The Danish harbour at Thyborøn has in the recent years observed increasingly larger waves in the approach channel as well as damaging overtopping of the outer protection structures.

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 has not been observed earlier where the prevailing conditions were acceptable under almost all weather situations.

Simulation of waves propagating from WNW using DHI’s MIKE 21 BW model	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 revealed that the 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. 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.