This environmental impact assessment for Kriegers flak ... - Vattenfall

) Biological surveys
Extensive investigations to determine the occurrence
of seabed living animals, Þ sh, mammals and ß ora have
been made in the area using aircrafts, ships and divers.
The occurrence of migrating and resting birds as well
as migration routes for bats in the area has been investigates.
All of these studies have been supplemented by
documentary studies.
c) Oceanographic surveys.
The IfAÖ has amongst others investigated salt and oxygen
contents as well as water temperature.
Ice conditions have been studied by Germanische
Lloyd and BSH.
SMHI has made a worst case scenario estimate of
the mixing of salt water between upper and lower layers.
An estimate of the cumulative impact of building
both the German and Swedish wind farms at Kriegers
Flak has also been carried out by SMHI. The hydrographical
conditions of the area have been surveyed
and summarised by Hydromod.
5.6.2. The construction phase
As previously stated, it has not yet been decided which
type of foundation that will be used although it is likely
that monopiles will be used in shallower (down to 25
metres) and tripods in deeper waters. The foundations
will be piled or drilled some 30 metres into the seabed.
The aim, as far as possible, is to pile the foundations
into the seabed. If this proves impossible, for example
DESCRIPTION OF THE WIND FARM 31
due to rocks and other solid ground, the foundations
will be drilled into the seabed. In order to determine
the right foundation dimension and decide whether to
pile or drill, preparatory work will be carried out at
each speciÞ c foundation location. This encompasses
geophysical surveys, such as using sonar and
sidescan sonar, seismic surveys and videotaping,
as well as geotechnical surveys such as
drilling, sounding, vibration testing and sampling
of the seabed layers. Proposals regarding
this preparatory work can be found in the
SIG report (Attachment 4.3, chapter 6).
Drilling at the site will be carried out
inside the steel tube casing that constitutes the
foundation cylinder. The drill mud is sucked
through a hose leading up to the drill ship.
Onboard the ship, there are two ways to make
use of the mud. Either the contents are fed
back into the sea where the currents are strong
as is the case at the site. The currents will result
in quick spreading of the sediments. The
second alternative is to dispose of the mud in
a container onboard the ship. The mud will
sink to the bottom of the container and the water will
thereafter be let back into the sea. The remaining sediment
will then be released back through the foundation
casing. Thereafter the piling can continue down to the
target depth.
To get rid of a solid obstacle, directional drilling
can be applied from several angles with a smaller drill.
The obstacle will be broken up and the piling can be
continued.
The foundation surface will be treated with biodegradable
corrosion protection.
The technology for assembling wind turbines is rapidly
improving. It will quite soon be likely that turbines
will be assembled in their entirety onshore and that
large special purpose vessels will carry them to the
site. As this is a cost saving and less time consuming
technique it will, if possible, be used at Kriegers Flak.
If this latter alternative will not be possible at the
time of building the wind farm, the assembly process
will look as follows:
As far as possible, the assembly of the turbines will
be carried out onshore. The following four components
will then be assembled at the site:
• The lower part of the tower