Morphodynamic Processes on Tidal Flats in Estuaries

Tidal flats of estuaries are affected by intense morphodynamic processes. Changes of sedimentation and erosion occur on different time scales and challenge the decision makers in the authorities due to the high importance of a sustainable sediment management. To evaluate different actions and their effects, e.g. by means of numerical models, an improved knowledge about morphodynamic processes on tidal flats is required. For three years the Institute of River and Coastal Engineering at the Hamburg University of Technology recorded water levels, waves, flow parameters and suspended sediment concentrations in an investigation area in the mouth of the Elbe estuary. In frequent intervals and after extreme events the bathymetry was determined with a multi-beam echo sounder. On the basis of the field measurements the transport capacity and transport direction could be calculated for various conditions. Certain patterns in the course of the sediment concentration depending on the flow velocity were observed. The eastward-directed sediment transport leads to morphological changes of the bottom structures with strongest influences appearing at the inlet of the main tidal creek of the area. Larger morphological changes occurred especially during certain conditions depending on wind, water levels, tidal currents and waves. Single extreme events did not significant impacts on the bathymetry as longer periods with increased wind velocities especially from eastern directions did.