Barrow Offshore Wind Farm Post-Construction Monitoring Report

Report

Title: Barrow Offshore Wind Farm Post-Construction Monitoring Report
Publication Date:
January 15, 2008
Document Number: FLS-034378
Pages: 60

Document Access

Attachment: Access File
(6 MB)

Citation

Barrow Offshore Wind (2008). Barrow Offshore Wind Farm Post-Construction Monitoring Report. Report by BOWind, Centrica Renewable Energy Ltd, and Dong Energy. pp 60.
Abstract: 

Barrow Offshore Wind Farm is located in the eastern Irish Sea near Barrow-in-Furness. The transmission cable runs into Morecambe Bay where it is connected to the National Grid transformer station in Heysham.

 

The construction of Barrow Offshore Wind Farm took place between March 2005 and July 2006. The wind farm became operational in July 2006.

 

This document describes the environmental monitoring undertaken during the post construction phase in 2006–2007. The environmental monitoring reported in this document should be seen as a continuation of the pre-construction and construction monitoring. Postconstruction monitoring activities are made for a period of three years after construction and will be reported annually to the licensing authority, as described in the FEPA licence. This is the first of three post-construction monitoring reports.

 

The environmental monitoring did not register major or unforeseen environmental impacts during the first year of operation. The following paragraphs summarise the primary results from the monitoring programme.

 

Fishery: Catches from inside the wind farm were compared to external control sites. No significant differences were obtained between the two sites. The most abundant commercial species caught by otter trawl and beam trawl was dab and shrimp, respectively. Thornback ray and basking shark are electro sensitive and thus of special interest. Both species have been observed in the vicinity of the Barrow site during the surveys undertaken for the Environmental Impact Assessment. At the post construction surveys no basking sharks were detected. Concerning Thornback ray, 20 and 40 individuals were collected at the surveys in December 2006 and March 2007, respectively. They were detected both at the control site and within the wind farm area.

 

Benthic and Sediment Contaminants Surveys: The grain sizes across both the windfarm site and reference sites have generally increased between 2004 and 2007. Due to relatively consistent changes taking place across the whole survey area, and that some of these changes took place, before construction of the windfarm began, it would appear that they are natural fluctuations and probably influenced by the general sediment movement patterns in the Irish Sea. TOC levels have generally decreased throughout the period 2002 – 2007 across the survey area, again probably with little influence from the construction or operation of the windfarm.

 

There have been changes in the benthic communities present across the windfarm and its reference sites between the pre- and post-construction surveys. Similarity analysis shows that the sites from 2004 as a group are more similar to themselves than they are to any of the sites sampled in 2007. The main differences in similarity between the groups are probably the high numbers of Ophiura present in the postconstruction survey and the more frequent occurrence of Nephtys and high numbers of Amphiura in the pre-construction survey. This result reflects the recorded changes in sediment grain size, with Amphiura preferring a finer sediment than Ophiura.

 

There are significant correlations between the concentrations of a number of the metals, but not between metals and the grain sizes or TOC. An analysis of the physical and chemical parameters and the communities present show that grain size and TOC influence the communities present, but no other environmental variables have a significant influence on the communities.

 

Operational Underwater Noise: The survey results indicate that there is a marginal increase in very low frequency noise around individual wind turbines. This increase is detectable to a range of approximately 600m. The results from measurements taken at ranges of 5 m from an operational wind turbine indicate that the underwater noise is unlikely to cause a behavioural (avoidance) response in marine fish and marine mammals in the region.

 

Oceanography: In all cases wakes could be traced out to a distance of at least 6–10 diameters distance downstream of each monopile (30– 50 m) and often a good deal further, in the order of 100–200 m. Bubble clouds entrained in the wakes forming behind turbine monopiles are traceable over even longer distances, as far as 200 m and possibly further, although there is no evidence to suggest whether there is any flow structure associated with them or whether they simply represent surface slicks. From the flow modelling undertaken prior to construction, it was suggested that due to the separation of 500 m between each monopile, they could be considered as independent in respect of the impact on the currents. On the basis of the wake surveys, it would appear that this may still be the case since no obvious structures were visible in the velocity records extending beyond 300 m from the nearest pile.

 

Bathymetry, Seabed Morphology and Scour: With the exception of the localised areas of scour around many of the individual turbines, seabed levels across the whole area are very similar to those surveyed during the two previous surveys. Scour surveys were made around 9 turbines in November 2006 and April 2007, respectively. Scours were detected around 7 turbines. The depths of the scours were between 1 and 6 meters. In general, by time, the scours expanded horizontally, but were partially infilled by natural sedimentation processes. Faint remnants of the inter-turbine cable installation were seen around many of the turbines.

 

Side Scan Sonar Surveys and Archaeology: Side Scan Sonar Surveys were undertaken within the wind farm area and along the associated cable and navigation routes.

 

For the cable route surveys it should be noted that the position of the cable route centre line was changed between the preconstruction and construction stages.

 

An archaeological assessment was made of the side scan sonar data. Only two new sites of high archaeological potential have been identified, both of which are located on the cable route. These sites are situated in areas of complex geology and may have natural origin. The exclusion zones defined in earlier studies were re-identified and have shown to be effective in protecting sites of archaeological interest. No sites of high archaeological interest were identified within the navigation route area or outside the exclusion zones within the wind farm area.

 

Ornithology: In the beginning of 2007 a detailed post construction bird monitoring programme was agreed with Natural England. Aerial surveys as well as boat surveys form part of the monitoring program. In addition, a shore based survey from Walney Island was performed in 2007 to study Whooper Swan or Pink-footed Goose passage. The aerial surveys in the first year of post construction monitoring showed a very similar pattern, to surveys before and during construction, in the abundance and distribution of birds in the vicinity of Barrow Offshore Wind Farm. The results indicate that the establishment of Barrow Offshore Wind Farm did not lead to significant changes in the occurrence and distribution of Common Scoter, divers or other wildfowl in the vicinity of the windfarm.

 

The bird surveys before, during and the first year after construction of the windfarm have not found bird populations of conservation concern significantly using the site. No collisions have been observed during any of the surveys.

 

The findings from the Walney Island study indicate that the Barrow Offshore Wind Farm do not constitute a barrier that prevents Whooper Swan or Pink-footed Goose from passing or moving through the site.

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