Morphological model for the River Meuse : initial calibration of Grave-Lith v0.8

The current report concerns the setup and calibration of the morphological model of the Meuse between Grave and Lith. The river stretch Grave-Lith is located between river-kilometre (rkm) 175 and rkm 202. The riverbed is important for many different river functions, as it influences water levels, determines the dimensions of the navigation channel, determines the stability of man-made structures (in and beside the river), and is important for habitats. Knowledge of how the riverbed develops is important considering: - The design of measures along the main channel (river training works and sediment management); - The evaluation of the effect of measures (Rivierkundig Beoordelingskader); - Aiding in the monitoring of pilot locations (river widening and deepening, eroding banks, etc.); - Long-term system development considering different maintenance strategies. Currently, there are a few options for how to assess these developments, namely expert judgment, computation of equilibrium development for small-scale measures in the winterbed of up to 5 km (WAQMORF, D-FAST MI), and since 2020, a Delft3D FM 1D model of the Meuse. The development of a two-dimensional Delft3D FM model will extend and standardize the available options to assess the riverbed of the Meuse with that of the Rhine and allow for easier implementation of measures, and at a finer resolution than in the Delft3D FM 1D model. The model developments take place over the course of several years and started in 2023. The work carried out in 2023 is reported in Ottevanger et al. (2024a) and led to model version v0.5 (uncalibrated). The current report is a progress report that describes only changes or additions that were made in 2024 and resulted in model version v0.8 (partially 1D calibrated). Choices made in 2023 and 2024 may be changed in the following years to further improve model performance. Once the model of the entire Meuse is ready, a final report will be made that contains a full description of all data, methods, and results used for the final version v1 of the model. In the current report, a method was refined to set up a submodel for the reach based on the 20m Meuse grid and boundary conditions, initial conditions, and weir settings from the 40m hydrodynamic Meuse model. The approach was refined to align as much as possible with the current hydrodynamic models of the Meuse. A data analysis of the bed level changes showed the importance of knowing the locations of dredging as well as the bed level changes caused by maintenance dredging. Using a schematized hydrograph between 2011 and 2021, a net reduction in bed material transport of roughly 10,000m³ (including pores) was found between rkm 176 and rkm 181 at a location where the main channel was lowered. Using the above estimate, it was possible to make a first estimate of suitable parameters for the sediment transport formula. This choice was imposed in the simulation, which led to a reasonable first estimate of the bed level changes for the reach. Different recommendations for future steps are discussed, which include the assessment of the model sensitivity results to the initial bed levels, and further one- and two-dimensional calibration.