Sensitivity of salt intrusion in estuarine networks to geometry using an idealised model

Salt intrusion in estuaries threatens freshwater availability and agriculture in coastal regions. The geometries of most estuaries are heavily anthropogenically modified, for instance for shipping, land reclamation and flood protection. The response of the salt intrusion to modifications of the geometry is thoroughly studied for single channel estuaries. However, a significant fraction of earths estuaries consists of a network of channels, in which the dynamics are more complex, because it includes the distribution of water and salt at branching points. We aim to identify, quantify, and understand the differences in response to changes in the geometry occurring in estuarine networks compared to salt intrusion in single channel estuaries. To achieve this, we have developed an idealized width-averaged model, which solves for hydrodynamics and salt intrusion in an estuarine network. The advantages of this model are that it is flexible in its geometry and has a short runtime. The Rhine-Meuse Delta (the Netherlands) is taken as a reference case. A set of simulations using different geometries is performed with the calibrated model. An example of a result which we obtained is that channel deepening increases salt intrusion locally, but decreases salt intrusion elsewhere in the channel network. These results give insights in the vulnerability of salt intrusion in estuarine channel networks.