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

68 PRESENTATION OF THE AREA
varies between 16 and 25 metres, increasing towards
north east. Along the outskirts of the shallow area, the
depth quickly increases towards 40 metres.
In principle, all Þ ne-grained sediments have already
eroded from the top of Kriegers Flak, and the seabed
therefore mainly consists of clay moraine, which
probably, according to seismic and sonar research, is
covered by courser sediments such as stones and rocks.
Locally, the clay moraine is covered by thin sand lines
even within the shallow area.
As the water depth increases towards northwest and
gradually towards east/northeast, the seabed is inß uenced
to a lesser extent by currents and movements
of water, why Þ ner coursed sediments can be found.
In the outskirts of the shallow area at a water depth of
around 40 metres, ß uvial sediments can be found with
a powerfulness of between 5 and 10 metres. The ß uvial
sediments are heterogeneous in their composition with
grain sizes varying from mainly silt and clay soils, and
locally with elements of organic material, passing from
clay to mud-like soil. The ß uvial sediments on top of
the clay moraine, are usually covered by a layer of sand
with powerfulness of a couple of metres. The seabed
outside the peripherals generally stretches horizontally,
showing only small variations in depth within the area
studied. Locally, a limited number of cavities can be
noted. In these cavities an increased powerfulness can
be noted on both the ß uvial sediments and covering
sand layer. The sediments may also contain courser
material such as gravel, stone and rock.
As mentioned previously, moraine ridges along the
seabed can be observed in the north-eastern part of
Kriegers Flak. The ridges show a height of around 5
metres.
The peripherals of the bank are in the north-eastern
part covered by gravel, stone and rock.
For a more detailed description of the speciÞ c geotechnical
conditions, see Attachment 4.3.
11.2 Hydrography
11.2.1 Current conditions/fl ow of salt water
in the Baltic Sea
Kriegers Flak is situated in the south-eastern part of
the Baltic Sea on the western edge of the Arcona basin,
which is the most westerly of a number of cascade
shaped basins in the southern Baltic. The deepest basin
is the Gotland basin at 460 metres.
The Kriegers Flak bank is an area with around 20
metres depth surrounded by a seabed with a depth of
35-40 metres. The water depth east of Kriegers Flak
in the central parts of the Arcona basin is around 45
metres.
The Baltic is generally completely surrounded by
land masses and the only connection with the North
Sea is via Store and Lille Bælt and the strait of Öresund.
The cross-section of these straits is small in comparison
with the total area of the Baltic, obstructing the
natural ß ow of water. The ß ow is further restricted by
two thresholds at 18 and 8 metres depth respectively
(Darss and Drogden). On its way through the Belts,
salty water mixes partly with out ß owing bracken
water, and has by the time it reaches the threshold
received the salinity and oxygen needed for the forma-
Salt and oxygen levels, the sea of Arcona