The Danish harbour at Thyborøn has in the later years experienced increasing problems with large waves in the approach channel as well as damaging overtopping of the outer protection structures.
The harbour has therefore in collaboration with DHI launched a study to determine the cause of the problems and not least what can be done to reduce the wave agitation within the harbour and the eliminate the overtopping of the breakwaters.
Thyborøn is located on the west coast of Jutland, Denmark.
Simulation of waves propagating from WNW using DHI’s MIKE 21 BW model |
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It is particularly during and after periods with strong westerly and north-westerly winds that the waves at the harbour become very large. This phenomenon was not observed earlier where the prevailing conditions were acceptable under almost all weather situations.
Video recording February 6th 2008. The wave height outside the Thyborøn entrance channel was 3-4 meters (significant wave height) and the waves came from WNW. |
The study carried out by DHI has initially focused on why the problems have arisen and have included:
- Analysis of the historical development of the bathymetry
- Analysis of wave climate variations in latter years
- Simulation of the wave transformation from the North Sea and into the harbour based on current bathymetric conditions as well as prevailing conditions 4-5 years ago.
The study has revealed that bathymetry at the outer part of the Thyborøn entrance channel and just outside the harbour has changed in latter years. The water depth has been reduced in an area outside and north of the harbour. At the same time the water depth has increased along the eastern side of the channel.
The bathymetry has changed significantly over the last four years
As a consequence of changes in the bathymetry waves from the North Sea propagate differently as compared to what they used to do. The waves propagate towards the harbour instead of just passing it.
Investigations to clarify what can be done in the future are under way.