Dan, S.; Vandenabeele S.; Verwaest, T., and Montreuil, A-L., 2020. Hydrodynamics versus sediment concentration at the Belgian coast. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 632–636. Coconut Creek (Florida), ISSN 0749-0208.
The most important process for the stability of a coast is the sediment transport, a process which is controlled by the local hydrodynamics. Insight into this process can be obtained by measuring the marine currents and sediment concentration simultaneously at the exact same location. This was the case at the beach south of Ostend harbor (central Belgian coast) where three frames carrying instruments which measure the marine currents (Aquadopp ©Nortek), the waves (AWAC, 4Hz ©Nortek) and the suspended sediment concentration (Optical Backscatter Sensors – OBS, 4Hz ©Campbell) were deployed for in several campaigns, at depths of -3.5 and -6.5m TAW. These instruments measure in bursts of 10 minutes simultaneously every hour for three weeks. The objective of this research is to establish correlation between local hydrodynamics, especially tide and wave induced currents, and the suspended sediment concentration (SSC). The analysis results show that the currents direction (ENE direction during flood, WSW at ebb tide) and velocities are controlled by the tidal cycles during calm weather and strongly disturbed the wave induced currents during storms. The sediment concentration decrease vertically towards the water surface and it has a strong temporal variability, sometimes ranging from near zero to hundreds of mg/l. The peaks in SSC appear to be related to higher waves and the change in currents direction, particularly during the rising tide. The hydrodynamics is controlled by the tide, while wave induced turbulence increases considerably the SSC, mainly during storms and at shallow depths.