A part of the domestic waste of the city of Geneva (Switzerland) is transported with ship convoys on the Rhone River to the waste incineration station. These convoys generate waves, which partially endangers the stability of the river banks and the riparian fauna. To reduce the dominant wave peaks, a flap was added at the stern of the barge. The efficiency of that flap was tested in physical and numerical model tests, and then compared to in-situ measurements. This case study focuses on a discussion of the appropriateness of the two models, by describing their accuracy for the present case. It indicates that the physical model reproduces the wave heights almost correctly, but does not re-produce adequately the dominant frequencies. In contrast, the numerical model damps the wave heights significantly, but gives correct dominant frequencies.