Reconstructing 800-year historical evolution of tidal characteristics and sediment transport in the Scheldt estuary

Changes in estuarine basin geometry alter tidal wave propagation, and consequently influence sediment transport, morphodynamics and coastal flood risk, particularly in estuaries subject to intense human intervention. This study aims to quantify and assess historic changes of tidal phasing, tidal asymmetry and associated sand transports in the Scheldt estuary (SW-Netherlands) based on numerical hydrodynamic modeling historically reconstructed landscapes over 800 years. Specifically, we focus on the Scheldt estuary by applying a numerical model (General Estuarine Transport Model, GETM) to seven selected stages from the period 1200 AD to the present, supported by well-documented historical maps and dike records. Building on these reconstructions, we put forward a new approach to uniquely identify amplitude and phase of the tidal current by projecting the horizontal tidal currents on their dominant axis; this allows us to distinguish standing and progressive tidal wave characteristics. Our results show that the estuary has shown a qualitative shift in tidal-wave propagation evolving from a largely progressive system to a more standing-wave regime, led to amplified tidal ranges and increased tidal asymmetry. The analysis of tidal current asymmetry further reveals evolving patterns of sand redistribution, where, due to the strengthening of flood-dominance, the sand flux into the Scheldt is suggested to have increased by an order of magnitude over the past 800 years. At the same time, the location of peak sand deposits has shifted from the estuary mouth towards the upstream region. These findings demonstrate how historical interventions have shaped present-day hydrodynamic conditions, thereby influencing sediment redistribution and long-term morphological evolution.