Modelling of hydro-geomorphological processes related to sediment transport: case study of the baganza river (Italy)

Sediment transport and the processes that shape river landscapes have a significant impact on flood dynamics. This interdisciplinary study combines Earth Sciences and Hydraulic Engineering principles to investigate sediment bahaviour within the Baganza River catchment in Northern Italy. The research particularly focuses on developing a robust sediment transport numerical model, which is essential for simulating the bed morphological changes in river systems. It’s imperative to note that while numerical models are valuable tools, their effectiveness depends on addressing various limitations, such as spatial and temporal scales, data requirements, model complexity, numerical stability, and computational demands. This research aims to overcome these constraints by examining a 2D numerical model specifically designed for simulating bedload transport in real-world applications. The model incorporates weak coupling of shallow water and Exner equations, which represent the liquid and solid phases, respectively. Besides the modification and improvement of the pre-existing numerical model, one of the novelties of this research lies in the fact that it incorporates actual grain size obtained from field-derived data, used as input parameter for the model. The technique employed for obtaining granulometric distribution is of hybrid nature i.e., combining sieve analysis and photogrammetric technique. This offers an efficient and cost-effective approach, enhancing sediment analysis precision while reducing fieldwork demands. By applying the built model to the Baganza River, it provides valuable insights into sediment conveyance, flow-bed interactions, erosion, and deposition. To estimate sediment discharge, equations by Meyer-Peter and Müller (1948) and Smart (1984) were employed, which are optimized for computational efficiency using Graphics Processing Unit (GPU) parallelization. Hereafter, Smart (1984) will be referred to as the SMART and Meyer-Peter and Müller (1948) as the MPM approach. The model simulates morphological transformations that occurred in the Baganza River between 2008 and 2014, utilizing a high-resolution (4 m x 4 m) Digital Terrain Model (DTM). The model’s accuracy is validated by benchmark testing against 1D and 2D dam break scenarios with mobile bed conditions, including sensitivity analyses of model input parameters. In the absence of calibration data, sensitivity analysis explores the influence of key input parameters on the predictive capabilities of the bedload transport model. Three distinct cases are considered, each examining the model’s response to alterations in specific parameters, i.e. median grain size D50 and manning roughness “n” value while keeping other variables constant. The results of the sensitivity analysis shed light on the performance of the 2D sediment transport model. The findings contribute to best parameter selection and model enhancements, ultimately improving the model’s predictive capabilities. Furthermore, the analysis of 2D model outputs related to the Baganza River delineates eight distinct in-channel bed Morphological Units (MU’s), based on thresholds measuring depth and Froude number. These units encompass pools, runs, chutes, riffles, riffle transitions, fast glides, slow glides, and slackwater zones. In conclusion, this research underscores the significance of an interdisciplinary approach in comprehending the intricate sediment dynamics of riverine environments.