Appendix 4: Sejerø Bugt Offshore Wind Farm

Appendix 4: Sejerø Bugt Offshore
Wind Farm – Technical
Description, Offshore
Appendix 4: Sejerø Bugt Offshore Wind Farm – Technical Description, Offshore
Appendix 4: Sejerø Bugt Offshore Wind Farm – Technical
Description, Offshore
Published by Energinet.dk
Published as Internet version only:
Report no. 13/98200-2
Rapporten kan fås ved henvendelse til:
Energinet.dk
Tonne Kjærsvej 65
7000 Fredericia
Tlf. 70 10 22 44
The report may be downloaded the Danish Energy Agency’s (Energistyrelsens)
website:
www.ens.dk
2015
Dok. 13/98200-2
2/16
Energinet.dk
Table of contents
1. Location ........................................................................................ 2 2. Wind farm layout ............................................................................ 3 3. Foundation and installation .............................................................. 4 3.1 Foundation ......................................................................... 4 3.2 Construction features vs. water depths ................................... 5 3.3 Installation scenario ............................................................. 6 4. Pre-investigations ........................................................................... 7 4.1 Investigations ..................................................................... 7 4.2 Summary of seabed survey ................................................... 7 5. List of enclosures.......................................................................... 13 Dok. 13/98200-2
3/16
Appendix 4: Sejerø Bugt Offshore Wind Farm – Technical Description, Offshore
1. Location
Sejerø Bugt Offshore Wind Farm (OWF) is located north of the peninsula of
Røsnæs 4 km off the coast. The area appointed for the wind farm is
approximately 61 km2, reduced however to approximately 53 km2 by a cable
corridor across the area in N-S direction, where turbines cannot be installed. The
water depth in the area varies between 8 and 25 m. A western and an eastern
cable corridor, each 500 m wide, are identified for routing cables to the coast.
The wind farm area with cable corridors is shown in Figure 1 with bordering
coordinates listed in Table 1.
Figure 1 Sejerø Bugt offshore pre-investigation area and cable corridors. Black
numbers represents coordinates for OWF area, red numbers represents
coordinates for export cable corridors.
Dok. 13/98200-2
2/16
Energinet.dk
Table 1
List of coordinates for pre-investigation area and export cable corridors
for Sejerø Bugt Offshore Wind Farm
SITENAME Sejerø Bugt Sejerø Bugt Sejerø Bugt Sejerø Bugt Sejerø Bugt Sejerø Bugt Sejerø Bugt Sejerø Bugt Sejerø Bugt Sejerø Bugt Sejerø Bugt Sejerø Bugt ID 1 2 3 4 1 2 3 4 5 6 7 8 AREA EASTING NORTHING
UTMSYSTEM Cable 623002
6184114 WGS84_UTM32N Cable 623623
6179820 WGS84_UTM32N Cable 625860
6184112 WGS84_UTM32N Cable 626922
6178544 WGS84_UTM32N Investigation area 626075
6193553 WGS84_UTM32N Investigation area 627720
6192572 WGS84_UTM32N Investigation area 632622
6187536 WGS84_UTM32N Investigation area 632515
6186148 WGS84_UTM32N Investigation area 629426
6186177 WGS84_UTM32N Investigation area 626960
6186201 WGS84_UTM32N Investigation area 626960
6184111 WGS84_UTM32N Investigation area 619895
6184117 WGS84_UTM32N 2. Wind farm layout
A maximum of 200 MW wind power may be installed at Sejerø Bugt Offshore
Wind Farm. Preliminary layouts for the wind farm have been developed by DTU
Wind Energy for the purpose of serving as worst case scenarios for the
Environmental Impact Assessment (refer to Enclosure 1). Layouts for 3.0 MW
and 10.0 MW WTGs, respectively, are presented in Figure 2. The final layout will
eventually be decided by the developer, based on an optimization of a number
of parameters, within the frame of the consent to be issued by the authorities.
Dok. 13/98200-2
3/16
Energinet.dk
Figure 2 Sejerø Bugt Offshore Wind Farm study area and preliminary wind farm
layout for 3.0 MW and 10.0 MW WTGs, respectively
3. Foundation and installation
3.1
Foundation
Foundation dimensions are given in tables below, based on the general
indicative dimensions given in generic technical project description.
Table 2
Estimated monopile foundation dimensions
Monopile
Turbine capacity, MW
Diameter at seabed
level, m
Pile Length, m
Weight, t
Penetration depth, m
3.0
3.6
4.0
8.0
10.0
4.0-5.0
4.5-6.0
5.0-6.5
6,0-7.0
6.0-8.5
35-45
35-50
40-60
50-70
50-80
200-450
300-600
300-600
500-800
600-1,000
15-22
15-25
20-31
30-34
35-39
150-250
150-250
160-260
200-350
250-400
Transition piece
Weight, t
Dok. 13/98200-2
4/16
Energinet.dk
Grout volume , m3
15-35
15-35
20-40
25-60
30-65
Scour protection
Volume, m3
2,200
2,200
2,600
3,100
3,600
Footprint, m2
1,600
1,600
1,700
1,750
2,100
Table 3
Estimated GBS foundation dimensions
Gravity Base
Turbine capacity, MW
3.0
3.6
4.0
8.0
10.0
Shaft diameter, m
4,0-5.0
4.0-5.0
4.0-5.0
4.5-6.0
5.0-7.0
Base area, m2
250-450
320-490
320-490
490-960
700-1250
Weight, t
1,2001,700
1,5002,000
1,5002,200
2,5003,000
2,5004,000
Ballast, t
700-1,000
1,0001.200
1,0001.200
2,0002,800
2,0003,200
400-600
400-700
400-850
500-1,600
530-1,950
1,0001,300
1,0001,500
1,2001,600
1,4002,200
1,6002,800
600-900
600-1,000
750-1,000
800-1,400
900-1,700
Footprint, m2
1,3003,900
1,6004,000
1,6004,000
2,6006,900
4,70010,000
Volume, m3
2,0004,500
2,5004,500
2,5004,500
3,5008,000
5,50011,000
Excavation
Excavation area, m2
Material excavation, m3
Gravel bed, m3
Scour protection
Table 4
Estimated jacket foundation dimensions
Jacket
Turbine capacity; MW
3.0
3.6
4.0
8.0
10.0
Footprint at top, m
8x8
10x10
12x12
15x15
18x18
Footprint at sea bed, m
15x15
17x17
20x20
25x25
32x32
Weight, jacket, t
200
350
-
1,000
1,100
Weight, 4 piles, t
150
200
-
500
600
Suction bucket foundations are at a prototype/testing stage and dimensions are
uncertain, but they will be smaller than a GBS. For the purpose of environmental
impact assessment they are assumed of smaller dimensions than a GBS.
3.2
Construction features vs. water depths
The 3 MW layout consists of 66 positions placed in 10 rows, largely
perpendicular to the north coast of Røsnæs, Sjælland. The area is deepest
towards the south-west corner (approx. -22 m) and shallowest towards the east
Dok. 13/98200-2
5/16
Energinet.dk
(approx. -8m). The water depths do not exclude 3 MW WTGs from being
installed at any of these foundations.
The 10 MW layout consists of 20 positions placed in 6 rows largely
perpendicular to the coast. Water depths are sufficient to allow installation all
over, from the south-western “row” consisting of just one position at approx. 22m to the 2 north-eastern positions are at approx. -10m to -13m; although at
the shallowest it may be challenging to operate sufficient capacity vessels under
unfavourable soil conditions (affecting jacking operations) or weather conditions.
Figure 3 Sejerø Bugt Offshore Wind Farm bathymetry and shallow water
limitations
3.3
Installation scenario
An indicative construction schedule as shown in section 6.5 of the generic
technical project description is assumed, and installation equipment and
duration of operations are as indicated in section 3 of the generic technical
project description:


Seabed preparations/excavation and installation of gravel bed 5 days
Installation of foundations, 1 day
Dok. 13/98200-2
6/16
Energinet.dk

Installation of turbines 1 day
Seaward transport of materials, mainly turbines, foundations and stone material,
are assumed from appropriate port within 50 NM distance.
4. Pre-investigations
4.1
Investigations
The Sejerø Bugt offshore wind farm area and adjacent export cable corridors
have been investigated using geophysical and geotechnical techniques and a
Metocean modeling study have be performed for the site.
The geophysical survey includes bathymetric mapping, side scan sonar mapping,
single and multichannel sub-bottom profiling, magnetic profiling and ground
truth sampling to facilitate seabed interpretation. Results and interpretation of
the geophysical survey at Sejerø Bugt can be found in Enclosure 2.
The geotechnical campaign included 2 investigations to depths of 70 m below
seabed using combined borehole drilling and CPT testing. Furthermore 9 single
CPT tests were completed using either a push CPT or a seabed unit CPT system
reaching depths 3 – 30 m below seabed. The results are presented in Enclosure
3.
A Metocean study including provision of information and data on wind, waves,
water levels, currents, ice etc. was conducted for Sæby offshore wind farm area.
Furthermore provision of wind data and information on wind resource estimation
was performed. Results and reports can be found in Enclosure 4.
4.2
Summary of seabed survey
Geophysical survey
The objective of the site surveys is to provide an input to the Environmental
Impact Assessments and an initial evaluation of the foundation of the wind
turbines, as well as lower the risk for companies with interest in acquiring the
license in 2015 to build and operate the wind farms providing a general
assessment of the areas.
To meet the project objectives, a full geophysical and bathymetric survey was
conducted with activities including:

Bathymetric mapping with full seafloor search (>100% coverage) within
the survey area.
Dok. 13/98200-2
7/16
Energinet.dk

Side-scan sonar mapping (overlap >100% to cover nadir regions of
adjacent survey lines).

Sub-bottom profiling with two systems; one high resolution pinger
(chirp) single channel system plus one deep penetration sparker multichannel system.

Magnetic profiling along all survey lines.

Ground-truth sampling (grabs) to support seabed interpretation.
The survey was conducted in a single operational phase, using the survey
vessel; EGS Pioneer, on a 24hr basis operating out of the port of Kalundborg.
The main equipment spread for the vessel consisted of a Kongsberg 2040 MBES,
a Klein 3000 dual frequency SSS, a Knudsen 3260 Chirp, a Geo-Source Sparker
and a Geometrics G882 marine magnetometer. An Applanix POSMV 320 Elite
was used for all (horizontal, vertical and motion reference) positioning
(primary), in combination with a Sonardyne Scout Plus USBL system for the
subsurface towed equipment (interfaced into the QPS QINSy navigation
package).
All positions in this report and associated data are referenced to geographic
(WGS84 Lat/Long) or projected (UTM32N) coordinates. All reported elevations
and depths are referenced to the DVR90 vertical elevation system represented
by the DKGEOID02 geoid model from the Danish Geodata Agency. The DVR90
system is considered as a valid approximation to MSL.
The survey specifications required lines to be run with 65m line spacing over an
approximate area of 61km2. This equated to a total planned line length of
1009.9km, including cross lines spaced at 1km intervals. In total 1404.7 line
kilometers of SSS acoustic imagery, SBP (both chirp and MCS) records, MAG
data profiles and MBES bathymetric data were acquired (extra kilometers due to
reruns and infill), processed and interpreted resulting in the interpretation of
bathymetry, seabed features and shallow geological profiles. Full data coverage
was achieved during survey operations. A total of 25 grab samples were taken
as a ground-truth, primarily to the sonar data.
The survey results have been presented as a series of 53 charts generated in
ESRI ArcMap. These have been delivered both as PDFs and as ESRI projects to
allow for full digital interaction with the supplied charted data. Of the 53 charts,
an overview chart showing the coastline and the survey area, a vessel track
chart plotting the common reference point (CRP) of the vessel, a bathymetric
chart displaying shaded relief and contours, an SSS mosaic chart, and five
charts displaying elements of the seabed features, morphology and sediments
were charted at a 1:25,000 scale. An overview SBF chart has also been created
at a scale of 1:25,000. Eight significant sub-seabed geological components were
Dok. 13/98200-2
8/16
Energinet.dk
also charted at a 1:25,000 scale. Further to this, the geological interpretation for
10 mainlines and 10 cross lines were charted in profile at a scale of 1:7,500 and
have been supplied as ESRI ArcScene 3D mapping projects. Digital datasets
supporting the interpretation, reporting and charting have been delivered in CSV
and shapefile formats. Processed seismic data, both single and multichannel,
has also been supplied to facilitate additional future interpretation and quality
control of this dataset.
Figure 4. Overview of the Sejerø Bugt Site Bathymetri (Figure 19 in original
report)
The limits of surveyed bathymetric data within the survey area of Site 4 range
from a minimum of approximately 6m below DVR90 along the glacial ridges and
outcrops located towards the eastern and northeastern extents of the site, to a
maximum of approximately 25m below DVR90 in the deeper sections of the site
towards the northwest. Figure 4 presents an overview of the bathymetry
throughout the entire site.
Dok. 13/98200-2
9/16
Energinet.dk
Figure 5. Overview of the Sejerø Bugt Seabed Features (Figure 24 in original
report)
While the initial specifications from the Scope of Services required 200%
coverage of the site, a reduction in scope to 100% coverage was accepted by
Energinet during Site 4 operations due to the degree of stratification of the
water column and the impact of this stratification on the sonar data. The surficial
material along the north-eastern margin of the survey area and in patches in the
north centre of the survey area has been found to consist of outcropping glacial
till with surrounding areas of gravelly seabed. The seabed sediments are
composed of patches of outcropping till interspersed with a lag deposit of gravel,
cobbles and boulders. The till is expected to consist of a stiff clay matrix
containing pebbles, cobbles and boulders. Numerous seabed boulders are
concentrated on the seabed in these areas. The seabed across the rest of the
survey area consists of a thin veneer of sand over soft clay apart from an
elevated bank of sand in the southeastern corner and an area of sand and gravel
patches in the north-east corner of the site. Figure 5 presents an overview of the
seabed features throughout the entire site.
A total of 2228 sonar contacts were identified, including 16 contacts interpreted
as items of debris (of possible man-made origin) and one interpreted as a
possible wreck (uncharted). The remaining 2211 contacts have interpreted as
boulders, including those marked representatively. Areas of numerous boulders
can be expected to be encountered close to the areas of till outcrop in the
Dok. 13/98200-2
10/16
Energinet.dk
northeastern margin and the central northern area of the site. Outside of these
areas the boulder distribution is much less dense or absent.
The sub-surface sediments have been mapped on the basis of seismic
evidences. The distribution of the most significant geological units has been
mapped as a background for the geotechnical evaluations of the turbines. The
interpretations are primarily done on the basis of the seismic reflection pattern.
The primary basement of Pre-Quaternary sediments has been located
representing Eocene silt and clay. In general, the Pre-Quaternary surface is
located 130-25 meter below seabed. The mapping also revealed information on
the presence of a unit representing Weichselian glaciogene. The deposits from
this period show evidences of moderate to high degree of glacial deformations
like folding and thrusting. Glaciogene sand, silt and clay from this period is
found in onshore boreholes close to the study area. A significant unconformity
represents an overgrown early Holocene surface. The distribution of Holocene
sediments in general covers most of the study area. The Holocene units have
been located in lows into the underlying strata. Here fine grained sediments
including organic material have been deposited in freshwater lakes and channels
during the early Holocene period. As transgression toke place across the sub-air
surface sand and gytje covered the surface. Sub-recent sand and gravel are
found in bares and thin veneers some areas.
Using a target detection threshold of 2nT, 167 magnetic contacts were
identified. In general the distribution of magnetic contacts appears well spread
throughout the site. A higher density of relatively larger amplitude contacts is
located towards the southwest corner of the site and an aparently linear
magnetic feature of relatively low amplitude exists in the north. This feature is
attributed to the edge of a boulder field.
Geotechnical survey
INTRODUCTION
A preliminary geotechnical investigation was carried out by Fugro Seacore
Limited (FSCL) on behalf of Energinet.dk (the Employer) and under the
supervision of Ramboll. The site of the investigation was located in Kattegat,
approximately 5km north west of the coast of Sjælland, north of the peninsula
Røsnæs and south west of the island Sejerø, in Denmark.
OBJECTIVES OF THE GROUND INVESTIGATION
The purpose of the ground investigation was to provide sufficient geotechnical
data to allow for the evaluation of the site for further investigation and
development into a nearshore wind farm.
SCOPE OF THE GROUND INVESTIGATION
Dok. 13/98200-2
11/16
Energinet.dk
The nearshore ground investigation was undertaken from Fugro’s jack-up
platform ‘Excalibur’ and vessel ‘Fugro Commander’. The site work conducted
from Excalibur was undertaken between 6th and 16th June 2014; the site work
conducted from Fugro Commander was undertaken between 30th May and 2nd
June 2014.
The scope of the ground investigation comprised:

Two sampling boreholes constructed using a combination of rotary open
hole and rotary

coring techniques, carried out from Excalibur,

One cone penetration test, using the top-push system and the WISON
XP system, with

rotary coring at selected depths, carried out from Excalibur,

One cone penetration test, using the top-push system and the WISON
XP system, carried out from Excalibur,

Nine cone penetration tests, using the Fugro Seacalf Block-Drive seabed
system, carried out from Fugro Commander. These tests, undertaken at
seven exploratory locations, included two re-tests carried out in an
attempt to reach the required depths due to previous refusal,

Seven Ménard pressuremeter tests carried out within the sampling
boreholes at

appropriate depths; one test failed.
REPORTING
The ground report is presented in three parts:

Operations Report; including information on the field operations, health
and safety and environmental information, procedures for the field
testing and sampling techniques used, and data sheets and calibration
certificates.

Factual Report; including site setting, the exploratory hole and field
testing records, laboratory test results, an overview of the ground
conditions encountered and geotechnical evaluation of the field and
laboratory test results.

Cyclic Laboratory Test Report; including the cyclic triaxial and cyclic
shear test results.
FINDINGS OF THE GROUND INVESTIGATION
The ground investigation encountered the following succession of strata:

Recent Marine Deposits

Late Glacial Deposits
Dok. 13/98200-2
12/16
Energinet.dk

Late Weichselian Cohesive Outwash

Late Weichselian Granular Outwash

Baelthav Till

East Jylland Till

Intermediary Granular Deposits

Mid Danish Till

Mid Weichselian Interstadial Formation

Kattegat Till

Klintholm Till

Ristinge Klint Till

Lillebælt Clay
5. List of enclosures
Enclosure 1 - Wind farm layout:
Wind farm layouts for Sejerø Bugt. DTU Wind Energy, Report-I-0198(EN),
February 28, 2014.
Enclosure 2 – Geophysical surveys:
Danish Wind Farm Site Surveys. EGS Earth Sciences & Surveying report to
Energinet.dk, 2014.
Volume 1: Operations report. Site 5 – Sejerø Bugt. January 2014
Volume 2: Interpretive Report. Site 5 – Sejerø Bugt, April 2014;
Volume 3: Results report. Site 5 – Sejerø Bugt, April 2014
Enclosure 3 – Geotechnical surveys:
Preliminary geotechnical investigations 2014. Sejerø Bugt Nearshore Wind Farm.
Fugro Seacore Limited report to Energinet.dk. October 2014.

Factual report on ground investigation

Operations report on ground investigation

Report on cyclic laboratory tests
Enclosure 4 - Metocean:
Sejerø Bugt offshore windfarm – met-ocean report. COWI A/S report to
Energinet.dk, January 2015
Six Nearshore Wind Farms – Study Related to Wind Resource – Wind Resource
Report. COWI A/S report to Energinet.dk, November 2014.
Dok. 13/98200-2
13/16
Energinet.dk
Six Nearshore Wind Farms – Study Related to Wind Resource – Validation
Report. COWI A/S report to Energinet.dk, November 2014.
Dok. 13/98200-2
14/16