Investigating the reshaping of estuarine shoals through sediment relocation
Type:
Presented during:
CEDA Dredging Days 2026
Authors:
B. Roest, T. Wolf and G. van Holland
Abstract
The Scheldt estuary's main channel (The Netherlands and Belgium) is continuously being dredged enabling access to the Port of Antwerp. Because of legislation, sediment must remain in the estuarine system. Therefore, dredged sediments are relocated to designated zones in the main channel's deep parts and shoal margins. The goal of relocating sediment to shoal margins was to increase the intertidal area for ecological reasons.[1] However, shoal margins in multi-channel estuaries show large morphological activity and sediment transport rates. Analysis of a fifteen-year long record of sediment relocation volumes and consecutive two-monthly soundings of the shoal 'Plaat van Walsoorden' shows that initial sediment losses are high, while the remaining sediment is moving and dispersing slowly over the shoal margin over the course of years. This alters the morphology of the shoal, which in return changes the local hydrodynamics. Simulations with the numerical Scheldt model (TELEMAC-3D) reveal evolutions in dominant transport directions on surrounding shoal margins, which are in line with the observed sediment dispersion direction.[2,3] The combined analysis of measured bathymetry and numerical model data shows that the position and shape of the shoal margin's shallow end are largely dictated by the balance between two opposing pathways of high gross transport. By tracking these sediment pathways over the same years, it has become evident that distinct morphological states of the larger shoal area result in varying levels of sediment retention²³. Furthermore, morphological response of the main disposal site persists over multiple years, influencing the surrounding ebb- and flood-channel system. This combined analysis has successfully demonstrated its capability to serve as investigation- and decision-making tool for past and future sediment relocations in estuarine environments.
[1] Consortium Arcadis-Technum, 'Hoofdrapport Milieueffectenrapport Verruiming vaargeul Beneden-Zeeschelde en Westerschelde',2007. [2] IMDC, 'Modelondersteuning conceptueel model morfologische ontwikkeling Schaar van Valkenisse',2024. [3] IMDC, 'Morfologische ontwikkeling Zuidergat en Plaat van Walsoorden',2025.