Impacts of submarine cables on the marine environment — A literature review — September 2006 Funding agency: Federal Agency of Nature Conservation Contractor: Institute of Applied Ecology Ltd Alte Dorfstrasse 11 18184 Neu Broderstorf Phone: 038204 618-0 Fax: 038204 618-10 email: [email protected] Authors: Dr Karin Meißner Holger Schabelon (Qualified Geographer) Dr. Jochen Bellebaum Prof Holmer Sordyl Impacts of submarine cables on the marine environment - A literature review Institute of Applied Ecology Ltd Contents 1 Background and Objectives............................................................................... 1 2 Technical aspects of subsea cables.................................................................. 3 2.1 Fields of application for subsea cables............................................................. 3 2.1.1 Telecommunication cables.................................................................................... 3 2.1.2 Power transmission by cables............................................................................... 4 2.1.2.1 Direct current transmission ................................................................................... 4 2.1.2.2 Alternating current transmission............................................................................ 6 2.1.2.3 Cable types........................................................................................................... 6 2.1.3 Electrical heating of subsea flowlines (oil and gas pipelines) .............................. 10 2.2 Cable installation .............................................................................................. 11 2.3 Cable protection................................................................................................ 15 3 Environmental impacts associated with subsea cables ................................ 16 3.1 Noise.................................................................................................................. 16 3.1.1 Introduction......................................................................................................... 16 3.1.2 The DeciBel scale............................................................................................... 16 3.1.3 Anthropogenic noise emission related to submarine cables ................................ 17 3.1.3.1 General assessments, modelling of potential noise impacts and noise measurements .................................................................................................... 18 3.1.3.2 Impact of noise on fauna..................................................................................... 24 3.1.4 Conclusions in regard to noise impacts............................................................... 28 3.2 Heat dissipation ................................................................................................ 30 3.2.1 Introduction......................................................................................................... 30 3.2.2 Project-specific assessments on heat generation................................................ 32 3.2.3 Field measurements of seabed temperature in the vicinity of power cables ................................................................................................................. 33 3.2.4 Laboratory studies .............................................................................................. 39 3.2.5 Conclusions in regard to heat dissipation impacts............................................... 43 3.3 Electromagnetic Fields..................................................................................... 45 3.3.1 Introduction......................................................................................................... 45 3.3.2 Technical background......................................................................................... 45 Contents I Impacts of submarine cables on the marine environment - A literature review Institute of Applied Ecology Ltd 3.3.3 Strength of electric and magnetic fields in the environment of power cables ................................................................................................................. 47 3.3.4 Impacts on fauna ................................................................................................ 53 3.3.5 Conclusions in regard to electromagnetic fields .................................................. 58 3.4 Contamination................................................................................................... 60 3.4.1 Introduction......................................................................................................... 60 3.4.2 Contamination related to seabed disturbance ..................................................... 60 3.4.3 Contamination related to cable deterioration ....................................................... 62 3.4.4 Contamination effects on fauna........................................................................... 62 3.4.5 Additional risks of contamination related to fluid-filled cables .............................. 64 3.4.6 Conclusions in regard to contamination .............................................................. 66 3.5 Disturbance....................................................................................................... 67 3.5.1 Introduction......................................................................................................... 67 3.5.2 Physical disturbance, damage, displacement and removal of flora and fauna................................................................................................................... 67 3.5.3 Water quality effects (turbidity)............................................................................ 68 3.5.4 Physical alteration to the seabed ........................................................................ 74 3.5.5 Conclusions in regard to disturbance .................................................................. 76 4 Conclusions and Recommendations .............................................................. 77 5 References ........................................................................................................ 81 Contents II Impacts of submarine cables on the marine environment - A literature review Institute of Applied Ecology Ltd Table Contents List Tab. 1 HVDC interconnectors with subsea link (from NATIONAL GRID 2000)...................... 5 Tab. 2 Information on recent submarine cable projects (taken from JACQUES WHITFORD LIMITED 2006a)...................................................................................... 7 Tab. 3 Information provided by the company Nexans on installation of direct electrical heating systems at pipelines in selected oil fields (NEXANS NORWAY AS 2005)...............................................................................................................11 Tab. 4 Typical subsea cable burial depths (after EMU LTD 2004)......................................12 Tab. 5 Classification of avoidance reaction in fish proposed by NEDWELL ET AL. (2003). ..................................................................................................................24 Tab. 6 Temperatures recorded at the 26th Oct 2006 (date of maximum difference of seabed temperature between the affected site in vicinity of the 132 kV cable and the control site) at Nysted offshore windfarm by IfAÖ Ltd...............................36 Tab. 7 Thermal resistance of different types of marine sediment (after different authors). ...............................................................................................................37 Tab. 8 Data on electromagnetic field strength for various cables obtained by both calculations and *measurements. .........................................................................52 Tab. 9 Intensity and extent of sedimentation caused by using a hydro plow at sandy conditions (after GALAGAN ET AL. 2003) .................................................................71 Tab. 10 Intensity and extent of turbidity disturbance caused by using a hydro plow at sandy conditions (from GALAGAN ET AL. 2003, amended by IfAÖ) .........................71 Tab. 11 Settling velocities of unhindered discrete particles (from BCTC 2006, according to HITCHCOCK ET AL. 1999), characteristics of the receiving environment (water depth, salinity, density, tidal current etc.) not taken into account. ................................................................................................................72 Tab. 12 Concentrations of suspended solids (mg/l) at coastal waters of Mecklenburg- Vorpommern, 2000 (LUNG M-V 2004)..................................................................73 Tab. 13 List of total suspended matter (TSM) in European coastal waters (FERRARIA ET AL. 2003) .........................................................................................73 List of Figures Fig. 1 Subsea cables in the southern part of the Baltic Sea (not complete), sources: ...... 1 Fig. 2 Subsea cables in the North Sea............................................................................. 2 Fig. 3 Fibre optic cable..................................................................................................... 3 Fig. 4 Latest technical trends in underground and submarine cables after HATA (2006). ................................................................................................................... 8 Fig. 5 Example for a standard