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Geomorphic responses of restored frequently flowing side channels along the Rhône River

Abstract : From early stages to more mature conditions, temporal patterns of fine sedimentation are well known in side channels that have been restored along the Rhône River. Since the beginning of the restoration program in the 1990s, a scientific monitoring has been performed to provide data from a set of restored channels along the river continuum to understand how they adjust to their new conditions after restoration. However, there is still a lack of knowledge regarding the geomorphic processes in the active side channels (i.e., upstream and downstream frequently connected with the main channel) and their bedload transport conditions. We can observe in some of them a terrestrialization pattern (i.e., gradual water lowering) that can be linked to: (i) bedload input from the main channel which in turns is controlled by geometric characters of the channel or its entrance as bifurcation angles, and/or (ii) morphological adjustments of the main channel or the side-channel itself. we show here the results of a multi-technical approach which aim at characterizing terrestrialization patterns, in time and space, of five restored active side-channels located on three bypassed reaches of the Rhône River. We first characterized conditions prior artificial disconnection from historical data and archives. Then, geomorphic trajectories since the first implementation of longitudinal dykes [1850’s-1930’s] and flow diversion due to by-passing [1948-1986] until restoration (for over a century since cutoff) and then from restoration to the present day (i.e., from 3 to 16 years after restoration works), are assessed from a combination of existing topo-bathymetric data and new acquisitions. These new acquisitions consist on in situ measurements of bed grain size characteristics by underwater imagery, bedload transport assessment using RFID technology, interstitial clogging by volumetric analysis and evaluation of hydraulic conditions in channels with limnimetric data series. Finally, geomorphic responses of active side channels and their life span are discussed with regard to the evolution of the main channel itself over the last two centuries.
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https://hal.archives-ouvertes.fr/hal-03338027
Contributor : Jérémie Riquier Connect in order to contact the contributor
Submitted on : Wednesday, September 8, 2021 - 1:35:49 PM
Last modification on : Monday, November 22, 2021 - 4:02:48 PM

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  • HAL Id : hal-03338027, version 1

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Nicolas Tissot, Jérémie Riquier, Hervé Piégay, Lise Vaudor. Geomorphic responses of restored frequently flowing side channels along the Rhône River. International Conference on the Status and Future of the World's Large Rivers, Session "“Sediment Transport & River Morphology”", Aug 2021, Moscou, Russia. ⟨hal-03338027⟩

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