Developing an Approach to Assess and Regulate Cumulative Effects of Offshore Wind Farms

The national “Energy agreement for sustainable growth” in the Netherlands means that the offshore wind capacity of the country will increase from the current 1000 MW to 4500 MW in the upcoming 5 years (2019-2023). The... [ view full abstract ]

The national “Energy agreement for sustainable growth” in the Netherlands means that the offshore wind capacity of the country will increase from the current 1000 MW to 4500 MW in the upcoming 5 years (2019-2023). The construction of 10 windfarms with a total capacity of 3500 MW was the motive for the Dutch government to develop a framework for the assessment of ecological and cumulative effects of offshore windfarms. A framework that firstly focusses on the effects of the development of offshore windfarms on birds, bats and marine mammals. In time the framework can be expanded to other human activities and other species of concern. The framework utilizes models and results of scientific studies relating to effect thresholds. It can however accommodate other models and studies as they become available. During the work carried out for the framework the gaps in knowledge were also identified to be addressed in the future.

The framework is based on the DPSIR method. In a 6-step approach the relevant activities are selected, the pressures they represent identified and the impact it has on selected relevant species and habitats quantified. These effects are then assessed and if necessary mitigation measures are prescribed.
1. Identify the relevant pressures the envisaged activities could cause.
2. Identify the habitats and species that may be affected by these pressures.
3. Describe all other activities that could affect the same species.
4. Describe the nature and scale of the cumulative effects of all the activities selected in Step 3 on the selected habitats and species.
5. Evaluate the significance of the effects on the selected habitats and species.
6. If necessary, adapt the activity by taking measures to prevent the activity causing significant effects.

The quantification of effects on birds, bats and marine mammals most sensitive to disturbance on the Dutch continental shelf, has resulted in the implementation of multiple mitigation measures in the wind farm site decisions. These decisions contain the constraints under which offshore wind farms may be built. For birds and bats, limits were set to size in combination with number of turbines and rotor blades will need to be turned out of the wind during sensitive times. For marine mammals a flexible sound threshold for piling was determined. These mitigation measures aim to keep the effects under the determined thresholds. Additionally an offshore wind ecological program (Wozep) was started by the Dutch government: a 5-year research program that will further investigate the ecological effects of offshore wind. The framework will be regularly updated with results from this program and from other research around the world.