Environmental Statement - Maersk Oil

Balloch Field Development Environmental Statement
Section 3 Baseline Environment
Figure 3‐8 North Sea sediment distribution (MESH, 2007).
In relation to offshore developments, the transport of sediments by seabed currents or sand wave
activity may be an issue in terms of the disturbance of drilling solids and cement during installation
operations. There is a direct relationship between particle size and bottom current strength at the
final site of sedimentation. Fine‐grained sediments are typical of low energy conditions whilst coarse
sediments are typical of high energy conditions. It is likely that lighter particles would be transported
further from the discharge point than heavier particles.
The nature of the local seabed sediments also plays a very important role in determining the flora and
fauna present. Seabed sediments provide habitats and a food source for benthic infauna which in
turn are preyed upon by other species such as fish and shellfish. Whilst gravely sediments are
important to bottom spawning fish species, muddy sediments are favoured by burrowing shellfish
species such as Norway lobster (Nephrops norvegicus).
The characteristics of the local sediments and the amount of sediment transport within a
development area are important in determining the potential effects of possible future developments
(drill cuttings, installation of pipelines, anchor scouring, etc.) on the local seabed environment.
Particles of various types and sizes, notably the silt/clay fraction, can absorb petroleum hydrocarbons
from sea water. Through this pathway, hydrocarbons become incorporated into the sediment
system. Organic matter within the sediment matrix is also likely to absorb hydrocarbons and heavy
metals, providing a means of transport and incorporation into sediments. The bioavailability of
contaminants that are adsorbed to sediment or organic matter is poorly understood.
3.5.2. SEDIMENT CHARACTERISTICS
The distribution of seabed sediments within the CNS results from a combination of hydrographic
conditions, bathymetry and sediment supply. Sediments classified as sand and slightly gravely sand
cover approximately 80 % of the CNS (Gatliff, 1994). These sandy sediments occur over a wide range
of water depths, from the shallow coastal zone down to about 110 m in the north and to below 120 m
in isolated depths to the south and west. The carbonate content of the sand fraction is generally less
than 10 % (Gatliff, 1994).
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