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Etude et gestion de la dynamique sédimentaire d'un tronçon fluvial à l'aval d'un barrage : le cas de la basse vallée de l'Ain

Abstract : Our ability to evaluate the impacts of dams on river channels is limited by a lack of adequate field observations and natural variability between river systems. Although understood in a qualitative sense, quantitative data has been difficult to collect and the complexity of the problem has meant that the application of predictive models of channel evolution remains a delicate process (Chapter 1). In addition, while we can now anticipate and alleviate the adverse effects associated with flood regulation, there are few defined options for the reduction or elimination of the sedimentary deficit downstream of dams. A number of restoration plans that address the issue of sediment supply have been put into place in California and on the Rhine River, but they have used non-native sediments for which the associated costs have been high. The Ain river valley represents an ideal site for the continued study of this problem: the floodplain and river corridor are relatively intact, having been spared problems associated with large gravel extraction operations, widescale construction of dykes or dredging of the channel for navigation purposes, and a series of hydroelectric dams have been constructed.
As a first step, we identified the impacts that the dams and other anthropomorphic changes have had on both the control variables and the morphology of the Ain River (Chapter 2). We focused on two morphological variables, the channel width and the longitudinal profile, in order to determine the current trajectory of river adjustments. From this we were able to distinguish the perturbation to morphology that has resulted from dam-related modification to sediment continuity beginning in 1931 and flood regulation since 1968. The magnitude of modifications to the control variables and the spatial extent of the morphological adjustments were determined from available data, including aerial photographs, and field characterizations of the sedimentology.
As a second step, we tried to understand a number of relevant processes, including sedimentary inputs to the system, sites of deposition, the transport capacity of the river and the quantification of excess shear stress, in order to not only quantify the current sedimentary deficit, but to also give some estimates of future adjustments and identify suitable management strategies (Chapter 3). Three approaches were utilized: the determination of a sedimentary budget for a series of homogenous reaches, direct measurement of sediment transport, and the calculation of transport capacity from available hydraulic relations. These three techniques allowed a cross-validation of the results, which showed the need to immediately address the sediment deficit in the upstream reaches of the system. It appears that the channel is no longer able to ensure its own sedimentary recharge and that there is no sedimentary input that is capable of checking the downstream progression of a sedimentary deficit of 10-15 000 m3.year -1.
These results were used as a basis to outline a sustainable management plan for the sedimentary dynamics of the Ain River (Chapter 4). The objectives of this management plan are both preventative, in that they seek to preserve actively meandering reaches, and curative, in that they suggest ways to restore lateral dynamics in reaches that have already been impacted by the sedimentary deficit. After presenting the full range of possible actions for the reaches downstream of the dams, we selected the actions that were the most technically and economically suited to our context. Finally, we present preliminary results from sediment recharge operations that were carried out following the identification of suitable management strategies.
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Submitted on : Monday, January 28, 2008 - 2:51:09 PM
Last modification on : Friday, October 23, 2020 - 4:51:09 PM
Long-term archiving on: : Friday, April 30, 2010 - 12:23:19 AM


  • HAL Id : tel-00221368, version 1


Anne-Julia Rollet. Etude et gestion de la dynamique sédimentaire d'un tronçon fluvial à l'aval d'un barrage : le cas de la basse vallée de l'Ain. Géomorphologie. Université Jean Moulin - Lyon III, 2007. Français. ⟨tel-00221368⟩



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