Channelization of a large Alpine river: what is left of its original morphodynamics?

Abstract

The Adige River drains 12 200 km2 of the Eastern Alps and flows for 213 km within this mountain range. Similar to other large rivers in Central Europe, the Adige River was subject to massive channelization works during the 19th century. Thanks to the availability of several historical maps, this river represents a very valuable case study to document the extent to which the morphology of the river changed due to channelization and to understand how much is left of its original morphodynamics. The study was based on the analysis of seven sets of historical maps dating from 1803–1805 to 1915–1927, on geomorphological analysis, on the application of mathematical morphodynamic theories and on the application of bar and channel pattern prediction models. The study concerns 115 km of the main stem and 29 km of its tributaries. In the pre‐channelization conditions, the Adige River presented a prevalence of single‐thread channel planforms. Multi‐thread patterns developed only immediately downstream of the main confluences. During the 19th century, the Adige underwent considerable channel adjustment, consisting of channel narrowing, straightening, and reduction of bars and islands. Multi‐thread and single‐thread reaches evolved through different evolutionary trajectories, considering both the channel width and the bar/vegetation interaction. Bar and channel pattern predictors showed good correspondence with the observed patterns, including the development of multi‐thread morphologies downstream of the confluences. Application of the free‐bar predictor helped to interpret the strong reduction – almost complete loss – of exposed sediment bars after the channelization works, quantifying the riverbed inclination to form alternate bars. This morphological evolution can be observed in other Alpine rivers of similar size and similar massive channelization, therefore, a simplified conceptual model for large rivers subjected to channelization is proposed, showing that a relatively small difference in the engineered channel width may have a strong impact on the river dynamics, specifically on bar formation. Copyright © 2017 John Wiley & Sons, Ltd.

Biomorphodynamics of alternate bars in a channelized, regulated river: An integrated historical and modelling analysis

“…Also, free bars are downstream migrating, while hybrid bars are non-migrating. Besides the specific theoretical literature, further details on the application of such theories to field cases can be found in Zolezzi et al (2012), Jaballah et al (2015), Rodrigues et al (2015), Adami et al (2016) and Scorpio et al (2018).…”

“…the Alpine Rhine, Jäggi, 1984;Adami et al, 2016), whereas bars are almost absent in others (e.g. the Rhone in Switzerland, Stäuble et al, 2008; the Alpine Rhine downstream of the Ill confluence, Adami et al, 2016;and the Adige in northeast Italy, Scorpio et al, 2018). Following decades of mathematical theories concerning alternate bars (e.g.…”

“…While alternate bar development can be clearly related to channelization, controls on such biophysical interactions might also reflect many other human actions occurring within the same catchment, which can be investigated across a spectrum of temporal and spatial scales using a wide range of historical information sources (for a recent review see Grabowski et al, 2014) and integrating such analysis with modelling approaches (e.g. Scorpio et al, 2018).…”

Morphodynamics of alternate bars in the presence of riparian vegetation

“…Cordier et al, 2019;Crosato et al, 2012), and field studies (e.g. Adami et al, 2016;Jaballah et al, 2015;Scorpio et al, 2018). Periodic bars can be characterized as free bars or hybrid bars (Duró et al, 2016).…”

Numerical Study of Alternate Bars in Alluvial Channels With Nonuniform Sediment

“…Eekhout et al () and Rodrigues et al () discussed this ambiguity of using the term “forced bars” for two types of bars, albeit without proposing a new terminology. To resolve the old ambiguity, the Delft School introduced the term “hybrid bars,” which was then gratefully adopted by Duró et al (), Le, Crosato, Mosselman, and Uijttewaal (), Le, Crosato, and Uijttewaal (), and Scorpio et al (). This second and more recent classification distinguishes two types of periodic bars: free and hybrid bars.…”