Screening of seabed geological conditions for the offshore wind farm area Kattegat II and the adjacent cable corridor area: Desk study for Energinet

Energinet has asked GEUS to perform a geological desktop screening study of the offshore wind farm (OWF) area Kattegat II and the potential cable corridor to the coast of Djursland. The results are to be used as background for evaluation of the suitability of the areas for a wind farm site and cable corridor to land. This report compiles the results of a previous screening study also covering the current OWF area Kattegat II (GEUS 2021) and a new study covering the potential cable corridor.

A combination of published work, GEUS archive seismic data and sediment core data, research data and new seismic data from other projects have been used to assess the general geological development of the southern Kattegat area, including the current Kattegat II OWF area and the potential cable corridor.

A geological description is provided, and a geological model has been developed.

As part of the geological desk study, a relative Late Glacial and Holocene sea-level curve for the area is presented and a screening for archaeological interests has been performed based on the development of the distribution of land and sea after the last deglaciation.

The general geological description includes the complete geological succession from the pre-Quaternary framework, the pre-Quaternary surface, glacial deposits, the deglaciation and Late Glacial and Holocene deposits.

The geological model of the southern Kattegat is based on previous geological screening reports (GEUS 2020; GEUS 2021), the seismic interpretation report Fugro (2021) and the geotechnical report Gardline (2021).

The mapping results are presented as seismic examples and general thickness maps of geotechnical soft sediments in the current Kattegat II OWF area and cable corridor, together with thickness maps of geotechnical soft sediment for the previous Hesselø OWF area and other previous OWF areas as well as the Anholt OWF.

Several conclusions relevant for the future geotechnical and archaeological evaluations of the Kattegat II OWF area are presented and can be summarized in these statements: The soil conditions in the Kattegat II OWF area are expected to be similar to the soil conditions in the southern part of the Anholt OWF. This means, from a geological point of view, that it is most likely possible to establish an OWF in the Kattegat II OWF area.

Also, the soil conditions in most of the cable corridor is similar to the soil conditions in the southern part of the Anholt OWF. However, in the northern part of the area a large northeast–southwest-oriented incised valley with infill of soft sediments up to 20-30 m in thickness and locally up to 40-50 m is found.