Projects

Salt exchange at tidal junctions in channel networks

The main objective of this subproject is to better understand salt exchange processes at tidal channel junctions, and to propose novel parametrisations that capture the essential three-dimensional dynamics to be used in advanced one-dimensional models.

Towards this goal, four sub-goals and corresponding work packages are formulated.

1. Development of idealised, subtidal, three-dimensional channel junction model.

We will develop and analyse an idealised, subtidal 3D model, specifically geared towards the unravelling of salt dynamics at tidal junctions. The water motion is described by the subtidal 3D shallow water equations, dynamically coupled to the subtidal salt conservation equation. To allow for the identification of the essential physical mechanisms and to be able to do extensive sensitivity analyses, only those processes essential to capture the subtidal behaviour in regions of complex geometry and channel junctions are retained, while other processes are parametrically taken into account (including the effects of tides).

2. Analysis of existing field data (salt flux decomposition).

The main goal of this work package is to distinguish the primary and secondary processes governing the subtidal salt exchange across the branches at tidal channel junctions (such as lateral tidal phase differences, flow separation and turbulent salt dispersion across the branches), which helps in the development of the 3D subtidal model. The data to be analysed were gathered at the junction of the Rotterdam Waterway and the Old/New Meuse, and at the junction of the Old Meuse and the Hartel Canal.

3. Model validation and sensitivity analysis.

In this work package, our subtidal junction model will be compared to high-complexity simulation models and data. This will be done in cooperation with partners in the SALTISolutions research programme. Our model will be compared to a complex model that is already available, such as the 3D model of the Port of Rotterdam and the Deltares Delft3D model, and the to be developed 3D model of SaltiSolutions WP3. Additionally, a model-data comparison will be made using the data that will be collected in cooperation with Daan van Keulen (WP4.1 of SaltiSolutions), composed of ADCP, CTD and micro-CTD data.

4. Translate three-dimensional exchange processes at channel junctions into simple nodal point relations to be used on 1D salt intrusion models.

Firstly, we will capture the three-dimensional flow and salt behaviour from the (validated) subtidal junction model in a mathematical formulation that includes physical parameters, such as bifurcation angles, bathymetry jumps or relative cross-sectional areas. Thereafter, these expressions will be manipulated to derive parametrisations in the form of nodal point relations which are suitable for channel network models. Subsequently, sensitivity analyses and benchmark tests will be performed to validate the parametrisations, comparing them to our own subtidal model. This also entails assessments of alternative measures to counter salt intrusion. Finally, in cooperation with SaltiSolutions WP5.1, we will formulate a channel network model using the new junction behaviour parametrisations.