A two-dimensional (x−z) model of tidal straining in the Rhine ROFI

Recent observations of the Rhine ROFI system in the North Sea suggest that the dynamics and structure are very variable, due to the fact that the system responds very rapidly to changes in the stirring conditions due to tides and winds. They also show very strong semi-diurnal variability, which is the result of the interaction between tidal straining and the cross-shore density gradients. This hypothesis is tested using a two-dimensional slice model. The model is successful in reproducing the qualitative behaviour of the observations, with the semi-diurnal oscillations in stratification of the right amplitude and at the same phase of the tidal cycle as the observations. The model also shows the effect of the stratification on generating the cross-shore tidal shear which then interacts with the main density gradients, hence the semi-diurnal variability in stratification. The model confirms previous hypotheses that suggest the importance of wind direction in enhancing or suppressing stratification.