Abstract
Within Wozep (the Dutch offshore wind ecological programme) research has been started to investigate the potential effects of offshore wind on the ecosystem through changes in the physical functioning of the system. Earlier in 2021 the first results of scenario studies with state-of-the-art combined hydrodynamic-ecological models have been delivered. Although the models still need further development, the results indicate substantial effects on primary production and ecosystem functioning with a large upscaling scenario for offshore wind. This scenario also indicated large differences between different regions in the North Sea. Within the Framework for the Assessment of Ecological and Cumulative Effects (KEC) (developed to look at how offshore wind in cumulation may affect protected species in the North Sea) Deltares was asked to indicate how the scientific insights yielded by the Wozep study, can currently be used in the KEC procedures taking into account the model uncertainties. This report outlines the application possibilities of these tools in assessing effects and in ascertaining options to mitigate effects.
The Wozep results indicate that different regions in the North Sea have a different sensitivity to ecosystem effects. Despite model uncertainty, these differences are substantial and are supported by underlying knowledge of the system. These preliminary results can therefore with care be used in the current planning process. The Wozep results also indicate that the cumulative effect of many wind farms in relatively close proximity are likely much larger than the sum of effects of individual, isolated farms. With the current projections for windfarm development both parameters (sensitivity of the location and planned density of farms) need to be considered.
The Wozep model results indicate that the central North Sea (with seasonal stratification) and the German Bight are most sensitive to changes due to enhanced mixing and possible destratification of the water column. In the Holland Coast area, a potential effect is identified regarding the transport of fine sediment towards the Wadden Sea. This is an issue that is seen as very sensitive, due to the UNESCO World Heritage status of the Wadden Sea. In the current projections used in KEC 4.0 for development of offshore wind farms, we see that large upscaling is foreseen in the Holland Coast. Most of these developments have already started or tenders will start within the next few years. In the German Bight, there are significant search areas on the Dutch side, as well as large ongoing developments in the German EEZ. The German Bight is physically and ecologically complex and shows a high sensitivity of ecosystem processes to offshore wind. With the large density of wind farms already foreseen in this area, it may be sensible to consider delaying further upscaling until we have more insight in cumulative effects and the consequences of design options in farm layout that can diminish or mitigate effects