Evolutionary trajectory of channel planforms in the middle Garonne River (Toulouse, SW France) over a 130-year period: Contribution of mixed multiple factor analysis (MFAmix)

Abstract

International audienceThe purpose of this study is to propose a methodological essay for defining evolutionary trajectories of channel planforms and to examine the channel change in the middle Garonne River (southwest France) over a 130-year period. The study focuses on a reach of ~90 km situated downstream from the city of Toulouse. A set of four historical maps (1868, 1940s, 1970s, and 2000s) is used to build a geomorphometric diachronic database. Data processing through mixed multiple factor analysis (MFAmix) and hierarchical cluster analysis (HCA) allows distinction between four homogeneous zones within the study reach, depending on their evolutionary trajectories. Channel behavior in the upstream and median zones evolved as of the beginning of the study period (narrowing of the fluvial area, colonization by vegetation, and removal of alluvial bars), likely owing to punctual anthropogenic actions. The downstream zone is characterized by stabilization of the channel and alluvial bar removal over the second half of the twentieth century, coinciding with the campaign undertaken by French local authorities between 1960 and 1984 to protect river banks. The role of ACCEPTED MANUSCRIPT climate transition between the Little Ice Age (LIA) and the onset of the Global Warming period (GW) is also discussed. Results generally are consistent with the chronology established for most European rivers

Long-term river trajectories to enhance restoration efficiency and sustainability on the Upper Rhine: an interdisciplinary study (Rohrschollen Island, France)

“…This is interpreted as the consequence of sediment deposition in the disconnected parts of the main channel, inducing channel narrowing, and forest and agriculture expansion, as intended by the correction works (Bernhardt, 2000). These types of morphodynamic disturbances driven by channel correction were also observed by David et al (2016) Hydrol …”

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

“…The sequence of different planform configurations, from braided/anabranching to sinuous with alternate bars and finally to sinuous or meandering reaches (Figure ), represents an interesting example of the longitudinal shift from multi‐thread to single‐thread observed also in other river systems (Church, ; Beechie et al ., ; Beechie and Imaki, ). The cause for this shift has been associated with decreasing channel slope and thus transport capacity, and/or increasing sediment supply and grain size (Schumm, ; Rice and Church, ; Church, ; Benda et al ., , ; David et al ., ).…”

“…Study of historical evolution of river channels has been a central theme in geomorphology for decades (Petts, 1989;Wyżga, 1993;Liébault and Piégay, 2002;Surian and Rinaldi, 2003;Surian et al, 2009a;Scorpio et al, 2015;David et al, 2016). Most studies, at both Italian and European level, have addressed reaches characterized by originally wide braided morphologies, while studies analyzing rivers with original single-thread or anastomosed morphologies are very few, i.e.…”

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

“…Similar trajectories of vegetation encroachment related to a variety of human impacts have been described in other river systems with different morphologies (e.g. Tal et al ., ; David et al ., ; Liébault and Piégay, ).…”