The relative impact of sea level rise and dredging strategies on the morphodynamic evolution of the Western Scheldt estuary (The Netherlands)

Abstract

Worldwide, estuaries face challenges related to climate change and human interventions. The objective of this study is to gain insight into the relative impact of (extreme) sea level rise (SLR), dredging and disposal (DAD) activities and coastal nourishments on the century timescale hydro- and morphodynamic behaviour of the Western Scheldt estuary (i.e. the Dutch part of the Scheldt river). For this, we apply a two-dimensional process-based numerical morphodynamic model including wave action (Delft3D 4), that allows for detailed analyses of the changing hydro- and morphodynamic conditions under various scenarios.

Scenario simulations for the period 2020–2100 are carried out based on downscaled SLR and tidal projections from a global tide model. Our model results suggest that SLR causes more resonant behaviour of the tidal wave and leads to less flood or increased ebb dominance throughout the estuary. Morphodynamic development lags behind SLR, which decreases intertidal area, changes the tidal asymmetry and enhances export or decreases import of sediment in the Western Scheldt. Excluding morphodynamic change in the model drowns the intertidal area even faster. Regarding possible sediment management strategies, the model indicates that the SLR induced enhanced sediment export trend can be locally counteracted by disposing a larger portion of dredged material in the more upstream parts of the estuary and/or by performing nourishments in the mouth area.

Our study shows the potential of using process-based models for SLR impact studies in estuaries albeit that more robust conclusions can be drawn when combined with other modelling approaches. Future work may improve hindcast and forecast efforts by using a three-dimensional modelling approach, adding mud dynamics and applying a more advanced wind, wave and DAD schematisation.