Van de Wiel, Marco J. and Darby, Stephen E.
A new model to analyse the impact of woody riparian vegetation on the geotechnical stability of riverbanks
Earth Surface Processes and Landforms, 32, (14), . (doi:10.1002/esp.1522).
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We present a geotechnical stability analysis for the planar failure of riverbanks, which
incorporates the effects of root reinforcement and surcharge for mature stands of woody
riparian vegetation. The analysis relies on a new method of representing the root distribution
in the soil, which evaluates the effects of the vegetation’s position on the bank.
The model is used in a series of sensitivity analyses performed for a wide range of bank
morphological (bank slope and height) and sedimentological (bank cohesion and friction
angle) conditions, enabling discrimination of the types of bank environment for which
vegetation has an effect on bank stability. The results indicate that woody vegetation
elements have a maximal impact on bank stability when they are located at the ends of
the incipient failure plane (i.e. at the bank toe or at the intersection of the failure plane
with the floodplain) and that vegetation has a greater effect on net bank stability when
it is growing on low, shallow, banks comprised of weakly cohesive sediments. However,
the magnitude of these effects is limited, with vegetation typically inducing changes (relative
to non-vegetated banks) in simulated factors of safety of less than 5%. If correct, this
suggests that the well documented effects of vegetation on channel morphology must
be related to alternative process mechanisms (such as the interaction of vegetation with
river flows) rather than the mechanical effects of vegetation on bank failure, except in
special cases where the equivalent non-vegetated bank has a highly marginal stability status.
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