J. Mi1,2*, T.Gerkema1, P.W.J.M.Willemsen3,4, J. van der Molen1, J. van de Koppel1,5, M. van der Wegen4,6,T.J. Bouma1,2
1NIOZ, Netherlands; 2Utrecht University, Netherlands; 3 Wageningen University and Research, Netherlands; 4Deltares, Netherlands; 5University of Groningen, Netherlands; 6IHE Delft, Netherlands
*Corresponding author: jie.mi@nioz.nl
Introduction
Like many estuaries, the Western Scheldt has undergone significant morphodynamic changes due to both natural evolution and human interventions since the Middle Ages, heightening its vulnerability to sea-level rise and storm surges (Leuven et al., 2019). This study investigates how historical morphological evolution has changed tides in the Western and Eastern Scheldt.
Objective and Methods
We used old maps combined with modern measurements and tools to reconstruct bathymetries starting from the year 1200. Applying the General Estuarine Transport Model (GETM; Burchard and Bolding, 2002) on these bathymetries revealed how tidal dynamics respond to historic morphological changes.
Results
Our bathymetric reconstructions involve major transformations of the estuary, particularly in tidal basin connectivity and hypsometry, which can be classified in three distinct stages: 1) Expansion stage (13th–15th century): The Honte was not yet fully connected to the Scheldt, and characterized by shallow waterways and abundant intertidal zones. 2) Transition stage (16th–18th century): The Western Scheldt gradually replaced the Eastern Scheldt as the dominant tidal channel. 3) Closure stage (19th century–present): The connectivity between two Scheldt basins was gradually blocked and dredging substantially deepened the Western Scheldt.
The model results illustrate how tidal dynamics evolved in response to these morphological changes, showing that the Western Scheldt estuary transitioned from a tidal range absorber to an amplifier. We found that the empirical relationship between tidal prism and morphological parameters has remained robust on a long-time scale, tidal amplification is a trend in tide-dominated estuaries. This trend has significantly intensified since the 19th century. We will further explore the distinct impact of dredging and land reclamation on tidal amplification. These historical reconstructions provide valuable insights for current and future estuarine management.
Fig 1. Historical bathymetrical reconstruction
References
Burchard, H., and Bolding, K., 2002. GETM – a General Estuarine Transport Model. Scientific Documentation. Brussels: European Commission. Tech. Rep. EUR 20253 EN.
Leuven, J.R.F.W., et al., 2019. Sea-level-rise-induced threats depend on the size of tide-influenced estuaries worldwide. Nature Climate Change, 9(12): 986-992.
