EON Multi-annual Offshore Wind Farm Surveys

Geomara has been contracted by E.ON Climate and Renewables Uk to undertake multiannual bathymetric and geophysical condition surveys at their fleet of Offshore Windfarms. Geomara has completed a number of full condition surveys at Robin Rigg wind farm. The Robin Rigg Windfarm is located offshore from Whitehaven; approximately 12 km into the Solway Firth and consists of 58 x 3 MW turbines and two offshore substations.  In addition, there are two export cables from the field to the shore and the beach landing is at Northside in Workington.

Geomara has  used the condition survey data to produce some analysis of the temporal changes and sand wave migration at the site. The ungridded point cloud data from a number of WTG locations (H7, G1, D2, G7, H1 and H6) was examined to analyze some apparent observed contradictions in the seabed morphology, particularly with regard to depth of scour and changes in scour profile.

A comparison of the ungridded point cloud data at WTG H7 is shown in two profiles below. Bathymetry survey data at WTG H7 was collected on the 09th (red data set) and 17th May 2017 (green data set) with almost 90% overlap at this location. The survey data from 09th indicates a maximum scour depth at H7 of approximately 11m CD whereas the data from 17th May indicates a maximum scour at this location of an approximately 8.5m CD. A significant change to the outer boundary and side slope of the scour pit is also evident, focussed on one area. There is good agreement between the data sets outside of this.

The ungridded point cloud data from a number of different survey days was examined further to look at temporal changes observed previously. Of particular interest was the area of data overlap with the last dataset recorded within the OWF boundaries which was collected on 17th May 2017.  Difference models were compiled to check for temporal changes in the seabed morphology, particularly to investigate the stability of sand waves in what appears to be a highly mobile environment.

Sand waves are evident over much of the Robin Rigg OWF site and annual surveys have demonstrated previously that in general, the Robin Rigg sandbank is very dynamic with significant changes happening as these sand waves migrate and as scour at the base of the WTG monopiles develops and fluctuates.