Debris Clearance and UXO Survey

Bibby HydroMap were commissioned to carry out a clearance survey at the proposed Humber Gateway offshore wind farm.

The proposed wind farm lies 8km east of Spurn Head, with water depths on site ranging from 10.0 m below CD to 17.0 m below CD.

The main objective of the seabed features survey was to allow a risk assessment to be undertaken prior to any geotechnical investigations.  Data was acquired using a magnetometer, side scan sonar and multibeam echo sounder to identify targets with the potential to disrupt drilling operations.

Survey lines were orientated at 345° with a centre line and 12 lines either side at 5m line spacing. Magnetometer was run on all survey lines, with side scan sonar and multi beam echo sounder run on 4 lines to gain coverage. 3 cross lines, orientated at 75° at 30m offsets, were run across each proposed turbine location. Magnetometer was run on all three cross lines for data coverage, and multi beam echo sounder was run on the central cross line to QC the tide application during processing.

Data acquisition was undertaken from Bibby HydroMap's own dedicated shallow draft vessel Chartwell, equipped with C-Nav RTK GPS, a POS MV integrated IMU/GPS system, a Reson 7101 multibeam echo sounder, a Klein 3000 side scan sonar, and a GeoMetrics G882 Magnetometer.

The lines with all three sensors running were prioritised, given that the weather tolerances for the Reson 7101 multibeam echo sounder and Klein 3000 side scan sonar are limited to 1.2m or 1.3m wave heights.  Magnetometer only lines were therefore run after the multi-sensor lines were completed, given that the magnetometer was not so weather dependant, operating in wave heights of up to 1.8m.

A USBL system was utilised to position the side scan sonar, and was kept as close as possible to 4m above the seabed, with the magnetometer towed behind the sonar and kept as close as possible to ~2m above the seabed.

A Fisheries Liaison Officer (FLO) was onboard during all survey operations to ensure that no complications arose with any ongoing fishing activities in the area.  A Notice to Mariners was also issued, given the close proximity of the SE corner of the proposed windfarm to the Traffic Separation Zone.

Related Pages: Hydrographic and Geophysical Survey