Scroby Sands Offshore Wind Farm – Coastal Processes Monitoring. Final Report

Abstract:

<p>Over the last decade, the development of Offshore Wind Farms (OWF) has received significant attention. In March 2002, a FEPA licence was granted for the development of the first UK OWF, within coastal waters, at Scroby Sands, Great Yarmouth, Norfolk. This site was regarded at the time as the worst-case scenario in terms of potential impacts on coastal processes, involving the emplacement of 30 turbines situated upon monopile foundations 4.2 m in diameter in an environment with fast tidal currents and mobile bed sediments. During this licensing process, two environmental issues arose of major potential importance to the development of the adjacent inshore region, namely: <bl></br> <li>The potential for the OWF to cause wave focussing on parts of the adjacent coastline (studied in the Defra-funded project E1227);</li> <li>The potential for the OWF to alter sediment transport and consequently affect the stability of large-scale coastal geomorphic features, such as the sandbanks themselves and the associated channels.</li> </bl> This project performed research to investigate the latter issue, of sediment transport and sandbank stability. </p> <p>A programme of research and monitoring was undertaken at the Scroby Sands OWF, to observe, measure and quantify potential impacts of OWFs on coastal processes. This was achieved by a series of seabed surveys (side-scan sonar, swathe bathymetry) and deployment of seabed landers (Cefas 'MiniLanders') before, during and after construction of the OWF. These have been used to provide evidence of changes in seabed bathymetry, bedforms, currents, waves and suspended sediment concentrations that may lead to disturbance of sedimentary environments or sediment transport pathways.</p> <p>One of the main aims of this work was to assist in the creation of a generic framework for use by both regulators and developers in assessing coastal processes issues within the EIA process and relating to any consequent FEPA licence conditions, particularly those related to monitoring. </p> <p>The recommendations of this report are: <bl> <li>The design and placement of scour protection in future OWF construction should be considered in more detail, because poorly designed scour protection can lead to secondary scour effects; </li> <li>Swathe bathymetry surveys should be required as a standard method of monitoring OWFs (and other activities impacting on the seabed, such as port construction, aggregate extraction and disposals of dredged materials) because such surveys provide robust data with which to calculate the volumes of material disturbed and assess the interactions with coastal processes;</li> <li>Work should be undertaken to assess the magnitude and nature of the impacts on coastal processes of other types of wind-farm foundations (i.e. apart from monopiles) as well as of the structures associated with other energy-extracting devices in the 'wet renewables' sector (e.g. tidal and wave devices). Understanding of the impacts of monopile-based OWFs is improving. However, future OWFs may use a combination of hybrid or tripod structures and/or larger gravity-based structures (GBS). Further work is required to assess the magnitude and nature of the impacts of these structures on coastal processes. Similarly, the impact of fixed or moving structures for other wet renewables is also poorly known and needs to be assessed; </li> </bl></p> This report is divided into the following sections: <ol> <li>Background</li> <li>Survey Methods</li> <li>Results</li> <li>Analysis</li> <li>Conclusions</li> <li>References</li> <li>Acknowledgements</li> </ol>

Author(s):

CEFAS