore rather easy and straightforward to tackle.
TNO developed the original ROBIN system during the past twenty years for the Dutch royal air force
(Koninklijke Luchtmacht or KLu) and several European air forces too. Based on radar data obtained from
two KLu air control radars, ROBIN software is capable to fully detect and register all bird migration
movements (tracks) across Dutch air space. In other words tens of thousands tracks can be followed and
visualised simultaneously. The new bird radar system is based on integrating the above-mentioned
modules into a single system entity. This system in turn is characterised by a number of distinct features
including adequate detection sensitivity, easy-to-operate built-in capabilities, and is finally for clients
relatively inexpensive to obtain.
The new bird radar system will be extensively tested and validated offshore. These bird migration
detection and tracking tests will be conducted in parallel with a ‘conventional’ state-of-the-art radar
system, as well as human observation techniques. The test variables cover a range of different weather
conditions, which include bird monitoring during daylight hours and during dusk and darkness at night.
ROBIN Lite design specifications
In the project predefining stage extensive consultation talks have been organised with potential user
groups as well as biologists and ornithologists aimed at determining the ROBIN Lite’s minimal design
specifications:
1 Range minimal 4km for a medium-size bird at sea state 2;
2 Height range water surface to minimal 2,000m (minimum tracking angle 18º);
3 Bird flight path registration in 2D;
4 Vertical bird flight height and flux registration in 2D;
5 Localised bird flight path and flying height registration in 3D;
6 Continuously 365/24/7 operational;
7 Remote control en data access;
8 Automated bird migration data processing and storage in a dedicated database;
9 Automated data transfer to shore;
10 Bird migration pattern visualisation;
11 Bird species recognition;
12 Bird numbers and bird flux registration;
13 GIS information application;
14 Sea-clutter filtering;
15 Additional rain, land and wind turbine rotor reflection filters;
16 Low-cost product.
As a main outcome of an extensive customer product demand evaluation TNO decided for a system
configuration based upon a combination of two distinct radars. For obtaining relevant 3D bird migration
data a horizontal as well as a vertical radar system are required. Horizontal radar thereby records bird
migration patterns in the horizontal
plane, while the vertical radar adds height-related data. In total two ROBIN Lite test systems have been
developed. One system is located on the roof of the TNO division’s The Hague based laboratory, while a
second system is available for field testing.
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ROBIN Lite horizontal radar
For the horizontal radar system component any state-of-the-art maritime (shipping) radar with X-band
and S-band frequencies can be applied. With regard to the radar hardware only minor modifications
proved necessary, and an initial choice was made for X-band radar made by Furuno. An X-band
frequency is compared to S-band better suited to detect small singing birds, but is as a disadvantage
more sensitive for weather-related effects like rain and snow. The range is also slightly shorter compared
to S-band.
A bigger challenge proved the system electronics required for generating and processing radar signals
into bird-specific information. One of the added difficulties is the fact that bird radar reflection hardly
exceeds radar system-related noise. That in turn puts high technical and other demands to data
acquisition quality. These demands are of such a high-level that the required system electronics is not
available from Commercial Of The Shelf (COTS) market supply sources. TNO therefore engaged a
specialised Dutch electronic system developer for supplying the data-acquisition hardware. Due to the
generic nature of these system electronics it can as part of ROBIN Lite be connected to Furono radars as
well as comparable radars of competing makes.
ROBIN Lite horizontal radar in testing mode at a wind farm near Dresden, Germany
ROBIN Lite vertical radar
Dictated by customer demand for an adjustable height range in a combination with bird species
recognition capability the application of a
tilted (horizontal) type shipping radar system proved impossible. The main reason is that shipping radar
transmits relatively high-performance pulses (maximum 25kW). However, for bird species recognition a
system capability to continuously ‘spot’ a bird is essential. As a key precondition the radar should not
rotate too fast in order to continuously keep track of this given bird. However, with modern shipping
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radar application the latter capability is prohibited for safety reasons. When this specific radar type stops
rotating, than also the radar pulse transmission process ceases.
A radar technology that allows the continuous ‘spotting’ of a bird is known as Frequency Modulated
Continuous Wave (FMCW) technology. The latter radar type does transmit power continuously instead of
by pulses. One main consequence from a radar technology point of view is that two antenna’s are
required, one for transmitting and a second for receiving radar signals. And not unimportant an FMCW
radar is known as a so-called Solid State system. This implies that the radar energy is not generated
anymore as pulses in a radar-magnetron. A key advantage of a Solid State radar system is the much
reduced upkeep requirement compared to standard pulse radars.
The trials showed that birds could be detected from about 3 kilometres distance. Initially the FMCW radar
transmitting power was 25 mW, but now this capacity is being raised to about 700 mW.
ROBIN Lite vertical radar
Data transfer, data processing and storage
Remote control is an important aspect of the ROBIN Lite system development. This feature has been
implemented and field tested during trials at a wind farm near Dresden (Germany) and at the Dutch
Woensdrecht
air force base. One of the positive findings was that the system operated continuously for several
months, and during that period all data generated were successfully transmitted to TNO’s The Hague
office. Generic designed data transfer is based upon TCP/IP Wide Arena Networks (TCP/IP WAN). That in
turn can be achieved with different methods. These have been implemented and tested with the aid of
SATCOM, WiFi en ADSL connections. Bird information in the form of bird flight tracks including variables
like position, speed, direction, and reflection density needs to be stored in database format. State-of-theart formats include among others MS-Acces, MySQL, and PostGreSQL.
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Mobile ROBIN Lite application
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Mobile ROBIN Lite application
ROBIN Lite data visualisation
Depending on client wishes ROBIN Lite results can be visualised in different manners. One option is to
store radar images as unprocessed data, which as an advantage offers the possibility to keep these
source data available for (renewed) future processing. A disadvantage is that the data volume increases
very fast, which can quickly result in data storage and data transfer bottlenecks. The latter especially
occurs when data transmission takes place via a data line with limited bandwidth. This is method is
therefore only applied for development purposes. Another option is to store radar images as ‘streaming
video’. That offers the possibility to maintain a capacity to analyse the source data either manually
and/or visually, see the radar image example below.
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ROBIN Lite radar streaming video image of wind farm near Dresden
The most user-friendly data visualisation method applied today makes use of synthetic data stored in a
database. This means in practice that - based on database queries - relevant bird tracks can be preselected and visualised with the aid of a GIS (Geographic Information System). The latter method offers
by comparison a much-improved understanding of bird movement. A good example offered by bird
migration data obtained from Google Earth is for instance represented in the picture below.
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Half hour bird migration monitoring image around the Woensdrecht air force base
The ROBIN Lite system finally still needs to be validated by TNO’s Dutch project partners Bureau
Waardenburg en IMARES
ROBIN Lite validation trials at Woensdrecht air force base
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C140.10 Report Spatial management...Dutch

Transcription

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