Biomorphological scaling laws from convectively accelerated streams

Abstract

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.

Return period of vegetation uprooting by flow

“…However, riparian vegetation may withstand many more erosion events during its life. This suggests that the interval between consecutive peak events and the ability for riparian species to recover and grow in this interval play a fundamental role in the evolution of water driven patterns (Bertagni et al, 2018), both from the biological and the morphological point of view (Edmaier et al, 2015;Perona and Crouzy, 2018;Calvani et al, 2019b). For this reason, the role of the intertime between consecutive flood events and their cumulative effects should be further investigated.…”

“…Accordingly, riparian and aquatic species would have adapted their biomechanical properties in order to withstand the flow regime and increase survival chances during stress periods, due to either drought or flood events (Karrenberg et al, 2002;Gibling and Davies, 2012;Gurnell, 2014). As a result, the link between vegetation dynamics and hydromorphological time scales may represent the key factor to understand the biological evolution of riparian species and predict their effects on ecosystem dynamics (Calvani et al, 2019b). Such link was seldom investigated in literature, mostly by focusing on short time horizon only (Corenblit et al, 2015), although the interactions among native and invasive alien species and river morphodynamics employ decades to evolve (Habersack, 2000;Solari et al, 2016).…”

River, Coastal and Estuarine Morphodynamics Selected papers from the 10th anniversary of the RCEM Symposium

“…Calvani et al . () analyse the interactions between river morphodynamics and vegetation properties at the reach scale by using field observations and theoretical modelling. The study derives general scaling laws to capture how the hydrodynamic‐induced vegetation mortality, and hence the flood regime of a river, can lead to vegetation zonation in convergent streams.…”

“…The 17 collected contributions include four state-of-science papers concerning the most recent advances in computational morphodynamic modelling of coupled flow-bed-sediment systems (Shimizu et al, 2019), a critical analysis of existing data on vegetation-flow-sediment interactions obtained through both laboratory experiments and field campaigns (Tinoco et al, 2020), a review of existing moving-boundary theories of shorelines with two extensions to allow inclusion of firstorder effects of waves and tides (Voller et al, 2020), and an overall assessment of the role played by wave forcing on the hydro-morphodynamics in shallow nearshore areas and at river mouths (Brocchini, 2019). The other 13 papers cover different topics about morphodynamics, spanning multiple environments, tackling concepts and processes with the aid of refined theoretical and numerical tools (Redolfi et al, 2019;Tambroni et al, 2019), grounding the results on laboratory data (Finotello et al, 2019;Geng et al, 2019;Matoušek et al, 2019, Porcile et al, 2020 and field observations (Fogarin et al, 2019;Tommasini et al, 2019), and making use of interdisciplinary approaches (Calvani et al, 2019;Chen et al, 2019;Pivato et al, 2019;van de Vijsel et al, 2020) also to develop new conceptualizations (Schlömer et al, 2020).…”

“…Finally, the papers by Calvani et al (2019), Chen et al (2019), Pivato et al (2019) and Schlömer et al (2020) focus on the complex interactions between morphodynamics and biological processes, reflecting the interdisciplinary spirit invoked in RCEM symposia. Calvani et al (2019) analyse the interactions between river morphodynamics and vegetation properties at the reach scale by using field observations and theoretical modelling. The study derives general scaling laws to capture how the hydrodynamic-induced vegetation mortality, and hence the flood regime of a river, can lead to vegetation zonation in convergent streams.…”