TOPIC SHEET NUMBER 9 V2

TIDAL STREAM POWER GENERATION: SEABED SURVEYS IN THE PENTLAND AND AREAS 2009

MRV SCOTIA

Introduction Following initial surveys undertaken by Marine (formerly Fisheries Research Services) in 2008, an 18 day cruise was undertaken to extend the original bathymetric survey work. The sites surveyed included areas identified by The as being of particular importance in relation to the recent seabed leasing of the Pentland Firth and waters adjacent to Orkney. The areas were primarily of interest with regard to tidal stream power generation.

PENTLAND FIRTH AND ORKNEY ISLANDS MULTIBEAM SURVEY SITES Cruise Dates • Single beam echosounder system: RoxAnn™ MRV Scotia, 18th July - 5th August 2009 The RoxAnn™ system provides information on the hardness and roughness of the sea bed. This Equipment Used makes it is possible to infer information about the • Multi-beam echosounder system: Reson character (rock, sand, mud, boulders, etc) of the 7125 and sound velocity profiler. seabed. The system provides detailed information on the depth and shape of the surface of the • Drop Frame TV: digital video, stills and seabed. The multi-beam echosounder (swathe Seabird 19+ CTD bathymetry) data will be corrected for tidal The Drop Frame TV (digital video and stills) was variability. Typically, the spacing between used in some areas to provide images of the swathe lines ensured at least 50% overlap seabed and the associated benthos, and to ‘ground between survey lines. truth’ the RoxAnn™ data. The Seabird 19+ CTD was

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attached to the drop frame TV to record vertical Twenty-four TV tows were undertaken during and spatial variability in the physical properties the cruise and amount to approximately eight of sea water such as conductivity (salinity), hours of video footage. The majority of the temperature and pressure (depth). tows and video footage were collected (see • Vessel mounted acoustic doppler current left) from the west of and the west of profiler (ADCP) mainland Orkney, although further sites within The vessel mounted ADCP provides information the Pentland Firth were also investigated. Digital on tidal current speed and direction encountered stills were collected from each of the tows along a transect between two fixed stations. where practicable. In addition, conductivity, temperature and depth were recorded during Scope of Survey the deployment, operation and recovery of the Nine blocks of seabed were surveyed using the Seabird 19+ CTD. multi-beam and RoxAnn™ echosounders, and No. TV seabed images were obtained from five of these Location Video Footage (hrs) Tows blocks. The total area surveyed amounted to West of Mainland Orkney 15 4hr 48min approximately 280 km2, with 85% of the survey West of Hoy 5 1hr 20min area located within the Pentland Firth. Pentland Firth 4 2hr 15min

Area Location Echosounders km2 Approximately 18 hrs of current data were West of Mainland Orkney 30 Swathe and RoxAnn™ collected from two transects east and west of West of Hoy 15 Swathe and RoxAnn™ Stroma using the vessel mounted ADCP. West of Stroma 32 Swathe and RoxAnn™ East of Stroma 20 Swathe and RoxAnn™ The data are available through Marine Scotland South of Stroma 5 Swathe and RoxAnn™ Interactive http://www.gov.scot/marinescotlandinteractive Pentland Firth Main Channel 106 Swathe and RoxAnn™ South of Hoy and Scapa Flow 45 Swathe and RoxAnn™ View video clips from the survey on East of 15 Swathe and RoxAnn™ http://www.youtube.com/user/ South of 16 Swathe and RoxAnn™ MarineLaboratory

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