Assessment of intermediate fine sediment storage in a braided river reach (southern French Prealps) |
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| Authors: | O Navratil C Legout D Gateuille M Esteves F Liebault |
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| Institution: | 1. Laboratoire d'étude des Transferts en Hydrologie et en Environnement (LTHE), Observatoire des Sciences de l'Univers de Grenoble, 38 041 Grenoble Cedex 09, France;2. National Institute of Water and Atmospheric Research (NIWA), Sediment Processes Team, Christchurch, New Zealand;3. Cemagref, Unité de recherche Erosion Torrentielle, Neige et Avalanches (ETNA), Grenoble, France |
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| Abstract: | This paper presents a field investigation on river channel storage of fine sediments in an unglaciated braided river, the Bès River, located in a mountainous region in the southern French Prealps. Braided rivers transport a very large quantity of bedload and suspended sediment load because they are generally located in the vicinity of highly erosive hillslopes. Consequently, these rivers play an important role because they supply and control the sediment load of the entire downstream fluvial network. Field measurements and aerial photograph analyses were considered together to evaluate the variability of fine sediment quantity stored in a 2·5‐km‐long river reach. This study found very large quantities of fine sediment stored in this reach: 1100 t per unit depth (1 dm). Given that this reach accounts for 17% of the braided channel surface area of the river basin, the quantities of fine sediment stored in the river network were found to be approximately 80% of the mean annual suspended sediment yields (SSYs) (66 200 t year?1), comparable to the SSYs at the flood event scale: from 1000 t to 12 000 t depending on the flood event magnitude. These results could explain the clockwise hysteretic relationships between suspended sediment concentrations and discharges for 80% of floods. This pattern is associated with the rapid availability of the fine sediments stored in the river channel. This study shows the need to focus on not only the mechanisms of fine sediment production from hillslope erosion but also the spatiotemporal dynamics of fine sediment transfer in braided rivers. Copyright © 2010 John Wiley & Sons, Ltd. |
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| Keywords: | fine sediment suspended sediment turbidity braided river sediment storage erosion and deposition mechanisms bars |
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