"Recent Sediment Bar Dynamics in the Po River Corridor Observed by Monthly Satellite Imagery"

Abstract: This thesis examines the changes in sediment bars along the Po River corridor in northern Italy from 2017 to 2023. The study uses monthly Sentinel-2 images with 10 m resolution. These images were processed through a two-step classification to distinguish between water, sediment, and vegetation. From these results, two persistence indicators were defined. Highly Stable Sediment (HSS) refers to pixels that appear as bare sediment in more than 80% of the yearly images. Moderately Stable Sediment (MSS) refers to pixels identified as sediment between 50% and 80% of the time. These measures allow tracking how stable exposed bars are across the river system. The assessment took two directions. First, it compared different areas of the river by looking at the upstream multi-channel reaches and the largely single-threaded channel downstream. Multi-channel sections showed limited HSS and varied MSS, indicating mobile bars and weak connections to the floodplain. In the lower river, HSS was more prominent, suggesting long-term stability, though some local variability remained. Second, year-to-year variability was assessed in relation to discharge. In wet years like 2018 and 2019, when daily peaks (Qmax) exceeded 8,000 m³/s, extensive reworking took place: HSS decreased while MSS increased. In contrast, the dry period from 2020 to 2022 encouraged consolidation and growth of HSS. Intermediate flows in 2023 allowed some reactivation of MSS. To provide concrete examples and insights beyond system-wide averages, three representative reaches—PO_5 (upstream), PO_11 (midstream), and PO_32 (downstream)—were examined in detail. This reach-scale analysis highlights processes that can be overlooked in broader assessments: rapid reworking and prevalence of MSS upstream, changing persistence in the middle course, and consolidation of HSS downstream. Overall, combining frequent satellite observations with hydrological records offers a practical way to assess morphodynamical trends in a regulated, sediment-limited river system. The reach-scale perspective provides additional insights that whole-system analysis may miss, clarifying how morphology and flow together influence sediment bar persistence. These results show that bar persistence (HSS/MSS) reflects the river's shape while also responding to changes in water flow.