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Sediment transport control by check dams and open check dams in Alpine torrents

Abstract : Mountain streams are a major sediment source for some rivers; however, they can also be responsible for substantial damage, particularly during sediment-laden floods. Torrents, i.e. very active mountain streams, have been subject to extensive erosion control operations since the 19th century (mainly reforestation, bioengineering, and check dams). More recently, check dams in headwaters have been completed using open check dams that aimed at trapping sediment lower in the valleys. Stream managers must mitigate flood hazards, but now also minimize the environmental impacts of the protection structures, while maintaining and adapting them to a changing context (climate, demography). This requires improved knowledge of the effects of check dams and open check dams on the sediment transport of torrents, and this thesis forms a contribution towards this end. The section on the current state of research reviews i) the diverse effects of check dams on sediment production and transfer; ii) descriptions of the hydraulics and sedimentation processes occurring in open check dams; and iii) woody debris production and trapping processes. This state of the art is completed with proposition of new bedload transport estimation methods, specifically developed for paved streams experiencing external supply or armour breaking. Experimental results are then provided. Firstly, flume experiments highlight the emergence of a more regular bedload transport when check dams are built in alluvial reaches. In a second stage, experiments were performed on a generic Froude scale model of an open check dam basin in order to capture the features of laterally-unconstrained, highly mobile flows. A new flow measurement and inverse-reconstruction procedure has been developed, using photogrammetry and large scale particle image velocimetry (LS-PIV). A preliminary analysis of the results describes flows that tend toward a critical regime and the occurrence of feedback mechanisms between geomorphology and hydraulics during massive bedload deposition. A general conclusion and some perspectives are then presented.
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  • HAL Id : tel-02603609, version 1
  • IRSTEA : PUB00048534

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Guillaume Piton. Sediment transport control by check dams and open check dams in Alpine torrents. Environmental Sciences. Doctorat Science de la Terre et Univers, Environnement, Université Grenoble Alpes, 2016. English. ⟨NNT : 2016GREAU041⟩. ⟨tel-02603609v1⟩

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