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Published on: 01/01/17

Eco-friendly design of scour protection: potential enhancement of ecological functioning in offshore wind farms

The aim of this study is to explore the possibilities to implement ‘Building with North Sea Nature’ in offshore infrastructures in the North Sea by providing guidelines for the eco-friendly design of scour protection structures around monopiles in planned wind farms to enhance ecological functioning. The guidelines include specifications on: The type of hard substrate material or products available and how these can potentially enhance ecological functioning (and have added value compared to regular types used); How different types of hard substrates and configurations can be (experimentally) designed to vary spatially, in such a systematic manner that the effect on ecological enhancement can be determined empirically; How the effects of these scour protection structures can be monitored and evaluated; Whether site-specific conditions apply to wind planned farm locations in the Dutch North Sea. Eco-friendly design in this study entails optimising the scour protection of offshore wind farms to enhance its ecological functioning. Enhancement of ecological functioning has been defined as: increasing habitat suitability for species (or communities) occurring naturally in the Dutch North Sea, in particular, for policy-relevant (from a conservation perspective) and endangered species, such as those
listed in the EU Habitats Directive, OSPAR or national red lists (see Annex 2 in Bos et al. in prep.). Where previous work has explored the more general possibility for enhancement of ecological functioning in offshore wind farms (van Duren et al. 2016; Smaal et al. in prep.), this study provides explicit steps towards realising an eco-friendly design of scour protection and a practical field experiment to allow for scientific evaluation. From an analysis of physical conditions in the North Sea that influence both biodiversity and scouring mechanisms at wind farm locations, it is concluded that scour protection will be required in most, or all, future offshore wind farms on the Dutch Continental Shelf. It is also concluded that scour protection design could be altered to benefit the ecology, but that new designs will require additional testing for
anti-scouring effects. Based on a selection of policy-relevant species for the North Sea, two umbrella species were selected: Atlantic cod (Gadus morhua) and European flat oyster (Ostrea edulis). Focussing design variables and principles on these two umbrella species is expected to result in optimising the habitat for a wide range of native hard substrate biodiversity. Based on existing data from current wind farm scour protection, other artificial hard substrates and natural hard substrates from the North Sea, it is hypothesized that an optimised design of scour protection will yield increased populations of umbrella species or increased native biodiversity in general, including policy-relevant species.
Based on available knowledge on ecological principles and expert judgement of North Sea hard substrate ecologists, four design variables for optimised scour protection are defined: 1. Adding larger structures than conventional scour protection to create large holes and crevices, to provide adequate shelter / holes for large mobile species. 2. Adding more small-scale structures than conventional scour protection to create more small-scale holes and crevices but also attachment substrate and settlement substrate. 3. Providing or mimicking natural (biogenic) chemical substrate properties to facilitate species. An example is to provide chalk-rich substrate such as concrete with added chalk, or even natural substrate such as shell material. 4. Active introduction of specimens of target species to enhance establishment of new populations. This is to facilitate recruitment at locations where reproduction by naturally occurring adults is These design variables are made practically applicable by providing example
materials and specifications for implementation in the field and, a cost overview is provided for example materials. Combining the above information, this study provides design guidelines for wind farms with optimised scour protection to enhance ecological functioning. In addition it defines a minimum and a standardized approach for deployment and monitoring of a subset of locations to allow for scientific evaluation. The monitoring techniques that are required to do so, are described and a cost estimate for the monitoring is provided.
In conclusion, this study provides eco-friendly design principles for scour protection and a first experimental design to implement ‘Building with North Sea Nature’: ecological enhancement by optimising scour protection in offshore wind farms. This is considered as a first step in a process that should result in ‘learning by doing’.

W. Lengkeek, K. Didderen, M. Teunis, F. Driessen, J. W.P. Coolen, Oscar G. Bos, S.A. Vergouwen, T.C. Raaijmakers, M.B. de Vries, M. van Koningsveld

Bureau Waardenburg