Investigating sediment re-mobilisation due to wave action by means of ADCP echo intensity data : Field data from the Tromper Wiek, western Baltic Sea

The Tromper Wiek is a semi-enclosed bay in the western Baltic Sea where gravel extraction by means of anchor hopper dredging has been carried out for many years. After an initial refilling of the extraction craters with material <2mm that had been spilled during the extraction process, the craters are relatively stable for several years. Acoustic Doppler current profiler echo intensity raw data in combination with wave, current, and wind data are used to correlate sediment re-mobilisation events with hydrodynamic and meteorological conditions in the bay. Near-bottom orbital movements generated by surface waves entering the bay from the open sea proved to be the key mechanisms of sediment re-mobilisation. The strong correlation between wind speed from certain directions and local wave height, and between wave height and maximum horizontal orbital velocity at the bottom, enabled the frequency, duration, and intensity of sediment re-mobilisation events to be estimated from local wind data.