Environmental Statement - Maersk Oil

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3 ‐ 2 Survey Reference Balloch Field Development Environmental Statement Table 3‐1 Survey information sources in the Balloch development area. Title and Description BP (1990) Environmental site survey for exploration well 15/20a‐m. ERT (1998) Section 3 Baseline Environment Environmental decommissioning survey of the Donan field. Environmental survey carried out after the field infrastructure was removed. Gardline (2004) Donan to MacCulloch and Tiffany pipeline route survey in 2004. Fugro (2005) Fugro (2010) 3.3. METOCEAN CONDITIONS Site survey of Block 15/20 for two proposed drilling locations. The survey comprised of a geophysical and environmental survey programme. The environmental survey consisted of a seabed investigation of six sampling sites. The survey was centred southeast of the Balloch location. Site survey of Block 15/20 comprising geophysical and environmental survey programme in 2009 for the proposed 15/20b‐r Dunglass ‐ Balloch Appraisal Well drilling location. The survey used single and multi‐beam echo sounders, sidescan sonar, a magnetometer, pinger, boomer, coring and Cone Penetration Testing (CPT) equipment to provide a detailed assessment of the area (Fugro, 2010). The habitat assessment and environmental baseline survey consisted of seabed imagery using a digital stills camera and video system, along with seabed sampling utilising a Day grab. Overall, eight sampling stations were analysed using a 0.1 m 2 Day grab. The samples obtained were used to undertake hydrocarbon analysis, heavy metals and particle size analysis and macrofaunal analysis. Figure 3‐2 Environmental sampling stations and seabed bathymetry. In order to design and operate offshore installations in a safe and efficient manner, it is essential that there is a good knowledge of the metocean (meteorological and oceanographic) conditions to which the installation may be exposed. Sediment type, currents, tides and circulation patterns all influence the type and distribution of marine life in an area. Metocean conditions also influence the behaviour
Balloch Field Development Environmental Statement Section 3 Baseline Environment of emissions, discharges and releases from offshore facilities. For example, the speed and direction of water currents have a direct effect on the transport, dispersion and ultimate fate of any discharges from an installation, while sediment type can influence the levels of contaminants that may be retained in an area. 3.3.1. WATER MASSES, CURRENTS AND TIDES The Balloch development is situated within the CNS where the water depths gradually deepen from south to north. The major water masses in the North Sea can be classified as Atlantic water, Scottish coastal water, Northern North Sea (NNS) water, Jutland coastal water and Channel water (Turell, 1992). The predominant regional current in the CNS originates from the vertically well‐mixed coastal water, the Atlantic inflow from the north and, to a lesser extent, the Fair Isle/Dooley current which enters the North Sea north of the Orkney Isles (Figure 3‐3). The residual flow in the CNS (associated with North Sea circulation patterns) is typically 0.2 m/s towards the south (DTI, 2001). Therefore, this pattern of water movement is likely to transport any discharges towards the south and southeast. However, it should be noted that this generalised pattern of water movement may be influenced by short‐ or medium‐term weather conditions, resulting in seasonal and annual variability. The Balloch development lies on the eastern edge of the anticyclonic system of the east of Shetland Atlantic inflow. Stratification of the water column in the development area is expected, due to the depth of the water column and the presence of two water bodies with differing temperatures and salinity profiles. A colder, denser water column originating from the depths of the Fladen Ground underlies a warmer water mass that originates from the east of Shetland Atlantic inflow. Figure 3‐3 A schematic diagram of the general circulation in the North Sea (EEA, 2002). Mixing in the water column intensifies with increased tidal current speed, which is influenced by weather and seasonal factors. Over most of the North Sea, the strength of tidal streams is generally less than 0.51 m/s, even at mean spring tide. Tidal currents over the proposed development area are relatively weak, with surface current velocities for mean spring tides ranging from 0.2 ‐ 1.4 m/s. The velocity of current profiles decreases with increasing depth through the water column. Semi‐diurnal tidal currents are relatively weak in offshore NNS and CNS areas (DTI, 2001). Surge and wind–driven currents, caused by changes in atmospheric conditions, can be much stronger and are generally more severe during winter. Storm events may also generate near‐bed, wave‐induced currents that are sufficient to cause sediment mobilisation (DTI, 2001). The maximum 50 year surge current in the region of the development is approximately 0.4 m/s (BODC, 1998). 3 ‐ 3
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Physical presence Oil and gas infra
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Major accidental events Other envir
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Environmental Statement - Maersk Oil

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