Meandering streamflows across landscapes and scales: a review and discussion Free

Meandering patterns designed by fluid flows are among the most stunning geomorphological features in nature. Meanders manifest in various environments, including rivers, estuaries, incised bedrock channels, deep-marine settings, supraglacial streams and planets such as Mars and Venus (Fig. 1). Scientists from diverse fields, including fluid mechanics, geomorphology, ecology, civil and petroleum engineering and geology, have extensively studied meandering streamflows. These investigations span a wide range of spatiotemporal scales and environmental domains, employing various conceptual and methodological approaches. Such an enduring and widespread interest in meandering can likely be attributed to two factors. First, meandering serves as a captivating illustration of nature's ability to develop highly regular forms, a characteristic that has long fascinated scientists and engineers. Second, understanding meandering has practical significance in a number of areas, including (though not limited to) river and wetland restoration, land management, infrastructure design, water resources, hydrocarbon exploration and production, carbon sequestration, hazard mitigation and planetary palaeoenvironmental reconstructions.

While meandering is typically discussed as a consequence of bank migration in channelized flows, it is also evident in streamflows with minimal or no lateral confinement, such as oceanic and atmospheric currents and glass rivulets (e.g. Fig. 1g). These examples highlight that meandering can emerge in diverse geophysical flows, possibly implying shared characteristics that are intrinsic to curved flows. However, the term ‘meandering’ is commonly associated with channelized flows, and the principles governing meandering pattern development often involve interactions between open-channel fluid dynamics, sediment transport and related morphological changes. Discussion in this chapter, as well as in this volume, is confined to channelized meandering streamflows, including gravel- and sand-bedded rivers meandering through flat valleys, turbidity currents flowing through submarine fans at the base of the continental slope and sinuous tidal channels dissecting intertidal coastal landscapes.

This Special Publication has arisen in part from contributions to two special sessions that were held, during the COVID-19 pandemic, at the 2020 AGU Fall Meeting and the 35th IAS International Meeting of Sedimentology 2021 and aims at reconciling results from field, laboratory and numerical investigations of meandering streamflows found in distinct environmental and geological contexts, as well as providing new perspectives on stream meandering in a variety of settings. The contributions in this volume focus on how the interactions of autogenic and allogenic processes, both in the horizontal and vertical dimensions, affect meander kinematics and the resulting morphology, sedimentology and stratigraphic architecture. Structural, geophysical, sedimentological, stratigraphic, geomorphological, numerical and remote sensing analyses are used to decipher the complex eco-morphodynamic feedback that shape meandering streamflows and to unravel both the commonalities and differences that pertain to sinuous channels found in distinct environmental settings. Specifically, the thirteen contributions include three state-of-the-science and perspective papers covering recent advances in the study of meandering river (eco)morphodynamics and meander cutoff processes (Gao and Li 2023 ; Kleinhans et al. 2023 ) and meander morphodynamics and sedimentology in macrotidal mudflats (Choi et al. 2024 ). The other ten papers cover a range of topics and environments, tackling concepts and processes using theoretical and numerical tools (e.g. Lemay et al. 2023 ; Sgarabotto et al. 2023 ; Yan et al. 2023 ), laboratory experiments (Kozarek et al. 2023 ), field observations (e.g. McMahon et al. 2023 ; Barrera and Ielpi 2024 ) and remote sensing analyses (e.g. Chamberlin 2023 ; Speed et al. 2024 ), and interdisciplinary approaches to develop new conceptualizations and methodologies (e.g. Koyuncu and Le 2023 ; Morris et al. 2023 ; Speed et al. 2024 ). These contributions provide a comprehensive perspective on the interdisciplinary approach taken when examining meandering streamflows. They consider the interplay among morphology, fluid dynamics and various environmental factors in shaping the patterns and dynamics of meandering streams across diverse spatial and temporal scales: from descriptions of local turbulent flow and related bank erosion at the sub-bend scale (e.g. Kozarek et al. 2023 ) to investigations of the evolution of individual meander bends (e.g. Gao and Li 2023 ; Sgarabotto et al. 2023 ) and meander trains (i.e. a series of meander bends; e.g. Morris et al. 2023 ; Speed et al. 2024 ); from the response of individual bends to a single channel-forming event (e.g. Koyuncu and Le 2023 ) to the evolution of meandering channel belts and floodplains over geological timescales (e.g. Lemay et al. 2023 ; Yan et al. 2023;Barrera and Ielpi 2024 ).

The articles comprising this volume attest to the ever-noteworthy and continuously reinvigorating relevance that meandering streamflows have for scientific research, spanning both fundamental and applied topics, and showcase the wide-ranging scope of ongoing research in the scientific community. We hope that this interdisciplinary collection of research will lay the foundation for future developments in meandering studies. In an attempt to contextualize this volume within the rapidly evolving research field, in this introductory chapter we focus on four themes deemed particularly relevant moving forwards. Each of these themes is discussed in separate sections, where we provide an overview of how scientific research on the topic has evolved through time and summarize both settled and unsettled issues using past results and novel research insights. Due to the broad nature of the subject, we will only cover a few aspects, a selection that is biased by our own research interests. Our major focus will be on meandering morphodynamics in rivers (Fig. 1a), which represent the best-known and most extensively studied examples of meandering streamflows in nature. While this predominance stems directly from the importance of meandering rivers from engineering and management perspectives (e.g. flood control, navigation, bank erosion, protection of land and infrastructure, functions of river–floodplain ecosystems and related water quality; see, for instance, Brookes and Shields 1996; Lagasse et al. 2004; Piégay et al. 2005; Kondolf 2006; Hooke 2013; Rhoads 2020), it should not be interpreted as a lack of appreciation of the importance of meandering streamflows in other environmental contexts. Rather, it underscores the need to develop a more coherent and comprehensive framework for the understanding of the mechanics of meandering in channelized streamflows. Some of the contributions in this volume align with this objective as they explore meandering streams on the seafloor (Lemay et al. 2023 ; Morris et al. 2023 ; Fig. 1d) and in tidal landscapes (Choi et al. 2024 ; Fig. 1c).

The scientific interest in stream meandering is a long-lasting one. Significant advancements in understanding the form and origin of meandering occurred from the late nineteenth century to the mid-twentieth century. This progress was prompted by widespread observations that rivers seldom exhibit a straight planform and are often highly mobile, as well as by the realization that even entrenched rivers and incised river valleys (e.g. Fig. 1b) often follow sinuous paths (Thomson 1877; Kümmel 1895; Davis 1903, 1908, 1913; Bowman 1904; Tower 1904; Griggs 1906; Clements 1924; Exner and Davis 1924; Tarr 1924; Einstein 1926; Moore 1926a, b; Prandtl 1926; Cole 1930). Two crucial contributions played a key role in shedding light on the morphodynamics of meandering river bends during this period. First, Thomson (1877) provided the initial description of the helical secondary flow structure in river bends. Second, Fisk (1944) offered insights into the temporal evolution of the lower Mississippi River over geological timescales, meticulously mapping its bends in unprecedented detail.

In the following years, the general interest in meandering streams remained mostly focused on fluvial meanders, initially driven by issues related to meander migration in the lower Mississippi River (Kidwell 1948; Wright 1959). Tiffany and Nelson (1939) recreated a realistic sinuous stream in a laboratory experiment, observing that scour near bend apexes alternated with shallower areas between adjacent bends (‘pools and riffles’ pattern), and noting that an increase in sediment load accelerated the evolution of meander bends. Mathes (1941) proposed that the fundamental mechanism leading to meander migration was the transfer of sediment from the eroding concave-outer bank to the first downstream inner-convex bank. Sediment load, valley slope, river discharge and bed resistance were identified as the main drivers for meander dynamics, with floodplain heterogeneity and oxbow lakes produced by cutoff events also playing significant roles. Quraishy (1944) observed the formation of uniformly spaced alternate bars in a straight flume, causing the stream to adopt a sinuous course. Friedkin (1945) conducted a laboratory study to investigate the influence of factors like slope and discharge on meander dynamics, demonstrating active sediment transport from an outer bank to the first downstream convex bank.

The major era of quantitative research on river meanders began in the late 1950s and continued through the 1960s with the foundational work of Bagnold (1960), Langbein and Leopold (1966), Leopold et al. (1964), Leopold and Wolman (1957, 1960) and Schumm (1963). These studies established the groundwork for modern fluvial geomorphology and laid the foundation for a quantitative understanding of river meandering. Morphometric measurements and the relationships between processes and forms, such as the correlation between meander wavelength and discharge, were quantified (Leopold and Wolman 1960; Leopold et al. 1964). Morpho-sedimentary analyses also revealed that the presence of fine sediments promotes sinuosity, while large width–depth ratios discourage it (Ahnert 1960; Kinoshita 1961; Einstein and Shen 1964; Langbein and Leopold 1966; Shepard 1966). Detailed measurements of flow fields in meander bends were also carried out (e.g. Engelund 1974). Variations in sediment load were shown to influence meander features and dynamics, although meandering was observed to occur even in the absence of sediment load (e.g. meanders in glaciers, Parker 1975; Fig. 1e, h). The empirical observation that mutual distances between riffles in straight channels equal the distances between inflection points in meandering streams led to the hypothesis that the same mechanism that shapes meanders also operates in straight channels (Parker 1976). While this observation de facto laid the basis for modern ‘Bar Theory’, which poses that freely migrating alternate bars in rivers serve as precursors to meandering, the evolution of meanders was still viewed as a transient condition that was expected to transition, over sufficiently long timescales, to an equilibrium form. The latter was believed to conform to a sine-generated curve, and theoretical propositions were formulated to explain why rivers assumed this form, often tied to arguments about energy distribution and the minimization of shear stresses and friction (Kinoshita 1961; Langbein and Leopold 1966, 1970).

The long-term equilibrium hypothesis was challenged, during the 1970s, by observations that meander evolution takes place over short timescales (i.e. a few years), potentially producing complex transient morphologies (e.g. Langbein and Leopold 1970; Bluck 1971; Lewin 1972, 1976; Engelund and Skovgaard 1973; Gorycki 1973; Hickin 1974; Hickin and Nanson 1975; Leeder and Bridges 1975; Bridge and Jarvis 1976; Parker 1976; Knighton 1977; Dietrich et al. 1979). Meander cutoffs were identified along the Mississippi River, and the widespread presence of relict channels or oxbow lakes in river floodplains was noted. As research transitioned to focus on shorter-term processes, there was a shift towards investigating the dynamics of changes in river meanders, drawing from empirical field observations and historical evidence (e.g. Lewin 1972, 1976, 1978; Brice 1974; Hickin 1974, 1978; Hickin and Nanson 1975; Hooke 1979; Nanson 1980). Asymmetric and compound bends were recognized as important parts of meander development (Lewin 1972). Erosion and deposition were meticulously measured and analysed in groundbreaking studies on individual meander bends (e.g. Jackson 1975; Bridge and Jarvis 1976; Dietrich et al. 1979) and key papers were published on the sedimentology of meander point bars (e.g. Allen 1970; Bluck 1971).

By the 1980s, a substantial body of geomorphological evidence regarding meander behaviour had been generated, culminating with a special collection of papers (Elliot 1984). Afterwards, the amount of field-based research began to decline in favour of theoretical and modelling approaches that relied on engineering and fluid dynamics (e.g. Parker et al. 1983; Blondeaux and Seminara 1985; Andrews 1986; Furbish 1988; Ikeda and Parker 1989; Johannesson and Parker 1989a, b; Stølum 1996). ‘Bend Theory’, proposed by Ikeda et al. (1981) and Parker et al. (1982), explained bank erosion as originating from steady flow perturbations induced by channel curvature, without the need for alternate bars, as suggested by Bar Theory. Blondeaux and Seminara (1985) unified the two theories, showing that Bend Theory is a particular case of the more general Bar Theory. Linear stability analyses initially underpinned these theories, but subsequent research incorporated non-linearities and width variations, concluding that small random perturbations in river planforms eventually lead to meandering patterns due to bend instability. These insights led to significant advances in the numerical simulation of meandering river evolution (e.g. Ikeda et al. 1981; Parker et al. 1982; Howard and Knutson 1984; Johannesson and Parker 1985; Howard 1992), first based on relatively simple kinematic models and then transitioning to more refined, morphodynamic-based tools (e.g. Crosato 1990; Mosselman 1995; Meakin et al. 1996; Sun et al. 1996; Seminara et al. 2001; Zolezzi and Seminara 2001).

In the new millennium, technological advancements led to a resurgence of both empirical and modelling studies, exploring flow fields and sediment transport processes in meandering channels (e.g. Ferguson et al. 2003; Frothingham and Rhoads 2003; Parsons et al. 2004, 2013; Schnauder and Sukhodolov 2012; Sukhodolov 2012), also with a focus on sharp meander bends (e.g. Blanckaert and de Vriend 2004, 2005; Blanckaert and Graf 2004; Blanckaert 2009, 2011; Ottevanger et al. 2012). The accessibility of remotely sensed data, coupled with advances in data measurement and analysis, resulted in a large number of studies that focused on the planform dynamics of meandering rivers (e.g. Seminara et al. 2001; Zolezzi and Seminara 2001; Lanzoni and Seminara 2006; Frascati and Lanzoni 2009, 2010; Gutierrez et al. 2014; Gutierrez and Abad 2014; Schwenk et al. 2015). Several papers looked at the relationship between river lateral migration and curvature (e.g. Hooke 1995, 2007; Gilvear et al. 2000; Hudson and Kesel 2000; Lagasse et al. 2004; Güneralp and Rhoads 2009, 2010; Hooke and Yorke 2010; Finotello et al. 2019b; Monegaglia and Tubino 2019; Sylvester et al. 2019, 2021; Donovan et al. 2021; Limaye et al. 2021; Li and Limaye 2024) and the evolution of meander cutoffs (e.g. Gay et al. 1998; Constantine and Dunne 2008; Jugaru Tiron et al. 2009; Constantine et al. 2010a, b; Le Coz et al. 2010; Zinger et al. 2011, 2013; Han and Endreny 2014; Schwenk et al. 2015; Schwenk and Foufoula-Georgiou 2016; Richards et al. 2018; Viero et al. 2018; Li et al. 2017, 2020; Wang et al. 2020; see a detailed discussion in the ‘Meander cutoffs’ section). Attention was also given to the effects that spatial variability in floodplain sedimentology and resistance to erosion has on river morphodynamics (Güneralp and Rhoads 2011). Such variability can arise both as a consequence of allogenic forcings (e.g. valley confinement by bedrock and erosion-resistant layers; Burge and Smith 2009; Nicoll and Hickin 2010; Limaye and Lamb 2014; Parsapour-Moghaddam et al. 2018; Huffman et al. 2022) and autogenic processes (i.e. as a consequence of the system's internal dynamics; e.g. Ghinassi et al. 2016; Bogoni et al. 2017; Schwendel et al. 2018; Sylvester et al. 2021; see discussion in the ‘Meander migration, channel–floodplain interactions and resulting sedimentary deposits’ section).

Laboratory experiments also regained favour, with a focus on high-sinuosity meanders in small flumes and the influence of vegetation on channel stabilization (e.g. Tal and Paola 2007, 2010; Abad and Garcia 2009a, b; Braudrick et al. 2009; Termini 2009; Tal et al. 2013; van Dijk et al. 2013). However, reproducing laterally migrating, single-thread meandering rivers with repeated neck cutoffs in laboratory experiments remains a challenge (Parker 1998; Smith 1998; van Dijk et al. 2012; Song et al. 2016; Kyuka et al. 2021), leading researchers to predominantly rely on increasingly complex numerical models informed by field-based studies to model long-term meander morphodynamics (e.g. Parker et al. 2011; Posner and Duan 2012; Eke et al. 2014a, b; Dubon et al. 2019). However, laboratory experiments with fixed banks are still widely employed to study local flow structure as a function of bend morphology (e.g. Blanckaert and de Vriend 2005; Blanckaert 2009, 2010, 2011; Termini 2009, 2013, 2016; Termini and Piraino 2011; Ottevanger et al. 2012) and the effects of changes in vegetation and the rate of sediment supply (e.g. Keshavarzi et al. 2016; Azarisamani et al. 2020; Zhao et al. 2022; Modalavalasa et al. 2023).

Kozarek et al. (2023)  provide insights into the relationship between turbulent flow and bank erosion in meandering rivers using the unique Outdoor StreamLab (St. Anthony Falls Laboratory, University of Minnesota), an experimental meandering stream channel and floodplain system featuring a sandy mobile bed, vegetation and complex channel morphology that offers laboratory-quality measurements and control in a field-scale setting (Rominger et al. 2010; Palmsten et al. 2015; Hill et al. 2016; Lightbody et al. 2019). Gathering high-precision, synchronous measurements of the turbulent flow field and bed topography near erodible banks, the authors demonstrate that the rate of local bank erosion does not correlate with any single hydrodynamic parameter. This supports the notion that fluid shear contributions to outer bank erosion reflect multiple components of turbulent flow structure in river meanders and highlights the need for further experiments with different sediment properties as well as both bank and channel geometries to improve predicting bank erosion.

Currently available technologies such as terrestrial laser scanners, airborne LiDAR surveys, photogrammetry and surveying techniques based on the use of unmanned aerial vehicles enable detailed and repeated measurement of natural river systems up to the scale of individual meander bends and point bars (e.g. Lotsari et al. 2014; Mason and Mohrig 2019a, b; Levy and Cvijanovich 2023). This ability to collect high-resolution field data, coupled with the increasing availability of near-real-time satellite imagery (e.g. Boothroyd et al. 2021; Nagel et al. 2023), has also fostered studies in fluvial contexts different from classic sand- and gravel-bedded rivers flowing through vegetated floodplains in tropical, temperate and continental climate zones. A great deal of attention has been given, for example, to meandering rivers flowing through drylands and polar regions, where not only hydrological fluctuations can differ greatly from those in more temperate settings but also other morphodynamic processes come into play. For instance, in polar and cold-climate regions, meandering river morphodynamics is strongly affected by seasonal ice formation and breakups (e.g. Kämäri et al. 2017; Lotsari et al. 2017, 2019). Of particular interest is the study of 3D flow structure during ice-covered winter periods, not only to understand the hydrodynamic complexity (especially in terms of vertical velocity distributions) but also to understand and manage the forthcoming evolution of cold-landscape regions, as the spatiotemporal extent of river ice is projected to decrease due to climate change (IPCC 2023).

Koyuncu and Le (2023)  conducted detailed acoustic measurements in a North Dakota river to develop a theoretical model of cross-stream momentum balance for examining the distribution of bed shear stresses in ice-covered meandering rivers. Their results suggest that ice cover affects both primary (streamwise) and secondary (cross-stream) velocity distributions, increasing shear stresses at both the meander inner and outer banks and potentially exacerbating sediment transport and bank erosion processes.

In addition to seasonal ice coverage, bank erosion and lateral migration in meandering rivers at high latitudes are significantly influenced by the presence of permanently frozen soil (i.e. permafrost) in river banks. The impact of permafrost on river dynamics is a topic of active research (Kanevskiy et al. 2016; Ielpi et al. 2023a; Levy and Cvijanovich 2023; Rowland et al. 2023), especially for climate-change-induced permafrost thaw and related impacts on river morphodynamics and greenhouse gas emissions. In terms of river morphodynamics, the common intuition suggests that thawing permafrost, combined with increased river discharge from melting ice and heightened precipitation, is likely to weaken riverbanks and accelerate lateral migration rates (Douglas et al. 2023; Rowland et al. 2023). However, recent work highlights that thawing permafrost also promotes the greening of the Arctic and alterations in river–floodplain hydrology, which in turn favour bank stabilization (Ielpi et al. 2023a). Indeed, the presence or absence of floodplain vegetation has long been considered a critical factor in the formation and evolution of meandering rivers, and significant attention has been devoted to this topic over the last two decades at least (e.g. Perucca et al. 2007; Camporeale and Ridolfi 2010; van Oorschot et al. 2016; Zen et al. 2017; Ielpi et al. 2022). Until recently, the prevailing theory suggested that the structural support provided by plant roots, along with the associated development and retention of pedogenic muds, was essential for the sustainability of single-thread meandering rivers (e.g. Gibling and Davies 2012; McMahon and Davies 2018; Davies et al. 2020). However, growing empirical support (Ielpi et al. 2017; Ganti et al. 2019; Santos et al. 2019; Valenza et al. 2023; Finotello et al. 2024a) and physics-based modelling (Lapôtre et al. 2019) now indicate that meandering river formation is possible even in landscapes with minimal to no vegetation (Bray et al. 2007; Matsubara et al. 2015; Lapôtre and Ielpi 2020; Salese et al. 2020) given favourable terrain slope conditions and the presence of cohesive agents such as mud to provide sufficient bank strength. In addition, meandering channels are common on the seafloor, where vegetation is absent but there is plenty of mud to provide bank cohesion (e.g. Flood and Damuth 1987; Clark et al. 1992; Deptuck and Sylvester 2018). These observations have reignited interest in meandering river research, with efforts focused on reconstructing fluvial morphodynamics before the colonization of continents by vegetation (Santos et al. 2017; Ielpi et al. 2018; McMahon and Davies 2018; Ganti et al. 2019; Ielpi and Lapôtre 2019a; Hasson et al. 2023) and understanding meandering streamflows in extraterrestrial landscapes where vegetation likely never existed (Lapôtre and Ielpi 2020).

McMahon et al. (2023)  challenge the notion that single-thread meandering rivers were prevalent on the pre-vegetation Earth, by analysing the sedimentary architectures found in the c. 1 Ga Diabaig Formation. The authors argue that meandering in the absence of vegetation was facilitated in hydrologically closed endorheic basins of limited size due to (1) abundant cohesive sediment; (2) limited stream power; and (3) low palaeogradients towards the margins of lakes. They suggest that although these conditions were probably prevalent in other small, hydrologically closed pre-vegetation basins, they are unlikely to be relevant in craton-scale, externally drained systems. Regardless of whether these observations settle the dispute or not, it is clear that understanding meandering river morphodynamics requires analyses across a wide range of spatial and temporal scales (cf. Hooke 2023) and that it is difficult to attribute meander formation and development to a single dominating factor.

Kleinhans et al. (2023)  follow a similar line of reasoning, presenting a philosophical contribution aimed at reconciling previous studies and providing a systematic perspective on the state of science and a thorough investigation of the causes and mechanisms of meandering. Their discussion expands upon the content of this introductory chapter, covering the various approaches taken by previous researchers to understand meandering, encompassing observations from both Earth and Mars, conducted in both field and laboratory settings, and spanning from the present day to the stratigraphic record. They suggest that river meandering is caused by numerous processes rather than a single set of necessary and sufficient conditions. While substantial progress has been made, further research is needed to achieve a good understanding of the bio-morphodynamics of meandering channels across different spatial and temporal scales and in various environmental contexts (for further discussions on meandering in non-fluvial contexts, see the ‘Meandering streamflows in non-fluvial settings’ section).

In the long term, the morphodynamics of meandering rivers are strongly affected by cutoffs (Camporeale et al. 2005, 2008). Meander cutoffs occur when a single-thread river shortens itself as the two bend limbs connect, creating a more direct path for the river's flow. Two distinct cutoff styles are typically recognized: neck cutoffs and chute cutoffs. While the former takes place when a meandering channel erodes into itself through lateral movement, the latter occurs when a new and shorter channel (i.e. a chute channel) develops across a river bend over the floodplain or point bar.

Meander cutoffs initially attracted the attention of scientists and researchers because they represent a clear proxy for lateral migration (Davis 1903; Tower 1904). However, it immediately became clear how cutoff processes are important for the evolution of the entire river system. Macar (1934) recognized that the cutoff of a meander in entrenched rivers produces a fall or rapid that then migrates upstream through headward erosion. The hydrodynamic effects of cutoffs – such as river-path shortening and flood-stage lowering – were appreciated by engineers dealing with river management, especially along the lower Mississippi (e.g. Elam et al. 1948; Matthes 1948a, b). The processes leading to cutoff formation were investigated in detail (Johnson and Paynter 1967; Lewin 1972; Brice 1974; Erskine and Melville 1982; Gay et al. 1998; Micheli and Larsen 2011), and cutoffs have been used for inferring river formative conditions (e.g. Erskine et al. 1992; Guo et al. 2019) and reconstructing lateral migration rates based on the dating of infilled oxbows (e.g. Handy 1972). Other studies focused on the characteristic timescales of cutoff formation and infill rate, as well as the prevalence of cutoff types, neck v. chute (e.g. Lewis and Lewin 1983; Douglas Shields and Abt 1989; Li et al. 2020, Maitan et al. 2024), and their implications for effective river management. More recently, attention has been given to examining the intricate flow patterns that emerge at meander cutoffs, along with their associated morphodynamic and sedimentological implications (e.g. Fuller et al. 2003; Le Coz et al. 2010; Toonen et al. 2012; Zinger et al. 2013; Richards et al. 2018; Richards and Konsoer 2020; Z. Li et al. 2023). It is now widely recognized that meander cutoffs play a pivotal role in the intricate dynamics of meandering rivers by buffering river sinuosity, modulating the rate of sediment transport and river lateral migration and affecting floodplain sedimentology, stratigraphy and sediment residence times (e.g. Fisk 1944; Leopold and Wolman 1957; Wolman and Leopold 1957; Zinger et al. 2011; Schwenk et al. 2015; Schwenk and Foufoula-Georgiou 2016; Sylvester et al. 2021; Ielpi et al. 2023b). Meander cutoffs exert a key control on the evolution of both the rivers and their alluvial plain, ultimately contributing to the structure of meandering river floodplains (Stølum 1996; Constantine and Dunne 2008; Ielpi et al. 2023b), as well as to the formation of preserved meander belts in the geological record (e.g. Durkin et al. 2018a, b; see detailed discussion in the ‘Meander migration, channel–floodplain interactions and resulting sedimentary deposits’ section), with implications for fluxes of terrestrial organic carbon (Torres et al. 2017; Walcker et al. 2021; Ielpi et al. 2023b). Furthermore, meander cutoffs also leave behind crescent-shaped oxbow lakes, which serve as habitats with significant ecological value, supporting diverse plant and wildlife species (e.g. Amoros and Bornette 2002; Koc et al. 2009; Stella et al. 2011; Dieras 2013; Wang et al. 2020). From a morphodynamic standpoint, the abrupt channel shortening associated with a cutoff introduces significant non-linearities in river morphodynamics (Hooke 1995): the shortening and steepening of the river path consequent to a cutoff leads to enhanced sediment transport (e.g. Zinger et al. 2011; Monegaglia and Tubino 2019) and gives rise to sediment pulses that favour the formation of bars and an overall rearrangement of meandering bends both upstream and downstream to that bypassed by the cutoff (Schwenk and Foufoula-Georgiou 2016). As a result, cutoffs may accelerate the formation of more cutoffs in neighbouring bends, resulting in clusters of cutoffs across the floodplain (Hooke 2004; Ielpi et al. 2021).

Speed et al. (2024)  add to these observations through detailed mapping of meander cutoff kinematics, using 37 years of Landsat satellite imagery along the Trinity River (Texas, USA). Employing an innovative method for automated channel mapping and tracking, which facilitates detailed quantification of bend geometry and dynamics at the sub-bend scale, they establish connections between post-cutoff bend curvature and the spatiotemporal extent of cutoff impact. Their findings suggest that abnormally high curvature resulting from meander cutoff events has a more significant impact on both local and nonlocal bend dynamics compared to lower curvature counterparts. This impact sequentially affects adjacent bends, dissipating within c. 10 years after the cutoff event, even for bends with high curvature. In addition, using the simple kinematic model proposed by Howard and Knutson (1984), Speed et al. (2024)  demonstrate that the overall trends in post-cutoff river evolution can be predicted based on the initial cutoff geometry and known relationships between bend curvature and lateral migration rates.

Despite the significant progress made over the years, several key questions regarding the morphodynamics of meander cutoffs remain unanswered, particularly concerning the timing, location and rate of formation. Frequent occurrences of both neck and chute cutoffs are observed in nature, but the morphodynamic factors driving their formation remain unknown. Moreover, there remains ambiguity in clearly distinguishing between these two types of bends.

The occurrence of a neck cutoff is typically thought to require the formation of high-amplitude, highly sinuous bends (Guo et al. 2019) and is identified by examining whether the distance between two points along the channel axis is smaller than a critical value, usually on the order of the channel width. However, Gao and Li (2023)  highlight the limitations of assuming that neck width is equal to one channel width as the triggering condition for neck-cutoff formation, given the highly varied timing between when such a morphological threshold is met and the actual formation of the cutoff (Li et al. 2022b). Even more enigmatic are the dynamics of chute cutoffs, for which a physics-based framework is still missing (see Grenfell 2012; Grenfell et al. 2012; Viero et al. 2018). Moreover, we lack a mechanistic model to predict the location and timing of chute formation. This gap hampers our ability to forecast the distribution of sediments in chute-dominated fluvial systems and associated sedimentary deposits. Based on field observations, at least four mechanisms of chute-cutoff formation have been identified (Constantine et al. 2010b; Viero et al. 2018). These include headcut erosion of the bend's downstream limb, embayment formation in the bend's upstream limb, mid-channel bar formation and chute formation on scroll–slough patterns (see Gao and Li 2023  for more detail).

Several factors have been proposed to cause neck and chute cutoffs. These include hydrological variability, sediment supply rates, sediment cohesiveness, valley slope, degree of lateral confinement, bank erodibility and the density and type of riparian vegetation (e.g. Hooke 2004; Braudrick et al. 2009; Constantine et al. 2014; van Dijk et al. 2014; Eekhout and Hoitink 2015; Harrison et al. 2015; Schwendel et al. 2015; Ahmed et al. 2019; Ielpi and Lapôtre 2019b; Lewis et al. 2020; Ielpi et al. 2021; Li et al. 2022b; Maitan et al. 2024). However, the absence of a systematic assessment of the interactions among these factors has thus far hindered our understanding of what governs the cutoff regime. Recent insights by Maitan et al. (2024) suggest a dominant role of hydrological fluctuations, with neck cutoffs being prevalent in rivers characterized by limited variations in bankfull hydrology, typically associated with low-magnitude, long-lasting overbank floods. In contrast, short-lived, high-magnitude overbank floods promote the formation of chute cutoffs with further, though not strictly necessary, assistance from reduced riparian vegetation density and higher stream power related to enhanced lateral confinement and a steeper valley slope.

Another relevant and yet unresolved issue concerns the characteristic timescales associated with cutoff formation, isolation from the parent channel and the subsequent filling of oxbow lakes (e.g. Rowland et al. 2009). Initial efforts to quantify the infill rate of oxbows by measuring the reduction in water surface area over time did not reveal any consistent temporal patterns (Dieras 2013; Dieras et al. 2013). Recent analyses have underscored the highly variable nature of the time required for a meander bend to cutoff (Li et al. 2022b).

Several other existing challenges and possible future research directions related to meander cutoffs are highlighted by Gao and Li (2023) . Cutoffs are of interest not only to geomorphologists, sedimentologists and river engineers and managers but also to biologists and biogeochemists (e.g. Jackson and Austin 2013; Rechulicz et al. 2015; Seidel et al. 2017; Thomas et al. 2022). Improvements in the spatiotemporal resolution and cost-effectiveness of direct field measurement techniques, combined with the increasingly widespread availability and accessibility of remote sensing data, will enable the compilation of new datasets for river cutoffs. New generations of numerical models are also emerging, with high-resolution morphodynamic models of meander cutoffs proving critical in supporting findings from empirical analyses (e.g. Z. Li et al. 2023). Furthermore, the inclusion of chute cutoffs in widely used meandering river numerical models (e.g. Li and García 2020), supported by conceptualizations and parameterization derived directly from field and remote sensing data, will enable the expansion of investigations into floodplain structure and sedimentary deposit architecture beyond the classic neck-dominated alluvial settings (e.g. Ghinassi 2011). Laboratory experiments can also be beneficial for testing theoretical and empirical predictions. However, their relevance is likely to be limited to chute cutoffs (van Dijk et al. 2012, 2013), as necks are not easy to form automatically in scaled physical experiments (although flume studies on neck-cutoff formation have been conducted, starting from already sinuous, cutoff-prone planimetric configurations; see for instance Li et al. 2019, 2022a; Pannone and De Vincenzo 2022).

Meandering channels were identified early as key components of long-term landscape development in Davis's cycle of erosion (King and Schumm 1980). The migration of meandering rivers results from interactions among flow, sediment transport and channel forms that create complex stratal architectures (Seminara 2006). The sedimentary deposits formed by meandering rivers and submarine channels can host aquifers, which are the major source of groundwater, and serve as reservoirs for hydrocarbons, bearing also significant potential for subsurface carbon storage. The internal heterogeneity of meander-formed reservoirs translates to flow baffles and barriers when it comes to fluid flow (Willis and Tang 2010; Willis and Sech 2018a), but predicting the distribution of these heterogeneities remains challenging (e.g. Newell and Shariatipour 2016; Malenda et al. 2019; Yan et al. 2020; Sylvester et al. 2021; Bellizia et al. 2022b). The stratigraphy of meandering channel belts also has a significant impact on the burial and transport of organic carbon within river environments (Torres et al. 2017; Repasch et al. 2021; Scheingross et al. 2021; Douglas et al. 2022; Salerno et al. 2023; Barrera and Ielpi 2024 ).

After Fisk's (1944) groundbreaking mapping of the Mississippi floodplain, and following empirical evidence for the link between helical flow patterns and the lateral movement of meandering rivers (see the ‘Meandering streams: morphology, processes and dynamics’ section), conceptual models depicting the spatial and temporal distribution of sedimentary features within meandering river deposits, known as facies models, were introduced (Allen 1963; Bernard and Major 1963). These models emphasized how the lateral migration of river bends results in the formation of fining-upward point-bar deposits with large-scale inclined bedding. Observations from modern rivers and the geological record supported these models (e.g. Bluck 1971; Jackson 1975, 1976; Puigdefabregas and Van Vliet 1977; Nanson 1980, 1981), and were further refined in the 1980s with the recognition of laterally accreting ‘inclined heterolithic stratification’ (Thomas et al. 1987; see also Dietrich and Smith 1983; Smith 1988; Willis 1989). Since the early 1990s, technologies such as ground-penetrating radar, acoustic Doppler current profilers, LiDAR, photogrammetry imaging techniques and seismic reflection surveys have greatly facilitated the characterization of sedimentary deposits of meandering rivers. Simultaneously, facies models have been developed to depict deposits associated with meandering submarine channels in the deep sea (see the ‘Meandering streamflows in non-fluvial settings’ section). Interest in understanding point-bar sedimentary facies grew after the recognition of similarities between the Cretaceous McMurray Formation, which comprises the Athabasca oil sands in Alberta, Canada – the world's largest heavy crude oil deposit – and modern tidally influenced meandering rivers (Flach and Mossop 1985). The development of the Athabasca oil sands prompted a thorough characterization of point-bar deposits, with a focus on how transformations in meander planform impact sedimentary facies and architectures (e.g. Wightman and Pemberton 1997; Crerar and Arnott 2007; Fustic 2007; Smith et al. 2009; Labrecque et al. 2011; Musial et al. 2012; Hassanpour et al. 2013; Jablonski et al. 2014; Martinius et al. 2015; Jablonski and Dalrymple 2016; Durkin et al. 2017). This interest in point-bar architecture persists to the present day, with numerical studies (e.g. Yan et al. 2017, 2018; Colombera et al. 2018) complementing analyses from modern systems (Ghinassi et al. 2018c; Hartley et al. 2018; Russell et al. 2018; Swan et al. 2018; Willis and Sech 2018b; Clift et al. 2019) and the rock record (Durkin et al. 2017; Martinius et al. 2017; Musial et al. 2013; Nardin et al. 2013).

Over the years, significant progress has been introduced to classic models of point-bar deposition, which typically assume that river bends shift laterally through a process of erosion and deposition at the outer (concave) and inner (convex) banks, respectively. Seminal work by Burge and Smith (2009) and Smith et al. (2009) emphasized the common occurrence of translating meander bends and associated eddy-accretion and counter-point-bar deposits. Despite the prevalence of downstream-migrating meandering rivers (Seminara et al. 2001; Zolezzi and Seminara 2001), documentation of counter-point-bar and eddy-accretion deposits in the rock record remains scarce (Hubbard et al. 2011; Fustic et al. 2012; Ielpi and Ghinassi 2014; Alqahtani et al. 2015; Ghinassi and Ielpi 2015; Wu et al. 2015; Ghinassi et al. 2016; Durkin et al. 2020). However, the importance of these processes in determining the heterogeneities of meandering river deposits is now widely recognized (e.g. Nanson and Page 2009; Durkin et al. 2018b). Despite the long-held consensus that accretion on concave banks was limited to rivers in settings with variable bank erodibility where migration is inhibited (e.g. Page and Nanson 1982; Smith et al. 2009; Ghinassi et al. 2016), recent work on modern systems and simple modelling by Sylvester et al. (2021) suggests that concave bank deposition can form autogenically as well, as part of meander downstream translation. This kind of channel migration is common whenever short bends with high curvatures develop, often as the byproduct of cutoffs (see also Speed et al. 2024 ).

Channel-fill deposits resulting from river avulsion (e.g. Smith et al. 1989; Valenza et al. 2020) and meander cutoff events have also been identified as significant components of meandering channel belts (Schwendel et al. 2018), and various types of oxbow-lake fill have been demonstrated to exert significant control over the connectivity between point-bar bodies (e.g. Donselaar and Overeem 2008; Toonen et al. 2012).

Another outcome of meandering river lateral migration is the widespread presence of scroll bars, which are curvilinear ridges of sediment deposited on top of point bars (e.g. Leclerc and Hickin 1997; Strick et al. 2018). These arcuate topographic features, creating asymmetric ridge-and-swale topographies, are widely documented in planform exposures of ancient riverine deposits (Ielpi and Ghinassi 2014; Durkin et al. 2017; Wang and Bhattacharya 2017) and in remote sensing studies of other planets (Moore et al. 2003; Burr et al. 2009; Schon et al. 2012).

The reasons why some meandering rivers exhibit scroll bars while others do not, despite evident lateral migration, remain unclear. Various explanations for scroll-bar formation have been proposed, with consensus lacking even on whether they are formed by constructional or erosional processes (for a thorough discussion see Sundborg 1956; McGowen and Garner 1970; Hickin 1974; Jackson 1976; Nanson 1980; Ielpi and Ghinassi 2014; van de Lageweg et al. 2014; Zen et al. 2017; Mason and Mohrig 2019b; Chamberlin 2023 ). Scientists have long recognized scroll bars as closely linked to river channel migration, using scroll bars and patterns to reconstruct palaeochannel position, wavelength and curvature (e.g. Sgarabotto et al. 2023 ) and to estimate river lateral migration rates based on scroll-bar age and spacing (e.g. Hickin 1974; Hickin and Nanson 1975; Nanson and Hickin 1983; Schook et al. 2017). The factors controlling scroll-bar spacing remain a subject of debate (e.g. van de Lageweg et al. 2014; Strick et al. 2018). Chamberlin (2023)  points out that certain meandering river systems with scroll bars also feature chute channels. These chute channels have the ability to migrate laterally and form scroll bars that overlay the main point bar. By testing the relationship between channel and scroll-bar geometries across eight distinct rivers characterized by laterally migrating chute channels, Chamberlin (2023)  demonstrates that scrolls in both the chute and main channels are nearly identical in terms of spacing and relief. Additionally, they exhibit distinct relationships with the widths of their formative channels. This suggests that the observed relationships between channel width and scroll spacing are not solely determined by channel width itself. Other factors, such as lateral migration rate and flood inundation depth, play significant roles in shaping scroll-bar geometries.

The autogenic variability of meandering channel-belt deposits, coupled with allogenic constraints (e.g. valley bedrock confinement, Nicoll and Hickin 2010), introduce lithological heterogeneities. These heterogeneities can significantly impact both the morphodynamics of meandering (Güneralp and Rhoads 2011; Schwendel et al. 2015) and fluid flow in sedimentary deposits (e.g. Colombera et al. 2017; Willis and Sech 2018a, b), with implications for reservoir development and groundwater management (Hajek et al. 2010). Over geological time spans, the interplay between floodplain aggradation/degradation through sediment deposition/erosion and lateral river migration shapes the sedimentary architecture of the floodplain (e.g. van de Lageweg et al. 2016). Generally, the rate of sediment deposition on the floodplain decreases with distance from the river (Huffman et al. 2022; Ielpi et al. 2023b), and floodplain aggradation tends to bury and conceal the geomorphic features formed by channel dynamics, such as point-bar deposits, filled oxbow lakes, scroll bars and crevasse splays, while lateral channel migration may erode and ultimately obliterate them.

Significant effort has been dedicated to understanding and numerically modelling the coupled evolution of dynamic meandering rivers and related morpho-sedimentary products (e.g. Howard 1992; Meakin et al. 1996; Durkin et al. 2017, 2018a; Russell et al. 2018; Willis and Sech 2018b; Sylvester et al. 2021; Yan et al. 2021; Bellizia et al. 2022b, 2023) and to linking river dynamics with sediment storage time and sedimentological heterogeneities across the floodplain (Meakin et al. 1996; Bradley and Tucker 2013; Bogoni et al. 2017; Repasch et al. 2020; Huffman et al. 2022; Ielpi et al. 2023b). The three-dimensional internal architecture and preservation potential of meandering river belt deposits have been investigated using numerical simulations (e.g. Clevis et al. 2006; Willis and Tang 2010; van de Lageweg et al. 2016) and laboratory experiments (e.g. van de Lageweg et al. 2013), complementing studies from the geological record (e.g. Ghinassi et al. 2014). Numerical simulations coupling lateral migration with vertical erosion or aggradation have also been performed as part of studies focusing on river valley formation (Limaye and Lamb 2014; Limaye 2015) and submarine channel evolution (e.g. Sylvester et al. 2011; Sylvester and Covault 2016; see also the ‘Meandering streamflows in non-fluvial settings’ section for details about Lemay et al. 2023 ; Morris et al. 2023 ).

The ongoing continued integration between empirical data and state-of-the-art numerical models is expected to advance science in the near future and is already yielding results of both scientific and practical interest. Sgarabotto et al. (2023)  examine two medieval point-bar bodies in the southern Venetian Plain (NE Italy), using satellite imagery, geophysical methods and sediment-core data to numerically model palaeohydraulic parameters that explain sediment distribution patterns. Provided the channel's axis exhibits sufficiently mild curvature, the authors highlight a significant correlation between numerically modelled bed shear stresses and sediment sorting estimated from electromagnetic conductivity data. Consequently, the latter can be used to infer spatial patterns of sorting within point bars, with practical implications for estimating intra-point-bar heterogeneities that control groundwater flow.

Using a forward stratigraphic model and field-derived trajectories tracing the historical evolution of meandering river planforms, Yan et al. (2023)  assess changes in sediment preservation and accretion rates of fluvial meander-belt deposits. They conduct multiple analyses, considering different durations of the sedimentation phase and various types of meander planform transformations, ranging from simple meander accretion to complex meander-belt segments with multiple cutoffs. Their findings reveal distinct power-law relationships between the accretion rate and sedimentation duration across different architectural hierarchies. Scale effects are observed, influenced by both river size and the time window and temporal resolution used to reconstruct meander-belt evolution. Systematic fluctuations in reconstructed accretion rates are attributed to apparent variations in river migration rates over time, emphasizing the need for caution when employing numerical approaches to assess river migration rates, channel-belt accretion rates and sediment preservation across varying time windows.

The improved ability to link meandering river processes to deposits and stratigraphy (see Ghinassi et al. 2018a and references therein) is now prompting new studies on the implications of meandering river evolution for the study of terrestrial organic-carbon fluxes (Torres et al. 2017, 2020; Repasch et al. 2020, 2021; Golombek et al. 2021; Scheingross et al. 2021; Salerno et al. 2023).

In their work presented in this volume, Barrera and Ielpi (2024)  explore the relationship between soil organic-carbon stocks and floodplain forest characteristics, including vegetation type and age, along the meandering Vermilion River in Ontario, Canada. They also examine how the dynamics of meandering rivers influence the export of organic carbon. Through a combination of photogrammetric analysis, dynamic time warping of channel centrelines and assessment of topsoil bulk density and organic carbon, the authors discover that variations in organic-carbon stock per unit surface area and soil development are influenced by meander migration, which leads to the establishment of typical boreal-forest vegetation successions. The findings and analytical methods presented in this study may serve as a foundation for broader applications to rivers in diverse bioclimates, ultimately contributing to the development of supra-regional models that elucidate the interplay between fluvial and biogeochemical processes in watersheds – a critical advancement for carbon assessment in the context of evolving climate and land use patterns.

In the near future, further refinement is also required to understand how various hydrodynamic configurations are manifested in the facies architecture of point-bar deposits, particularly regarding their preservation potential (cf. Paola and Borgman 1991; see for instance van de Lageweg et al. 2013; Durkin et al. 2018a) in relation to hydrological modulation and sediment fluxes (e.g. Fielding et al. 2018; Ghinassi et al. 2019b; Hansford and Plink-Björklund 2020). Improving our understanding of the variability in facies within channel belts holds significant practical importance, especially in identifying how sands are compartmentalized by different types of fine-grained deposits (e.g. Colombera et al. 2017; Yan et al. 2017) and in forecasting petrophysical variations in meandering river deposits (Kjetil et al. 2014).

Meanders are common not only in river valleys but also in various sedimentary and non-sedimentary environments such as meltwater rivulets and supraglacial streams (Knighton 1972; Parker 1975; Pitcher and Smith 2019; St Germain and Moorman 2019; Fernández and Parker 2020; Fig. 1e, h), volcanic lava flows, atmospheric rivers, jet streams and oceanic currents (Fig. 1g), both on Earth and other planetary environments (Weihaupt 1974; Bray et al. 2007; Burr et al. 2009; Fig. 1f). Many of these meandering streamflow types have received limited attention in the scientific literature compared to their fluvial counterparts. At present, a systematic review is challenging due to this lack of information. For this reason, we only focus here on two types of meandering streamflows in settings other than fluvial ones: submarine meandering streams formed by turbidity currents (e.g. Flood and Damuth 1987; Deptuck and Sylvester 2018) and meandering streams dissecting coastal wetlands periodically flooded and drained by the action of tides (e.g. Marani et al. 2002; Solari et al. 2002). Although these meandering features drew the attention of the scientific community somewhat later than their fluvial counterparts, and despite the need for more research to clarify their origin and dynamics, a substantial body of literature already exists and allows for a noteworthy review.

Channels constructed by turbidity currents crossing deep-sea fans and basin floors resemble subaerial alluvial channels in terms of the sinuous pathway they trace (Shepard 1966; Lonsdale and Hollister 1979). However, it was believed that sinuous submarine channels were mostly characterized by trains of regular and generally low-amplitude bends, with interspersed tight bends occurring more by chance than as a consequence of ordered meander growth. Recognition of widespread, highly sinuous, high-amplitude meander bends in channels formed by turbidity currents on the submarine fans of the Amazon and Mississippi rivers during the 1980s (Damuth et al. 1983; Stelting 1985; Flood and Damuth 1987) suggested that submarine meander streams were, in fact, much more morphologically similar to their fluvial relatives. These geomorphological features are now recognized as being widespread in channels found in mature, passive-margin submarine fans, which are typically long, non-bifurcating and transport large amounts of sediments (e.g. Bellaiche et al. 1984; Pickering et al. 1986; Kenyon et al. 1995; Babonneau et al. 2002; Abreu et al. 2003; Deptuck and Sylvester 2018).

In recent years, the increasing availability of high-resolution data produced by new oceanographic bathymetric mapping technologies has prompted extensive research on submarine meandering channels (e.g. Sylvester et al. 2013). This has also been motivated by a scientific interest in source-to-sink studies aimed at improving geomorphic and stratigraphic predictive relationships for hydrocarbon exploration and continental-margin evolutionary models (e.g. Peakall et al. 2000; Wynn et al. 2007; Janocko 2011; Sylvester et al. 2011; Janocko et al. 2013a, b; Konsoer et al. 2013; Jobe et al. 2016; Lemay et al. 2020, 2023 ). Besides, sedimentary deposits associated with sinuous submarine channels have important implications for carbon sequestration and for palaeoenvironmental reconstructions, submarine fans being among the largest sedimentary deposits on Earth (e.g. Deptuck and Sylvester 2018). Several studies have provided a detailed description of hydrodynamic and sediment transport fields in submarine meandering streams (e.g. Keevil et al. 2006; Peakall et al. 2007; Azpiroz-Zabala et al. 2017; Dorrell et al. 2018; Simmons et al. 2020), along with a characterization of their geometry, migration rates and sedimentation patterns (e.g. Kolla et al. 2001, 2007; Babonneau et al. 2002, 2010; Deptuck et al. 2003, 2007; Kolla 2007; Dykstra and Kneller 2009; Parsons et al. 2010; Janocko 2011; Sylvester et al. 2011; Jobe et al. 2016; Shumaker et al. 2018; Lemay et al. 2020; D. Li et al. 2023; Morris et al. 2023 ).

It is now widely recognized that there are both similarities and differences between the physical processes operating in turbidity currents traversing sinuous submarine channels and those characteristic of meandering rivers. Differences stem from various factors. For instance, flow stratification is significant in turbidity currents and arises because the excess density is highest close to the stream bed. Turbidity currents also experience enhanced friction due to momentum transfer at the top of the flow, while they expand through ambient water ingestion (e.g. Fukushima et al. 1986; Peakall et al. 2000; Pirmez and Imran 2003; Konsoer et al. 2013; Dorrell et al. 2014; Luchi et al. 2018; Traer et al. 2018a, b; Wells and Dorrell 2021). This results in a distinctive vertical velocity profile compared to rivers, with the highest velocity often occurring closer to the bottom (Kneller and Buckee 2000; Peakall and Sumner 2015). This velocity profile leads to variations in the structure of the secondary flow (e.g. Corney et al. 2006; Keevil et al. 2006; Islam et al. 2008; Parsons et al. 2010; Abad et al. 2011; Davarpanah Jazi et al. 2020), thereby influencing the development of sinuosity in submarine channels (Azpiroz-Zabala et al. 2017; Dorrell et al. 2018).

Although it is likely that flow structure is more complicated in submarine channels compared to rivers, many studies suggest that submarine channels are formed through flow processes that broadly resemble those observed in rivers (Peakall et al. 2000; Kneller 2003; Pirmez and Imran 2003; Imran et al. 2007; Konsoer et al. 2013; Lemay et al. 2020). This involves the preferential preservation of deposits on the inner bank and long-term erosion on the outer bank, similar to rivers (e.g. Deptuck et al. 2003; Sylvester et al. 2011; Kolla et al. 2012; Maier et al. 2012). The similarity between river and submarine meandering is further supported by similarities in meander planform morphology and other geomorphic features (Peakall et al. 2000; Konsoer et al. 2013; Lemay et al. 2020), suggesting that concepts applicable to rivers, such as styles of channel migration and channel-forming flows, may also apply to submarine channels (Shumaker et al. 2018; Covault et al. 2019). However, the stratigraphic expression of submarine and fluvial meandering channels can be markedly different (Flood and Damuth 1987; Kolla et al. 2007; Covault et al. 2016). This is because in meandering rivers the rate of channel lateral migration largely exceeds the rate of vertical floodplain aggradation; in contrast, meandering in submarine channels is characterized by high rates of vertical aggradation, with channel levees also being more topographically prominent than in rivers. As a result, submarine channel belts are typically much more elevated compared to the surrounding seabed, and their sedimentary architecture is dominated by aggradational channel-fill deposits, in contrast to fluvial systems that mostly consist of laterally accreting point-bar deposits (Covault et al. 2016; Jobe et al. 2016).

Lemay et al. (2023)  and Morris et al. (2023)  address the different stratigraphic expressions produced by active meandering in fluvial and submarine channels, despite apparently similar stream dynamics. Morris et al. (2023)  present compelling evidence that similar mechanisms of channel migration, characterized by systematic meander expansion and downstream translation, operate in meandering deep-water channels and rivers alike, driving sinuosity increase through time potentially up to the point of neck cutoff. To illustrate this phenomenon, Morris et al. (2023)  focus on the deep-water channel-levee system of Joshua in the Eastern Gulf of Mexico, for which they reconstruct channel kinematics based on interpretations of horizons derived from a three-dimensional seismic reflection dataset. Coupling their empirical observation with a simple kinematic model for meander evolution, the authors demonstrate that channel aggradation in submarine channels can occur autogenically as a consequence of the progressive reduction in channel slope driven by increasing meander sinuosity. This highlights the role of autogenic channel processes in governing system evolution, a notion further emphasized by the research of Lemay et al. (2023) . Using a three-dimensional forward stratigraphic model, Lemay et al. (2023)  create synthetic stratigraphic architectures and correlate deep-water channel trajectories observed on vertical cross-sections with the dynamic evolution of meander bends. Their findings illustrate how the diversity of channel stacking patterns commonly observed in field studies based on two-dimensional seismic cross-sections arises autogenically as a consequence of the three-dimensional dynamics of meander bends, without necessitating significant alterations in channel geometry or allogenically driven variations in rates of channel aggradation and lateral migration.

As data collection from submarine channels and underwater turbidity currents is significantly more difficult and costly than from terrestrial rivers, direct observations of flows in sinuous submarine channels (Talling et al. 2023) and high-resolution mapping of changes in modern systems (Heijnen et al. 2020; Talling et al. 2022) remain highly valuable. Considering that monitoring the processes, formation and evolution of meandering submarine channels remains a daunting task despite the rapidly improving remote sensing and sampling technologies for deep-marine environments, it is likely that additional insights into submarine channel dynamics will continue to come from studies of seismic reflection and sediment-core and outcrop data, combined with numerical modelling, and using meandering terrestrial channels as a point of comparison.

Coastal wetlands such as mangroves, mudflats and salt marshes are typically intersected by networks of tidal channels (Fagherazzi et al. 1999; Rinaldo et al. 1999a, b), many of which exhibit meandering in planform (Marani et al. 2002, 2003; Hughes 2012). Although meandering is a secondary process in tidal channel evolution, it warrants detailed examination because of the significant influence it has on water, sediment and nutrient fluxes in coastal wetlands. This exerts prominent control on the long-term eco-morphodynamic evolution of tidal environments, with implications for management and restoration (Warren et al. 2002; D'Alpaos et al. 2005; Coco et al. 2013). The development of tidal meanders also influences the sedimentology and stratigraphy of the intertidal platforms they cut through (Allen 2000; Choi 2011a; Boaga et al. 2018; Cosma et al. 2019), controlling the preservation potential of intertidal sedimentary deposits, where channels are typically preserved in the form of lateral accreting tidal point bars (Barwis 1978; McClennen and Housley 2006; Choi 2011a; Donnici et al. 2017).

Despite their widespread occurrence, the characteristics and dynamics of meanders shaped by tidal flows lack the detailed inspection devoted to their fluvial counterparts. This is even more surprising considering that interest in stream meandering in coastal areas is hardly novel. Discussions of meandering in coastal streamflows affected by tides arose in the late 1920s, prompted by observations that some meandering rivers, especially the Mississippi, are characterized by reduced sinuosities and limited migration in the lower part of their course as they approach the shoreline, whereas other rivers feature sustained lateral migration as well as meander neck cutoffs (Campbell 1927; Barton 1928; Johnson 1929). After a century, this topic is still debated in the scientific community (e.g. Hudson and Kesel 2000; Hassenruck-Gudipati et al. 2023a, b; Wu et al. 2023a, b). In the years that followed the discussions of the late 1920s, scientific interest in tidal meanders waned, and the few published studies were driven by a broad interest in intertidal sedimentology rather than meandering per se (Ahnert 1960; Leeder and Bridges 1975; Bridges and Leeder 1976; Barwis 1978; Leopold et al. 1993). The depositional architecture of tidal point bars was investigated, though mostly with respect to meso- and macrotidal settings where bars are exposed at low tides (e.g. Bridges and Leeder 1976; Barwis 1978; de Mowbray 1983; Woodroffe et al. 1989; Knighton et al. 1991; Fenies and Faugères 1998; Fenies and Tastet 1998) or in tidally influenced fluvial reaches (e.g. Smith 1987; Lanier and Tessier 1998). It was noted that the mutually evasive paths typically followed by ebb and flood currents can alternatively result in deposition and erosion on the upstream and downstream banks of a meander, and that asymmetries in tidal flow velocities can lead to elongated point bars stretching out in the direction of the dominant tidal current, resulting in complex point-bar architecture (Robinson 1960; Barwis 1978). Additionally, erosion at two points along a meander bend may give rise to ‘cuspate’ and ‘box’ meanders, also known as ‘pinch and swale’ (Ahnert 1960; Dalrymple et al. 2010; Hughes 2012). The presence of this planform morphology on meanders is a clear indication of tidal influence (Woodroffe et al. 1989; Dalrymple et al. 2010; Davis and Dalrymple 2010; Hughes 2012). Observations have also indicated that flow separation and reversal at the meander's inner bank can produce bedforms with opposite symmetry and orientation relative to the locally dominant tidal flow (e.g. Barwis 1978; Fenies and Tastet 1998; Dalrymple and Choi 2007). While the range of facies expected within a tidal point bar varies with morphology and setting, it has generally been agreed that the mid-intertidal zones often exhibit inclined stratigraphy, with intercalated beds of muddier and sandier deposits (Land and Hoyt 1966; Bridges and Leeder 1976; Barwis 1978; de Mowbray 1983; Choi et al. 2004; Choi 2011a, b). As the stratal geometries of these deposits exhibit marked similarities with those of their fluvial counterparts, the basic architectural and facies models developed for fluvial meander bends have long been utilized to identify tidal point bars in the fossil record (e.g. Díez-Canseco et al. 2014). This incompleteness of facies models is reflected in the scarce documentation of tidal point bars in the stratigraphic record (Nio and Yang 1991; De Araújo Santos and De Fátima Rossetti 2006; Musial et al. 2012; Legler et al. 2013; Díez-Canseco et al. 2014; Chen et al. 2015; Olariu et al. 2015; Pelletier et al. 2016; Cosma et al. 2020), where these deposits are detected on the basis of the occurrence of bidirectional flows, the abundance of richly bioturbated mud and the presence of diagnostic tidal sedimentary structures such as rhythmites and bundles (Allen 1980; Allen and Matter 1982; Kvale et al. 1989; Tessier and Gigot 1989; Dalrymple et al. 1991, 2010, 2015; Choi et al. 2004; Choi and Dalrymple 2004; Davis and Dalrymple 2010; Olariu et al. 2012; Gingras et al. 2016; Jablonski and Dalrymple 2016).

The debate over whether tidal and fluvial meanders share similarities, and to what extent morphodynamic and architectural models derived from the study of fluvial meanders can be applied to their tidal counterparts, has persisted for some time. Key considerations when examining meanders in tidal channels include the periodic reversal of tidal flows, the asymmetry of ebb and flood flows in terms of magnitude and duration and the fact that maximum velocities do not necessarily correspond to bankfull conditions as in rivers and are not sustained for extended periods (e.g. Myrick and Leopold 1965; Bayliss-Smith et al. 1979; Pethick 1980; Healey et al. 1981; French and Stoddart 1992; Leopold et al. 1993; Fagherazzi and Furbish 2001; Fagherazzi et al. 2008; Kearney et al. 2017). These differences, combined with the presence of dense vegetation and roots in vegetated wetlands, have been cited to explain the peculiar ‘cuspated’ and ‘box’ morphologies (Zeff 1999; Marani et al. 2002) and apparent stability of sinuous tidal channels – or at least the relative subtlety of their meandering dynamics (Solari et al. 2002; Fagherazzi et al. 2004; Garotta et al. 2008). Despite clear indicators of active bank erosion and channel migration, such as meander cutoffs and slump-blocks, tidal channels have been paradoxically regarded as highly stable, with lateral migration rates ranging from a few centimetres per year to imperceptible, depending on the characteristics of bank vegetation and channel size (Redfield 1972; Garofalo 1980; Gabet 1998).

In the last two decades, significant advances have been made in understanding the morphodynamics and sedimentology of meandering streams wandering through tidal landscapes (e.g. Marani et al. 2002; Solari et al. 2002; Garotta et al. 2007; Gao et al. 2022b), from barren tidal mudflats (Kleinhans et al. 2009; Choi 2011a; Choi et al. 2013; Choi and Jo 2015b; Gao et al. 2022a) to vegetated mangrove forests and salt marshes (Fagherazzi et al. 2004; Brivio et al. 2016; Finotello et al. 2018, 2020b; Ghinassi et al. 2018a, 2019a; Cosma et al. 2019, 2020). Appreciation has been given to the fact that tidal channels evolve under the interaction of intertwined eco-morphodynamic processes, which mediate bank migration rates and cause variations in water discharge and sediment supply (Marani et al. 2002; Solari et al. 2002; Fagherazzi et al. 2004; Garotta et al. 2007, 2008; Kleinhans et al. 2009). Among these processes, the development of tidal asymmetries and the presence of multiple tributary channels have been identified as important factors influencing the evolution of tidal bends (Tambroni et al. 2017; Ghinassi et al. 2018b; Finotello et al. 2019a, 2022; Leuven and Kleinhans 2019; Gao et al. 2022b). However, detecting clear signatures of these processes in the associated point-bar deposits remains challenging (e.g. Ghinassi et al. 2018b).

In recent years, most studies have continued to rely on methods and concepts used in the study of meandering rivers, although only recently has empirical evidence emerged to support these similarities (e.g. Finotello et al. 2018, 2019a, 2020a, 2022; Leuven et al. 2018; Gao et al. 2024). The conventional notion of tidal meanders being stable geomorphic features has been challenged by evidence showing rapid evolution of tidal meanders, with migration rates comparable to those of fluvial meanders when appropriately scaled with channel width (e.g. Hood 2010; D'Alpaos et al. 2017; Finotello et al. 2018, 2022; Shimozono et al. 2019; Jarriel et al. 2021). This similarity extends not only to width-adjusted migration rates but also to meander planform dynamics and morphodynamic regimes in high-amplitude bends (Leuven et al. 2016, 2018; Finotello et al. 2022; Gao et al. 2022b). However, the reasons behind the apparent stability of larger meandering tidal channels (width >100 m) compared to smaller channels in similar settings remain unclear. One potential explanation lies in the relatively low volume of transported sediments, the latter being required to bring about noticeable changes. Nevertheless, recent work suggests that the perceived stability of large tidal channels may stem from periodic fluctuations in local tidal asymmetries (Finotello et al. 2019b, 2022), which control sediment transport and related in-channel depositional/erosional patterns (Tambroni et al. 2017). In large channels, frequent changes in local asymmetries can occur in response to natural and anthropogenically induced alterations in both external forces (i.e. waves and tides) and tidal basin morphology (Finotello et al. 2019a, 2022), leading to punctuated shifts in meander planform evolution. Consequently, active bank migration in large tidal channels takes place in a back-and-forth fashion, with negligible net migration over time. Changes in local asymmetries are in contrast less likely in low-order tidal channels, where flow is typically ebb-dominated owing to the geomorphic control of overbank areas on tidal hydrodynamics (e.g. Fagherazzi et al. 2008; Hughes 2012; D'Alpaos et al. 2021).

Questions also persist regarding the apparent absence of two typical byproducts of meander migration that are commonly observed in rivers: scroll bars and meander cutoffs (see the first three sections of this chapter). The scarcity of tidal meander cutoffs has recently been challenged by Gao et al. (2024) through a two-fold argument. First, they argue that meander cutoffs in tidal settings are widespread, but they are challenging to identify, especially using remote sensing imagery, due to their small scale. Second, the formation of cutoffs is hindered by the high density of tidal channels in tidal wetlands (Marani et al. 2003), which restricts meanders from freely migrating laterally and fully developing to the cutoff stage. Indeed, the lateral migration of meandering tidal channels often results in channel piracies, also known as stream captures, when two channels merge courses (e.g. Letzsch and Frey 1980; Vilas et al. 1999). This previously overlooked process might have significant implications for how tidal prisms are redistributed across the network and has been conjectured to significantly impact the sedimentary architecture of tidal meander deposits by prematurely interrupting meander evolution and resulting in limited width-to-depth ratios of point-bar bodies (Cosma et al. 2020).

Meander scrolls are largely absent in tidal settings, perhaps due to the lack of high-magnitude discharge events (i.e. floods) in tidal channels. Reduced hydrological fluctuations might cause tidal meanders to undergo small and yet continuous incremental lateral migration steps, thereby hindering the development of scroll bars as inner bank levees that form in rivers during major flood events (Wu et al. 2016; Mason and Mohrig 2019a). Another possible explanation for the observed lack of meander scrolls is the significantly lower reworking of sediments during tidal meander migration compared to river systems, particularly in relation to the characteristic rates of vertical accretion (cf. Howard 1996). In the fluvial realm, the absolute rate of channel migration (0.5–1.0 m a⁻¹; e.g. Moody and Meade 2014; Sylvester et al. 2021; Ielpi and Lapôtre 2020) is orders of magnitude higher than the rate of overbank aggradation (∼1–2 mm a⁻¹; e.g. Walling and He 1993, 1994; Walling et al. 1998), making it unlikely to affect bar dynamics and influence resulting stratal patterns. In contrast, coastal wetlands feature rates of channel lateral migration that rarely exceed 0.5 m a⁻¹ owing to their reduced size, while experiencing sustained rates of vertical aggradation (>5–10 mm a⁻¹) thanks to coupled organic and inorganic deposition in intertidal plains. Support for this inference is provided by the absence of scrolls in highly aggraded fluvial settings such as coastal backwater areas (Swartz et al. 2020), peatlands (Candel et al. 2017) and submarine channels (Jobe et al. 2016; Morris et al. 2023 ). Hence, it appears that sustained rates of vertical aggradation, common to tidal settings, are likely to prevent the formation of scroll bars by systematically suppressing any topographic irregularities (e.g. Brivio et al. 2016). Furthermore, the combination of reduced migration-to-aggradation rates plays a role in making the stratigraphy of tidal meanders different from fluvial ones, promoting a lateral-to-vertical accretion of channel deposits that is influenced by variations in channel cross-sectional area dictated by changes in tidal prism (Cosma et al. 2019).

Recent morpho-sedimentary analyses have also emphasized how distinctive point-bar dynamics do not diminish the observed similarity in meander planform transformations in tidal and fluvial realms (Brivio et al. 2016; Ghinassi et al. 2018a; Finotello et al. 2020b; Cosma et al. 2021). New research has also underscored the need for caution in using classic sedimentological proxies to infer tidal signatures in point-bar deposits. For example, the formation of bidirectional bedforms depends on the elevation of the point bar relative to the mean sea-level and on the local tidal range, which collectively determine the timing and intensity of ebb- and flood-current peaks (e.g. Ghinassi et al. 2018a). Flow separation and recirculation zones in sharp bends create complex depositional patterns and might also impede the formation of bidirectional bedforms as some portions of the bend never experience bidirectional flow (Leeder and Bridges 1975; Finotello et al. 2020b; Gao et al. 2022a). The position of point bars within the intertidal zone also determines the frequency and intensity of overbank events and influences the development of tidal rhythms and bundles. Hence, these rhythmic signals in tidal bar deposits are not necessarily ubiquitous within tidal point bars (Pearson and Gingras 2006; Choi 2011a, b; Fruergaard et al. 2011; Sisulak and Dashtgard 2012; Choi et al. 2013; Johnson and Dashtgard 2014; Choi and Jo 2015a; Souza et al. 2023). Rather, they are quite underdeveloped, or even absent, in low-energy, mud-rich microtidal settings (which incidentally are the most widespread globally), where point-bar deposits are poorly laminated and feature massive, bioturbated mud. Evidence of tidal cyclicity is more readily formed and preserved in highly energetic macrotidal settings (e.g. Cosma et al. 2022). Macrotidal environments, however, may be affected by other processes related to heavy-rainfall-induced surface runoff that can intensify ebb-induced sediment erosion (Choi 2011a, 2014). Even more complex are the morphodynamics and sedimentology of subtidal meandering channels (i.e. channels that are permanently submerged and never exposed at low tides e.g. Bellizia et al. 2022a). In these environments, the modulation of banks by in-channel secondary helical flow is potentially compounded by wave winnowing of the subaqueous overbank areas, which promotes sediment entrainment and facilitates bank collapse (e.g. Ghinassi et al. 2019a). Choi et al. (2024)  offer an overview of the morphodynamics of macrotidal meandering channels, drawing on multiannual monitoring data from South Korean tidal flats. Their study illustrates how meander bends frequently skew landwards and migrate downstream, in a manner reminiscent of fluvial systems (Seminara et al. 2001; Zolezzi and Seminara 2001), corroborating earlier research suggesting that meander morphodynamics are primarily influenced by ebb currents (Fagherazzi et al. 2004; Kleinhans et al. 2009; Finotello et al. 2019a; Gao et al. 2022a, b). Local tidal asymmetries are shown to change autogenically as a function of meander development stage, exerting significant control on channel migration. Ebb-dominated tidal flows, compounded by the temporary seasonal influence of heavy-rainfall-induced runoff discharge and mutually evasive eddy/flood-current patterns, lead to the preferential preservation of the downstream side of point bars. This results in a counterintuitive heterolithic stratified architecture dominated by bedforms formed by subordinate flood currents.

Reviews such as those presented by Choi et al. (2024)  require time and resource-consuming fieldwork campaigns spanning multiple years. However, the broad spectrum of meander-related topics that remain largely unexplored from morpho-sedimentary, biotic and biogeochemical perspectives justifies a comprehensive investigation of the issue at hand. In this regard, analyses of meandering channels within mangrove forests are notably underdeveloped, due to the dense vegetation canopy that hinders high-resolution monitoring using remote sensing data (e.g. Schwarz et al. 2022), and fieldwork is impeded by logistical difficulties in accessing study sites. Similarly, research on meander morphodynamics in tidal mudflats is still in its infancy. For example, the mechanisms behind the formation of small meandering creeks remain poorly understood (e.g. Kleinhans et al. 2009; Gao et al. 2022a). In these cohesive, erosional environments the dynamics of meanders do not primarily depend on curvature-induced helical flows and are most likely driven by sediment erosion imparted by high velocities and sustained seepage flows at late-ebb stages. Despite notable progress in hydroacoustic monitoring techniques, direct field measurements of flow structures through tidal meander loops remain scarce to date (e.g. Leeder and Bridges 1975; Finotello et al. 2020b; Gao et al. 2022a), as does the quantification of sediment transport dynamics in tidal channel bends and its impact on meander-bend architecture.

Finally, the incorporation of stream meandering into numerical models would enable detailed investigation into the effects of channel migration and related stream captures on the hydrological connectivity and morpho-sedimentary evolution of tidal channel networks (Mariotti and Finotello 2023). This represents an important step towards an improved understanding of the eco-morphodynamic evolution of coastal wetland systems, with implications for managing and restoration practices, projections of local sea-level changes and estimates of biogeochemical fluxes.

This introductory chapter demonstrates the need for further research to attain a better understanding of the bio-morphodynamics dictating the evolution of meandering channels across various scales and environmental domains. While disagreements remain on whether meandering streams in diverse environmental contexts are due to the same fundamental dynamics, a consensus is emerging that submarine and tidal streams evolve according to mechanisms akin to those governing meandering river morphodynamics. The latter is driven by a fundamental curvature-driven instability mechanism, that is, the instability of the mobile interface between the flow and the erodible boundary (Seminara 2006), whereby meander migration is controlled by both local and nonlocal values of curvature (Howard and Knutson 1984; Furbish 1988; Güneralp and Rhoads 2010; Sylvester et al. 2019). Likely, the observed disparities between meandering streams in fluvial and other environmental settings arise primarily due to different environmental conditions. These conditions may include variations in the ratio of characteristic lateral v. vertical channel movement, bank erodibility and the degree of lateral confinement. For instance, differences in channel kinematics and resulting stratigraphic architecture between submarine and fluvial meanders seem to stem from more pronounced channel aggradation relative to lateral migration (e.g. Jobe et al. 2016), rather than from dissimilarities in curvature-driven meander planform evolution (e.g. Covault et al. 2019; Morris et al. 2023 ). Similarly, meandering in coastal wetlands is driven by the same mechanism as the one operating in alluvial settings, although morpho-sedimentary outcomes differ due to environmental characteristics such as sustained overbank aggradation and an enhanced spatial density of sinuous channels (e.g. Cosma et al. 2019; Gao et al. 2024). The similarity in the main processes driving meander evolution is also supported by the remarkably consistent scaling of meander morphometrics (e.g. wavelength, amplitude, radius of curvature) across a variety of landscapes and meander sizes. More than 60 years ago, Leopold and Wolman (1960) proposed a diagram where meander wavelength observed in rivers, glaciers and the Gulf Stream was strongly correlated with channel width (see also Leopold et al. 1964). This scaling has remained consistent throughout the years as new data were added for a variety of meandering streamflows (e.g. tidal, submarine, bedrock river valleys; Leopold and Wolman 1960; Leopold et al. 1964; Barwis 1978; Williams 1986; Marani et al. 2002; Karlstrom et al. 2013; Finotello et al. 2020a, 2024b; Hayden et al. 2021).

Enclosed with this introductory chapter is a dataset of meander morphometrics (Fig. 2), derived from literature data, that spans five orders of magnitude in meander size and covers a variety of landscapes (alluvial and dryland rivers, the Gulf Stream, experimental laboratory flumes, lakes, alluvial fans, ridges on Mars, meandering river belts, inactive rivers and river valleys, submarine turbidity channels, supraglacial meltwater streams and tidal channels; Friedkin 1945; Flint and Fisk 1947; Rozovskii 1957; Leopold and Wolman 1960; Leopold et al. 1964; Schumm 1968; Kellerhals et al. 1972; Brice 1974; Parker 1975; Hey 1976; Barwis 1978; Andrews 1979; Knighton 1981; Marston 1983; Williams 1986; Pirmez and Flood 1995; Marani et al. 2002; Burr et al. 2009, 2010; Cohen et al. 2012; Karlstrom et al. 2013; Fernandes et al. 2016; Kite et al. 2019; Sylvester et al. 2019; Finotello et al. 2020a, 2024b; Hayden et al. 2021). This dataset confirms the strong similarity between meanders from different environments. However, the scatter is more pronounced than in the Leopold and Wolman (1960) graph. In addition, we shall stress here that subtle differences in the scaling relationships, typically obtained through regression fits of empirical data for meanders in different landscapes, do not offer a reliable diagnostic tool for distinguishing the origins of meandering. Prior research has shown that multivariate analyses of width-normalized, reach-averaged meander morphometrics are necessary to infer morphological similarities or differences (Howard and Hemberger 1991), and, even with such analyses, the differences tend to be subtle (e.g. Appels et al. 2008; Frascati and Lanzoni 2009; Bogoni et al. 2017; Finotello et al. 2020a). The limited diagnostic capability of scaling relationships stems from the frequently overlooked observation that the apparently robust scaling is driven in part by the finite-width nature of the measured sinuous features (Hayden et al. 2021). For example, a meander bend of constant width (W) would be cut off as soon as L = W (with L representing here the wavelength – or half the wavelength sensuLeopold et al. (1964) – of an individual meander bend, measured based on the position of the meander centreline, see Fig. 2), making L < W a geometrically impossible configuration. Similarly, a radius of curvature R = W/2 represents a physically meaningful lower bound, as the banks of a channel with a radius of curvature smaller than half its width would intersect each other (Hayden et al. 2021; Gao et al. 2024). Meander amplitude (A) can vary more freely (although it is required that A > 0 for a stream to be sinuous), and, indeed, the scatter in the A v. W plot is significant unless a minimum threshold of bend sinuosity is set to differentiate mildly sinuous features from more classic high-amplitude meander bends. This latter observation raises a fundamental, longstanding issue that is frequently overlooked in empirical analyses of meandering streams.

While extensive research has focused on unravelling the primary question of why rivers meander – proposing explanations ranging from the Coriolis force, energy optimization, bank erodibility, 3D flow structure involving helical and secondary flows in curved channels, the inherent properties of turbulent flows, pressure gradients and theories such as Bar Theory and Bend Theory (Quraishy 1944; Langbein and Leopold 1970; Rhoads and Welford 1991; Lanzoni and Seminara 2006; Seminara 2006; Teuling et al. 2006; Hafez 2022; Sahagian et al. 2022) – a well-defined, quantitative criterion is still lacking to distinguish sinuous channelized landforms emerging pseudo-randomly by chance (Langbein and Leopold 1966; Lazarus and Constantine 2013; Limaye et al. 2021) from genuinely meandering landforms shaped by ordered growth (Seminara 2006; Camporeale et al. 2007). In some instances, evidence of dynamic meander evolution can be readily inferred from direct observations or geological indicators such as meander cutoffs and associated oxbow lakes, scroll bars, terraces and eroded valley margins (e.g. Finnegan and Dietrich 2011; Hooke 2013). However, these proxies may be absent even in actively meandering streams, and their development is intimately linked to the characteristic evolution timescale of each landform. Consequently, even seemingly static sinuous features could either be actively meandering over a sufficiently long timescale or represent relict traces of previously meandering systems. Hence, the question of which streams are truly meandering, as posed by Kleinhans et al. (2023)  with reference to rivers, may seem trivial on the surface, but it is, in fact, quite nuanced, due to the many processes and spatiotemporal scales involved in meandering. Addressing this fundamental question would not only enhance our understanding of meandering in geophysical flows on Earth but also assist in deciphering the origin of single-thread sinuous channels shaped by various fluids on extraterrestrial planetary surfaces with varying substrates (e.g. Komatsu and Baker 1994; Karlstrom et al. 2013; Baker et al. 2015; Allen and Pavelsky 2018; Lapôtre and Ielpi 2020; Ielpi et al. 2022).

A first step towards a quantitative differentiation between sinuous and meandering streams was presented by Limaye et al. (2021), who suggested that only streamflows characterized by a sinuosity greater than 1.5 can unequivocally be attributed to sustained, ordered growth through curvature-driven channel lateral migration. The inclusion of this sinuosity threshold in the data reported in Figure 2 significantly enhances the correlation between meander width and other metrics (especially meander amplitude). Nevertheless, it remains plausible that sinuosity values below 1.5 could still be associated with truly meandering behaviour (e.g. Kleinhans et al. 2023). Sinuosity requires time to develop; therefore, low sinuosity values might simply be a reflection of low rates of lateral migration.

Additional research is needed to clarify which sinuous streams are truly meandering and whether meandering streamflows in various environmental settings share the same fundamental morphodynamics, although there has been significant progress over the last decades, along with renewed interest in meandering morphodynamics (Donovan et al. 2021; Limaye et al. 2021; Sylvester et al. 2021; Li and Limaye 2022; Chadwick et al. 2023; Hooke 2023; Morris et al. 2023 ). The increasing availability of remote sensing data (e.g. Boothroyd et al. 2021; Nagel et al. 2023) has led to a significant improvement in both temporal and spatial data resolution when it comes to quantifying meander migration. For instance, combining historical datasets with the widespread availability of satellite imagery with increased resolution and frequency, along with various multispectral signals, LiDAR and multibeam data collected by uncrewed vehicles such as drones, are revolutionizing our ability to detect and analyse morphodynamic changes (Schwenk et al. 2015; Li and Limaye 2022; Morris et al. 2023 ; Speed et al. 2024 ). This technology-assisted proliferation of data, coupled with continued improvements in techniques and methodologies for quantifying meandering streamflow morphologies and dynamics (Isikdogan et al. 2017; Monegaglia et al. 2018; Sylvester et al. 2021; Schwenk and Hariharan 2021; Liu et al. 2022; Chadwick et al. 2023), allows for a comprehensive exploration of the subject from unprecedented complementary perspectives (Kleinhans et al. 2023 ).

The progress in automated and semi-automated processing and the use of artificial intelligence to handle ‘Big Data’ are already proving useful in research on meandering rivers (e.g. Regan 2019; Guillon et al. 2020; Hossein et al. 2021; Deng et al. 2022; Dubon et al. 2023; Nyberg et al. 2023; Sun et al. 2023; Yan et al. 2024). However, automated and machine-learning approaches still necessitate supplementation with empirical data, preferably at a high spatiotemporal resolution and originating from different environmental settings. New empirical data should include meandering streams beyond the conventional coarse-bedded alluvial rivers found in temperate settings. Insights are also needed regarding the intricate dynamic interactions between flow patterns and landforms across a wide range of spatial and temporal scales (from short-term processes at the scale of individual meander bends to the long-term evolution of entire meandering systems) and their impacts on the surrounding landscapes and related sedimentary deposits.

Overall, our ability to advance the understanding of stream meandering in the near future hinges on a multidisciplinary approach focused on developing new insights through data-driven methods and analyses derived from investigations of modern and ancient systems, laboratory experiments and numerical simulations.

This introductory chapter has sought to contextualize the collective contributions of this volume within the broader realm of meandering channel research, while also outlining prospective research directions in the broad domains of Earth and planetary science. Although surely not exhaustive, we hope that these research pathways will inspire future generations of scientists, reigniting interest in the captivating and beautiful meandering patterns crafted by nature.

The authors thank Neil Mitchell and one anonymous reviewer for their helpful comments, and editor Mads Huuse for handling this manuscript.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

AF: conceptualization (equal), data curation (lead), visualization (lead), writing – original draft (lead), writing – review & editing (equal); PRD: conceptualization (equal), writing – original draft (supporting), writing – review & editing (equal); ZS: conceptualization (equal), writing – original draft (supporting), writing – review & editing (equal).

AF acknowledges support from the European Union – NextGenerationEU and by the University of Padua under the 2021 STARS Grants@Unipd programme ‘TiDyLLy – Tidal networks dynamics as drivers for ecomorphodynamics of low-lying coastal area’, as well as from the Italian Ministry of University and Research (MUR) through the project titled ‘The Geosciences for Sustainable Development’ (Budget MUR – Dipartimenti di Eccellenza 2023–2027; Project ID C93C23002690001). PD acknowledges support from the PaleoSed+ Research Group in the Clayton H. Riddell Faculty of Environment, Earth and Resources at the University of Manitoba. ZS acknowledges support from the Quantitative Clastics Laboratory research consortium at The University of Texas at Austin (https://qcl.beg.utexas.edu/).

The dataset compiled for this work and used to generate the plots in Figure 2 is freely available from Finotello et al. (2024b) (https://zenodo.org/doi/10.5281/zenodo.10820588).