Identifying the effects of parameter uncertainty on the reliability of modeling the stability of overhanging, multi-layered, river banks

Abstract

grained
material. In such banks, fluvial erosion of the lower, non-cohesive, layer typically occurs at a much
higher rate than erosion of the upper part of the bank. Consequently, such banks normally develop a
cantilevered bank profile, with bank retreat of the upper part of the bank taking place predominantly by the
failure of these cantilevers. To predict the undesirable impacts of this type of bank retreat, a number of bank
stability models have been presented in the literature. These models typically express bank stability by
defining a factor of safety as the ratio of resisting and driving forces acting on the incipient failure block. These
forces are affected by a range of controlling factors that include such aspects as the overhanging block
geometry, and the geotechnical properties of the bank materials. In this paper, we introduce a new bank
stability relation (for shear-type cantilever failures) that considers the hydrological status of cantilevered
riverbanks, while beam-type failures are analyzed using a previously proposed relation. We employ these
stability models to evaluate the effects of parameter uncertainty on the reliability of riverbank stability
modeling of overhanging banks. This is achieved by employing a simple model of overhanging failure with
respect to shear and beam failure mechanisms in a series of sensitivity tests and Monte Carlo analyses to
identify, for each model parameter, the range of values that induce significant changes in the simulated factor
of safety. The results show that care is required in parameterising (i) the geometrical shape of the
overhanging-block and (ii) the bank material cohesion and unit weight, as predictions of bank stability are
sensitive to variations of these factors.

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ORCID for Stephen E. Darby: orcid.org/0000-0001-8778-4394

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