Meandering Research Articles

Ichnology and sedimentological aspects of the Floriano Formation (Miocene of the Resende Basin), southeast of Brazil

Many previous studies identified depositional systems for the Resende Basin using sedimentological and petrographic techniques. However, the lack of ichnological research leaves a gap in our understanding of paleoenvironment and paleoecology of this basin. Therefore, this study reports the first occurrence of trace fossils in the Floriano Formation (Miocene) and suggests more refined paleoenvironmental interpretations for this unit. We only observed ichnofossils in an outcrop on the RJ-161 road in Resende Municipality, Rio de Janeiro State. The deposit represents a floodplain overlayed by a crevasse splay, both sedimented in a meandering fluvial context. Trace fossils of terraphilic organisms – represented by Taenidium isp., Planolites isp. and Arenicolites isp. – were found in the fine-grained sediments of the outcrop. This ichnocoenosis is composed of feeding (fodinichnia), locomotion (repichnia) and/or habitation (domichinia) structures produced by worm-like invertebrates. The ichnotaxonomic assemblage consists of the first record of Scoyenia ichnofacies for a typical meandering fluvial system in Brazil. Keywords: continental ichnology, sedimentology, ichnofacies, paleoenvironment.

Hydrostratigraphic decomposition of fluvio-deltaic sediments inferred from seismic geomorphology and geophysical well logs in the Pannonian Basin, Hungary

Heterogeneity and anisotropy of lithological units influences hydraulic conductivity on several scales. The purpose of this study is to develop a novel method supporting hydrostratigraphic classification by considering horizontal and vertical variations of sand content in relation with the paleo-depositional environment. The workflow was applied for the uppermost ca. 1800 m thick fluvio-deltaic deposits (Great Plain Aquifer) of late Neogene to Quaternary age basin-fill succession in the eastern part of the Pannonian basin in Hungary. Five combined 3D seismic volumes, seven master horizons, and 30 well logs were analyzed. First, RMS amplitude maps were extracted to interpret the seismic geomorphological features and depositional architectures. Their associated lithology was inferred from wireline logs (GR and SP) by calculating the shale volume and the net-to-gross sand ratio for 30 m thick intervals. These were used to calibrate the seismic facies as a proxy for the horizontal distribution of sand versus shale. This method allowed the identification of sand bodies, i.e.: deltaic lobes, complex channel belts, simple fluvial channels behaving as aquifers, and the dominantly muddy delta plain to flood plain suits as aquitard. The vertical pattern of sand distribution was also evaluated. Three major stratiform and some corridor-like minor hydrostratigraphic units were defined instead of the former regional (basin) scale aquifer unit. 1) Laterally extended interval of stacked deltaic lobes of high sand ratios and high rate of connectedness, at the bottom of the studied interval. 2) General presence of extended muddy floodplains with anastomosing river systems, characterized by 100–200 m wide channels, low sand ratio, and limited connectedness: 3) widespread meandering and/or braided river systems with high sand ratios and high connectedness in the Quaternary. Within unit 2) spatially and temporally variable appearance of major 500–3600 m wide meandering channel belts produce locally high sand-ratio corridors in the NE-SW direction. A workflow adapted from the oil-and-gas industry was successfully applied to distinguish units of varying sand content and hydraulic conductivity. This approach can be used on basin to local scale to build a spatially complex facies-based model of hydrostratigraphy. Thus, a robust heterogeneous geological model serves as a base for investigating fluid flow on the required scale.

The evolution of meandering rivers in sedimentary basins: Insights from the lower Drava (Hungary/Croatia)

AbstractRivers flowing through sedimentary basins are subjected to a variety of controls. The main goal of our study was to identify the effect of external (e.g. climate changes, tectonics) and internal controls (e.g. sediment transport, deposition, vegetation cover) on the evolution of meandering rivers flowing through sedimentary basins using the example of the lower Drava River (Europe, Hungary/Croatia). Field research was conducted along a 50‐km‐long section of the valley. Sedimentary data from boreholes and corings, 35 km of ground‐penetrating radar surveys and analyses of digital maps were conducted to reconstruct channel planform changes. Traces of four meander belts were identified, and 39 AMS radiocarbon dates were used to distinguish the chronology of the fluvial events. The evolution of the lower Drava River comprised alternating periods of deposition (formation of aggrading meander belt) and avulsions. The channel belts were formed owing to upstream sediment delivery and floodplain storage. Changes in climate humidity and the occurrence of high flows influenced the planform of the meanders within particular channel belts. The oldest channel was active at least ~40 000 cal. BP before being reworked by subsequent meanders active between the Late Pleniglacial (30 000–14 700 cal. BP) and Late Glacial (~11 000 cal. BP) periods. The channel belts shifted to the south in the Holocene, between ~11 000 and 250 cal. BP due to the presence of a thrust fault situated diagonally to the Drava Valley. Results show channel width, channel belt width and the surface area of point bar deposits increased in the succeeding generations of meanders and that the style and sedimentary architecture of the channel belts were dominantly dependent on autogenic controls, that is, sediment delivery, aggradation and erosional events (e.g. formation of chute cut‐offs).

Investigation of rivers planform change in a semi-arid region of high vulnerability to climate change: A case study of Tigris River and its tributaries in Iraq

In this paper, the planform changes of rivers in a semi-arid region, which are particularly vulnerable to the impacts of climate change, were investigated. This research provides valuable insights into the adaptation and mitigation efforts necessary for effective climate change risk management in this area. A comprehensive analysis was carried out using satellite images and GIS to investigate the changes in the planform of the Mosul-Makhool reach of the Tigris River and its Lesser Zab and Greater Zab tributaries as a case study. To date, no studies have examined the impact of dam construction and climate change on the planform changes of these rivers. A survey was conducted to analyze the channel planform from 1979 to 2021. Various channel planform features were computed, including sinuosity index, braiding index, erosion and accretion, migration rate, confluence point, and junction angle. Results demonstrated that the Tigris River has low meandering features, the Lesser Zab has moderate meandering features, and the Greater Zab has the highest sinuosity index value of 1.95, which indicates very high meandering features. The change in the sinuosity index was fairly small. Generally, the rivers tended slightly towards deposition rather than erosion. The migration rate of the meandering rivers was high, with the highest value recorded in the Tigris River and Greater Zab. The average movement rate of the Greater Zab-Tigris River confluence was 31.81 m/year, and the Lesser Zab-Tigris River confluence moved 20.2 m/year. The study results demonstrate that climate change and dam construction significantly impact the rivers' planform in semi-arid regions. This investigation holds significant importance in evaluating morphodynamic changes in river systems worldwide with great detail and accuracy using satellite data.

Wonder and Wisdom: Wandering through Space and Time

My article undertakes a journey to connect pathways between wonder and wisdom, starting with ancient Greek philosophy, the love of wisdom. Every journey, whether physical, emotional, intellectual, and/or spiritual, has at its core a conception of where one is situated in space and time. The ancient term kaleo (to be called, summoned, or invited) is relevant to the expression of my inner voice in these current wanderings of thought. To wonder is to consider origins: the wonder of time; the wonder of space; the wonder of life on earth. Understanding the world we inhabit and the cosmos we observe has been prevalent in religious, philosophical, and psychological thought throughout the millennia. An attribution to Socrates is the adage, “Wonder is the beginning of wisdom,” that derives from Plato’s Dialogues concerning the nature of knowledge, with Socrates recounted as saying: “Wonder is the feeling of a philosopher, and philosophy begins in wonder.” As in ancient times, how our planet earth, the sun, and the moon relate to the planets of our solar system and the galaxies; the composition of the stars; the music of the spheres; and the manifestation of humanity in the universe intrigue us to wonder. And to wander is to follow a winding pathway, like the course of the twisting Meander River in Asia Minor of antiquity. My reasoning for going on this winding, wondrous journey in exploring the wisdom of the past is to enhance and illuminate knowledge for present application and future consideration, transcendence, and transformation of nous, or mind.

Sedimentary texture of crevasse splays formed by present-day and palaeofloods against the background of floodplain geomorphology and lithofacies exposed in channel cut banks (in the Vistula River valley between Warsaw and Płock, Poland)

Abstract On the floodplain of a sandy, braided river in the Central European Lowland, we studied the sedimentary texture of two crevasse splays, which were: (1) formed due to a levee breach in the 2010 flood, and widely documented by hydrological, bathymetric and LIDAR data, (2) developed under natural conditions when the channel was not embanked by artificial levees (dikes). We compare the sedimentological results with a geomorphological map, a model of the floodplain geomorphology showing different facies of fluvial deposition derived from a meandering river, and deposits in cut banks of the river channel. The statistical parameters of the grain size composition and geomorphic features of the splay, shaped by overbank flow through the broken embankment, are similar to the natural landform. Most of the cut banks (60% of alluvial deposits were mapped there) consist of lithofacies representing proximal floodplain; 30% were distal floodplain (muds), and 10% channel (coarse sand with gravel, pebbles and cobbles). We speculate about the palaeogeography of the Lower Vistula, and the origin of muds and coarse deposits in the banks of the channel. We link these unusual sediments with avulsion, deposition in side arms during ice-jam conditions, and dredging of the channel bottom by suction excavator, which reached the fluvioglacial, suballuvial layer on the bedrock protrusion.

Effect of Shape and Size on the Transport of Floating Particles on the Free Surface in a Natural Stream

AbstractUnderstanding how floating particles are transported by streaming waters is crucial in predicting the transport of plastic pollution, which is dramatically abundant in rivers, lakes, and oceans. Using particle tracking velocimetry, we investigate the motion of floating particles of different shape and size on the turbulent free surface of a field‐scale meandering stream. We consider two different locations, where the role of surface waves on transport is deemed negligible. Millimeter‐sized spheres are used as tracers to characterize the surface flow. These are compared with centimeter‐sized discs and rods, approximating typical‐sized pieces of floating litter. The larger particles exhibit similar mean and fluctuating velocities as the tracers but filter out the extreme turbulent accelerations. Consequently, their motion is more time‐correlated and their spreading rate is larger. This behavior is also confirmed by complementary laboratory measurements in an open channel flow. The rotation of the rods, affected by a range of turbulent scales, reduces the correlation time scale of their translational motion, and leads to a slower dispersion compared to the discs, despite the rods' length being larger than the discs' diameter. Taken together, these results indicate that the motion of finite‐sized objects floating on the surface of weakly wavy turbulent waters is consistent with the behavior of inertial particles in three‐dimensional turbulence. These results can be valuable when constructing predictive models of floating plastics.

The Role of Bed Morphology and Channel Curvature on the Redistribution of Momentum in a Series of Meander Bends, Pearl River, USA

AbstractThree primary driving factors are responsible for the lateral flux of streamwise momentum within meander bends: topographic steering of the flow related to changes in channel morphology, rapid changes in channel curvature, and curvature‐driven helical motion. While these factors have been studied previously, their relative contributions to the net redistribution of streamwise momentum within a series of consecutive bends have not yet been fully documented. This study explores the relative contributions of these three mechanisms to the redistribution of streamwise momentum using three‐dimensional velocity data obtained along six consecutive meander bends on the Pearl River (Louisiana, USA) for two different discharges. The magnitudes of lateral momentum flux are systematically compared to spatial series of channel width, bed shape, and channel curvature to elucidate the interactions between channel form and flow structure. Results show that the lateral flux of streamwise momentum is primarily driven by topographic steering with values of momentum flux due to curvature‐driven secondary circulation on average an order of magnitude less than values of flux related to topographic steering. The spatial patterns of the lateral flux components show that momentum redistribution due to topographic steering is highest at the entrance to the bend, and momentum redistribution due to secondary circulation is typically highest downstream of the apex. The results of this study emphasize the important role that interaction between process and form plays in dynamics of natural meandering rivers.

Tectonic-geomorphological evolution and provenance-sedimentary response: Insights from the Middle Jurassic–Lower Cretaceous, Junggar Basin, China

Understanding the complex depositional systems within lake basins requires a comprehensive analysis of the interplay between tectonic-geomorphological evolution and climate change. Based on three-dimensional seismic data, outcrops, well logging, cores, thin sections, and heavy mineral data, this study reconstructed the tectonic-geomorphological evolution of the Middle Jurassic–Lower Cretaceous in the Junggar Basin and analysed the responses of sequence stratigraphy, sediment provenance, and depositional systems. The Jurassic Xishanyao and Cretaceous Qingshuihe Formations developed third-order sequences (SQ1 and SQ2, respectively), which both consisted of lake transgressive (TST) and regressive system tracts (RST). During the SQ1 period, the Chepaizi-Mosuowan palaeo-uplift underwent substantial erosion and supplied sediment to the surrounding sub-basins, where deposited braided-river deltas were formed. Middle Yanshanian tectonism resulted in rapid subsidence, and the Chepaizi-Mosuowan palaeo-uplift submerged. During the early TST stage of SQ2, sediment from the northeast and northwest formed shallow braided-river deltas in topographic lows surrounding the residual Chepaizi-Mosuowan palaeo-uplift and reduced topographic roughness, resulting in a gentle slope to the south. The rapid lacustrine transgression from southeast to north in the late TST stage of SQ2 formed local beach-bars at shallow depths. During the RST stage of SQ2, a climate transition occurred from arid to humid, resulting in depositional systems that evolved from braided to meandering river deltas. The sedimentary fillings of the SQ1 and SQ2 stages were mainly controlled by tectonic-geomorphology and climate change, respectively. Collectively, our results suggest that the tectonic-geomorphological evolution and climate change jointly controlled the sediment sources and determined the depositional features in the basin.

Gleysols genesis and fluvial dynamics in a quaternary floodplain of the meandering river, Minas Gerais, Brazil

Soils are good indicators of the stability of environmental systems. In meandering river floodplains, they assess river channel morphology, incision process, groundwater level dynamics, and avulsion processes. The morphological properties and physicochemical attributes give gleysols unique characteristics about formation conditions and evolution degrees related to fluvial dynamics, thus allowing elaborate models of floodplain evolution in meandering rivers. This manuscript aimed to analyze the relationship between gleysols evolution and fluvial dynamics, in the quaternary floodplain of a meandering river, in the Mogi Guaçu River basin in the State of Minas Gerais. We described three profiles, in concave and convex margins of the river, identifying facies and considering the morphological characteristics of the gley horizons. Physicochemical analyses, determination of major and minor elements, and oxides were carried out on the samples of horizons and deposits of the profiles. For the characterization of the river channel, morphometric parameters were measured. Concentrations of silica, titanium dioxide, alumina, ferric and manganese oxides, plus the molar relations of provenance (P), leaching (L), parent material (M1 and M2), oxidation (O), hydrolysis (H), and the alteration geochemical index (CIA-K) were determined to compare the profiles pedological evolution. The three analyzed profiles were classified as typic Dystrophic Tb Haplic Gleysol (P1 and P2) and typic Alic Tb Haplic Gleysol (P3) so that the relation silt/clay demonstrated profile 3 to be the most evolved (weathered). Concentrations and behavior of oxides, associated with molar relations and conditions of the surfaces S II and S III of the flat floodplains morphological, demonstrated that the meandering process, with avulsion linked to erosion and deposition, affects gleysols evolution, suggesting genesis with compound or polygenetic profiles. Under a cyclical interpretation, the evolution of gleysol profiles, with truncation and horizon overlaying, reflects processes of avulsion, incision, and floods, as well as are proxies for interpreting the quaternary evolution of the Mogi Guaçu River meandering process.

A conditional GAN-based approach to build 3D facies models sequentially upwards

This paper presents an alternative way of simulating 3D facies models using conditional generative adversarial networks (GANs) by reconstructing the 3D volume upward with customised thickness from generated 2D slices. To mimic natural fluvial reservoirs, GANs need to learn the complicated facies’ lateral and vertical sequences, connectivity patterns and spatial correlation, e.g. the distribution of channel deposits and lateral accretion packages, including channel lags and point bars in a meandering fluvial system. 3D GAN modelling remains challenging, despite some success in 3D, due to the increased data and GAN model complexity caused by the 3D training data. For example, a 3D facies model with a larger number of voxels introduces more complex geobody shapes and requires 3D convolutions that increases the computational burden compared to 2D convolutions.Our proposed conditional GAN-based framework predicts 2D upper layers slice by slice to build 3D facies models, mimicking the sedimentary process in a purely aggrading system, which is less computationally costly than generating the facies models used as training data and generating facies models directly in 3D from a GAN. Each upper layer is predicted conditionally to a lower layer that contains the facies distributions in all layers below the target using several unique training enhancements. All those methods help prevent the simulated 3D models from gradually losing realism and the preset sedimentary settings vertically while inferring the plausible evolution of the channel system. The results demonstrate that the trained conditional generator, a SPADE generator, can work as a simulator to produce unconditional 3D meandering fluvial facies models by inputting a user-defined spatial correlation strength between layers and the number of layers needed (thickness in metres) without post-processing or retraining. This framework’s performance was evaluated using a connectivity metric towards the range of avulsion scenarios that represent a range of depositional uncertainty.

Late Permian to early Middle Triassic palaeoenvironmental reconstructions of the High Atlas, Morocco: Geodynamic and climate implications in the intertropical western Peri-Tethyan domain

This study characterizes the depositional environment and climate evolution from the late Permian to the early Middle Triassic, based on detailed sedimentological and palaeosol analysis. Sequence stratigraphy and palaeoenvironmental reconstructions were used to define the Permian-Triassic (P-T) evolution of the High Atlas basins as well as to make a comparison with European basins.The late Permian in Morocco is dominated by distal fluvial fan environment, under arid to semi-arid paleoclimate conditions. Above the P-T unconformity (BS1), the Lower Triassic deposits, record a similar climate evolution from arid to subhumid conditions. In the Argana Basin, the Early Triassic starts by an aeolian deflation lag, followed by stacked debris flow lobes and sheetflood ephemeral alluvial fan deposits, showing immature to locally mature calcretes. The Marrakech High Atlas basins are further characterized by well-developed aeolian dunes in alluvial fan environment. These arid environments evolve through time from proximal to distal deposits, as a retrogradational trend, until well-developed floodplain or lacustrine deposits under semi-arid to subhumid climate (maximum flooding surface, MFS). From MFS, the evolution from distal to proximal environments, testified the progradational trend which is capped by a newly defined angular unconformity (BS2). Above this tectonically induced BS2, the sedimentary section, dated as Anisian is characterized by palaeoenvironments that include meandering river fluvial packages deposited in a semi-arid floodplain.Basin configuration, border fault direction, palaeoenvironments and palaeocurrents recorded in the Argana Basin confirm an independent system, separate from the Marrakech High Atlas (MHA) area during the Triassic. Above BS1, remnant topographies resulted in discrete catchment and discrete drainage systems are evidenced by palaeocurrent and palaeowind measurements controlled by border faults. Palaeoenvironment reconstructions show that the MHA was made up of numerous independent basins during the Early Triassic and the remnant topographies are progressively infilled until BS2. After the BS2, the palaeo-drainage became axial and basins were probably connected in the MHA. Above the P-T unconformity, a common climate evolution is observed in Morocco during the Lower Triassic until BS2, which could correspond to the European Hardegsen unconformity. The sedimentation record shows a similar change in climate and geodynamics to that recorded from both Europe and Morocco.

High-resolution modeling of meander neck cutoffs: laboratory and field scales

Meandering rivers are distinguished by their characteristic sinuosity, which is subject to modulation through channel cutoff, resulting in the formation of oxbow lakes within the abandoned meander loops. Throughout the evolutionary course of a river, these cutoffs establish a connection between the channel and floodplain systems, both crucial to maintaining the dynamic equilibrium of the river system. Nonetheless, the interactive dynamic between the channel and floodplain and its influence on the transient behavior of the channel’s morphodynamics during a cutoff event are frequently reduced to simplistic representations in computational models. This study introduces a comprehensive numerical model that elucidates the adaptive processes of bed and planform during and subsequent to the inception of cutoff and oxbow lakes. The model is assessed through its application to a laboratory scale cutoff, before being employed to a real-world meandering river, specifically the Ucayali River in Peru, in order to gain understanding into channel development and the intricate patterns of planform dynamics following cutoff events. The model is able to capture the main modes of planform migration, translation and expansion for the case of the bend in the Ucayali River. During the neck cutoff, the model simulates the progression of erosional and depositional waves traveling in upstream and downstream directions respectively, underscoring the importance of incorporating both hydrodynamic and morphodynamic factors in characterizing the river dynamics associated with meander cutoffs.

Development of Simple Formula for Transverse Dispersion Coefficient in Meandering Rivers

This study aims to develop a straightforward and practical formula to estimate transverse dispersion coefficients in meandering natural rivers, a critical factor for predicting solute transport. We present a novel expression for the transverse dispersion coefficient based on dispersion and hydraulic data sets obtained from tracer experiments conducted in natural rivers. A distinctive feature of the formula is its reliance on one dimensionless hydraulic parameter, u¯u*hRc. To assess the effectiveness and accuracy of our proposed formula, we compare it with previously established equations commonly employed in the field. Furthermore, we apply the formula to natural river bends situated in the Nakdong River of Korea. This equation serves to estimate the initial value of the dispersion coefficient in two-dimensional solute transport modeling. As a result, the calibrated value of the dimensionless transverse dispersion coefficient is 0.97, which is only a 16% difference between the initial value of 0.81 as obtained from the formula. The formula presented in this study, simplifying and utilizing the dimensionless hydraulic parameter, offers a promising approach to estimating transverse dispersion in natural meandering rivers in cases where tracer and secondary flow data are unavailable. Additionally, the formula can be refined with more recent dispersion data, leading to a clearer, more straightforward, and validated formulation that captures the intricate interplay between topography and transverse dispersion.

Meandering rivers that anabranch in the upper Midwest (USA): Prevalence, morphological characteristics, and power regimes

Channel planform is the result of present and past hydrologic, sedimentary, and geologic conditions, and represents an adjustment of fluvial systems to these conditions. An important yet overlooked aspect of planform diversity of rivers in intensively managed agricultural landscapes of the upper Midwest (USA) is the co-occurrence of single-thread meandering and multi-thread anabranching reaches. Recent work on the role of river corridors in critical-zone dynamics of intensively managed landscapes has revealed the existence of juxtaposed meandering and anabranching reaches, yet the prevalence of anabranching reaches within meandering rivers in the upper Midwest is unknown. In addition, the morphological characteristics of these reaches and whether the stream power domain of these reaches differs from that of meandering reaches are also unclear. This paper quantifies the prevalence, planform morphology, and stream power domain of anabranching reaches along numerous lowland meandering rivers in the upper Midwest. Anabranch prevalence is explored for five representative watersheds using Google Earth aerial imagery and airborne LiDAR data. Less than 1 % of the total stream length in these watersheds (∼42,000 km) exhibits anabranching, but no watershed is devoid of anabranching reaches. Most anabranching reaches are characterized by a two-channel looping configuration, although complex anabranches with more than three channels exist at a few locations. Mean bifurcation angles (70° ± 29°) of the anabranching reaches are higher than those of braided rivers (40°-60°), with maximum angles as high as 150°, whereas mean confluence angles (60° ± 28°) fall within the range of junction angles in stream networks (45°-75°). Stream power analysis indicates that the occurrence of anabranching reaches along meandering rivers in the upper Midwest is significantly related to local increases in channel slope. The stream power domain of most anabranching reaches in the upper Midwest falls within that of meandering rivers, although some reaches have power similar to that of braided or wandering gravel-bed rivers. When considered collectively, multi-thread reaches juxtaposed with meandering reaches do not fit neatly into existing classifications of anabranching rivers.

Fossil leaves, woods, gastropods, and a crocodile tooth: Is the Amagá Formation worth exploring?

We have generated a spatial framework for macrofossil searching based on the current knowledge of fossil localities and fossil beds reported for the Amagá Formation in the northwestern Andes in Colombia. Our results show that twenty-three fossil localities and ninety-five fossil beds are distributed along this sedimentary succession. Preservation potential is higher in the Lower Member, given the high accommodation space and the dominance of a meandering fluvial system, compared with the Upper Member, where there was less accommodation space with a braided fluvial system controlling it. Our findings show that even though paleontological studies are null in this area, there are several options to find terrestrial macrofossil assemblages that will allow us to investigate the possible biological role of global climatic changes and regional tectonics in the Neotropical biomes based on the Amagá Formation.

Glacial Isostatic Adjustment Modulates Lateral Migration Rate and Morphology of the Red River (North Dakota, USA and Manitoba, Canada)

AbstractThe lateral migration of a river meander is driven by erosion on the outer bank and deposition on the inner bank, both of which are affected by shear stress (and therefore channel slope) through complex morphodynamic feedbacks. To test the sensitivity of lateral migration to channel slope, we quantify slope change induced by glacial isostatic adjustment along the Red River (North Dakota, USA and Manitoba, Canada) and two of its tributaries over the past 8.5 ka. We demonstrate a statistically significant, positive relationship between normalized cutoff count, which we interpret as a proxy for channel lateral migration rate, and slope change. We interpret this relationship as the signature of slope change modulating the magnitude of shear stress on riverbanks, suggesting that slope changes that occur over thousands of years are recorded in river floodplain morphology.

A depositional model for meandering rivers without land plants

AbstractThe recognition of meandering rivers in Earth's prevegetation stratigraphic record is hindered by an absence of depositional models specifically tailored to unvegetated single‐channel rivers. As a result, their abundance on the early Earth is currently unknown. Here, sedimentological studies of two modern meandering river reaches with unvegetated banks were conducted. Both reaches are located in arid basins of Nevada, USA. Stratigraphy was analysed in conjunction with satellite imagery and high‐resolution topographic data to understand how channels and floodplains record past flow conditions. Analyses of point‐bar and channel‐fill deposits showed that lateral accretion sets are not heterolithic but, rather, composed of mixed sand and sand‐sized mud aggregates (clumps of clay and silt) interpreted to have formed through flocculation. Levées are present but subdued. Notably, downstream‐migrating outer‐bank‐attached bars are prominent architectural features that may be common in unvegetated meandering rivers in arid landscapes elsewhere. The identification of such depositional elements in the stratigraphic record may enhance recognition of ancient unvegetated meandering rivers and improve reconstructions of palaeohydrology on early Earth and Mars.

Characteristics of entrenched meanders in catchment landscapes: a case study of Java, Indonesia

The diversity of physiography on the island of Java reflects the existence of different landforms that have properties and characteristics in the interaction of river formation. Rivers respond to longitudinal profile deformation, one of which can form river meanders. Meander rivers in Java are formed on alluvial plains (free meanders) and in hilly areas (entrenched meanders). The meander river formation factor is the high flow volume, which can be seen from the morphometric conditions. This study aimed to determine the morphometric characteristics of water catchment in entrenched meander rivers on the island of Java, as well as its relationship with the geodynamic conditions. The method used is the identification of entrenched meander rivers on Java Island, and morphometric calculations are carried out; besides that, it is also associated with morphostructural conditions to determine the process of its formation. The results obtained that the catchment area of the entrenched meander river has a tendency for small volumes of water and relatively longer floods; this is different from the nature of the free meander. The morphostructure much controls the process of forming entrenched meander rivers.

The sinuosity patterns of lowland meandering rivers on Earth and Mars

The sinuosity patterns of lowland meandering rivers on Earth and Mars