Comparison between predicted and observed sand waves and sand banks in theNorth Sea

For the first time a prediction model of regular morphological patterns on the seabed was tested against observations of sand wave and sand bank occur rence in the entire North Sea. The model, which originates from first physi cal principles, predicts this occurrence via two dimensionless parameters o n the basis of the water depth, the tidal velocity amplitude, the level of zero intercept above the seabed (z(0)), and a viscosity variation parameter E. The latter two quantities were varied in a number of predictions for th e entire North Sea, whereas for the first two, local values were used. The range of realistic values of epsilon and z(0) was large enough to let these two parameters distinguish between the possible (combinations of) bed form s, as is shown in the shallower southern bight of the North Sea. The result s were more sensitive to variations in z(0) than in epsilon. A slightly mor e detailed approach focused on sand waves only in the southern North Sea an d estimated local values for z(0) using depth information. Quantification o f the results showed that the model was able to predict the cent-ours of th e sand wave patches, but it could not account for the absence of the bed fe atures within this area. The type of bed deposit partly explains the smalle r-scale variation. The work confirms the validity of the theoretical bed fo rm prediction model and verifies the hypothesis that the large-scale seabed features are formed as free instabilities of tide-topography interactions.