Residual water transport in the Marsdiep tidal inlet inferred from observations and a numerical model

At tidal inlets, large amounts of water are exchanged with the adjacent sea during the tidal cycle.The residual flows, the net effect of ebb and flood, are generally small compared with the gross flux;they vary in magnitude and sign from one tidal period to the other; and their long-term mean variesfrom year to year. Here, we focus on the temporal variability of the residual flows in the Marsdieptidal inlet, which is the western-most inlet of the Wadden Sea, a tidal lagoon along the coasts of theNetherlands, Germany, and Denmark. We compare the transport from a high-resolution numericalmodel with the transport from velocity profile data collected beneath a ferry that crosses the inletdaily. The comparison works in two ways: for the areas and times covered by the measurements, thedata serve to validate the model, and conversely, the model is employed to assess the consequencesof spatial and temporal gaps in the data. Modeled and observed transports over the region of theflow that is covered by the acoustic Doppler current profiler are in good agreement for gross andresidual quantities. Results indicate that uncertainties due to spatial gaps can be overcome with asimple extrapolation approach applied to the velocity profiles, whereas uncertainties due to temporalgaps are more problematic and leave large discrepancies in the residuals