A width‐based approach to estimating historical changes in coarse sediment fluxes at river reach and network scales

Abstract

Knowledge about historical changes in sediment fluxes in most coarse-bedded rivers worldwide is extremely limited. In consideration of this deficiency, we developed a width-based approach to estimating multi-decade changes in coarse sediment fluxes occurring at reaches of the Po River and 21 of its tributaries in northern Italy. The estimation was based on temporal variations in the reach-averaged width of the river's active channel, and such width was expressed through a dimensionless index of coarse bed material load (I q ). The index was determined in two periods: 1954-1998 and 1998-2020. Statistically significant relationships were found between temporal variations in I q occurring in reaches of the Po River and at key locations of each specific reach (i.e., upstream reaches and tributaries). Such evidence of coherent changes in sediment transfer through space and time led us to conclude that I q variations can be regarded as a reliable proxy for historical changes in sediment transport in a river reach. The application of the approach to the investigation of the Po River catchment provided new insights into the historical changes characterizing coarse sediment fluxes along the river and its major tributaries. From 1954 to 1998, an average decrease in coarse sediment fluxes of about À20% and À30% occurred along the river and the terminal sectors of its tributaries, respectively. The estimations showed that coarse sediment fluxes exhibited a slightly lower decrease in the last two decades, with sediment flux recovery occurring only in some tributaries. The results suggest that a profound change in sediment dynamics and fluxes has occurred, and is likely still ongoing, in the Po River system, despite the decrease in human disturbances (e.g., in-channel sediment mining) in more recent times.

Channel changes over the last 200 years: A meta data analysis on European rivers

“…Bank protections or levees were built in the channels flowing through the main valleys (Figure 11, e.g., Bravard et al, 1997; 1999; Liébault & Piégay, 2001, 2002; Taillefumier & Piégay, 2003). In the Italian Alps, erosion control interventions, decrease in rural population and land use transformations increased immediately after than in the French Alps—from the last decades of the 19th century—and later on in the North Apennines, that is, from the first decades of the 20th century (Figure 11, e.g., Brenna, Bizzi, & Surian, 2022; Scorpio & Piégay, 2021; Ziliani et al, 2020). In the Southern Apennines, in the Iberians and in the Carpathians, catchment scale human pressures presented a delay compared with the Alpine and northern Apennine rivers (Figure 11).…”

Remote sensing assessment of anthropogenic and climate variation effects on river channel morphology and vegetation: Impact of dry periods on a European piedmont river

“…Starting from 1958, a river barrage for hydroelectric production was built just upstream of Cremona, diverting the flow through the turbines and in the natural meander cutoff connected to the main channel 12 km downstream of the diversion (Bernardi et al, 2013; Bizzi et al, 2015; Lamberti & Schippa, 1994). The combination of these interventions has led to a significant oversimplification of the lowland part of the Po River, eventually changing the pattern from multi‐ to single‐thread (see, among many others, Surian & Rinaldi, 2003; AdBPo, 2008; Domeneghetti et al, 2015; Lanzoni et al, 2015; Maselli et al, 2018; Brenna et al, 2022, 2024). Such an oversimplification contributed to further degradation of the overall landscape, causing a shift from wet to dry soils and a dramatic loss of riparian waterbodies and wetlands (Viaroli et al, 2013).…”