Modelling Of Hydro-Geomorphological Processes Related To Sediment Transport: Case Study of the Baganza River (Italy)

The accuracy and reliability of sediment transport models is crucial for understanding and predicting geomorphological changes in river systems, which can have important implications for conserving riverine ecosystem. This information can be used to make better informed decisions about the management of the river, as well as to predict and prepare for potential hazards such as flash flooding. In the past, various approaches have been used to model these processes for suspended and bedload sediment transport. However, many of these models have limitations including spatial and temporal scales, data requirements, model complexity, numerical stability and computational cost, particularly when it comes to simulating the transport of bedload sediments.

In this study, we tried to address these limitations by testing a 2D weakly coupled numerical model for bedload transport in a real application. The model was implemented by adopting schemes presented in previous works (Vacondio et al. 2014, doi.org/10.1016/j.envsoft.2014.02.003; Juez et al. 2014, doi.org/10.1016/j.advwatres.2014.05.014). The advantage of using a weakly coupled model is that it is flexible, computationally efficient and can be used to simulate bedload transport in large-scale systems while producing consistent and reliable results over time. It is based on the finite-volume method and uses the Shallow water and Exner equations for the liquid and solid phases, respectively. High computational efficiency is guaranteed by parallelization on Graphics Processing Units.

We selected the case study of the Baganza River (Italy), characterized by a catchment area of 228 km² and a total length of 55 km. We focused on the 28 km-long stretch between Calestano and Parma, with an average slope in the order of 0.8-1.5% and grain sizes in the order of 2-30 mm. For the topography, we used high-resolution digital elevation model (DEM) from 2008, while grain size distribution data were obtained through a hybrid technique combining field sediment sampling and photogrammetry. The adopted approach for the characterization of fluvial sediments at different points along the river is desirable in order to accommodate the full range of particle sizes inside the riverbed. The inflow boundary condition is the 2008-2014 series of floods on the Baganza River, including a destructive flood that occurred in October 2014.The riverbed topography resulting from the numerical simulation was compared with the one extracted from the DEM provided by a LiDAR survey carried out after the October 2014 event. The overall fair agreement between measured and simulated results suggests the usefulness of 2D weakly coupled numerical model for simulating hydro-geomorphological processes in the Baganza River. Moreover, the hybrid technique adopted for the grain characterization provides realistic representation of the sediments and increases the accuracy and reliability of the model predictions.