High resolution bathymetric measurements reveal the super-imposition of bedforms in the Grådyb tidal inlet in the Danish Wadden Sea. Preliminary results of numerical model simulations are discussed: A linear stability model was tested to explain the large bedforms as being caused by tidal system instabilities. Results show comparable dimensions and migration rates. A three-dimensional morphodynamic model is shown to reproduce small scale transport rates but lacks realistic trends of morphodynamic evolution.