Multi‐decadal quantification of interactions between coarse sediment fluxes and channel management in South Tyrol, Eastern European Alps

Abstract

Channel incision and narrowing have occurred in the 20th century in most Alpine rivers. However, the causal links between sediment‐related human engineering and exploitation and morphological changes in rivers are mostly unclear. This study presents an analysis of the evolutionary trajectories of the main active channels in the upper Etsch/Adige River basin (Eastern European Alps) coupled with their modifications in terms of coarse sediment transport. Channel planform variations were quantified in 15 rivers (total length of 630 km) using multi‐temporal analysis of historical maps and orthophotos. Sediment volumes excavated from river channels or trapped by hydraulic structures (dams and retention basins) were retrieved from historical records, along with geospatial information regarding the presence of lateral and longitudinal consolidation works and land use variations. Results indicate that most rivers underwent slight narrowing and some of them experienced widening, from the mid‐19th century to the 1950s. From the 1950s to the late 1990s, severe variations in terms of narrowing and morphological simplification took place in all rivers. The analysis of channel changes in relation to human activities shows that gravel mining carried out in the period 1970s–1990s appears to have been the main cause of sediment imbalance in the rivers which narrowed the most. Since the 2000s, when gravel mining was banned by law, channel adjustments have become negligible throughout study area. Nevertheless, the trapping of a large share of coarse sediment fluxes—at the river basin scale—by retention check dams and hydropower dams has impeded rivers from recovering to their original conditions.

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

“…In-channel gravel mining was carried out mainly in the second half of the 20th century and was considered in most case studies, as the main factor of channel adjustment (e.g., Comiti & Scorpio, 2019;Rinaldi, Wyżga, & Surian, 2005;Surian, 2022). The presence of dams in Iberian rivers was indicated as sediment supply and channel morphology probably were the type of bedrock and its erodibility, the valley confinement, the valley slope, the basin relief, the land cover and the occurrence of glaciated areas in the proglacial streams (Bakker et al, 2018;Brardinoni et al, 2012;Hohensinner et al, 2020;Scorpio et al, 2024).…”

“…For the sake of simplicity broader classes of channel patterns were used (see also Section 2) except for the braided and anabranching morphologies for which a more detailed analysis is presented, as differences in their evolutions are worth to be shown. In particular, Scorpio et al, 2015Scorpio et al, , 2024. For the rivers in the Alps and in the Carpathians, the widening was associated with the wider channel width designed during channelisation, whereas for the rivers in Southern Apennines, the increase of channel width was linked to the delay in socio-economic transformation that started only in the 1930s-1950s (Figure 11).…”

“…Reach scale changes and drivers must always be considered within an integrated catchment perspective, bearing in mind that there is a time lag between causes and effects and that each anthropogenic action will cause effects propagating both upstream and downstream. This is a scientific and practical challenge because the most appropri- between sediment regimes, alterations in sediment flux and sediment connectivity and morphological changes (Casserly et al, 2021;Dépret et al, 2023Dépret et al, , 2019Liébault & Piégay, 2001;Scorpio et al, 2024;Vázquez-Tarrío et al, 2019). Quantification of sediments extracted for gravel mining or trapped at retention works and dams can allow for estimating the volumes subtracted from rivers (De Vincenzo et al, 2017;Scorpio et al, 2024).…”

“…This is a scientific and practical challenge because the most appropri- between sediment regimes, alterations in sediment flux and sediment connectivity and morphological changes (Casserly et al, 2021;Dépret et al, 2023Dépret et al, , 2019Liébault & Piégay, 2001;Scorpio et al, 2024;Vázquez-Tarrío et al, 2019). Quantification of sediments extracted for gravel mining or trapped at retention works and dams can allow for estimating the volumes subtracted from rivers (De Vincenzo et al, 2017;Scorpio et al, 2024). These data have to be used in concurrency with data on the historical management of the catchment, social information, statistics on population and livestock densities and databases with data on the magnitude and the timing of anthropogenic interventions (Scorpio & Piégay, 2021;Taillefumier & Piégay, 2003).…”

“…The 2000s-2010s decades were quite rich in terms of multiple, comparative investigations. Liébault & Piégay (2002), Belletti, Dufour and Piégay (2013) and Liébault et al (2013) addressed the overall river trends observed in the Southern French Alps; while Eastern Alpine rivers were the focus of the works by Comiti (2012), Marchese et al (2017), Hohensinner et al (2020) and Scorpio et al (2024). Rinaldi (2003), Surian and Rinaldi (2003), Surian, Rinaldi et al (2009), Scorpio et al (2015) and Scorpio and Piégay (2021) summarised the knowledge on the evolution of rivers across Italy.…”