The influence of the development of dunes on the stability of bifurcations in sand‐bed rivers

Abstract

Channel bifurcations are common features observed in fluvial landforms from upstream gravel-bed rivers to downstream deltas. Extensive research has been carried out to study the stability and equilibrium configurations of bifurcations in the last two decades. However, existing studies generally employed oversimplified flow resistance equations, and the influence of the development of bedforms on the stability of bifurcations is rarely explicitly considered. The morphological features of bedforms in sand-bed rivers vary with flow conditions, which in turn affect flow resistance and sediment transport processes. Such a mutual feedback process is expected to exert a significant influence on the evolution of a bifurcation. A theoretical one-dimensional (1D) model is built, based on the classical model proposed by Bolla Pittaluga et al. in 2003, to evaluate the influence of the development of dunes on the stability of bifurcations. Results show that the development of dunes

Defining the length parameter in river bifurcation models: a theoretical approach

“…It is worth noting that the above analysis does not explicitly account for the effect of stage-related changes in dune geometry on the Chézy coefficient (Jing & Qin, 2023). Therefore, resolving the cases illustrated in Figure 2c requires a slightly different procedure, which is explained in detail in Appendix A.…”

“…By comparison, the analysis of the BRT model provided by Jing & Qin (2023) returns the following expression for the critical aspect ratio:…”

“…However, it it is too simple to account for the effect of stage-related changes in bedform geometry on flow resistance. Following Jing & Qin (2023), this effect can be modeled by separating the grain-related Shields number θ 0 from its total value θ, the two being linked through the following expression (Engelund & Hansen, 1967):…”

“…The nodal point relation proposed by Bolla Pittaluga et al. (2003) (hereinafter BRT) has been employed to model a variety of phenomena, including the effect of channel width adaptation (Kleinhans et al., 2013; Miori et al., 2006a), channel curvature (Kleinhans et al., 2008), suspended sediment transport (Iwantoro et al., 2021), presence of dunes (Jing & Qin, 2023), interaction with downstream confluences (Ragno et al., 2021), chaos in channel networks (Salter et al., 2020), channel progradation in deltas (Salter et al., 2018), subsidence (Gupta et al., 2014) and tidal influence (Iwantoro et al., 2022; Ragno et al., 2020).…”

“…(2016) ( , right panels), as a function of the Shields number and for different values of the dimensionless Chézy coefficient . (a) gravel bed bifurcations, (b,c) sand bed cases, where in (c) the effect of dunes is explicitly considered as suggested by Jing & Qin (2023). The cross marker indicates conditions of Figure 1a.…”