This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights  We explore the correspondence between real plants and their rigid-cylinder description  Experiments, numerical models and real rivers are combined in the analyses  The cylinders diameter is relevant in representing the effects of the tested plants  Numerical models can represent the effects of high-density vegetation

Sediment deposition and bank accretion are promoted by the establishment and growth of pioneer plant species, a direct consequence of plant survival during flood events. Similarly, the uprooting of riparian vegetation on river bars during floods can subsequently alter hydraulics, sediment dynamics, and bar evolution. In this work, we focus on the removal of flexible seedlings due to both hydraulic forces and bed erosion, specifically examining failure mechanisms associated with root pull‐out. We provide a conceptual model and a new physical equation for predicting the flow and bed erosion conditions that promote the uprooting of plants. The model was validated by means of flume experiments employing two species of vegetation (i.e., common oats and a willow native to Europe). Furthermore, the Ombrone Pistoiese River (Tuscany, IT) was used as a case study to validate the physical model with respect to observed vegetation removal during a flood event. The results illustrate the capability of our model to predict conditions for vegetation removal and suggest that sediment transport is a necessary ingredient even for very young seedlings.

Worldwide convectively accelerated streams flowing in downstream‐narrowing river sections show that riverbed vegetation growing on alluvial sediment bars gradually disappears, forming a front beyond which vegetation is absent. We revise a recently proposed analytical model able to predict the expected longitudinal position of the vegetation front. The model was developed considering the steady state approximation of 1‐D ecomorphodynamics equations. While the model was tested against flume experiments, its extension and application to the field is not trivial as it requires the definition of proper scaling laws governing the observed phenomenon. In this work, we present a procedure to calculate vegetation parameters and flow magnitude governing the equilibrium at the reach scale between hydromorphological and biological components in rivers with converging boundaries. We collected from worldwide rivers data of section topography, hydrogeomorphological and riparian vegetation characteristics to perform a statistical analysis aimed to validate the proposed procedure. Results are presented in the form of scaling laws correlating biological parameters of growth and decay from different vegetation species to flood return period and duration, respectively. Such relationships demonstrate the existence of underlying selective processes determining the riparian vegetation both in terms of species and cover. We interpret the selection of vegetation species from ecomorphodynamic processes occurring in convectively accelerated streams as the orchestrated dynamic action of flow, sediment and vegetation characteristics. © 2019 John Wiley & Sons, Ltd.

Fluvial environments are dynamic systems whose evolution and management are strongly affected by the resilience of riparian vegetation to uprooting by flow. Similarly to other natural phenomena, the interactions between flow, sediment and vegetation uprooting is governed by both the magnitude and

The growth and establishment of riparian vegetation on river bedforms is of hydrological as well as ecological importance as it helps in enhancing spatial heterogeneity and thus the biodiversity of river corridors. Yet, during floods, flow drag and scouring may reduce the rooting length of plants determining plant mortality via uprooting. In order for uprooting to occur, bed scouring must proceed until the rooting length reaches a critical value and drag forces exceed root residual anchorage. Therefore, the critical rooting length of a plant represents a crucial parameter to estimate the probability of plant removal due to flow erosion. However, difficulties in quantifying such length at the field scale have limited so far the performances of biomorphodynamic models for river bed evolution. In this work, we propose to assess the critical rooting length from controlled plant pullout experiments. To this aim, a free-body model of the forces acting on a flexible plant in a stream at different erosion stages is developed. At incipient uprooting, we conjecture that the root resistance at the critical rooting length equals that of a plant with equal rooting length when pulled out in static conditions. To illustrate our approach, we validate our model on three different data sets obtained from small-and real-scale plant uprooting experiments. A comparison between modeling and experimental observations reveals that the model provides valid results, despite its deterministic approach. The critical rooting lengths are finally used to assess the probability density function of the time to uprooting via a physically based stochastic model.

Formulations for the threshold conditions between vegetated and barebed channel are derived • Threshold conditions are mainly related to species-dependent characteristics • Submerged plants are more vulnerable to removal than emergent as relative emergence reduces the threshold value

River bars often form at river confluences due to variation in flow discharges or in sediment transport capacity; once these bars are grown, they constitute favourable habitats for vegetation development. In this work, we analysed the effect of vegetation above confluence bars on the hydrodynamics of a river reach. The case study considered is the Arno River reach at the Greve junction, where confluence bars expanded towards the opposite bank. A two-dimensional hydraulic model was implemented through BASEMENT software varying the flow discharge. Three-dimensional topographic data were used to generate the calculation mesh. Dendrometric surveys were carried out to describe the current state of the vegetation. Seven different vegetative scenarios were considered for numerical simulations, depending on different vegetation management conditions. Such scenarios are characterised by various plant densities, diameters, heights and species (herbaceous, shrub and arboreal), and, accordingly, different formu-

River bars are large-scale perturbations of the riverbed elevation commonly found in alluvial channels. They are typically characterized by the succession of longer and wider regions subjected to deposition and shorter and narrower areas subjected to deeper erosion with or without the presence of vegetation (Figures 1a and 1b). The main characteristic of river bars (i.e., the number of deposit/scour regions in a cross section) is defined by the bar mode, m (Crosato & Mosselman, 2009). According to its definition, m = 1 identifies the configuration of alternate bars, m = 2 corresponds to central bars, whereas higher values of m reflect the presence of multiple bars (e.g., multichannel systems). The formation of bars may be induced by the presence of either morphodynamic instabilities (Colombini et al., 1987;Engelund, 1970) or geometrical discontinuities (Blondeaux & Seminara, 1985;Tubino & Seminara, 1990), and are called either free bars or forced bars, respectively. Free bars appear as periodic waves over both the longitudinal and transverse directions (i.e., double harmonics) and typically migrate in the downstream direction (e.g., Colombini et al., 1987;Crosato et al., 2012;Rodrigues et al., 2012), whereas conditions for upstream migration are less common (Zolezzi et al., 2005). Forced bars do not migrate as their development and evolution are intrinsically related to the dynamics of the external forcing (Redolfi et al., 2019). Typical forced bars are located at the inner bank of river bends. Furthermore, past studies have shown that the presence of localized alteration of the channel geometry may affect the morphological characteristics of free Abstract Alternate bars are bedforms recognizable in straight or weakly curved channels as a result of riverbed instability. The length and height of alternate bars scale with the river width and the water depth, respectively. During low water stages, alternate bars become exposed and can be colonized by riparian vegetation. The effects of established plants on the morphodynamics of alternate bars have been poorly investigated. In this work, we focus on the effects induced by rigid vegetation on the dynamics and morphology of previously developed alternate bars in a straight channel by means of flume experiments. We investigate three different spatial densities of plants to reproduce scenarios of vegetation establishment. The results illustrate that vegetation alters both the altimetric and planimetric characteristics of bar patterns. In particular, as compared to bare-bed bars, vegetated bars have a higher wave amplitude and scour, and this effect becomes stronger with plant density. Moreover, they exhibit decreasing wavenumbers according to vegetation density. A comparison with previous fundamental work for the planimetric instability of straight channels with bare-bed alternate bars, suggests that the established vegetated bars may promote the transition to river meandering.Plain Language Summary Vegetation is ubiquitous in rivers and plants may establish on the sedi...