Effect of man-made modifications on estuarine hydrodynamics and sediment dynamics

Sediment transport capacity is an important component of maritime management practice, and is influenced by several hydraulic parameters like unit discharge, mean flow velocity and tidal prism. This study focuses on sediment transport and tidal exchange dynamics in the Scheldt estuary at Zandvliet (the sluice complex Zandvliet-Berendrecht, Antwerp Harbour, Belgium) in the late 1990s and early 2000s. The involved parameters are tidal cycle measurements of total suspended sediment concentrations and fluxes, tidal water elevation, flow velocities, river discharges and tidal discharges. The data show that the measured depth-integrated suspended sediment concentration reaches up to 782 g m−3 and 497 g m−3 for the periods 1995-1998 and 2002-2005 respectively. The average sediment discharge ranges 1,016 – 1,883 kg s−1 for ebb and 728 – 1,916 kg s−1 for flood during 1995-1998, and 452 – 1,301 kg s−1 and 504 – 1,033 kg s−1 for ebb and flood respectively for the period 2002-2005. The sediment discharge versus tidal water discharge through a complete tidal cycle demonstrates a reasonable correlation with a R2 value of 0.7 for the period 1995-1998 and with a R2 value of 0.5 for the period 2002-2005. Quasi-equilibrium ebb and flood sediment mass load is found for both periods 1995-1998 and 2002-2005, though the mass load exhibits significant differences in magnitude. There are about twice more sediments transported in 1995-1998 than in 2002-2005. Evaluation of the temporal relation between sediment mass load and tidal water volume for a tidal phase, ebb and flood respectively, shows that with a similar tidal water volume a much higher amount of sediments is transported in 1995-1998 than in 2002-2005. The results indicate that over 40% more sediment mass load were transported by a similar amount of ebb tidal water in the period 1995-1998 than in the period 2002-2005. In 2002-2005, the mass load appears to be independent of tidal water volume. Computation the temporal relation between net sediment load and fresh water discharge, based on the available data sets, does not yield a correlation due to important discrepancy between the left and right side of the channel, and due to asymmetrical behaviors of the water flow and the sediment mass load which are significantly influenced by two underwater dams located respectively at upstream- and downstream side of the measuring sites.