Author(s): Jeroen Stark; Yves Plancke

Linked Author(s):

Keywords: Tidal hydrodynamics; Eddy formation; Numerical modeling; ADCP measurements; Scheldt Estuary

Abstract: In the Western Scheldt near the Ossenisse shoal, a large eddy regularly occurs during spring tide conditions, causing hazardous cross-currents in the navigation channel. Approximately 200 sailed ADCP measurement campaigns have been caried out by Rijkswaterstaat to monitor these flow conditions whenever strong crosscurrents were predicted. This extensive ADCP dataset was analyzed and several numerical modeling studies were performed to assess the predictability of the cross-currents and to gain insight in the physical mechanisms that cause the eddy. The correlation between the cross-current intensity and characteristics of the vertical tide, such as high water level, maximum water level slope and maximum vertical rising speed, is assessed. Linear relationships between these tidal indicators and the maximum cross-current are applied to compute occurrence probabilities of a specific cross-current strength. Furthermore, a validation exercise of the operational forecast model is performed to assess the direct predictability of these cross-currents, as well as to assess the representation of the forementioned tidal indicators. The hydrodynamic forecast model of the Scheldt Estuary is able to represent the eddy formation above the shallow plateau east of the Ossenisse shoal, but the strength of the cross-currents is underpredicted for the strongest and hence most hazardous tides. A brief calibration exercise suggests improved representation of the tidal parameters and cross-current intensity can be achieved by local adaptations of the bottom roughness. Recently, a high frequency radar system was installed in the area, allowing for real-time monitoring of the surface flow patterns.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p1089-cd

Year: 2023