Review of Cabling Techniques and Environmental Effects Applicable

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Review of Cabling Techniques and Environmental Effects Applicable to the Offshore Wind Farm Industry – Technical Report feeding efficiency. In addition many fish species such as herring rely on light levels to aid migration and shoaling behaviour. Low light levels caused by high levels of suspended sediment could impair the ability of species to shoal as part of migrations to spawning or feeding grounds. Studies described in Section 4.4 indicate short term and localised increases in turbidity over a number of tidal cycles (for those cable installation methods investigated). Smothering The blanketing or smothering of benthic animals and plants, may cause stress, reduced rates of growth or reproduction and in the worse cases the effects may be fatal (Bray, Bates & Land 1997). The impact of smothering on fish and shellfish will be a function of the settling behaviour of sediment resulting from increased suspended sediment concentrations relative to background levels, the sensitivity of certain species and/or lifestages to those increases and their ability to move to other areas. The significance of this impact is dependent on many variables including hydrography, seasonality, sediment type, species and the technique used to bury the cable (see Sections 4.2 and 4.3 for more details). The main impact on fish is the irritation and clogging of gills. Juveniles are more susceptible to this as adult fish would normally be able to detect significantly elevated levels of suspended sediment and move away from the affected area (ABP Research, 1997). Smothering can result in significant mortalities on shellfish beds as they are less mobile than fish species, with many having lifestages that are sensitive to variations in sediment particle size within the water. Respiratory and feeding apparatus may be clogged by the settlement of significant amounts of sediment that is mobilised by cable-laying operations. Filter feeders such as mussel, oyster and scallop are therefore among the most vulnerable to smothering effects. Shellfish are particularly susceptible during spring when spatfall occurs (Posford Duvivier & Hill, 2001). If sensitive spawning or shellfish beds cannot be avoided entirely, seasonal avoidance may be required. Water quality Cable installation requires extensive use of shipboard and subsea equipment which in many cases is hydraulically driven. There is a consequent risk of spillage of hydraulic fluid from vessels. The spillage is, however, limited by the system design. Perhaps the greatest risk is a major leak from a burial ROV system when operating on the seabed. Such systems have typical reservoir capacity of 60-100 litres. Spillage risks can be minimised by good practice: ● ● 118 Deck mounted hydraulic equipment should be fitted with saveall (cofferdam) surrounds to catch leakage and prevent discharge over the vessel side; Spare hydraulic oil should be securely stowed, preferably below decks;
● ● ● ● Potential impacts and mitigration measures Oil levels should be monitored regularly to safeguard against undetected leakage; Hydraulic systems should be designed to limit discharge in the event of a system failure with use of no return valves where possible; ROV hydraulic systems should not be all fed from a single common reservoir, but have a number of separate reservoirs to limit any potential impact from a system failure; and Appropriate spillage control procedures and equipment should be available on board the operations vessels. Other potential sources of pollution include lubricants used during horizontal directional drilling methods of cable installation. These are generally inert biodegradable substances such as bentonite which will disperse rapidly. Some localised and short term aesthetic impacts on the sea surface may be experienced. Water quality (and pollution prevention) will also be an important consideration where cable installation takes place within or near a designated Shellfish Water. The EU Shellfish Water Directive (adopted in 1979) outlines the requirements for the quality of designated waters which support shellfish (defined as bivalve and gastropod molluscs) and aims to protect these shellfish populations from the harmful consequences resulting from the discharge of polluting substances into the sea. This Directive has been transcribed into UK legislation under the Surface Waters (Shellfish) (Classification) Regulations 1997 and The Surface Waters (Shellfish) Directions 1997. Cable laying in these areas should be avoided; where avoidance is not possible, close liaison with fishery operators and management authorities, including the Environment Agency is recommended. Electro Magnetic Field (EMF) The transport of electricity through an export and inter-array power cable has the potential to emit a localised electromagnetic field (EMF) which could potentially affect the sensory mechanisms of some species of marine fauna. The degree of impact and the subsequent effect on marine communities was investigated by The Centre for Marine and Coastal studies and Cranfield University in 2003 and 2005, funded through Collaborative Offshore Wind Research into the Environment (COWRIE). The COWRIE investigations found that the EMF emitted by industry standard AC offshore cables had a magnetic field component and an induced electric field component (COWRIE, 2003). These EMF components were both within the range of detection by EM-sensitive aquatic species, such as sharks and rays (Elasmobranchii). It is generally acknowledged that elasombranchii will encounter multiple EMF components within the wind farm from the inter-turbine array and as a linear field from the export cables. From previous research it has been shown that iE-Fields can affect the behaviour of elasmobranchii when they reach a critical 119
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REVIEW OF CABLING TECHNIQUES AND EN
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Review of Cabling Techniques and En
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Abbreviations AIS Automatic Identif
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TTS Temporary Threshold Shift TWA T
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3 Cable types and 18 installation t
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Page 82 and 83: 4 Physical change 4.1 Introduction
Page 140 and 141: 6 Good practice measures This secti
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Page 144 and 145: References Introduction Sinden, G.
Page 156 and 157: Appendix A: Standards and codes of
Page 164: Printed in UK on recycled paper. De
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Review of Cabling Techniques and Environmental Effects Applicable

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