Abstract Rivers are fundamental water bodies supporting a wide range of ecosystem services. However, during the last century, river dynamics have been considerably modified by human engineering, notably channelized and dyked to prevent floods. In many Alpine rivers, this has led to the formation of a complex of alternate bars, gradually colonized by vegetation. Therefore, assessing spatial and temporal dynamics over large extents of these alternate bar systems represents a challenge to better understand the functioning of ecosystems in Alpine river and eventually to prevent flood risk. The three objectives of this study were 1) to create a database characterizing bars along a 30 km segment of the River Arc, in the French Alps, 2) to create a bar typology and to compare it to expert point of view, and 3) to assess the dynamics of the system after a 10‐year return period flood event that occurred in June 2013. High‐resolution LiDAR data and aerial photographs were used to localize major bed evolutions through a DEM of Difference (DoD), and to delineate and characterize gravel bars, including their volume, between two dates covering the flood event (in Sept. 2010 and Nov. 2013, respectively). Other river parameters such as sinuosity and river width were also calculated. A hierarchical clustering applied to the whole dataset revealed some bar morphological patterns, with three types of bars, depending in their functioning and age: large old vegetated bars with no mobility, very young, small and low elevated free bars without vegetation, and less mobile and more elongated bars, mostly corresponding to hybrid alternate bars. The results also highlight strong sediment dynamics resulting from the June 2013 flood. Bars were indeed statistically slightly thinner and shorter in 2013 than in 2010, corresponding to an enlargement of the main channel. Finally, these results proved the strong potential of remote sensing data—especially LiDAR data—to characterize sediment bars in channelized river over large extents.
Laslier et al. (Thu,) studied this question.