B. Biemond1*, H.E. de Swart1, H.A. Dijkstra1

1 Utrecht University

*corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Introduction

The Rhine-Meuse estuary is a heavily engineered estuarine delta in the Western Netherlands.

Recent summer droughts have shown that salt intrusion in this system is a topic of concerns and deserves further study. As part of the SALTISolutions project, our aim is to better understand and quantify the dependence of salt intrusion to various physical forcings such as river discharge for this system.

Methods

An idealized model of the Rhine-Meuse Delta will be presented. This model solves the simplified momentum balances, coupled with the salt balance, for currents and salinities in estuarine deltas. The new elements with respect to the one developed in Biemond et al. (2022) are the explicit solutions for tidal flow and tidally varying salinity and the geometry of a complicated channel network.
Salinity observations from Rijkswaterstaat are used to calibrate the model. Afterwards, the salt intrusion is calculated for different river discharge scenarios.

Results

After calibration, the salinity values from the model agree fairly well with the observed salinity values (Fig. 1). The river discharge scenarios indicate that different channels have a different sensitivity to changes in river flow. To gain a better understanding of the spatial heterogenous response, the salt transport in the model is decomposed into different contributions, and for each channel separately the dominant salt transport process is established. In strongly stratified channels, the density-driven current is the dominant salt import process, but in weaker stratified channels tidal pumping and horizontal diffusion is more important.

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Figure 1: An example of the model results for salt intrusion in the Rhine-Meuse Delta. (a) Discharge in the different branches. (b) Depth and tidally averaged salinity in the different branches.

References

Biemond, B., de Swart, H. E., Dijkstra, H. A., & D├Čez-Minguito, M. (2022). Estuarine salinity response to freshwater pulses. Journal of Geophysical Research: Oceans, 127, e2022JC018669. https://doi.org/10.1029/2022JC018669

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