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CABLE PROTECTION/SCOUR MITIGATION ADDITIONAL CONSIDERATIONS


Providing adequate protection for undersea cables, whether through sufficient burial or physical protection, is complicated by additional considerations such as the thermal properties of the soil and the impact on cable overheating and whether the cable is to be placed on a rocky seabed. If physical protection is required, ensuring its performance is able to accommodate the various bed level changes that may be encountered over a cable’s lifetime requires a risk- based approach that considers the environmental drivers that will impact on the stability, such as seabed properties, general bathymetric changes, local scour, hydrodynamic forcing and cable integrity. Where cabling stability issues have arisen after a period of operation, it is important to provide an effective solution which can be retrofitted to solve the specific scour problems and to provide remediation measures that future-proof against further issues arising. For tidal energy projects utilising areas of fast currents, the environments in which they are located often consist of rocky seabeds where cable scour need not be considered, but stability and increasing risk of cable fatigue through hydrodynamic loading and possible vortex-induced vibrations (VIV) may be inherent risks in addition to those risks due to anthropogenic actions, such as anchoring and bottom trawling. Cable burial is frequently not an option as it is not economically viable, however the use of scour protection methods can mitigate the risks.


CASE BY CASE BASIS


A number of approaches can be taken to inhibit or mitigate scour or provide protection and/or stability for the cables, either as planned for, or as a remedial measure. The actual method employed will be determined on a case by case basis, but may consist of rock or mattressing as two of the most frequently employed methods of protection. Other areas of potential high risk occur at locations where cables are crossing previously installed seabed infrastructure, such as other submarine cables. Careful


consideration during the route selection stage can potentially avoid some of these problems by choosing, for example, to cross at a point where the cable can be aligned along the flow direction, rather than perpendicular to it. John Harris, Technical Director at HR


Wallingford, commented: “Marine energy developments must continue to meet the need to develop cost- effective and structurally efficient foundations and cable layouts. Scour hazards will remain a challenge for next-generation foundations and it is important that these are addressed at the design stage, in order to reduce the cost over the lifetime of a project.”


MARINE SCOUR COURSE


HR Wallingford has developed a two-day Marine Scour Course which


MORE INFO FAST FLOW www.wavetidalenergynetwork.co.uk PAGE 11


introduces analysis procedures for assessing risk at marine structures, as well as the appropriate use of scour countermeasures, through a combination of theory, practical sessions and classroom discussions. Two of the sessions will focus on pipelines and cables specifically. The next course takes place from 14-15 June 2017. More details can be found through the QR Codes/Links below.


HR Wallingford Ltd


SCAN/CLICK


SCAN/CLICK


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