Using Numerical Simulations to Improve Insight on the Historical Evolution of Tides And Morphology in the Scheldt Estuary

Within the framework of the Dutch-Flemish “Agenda for the Future” research program for the Scheldt estuary, one of the goals was to improve insight on the interactions between historical changes in estuarine morphology and changes in estuarine tidal hydrodynamics. While a large amount of studies already focused on the relation between morphology and tides in the Scheldt estuary, the horizontal tide or time-related parameters (i.e., important for tidal asymmetry) were rarely assessed and existing studies were often limited to a small section of the estuary.

Therefore, five historical models were set up (i.e., for 1930, 1960, 1980, 2001 and 2013), making use of an available TELEMAC-3D model of the Scheldt estuary and the Belgian coastal zone. The mesh of the existing model was adapted to include historical tidal branches and intertidal areas. The historical models were simultaneously calibrated by making adjustments of the bottom friction coefficients in order to obtain the best overall model performance.

The historical models are then used to compute tidal characteristics, with a special focus on characteristics that could not be obtained from historical water level measurements, such as flow velocities, tidal discharges, tidal prisms and tidal asymmetry. In addition, model scenarios are performed to assess the impact of specific geometrical and morphological changes on tidal hydrodynamics. A distinction is made between subtidal changes, mainly consisting of channel enlargement, and intertidal changes, mainly consisting of intertidal area and volume loss. In particular, scenarios are set up in which the intertidal or subtidal 2013 bathymetry is alternately implemented in a specific area (i.e., the estuary was divided in multiple sections) of the 1930 model, or vice versa. In general, the scenarios show that intertidal changes mainly influenced tidal asymmetry and had limited impact on the tidal range, whereas subtidal changes also altered the tidal range. The scenarios also allow to identify estuarine sections in which morphological changes had the largest impact on tidal hydrodynamics.

Ultimately, it is intended that the historical models are used to simulate historical sediment transport patterns, historical distributions of suspended sediment concentrations or even attempt to hind cast the historical morphological development of the estuary.