HESS Hydrology and Earth System Sciences HESS Hydrol. Earth Syst. Sci. 1607-7938 Copernicus Publications Göttingen, Germany 10.5194/hess-15-1615-2011 Mechanisms of vegetation uprooting by flow in alluvial non-cohesive sediment Edmaier K. 2 1 Burlando P. 1 Perona P. 2 1 Institute for Environmental Engineering, ETHZ, Wolfgang-Pauli-Str. 15, 8093 Zurich, Switzerland now at: AHEAD, IIE, EPFL-ENAC, Station 2, Lausanne, Switzerland 26 05 2011 15 5 1615 1627 Copyright: © 2011 K. Edmaier et al. 2011 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://hess.copernicus.org/articles/15/1615/2011/hess-15-1615-2011.html The full text article is available as a PDF file from https://hess.copernicus.org/articles/15/1615/2011/hess-15-1615-2011.pdf

The establishment of riparian pioneer vegetation is of crucial importance within river restoration projects. After germination or vegetative reproduction on river bars juvenile plants are often exposed to mortality by uprooting caused by floods. At later stages of root development vegetation uprooting by flow is seen to occur as a consequence of a marked erosion gradually exposing the root system and accordingly reducing the mechanical anchoring. How time scales of flow-induced uprooting do depend on vegetation stages growing in alluvial non-cohesive sediment is currently an open question that we conceptually address in this work. After reviewing vegetation root issues in relation to morphodynamic processes, we then propose two modelling mechanisms (Type I and Type II), respectively concerning the uprooting time scales of early germinated and of mature vegetation. Type I is a purely flow-induced drag mechanism, which causes alone a nearly instantaneous uprooting when exceeding root resistance. Type II arises as a combination of substantial sediment erosion exposing the root system and resulting in a decreased anchoring resistance, eventually degenerating into a Type I mechanism. We support our conceptual models with some preliminary experimental data and discuss the importance of better understanding such mechanisms in order to formulate sounding mathematical models that are suitable to plan and to manage river restoration projects.

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